The ATM Forum Technical Committee Inverse Multiplexing for ATM (IMA) Specification Version 1.0 AF-PHY-0086.000 July, 1997 © 1997 by The ATM Forum. The ATM Forum hereby grants its members the limited right to reproduce in whole, but not in part, this specification for its members internal use only and not for further distribution. This right shall not be, and is not, transferable. All other rights reserved. Except as expressly stated in this notice, no part of this document may be reproduced or transmitted in any form or by any means, or stored in any information storage and retrieval system, without the prior written permission of The ATM Forum. The information in this publication is believed to be accurate as of its publication date. Such information is subject to change without notice and The ATM Forum is not responsible for any errors. The ATM Forum does not assume any responsibility to update or correct any information in this publication. 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For additional information contact: The ATM Forum Worldwide Headquarters 2570 West El Camino Real, Suite 304 Mountain View, CA 94040-1313 Tel: +1-650-949-6700 Fax: +1-650-949-6705 Acknowledgments The following people participated in the development of the IMA specification. Richard Cam Brian Carlton Marian Chan Jim Frimmel Andre Green John Guerrero Amar Gupta Frank Gurnee Thomas W. Hill Andreas Klug Ian Lewis Chris Martin David McDysan Michael Mroz Jim Millar Richard Proctor Richard Vallée Gerhard Vogt David Wetle Greg Wetzel Richard Vallée, Editor Rick Townsend, Chairman of the Physical Layer Working Group Table of Contents 1. Introduction 12 1.1 Overview of Inverse Multiplexing for ATM 12 1.2 Terminology 13 2. Terms and Definitions 15 3. IMA Objectives 20 4. IMA Reference Models 21 4.1 IMA Sublayer in Layer Reference Model 21 4.2 Reference Model of Unit Operating IMA 21 4.2.1 Source Interface 22 4.2.2 Cell Function 22 4.2.3 Inverse Multiplexing 22 4.2.4 Link Management 23 4.2.5 Unit Management 23 4.3 Timing Reference Model 23 5. Basic IMA Protocol Definitions 25 5.1 IMA Physical Link Characteristics 25 5.2 Transmission Convergence Sublayer Specification 25 5.2.1 Exceptions to the Interface Specific Transmission Convergence Sublayer 25 5.2.2 IMA Specific Transmission Convergence Sublayer Part 25 5.2.2.1 IMA General Characteristics 25 5.2.2.2 IMA OAM Cell Definition 26 5.2.2.2.1 Filler Cell Definition 27 5.2.2.2.2 ICP Cell Definition 27 5.2.2.3 IMA Frame Definition 30 5.2.2.3.1 ICP Cell Offset 31 5.2.2.3.2 IMA Frame Length (M) 32 5.2.2.4 Processing of the SCCI Field 32 5.2.2.5 IMA ID 33 5.2.2.6 Group Symmetry 33 6. Quality of Service (QoS) Requirements 35 7. Support for Common and Independent Transmit Clock Operations 36 8. IMA Data Cell Rate Implementation 38 8.1 Behavior of the Transmit End 38 8.1.1 Derivation of the Transmit IDCR from the TRL 39 8.1.2 Selection of the TRL 39 8.1.3 Stuffing on the TRL and Other Links 39 8.2 Behavior of the Receive End 39 9. Differential Link Delay on IMA 42 9.1 Differential Link Delay Requirement on Transmitter 42 9.2 Differential Link Delay Compensation at Receiver 42 10. IMA Interface Operation 43 10.1 IMA Link Operation 43 10.1.1 Overview of the Link State Machine 43 10.1.2 Definitions of the Transmit/Receive States and Events 45 10.1.2.1 Transmit Link States 45 10.1.2.2 Receive Link States 46 10.1.3 Definitions of the Transmit/Receive Link Actions 46 10.1.4 Link Events Driving the Link State Machines 47 10.1.5 Link State Transition Tables 47 10.1.6 Processing of the Tx and Rx State Fields 52 10.2 IMA Group Operation 53 10.2.1 IMA Group State Machine Definition 53 10.2.1.1 Overview of the Group State Machine 53 10.2.1.2 Detailed Group State Machine Definition 55 10.2.1.3 Synchronized Link Activation during Group Start-up Procedure 58 10.2.2 Link Addition and Slow Recovery (LASR) Procedure 62 11. IMA Frame Synchronization Mechanism 65 11.1 IMA Frame Synchronization with Stuff Events 67 12. IMA Interface OAM Implementation 69 12.1 IMA OAM Functions 69 12.1.1 IMA Group Maintenance Signals 69 12.1.2 IMA Link Maintenance Signals 69 12.1.3 IMA Link Error Handling 69 12.1.3.1 IMA Link Recovery Mechanisms 71 12.2 IMA Performance and Failure Alarm Monitoring 72 12.2.1 Performance Monitoring Objectives 73 12.2.2 Performance Monitoring Parameters 74 12.2.2.1 IMA Performance Primitives 74 12.2.2.2 IMA Performance Parameters 74 12.2.3 IMA Failure Alarms 76 13. Test Pattern Procedure 77 14. IMA Interaction with Plane Management 79 15. Management Information Base 80 15.1 The Network Management Framework 80 15.2 Overview 80 15.3 IMA Terminology 80 15.3.1 Error events 80 15.3.2 Defects 80 15.3.3 Performance Monitoring Parameters 80 15.3.4 Failure Alarm States 80 15.4 MIB-II and RFC 1573 Support 80 15.4.1 The ifStackTable 81 15.4.2 Interpretations of Interface Tables for IMA Groups 81 15.4.3 Interaction with ifAdminStatus 82 15.5 MIB Definition 82 16. References 105 Appendix A Example of Link Delay Synchronization 107 Appendix B Implementation Consideration 110 B.1 Dynamic Changes in ATM Layer Cell Rate 110 B.2 State Machine for De-Bouncing Error Condition Report 110 B.3 Maximum Link Differential Delay Limitation 111 B.4 Clock Variation Tolerance for IMA 112 B.4.1 Tolerance Due to IMA Stuffing Procedure 112 B.4.2 Tolerance Due to Periodically Stuffing on the Timing Reference Link 113 B.4.3 Tolerance Due to Maximum Stuff Event Insertion Rate 113 B.5 Example of IMA Data Cell Rate Recovery Implementation 114 Appendix C Asymmetric Operation 117 C.1 Introduction 117 C.2 Transmit and Receive State Transitions 117 C.3 Link Start-up 117 C.4 Group Start-Up 117 Appendix D Examples of Link State Exchanges 119 Appendix E IMA OAM Behaviors 125 Appendix F Numbers of IV-IMAs to Trigger SES-IMA 126 Appendix G Detailed IMA Clocking Configurations 127 G.1 IMA Group in CTC Mode 127 G.1.1 Non-transparent Links 127 G.1.1.1 Single Time Domain 128 G.1.1.2 Two or More Timing Domains 128 G.1.1.3 International or Inter Exchange Carrier (IEC) Timing Domains 129 G.1.2 Transparent Links 130 G.1.2.1 Master/Master Configuration 130 G.1.2.2 Master/Slave Configuration 131 G.2 Connections to Public ISDN 131 G.3 IMA Group in ITC Mode 131 G.3.1 Two or More Timing Domains - Un-synchronized 131 G.3.2 Non-Transparent/Transparent Mixed Configuration 132 List of Figures Figure 1 Inverse Multiplexing and De-multiplexing of ATM Cells via IMA Groups 12 Figure 2 Illustration of IMA Frames 13 Figure 3 IMA Sublayer in Layer Reference Model 21 Figure 4 Functional Blocks of Units Hosting an IMA Interface 22 Figure 5 IMA Timing Configuration Reference Model 24 Figure 6 Illustration of IMA Frames 31 Figure 7 Insertion of a Stuff Event over One Link (Using only Mandatory Advanced Indication) 37 Figure 8 Behavior of the Transmit End 38 Figure 9 Behavior of the IMA Receive End 40 Figure 10 Transmit Link State Machine Overview 44 Figure 11 Receive Link State Machine Overview 45 Figure 12 Overview of the Group State Machine 54 Figure 13 Group Traffic State Machine 55 Figure 14 Example of Synchronized Link Activation during Group Start-Up 60 Figure 15 Example of Synchronized Link Activation during Group Start-up over Time 61 Figure 16 Link Addition and Slow Recovery Procedure Example 63 Figure 17 Example of Link Addition Procedure over Time 64 Figure 18 IMA Frame Synchronization Mechanism 66 Figure 19 Error on ICP Cells Preceding and Comprising a Stuff Event 68 Figure 20 IMA Error/Maintenance State Diagram 70 Figure 21 IMA Error Handling Overview 71 Figure 22 Structure of anomaly and defect processing 72 Figure 23 Performance Monitoring Process (based on ANSI T1.231, Figure 4) 73 Figure 24 Example of Looped Test Pattern 77 Figure 25 Test Pattern Procedure over Time 78 Figure 26 Link Delay Compensation example 107 Figure 27 Snapshot of Buffers at T1 108 Figure 28 Snapshot of Buffers at T2 108 Figure 29 Snapshot of Buffers at T3 109 Figure 30 Snapshot of Buffers at T6 109 Figure 31 Rx Failed State Machine 111 Figure 32 Serving Delay Compensation Buffers 115 Figure 33 Insertion of Stuff Cell every Y*M Cells on the TRL 116 Figure 34 Exchange of the NE Tx and Rx State during Link Start-up - Rx Ready First 118 Figure 35 Link Start-up - Tx Ready First 118 Figure 36 Link addition with Overlapping Sequence (Symmetrical Operation) 119 Figure 37 Link addition with Non-Overlapping Sequence (Symmetrical Operation) 120 Figure 38 Transmit Link Deletion at One End (Symmetrical Operational) 121 Figure 39 Transmit Link Deletion at One End (Asymmetrical Operational) 121 Figure 40 Link De-activation due to Tx Fault (Symmetrical Operation) 122 Figure 41 Link De-activation due to Tx Fault (Symmetrical Operation) 122 Figure 42 Link De-activation/Recovery under Link Failed Condition (Symmetrical Operation) 123 Figure 43 Link De-activation/Recovery under Link Failed Condition (Asymmetrical Operation) 124 Figure 44 Single Link and IMA OAM Behaviors 125 Figure 45 Link Timing Reference Model 127 Figure 46 Single Time Domain 128 Figure 47 Two or More Timing Domains 129 Figure 48 International or Inter IEC Timing Domains 130 Figure 49 Master/Master Configuration 130 Figure 50 Master/Slave Configuration 131 Figure 51 Two or More Timing Domains - Un-synchronized 132 Figure 52 Non-Transparent/Transparent Mixed Configuration 133 List of Tables Table 1 Filler Cell Format 27 Table 2 ICP Cell Format 29 Table 3 Encoding of the Link Information Fields 30 Table 4 Valid and Invalid Combinations of Different Symmetrical Configurations 34 Table 5 Actions at the Transmit End 46 Table 6 Actions at the Receive End 47 Table 7 Local Events Driving the Transmit and Receive State Machines 47 Table 8 Detailed Transmit Link State Machine 49 Table 9 Detailed Receive Link State Machine 51 Table 10 Valid Combinations of the Tx and Rx states 52 Table 11 Description of GSM States 55 Table 12 Local Events Driving the GSM 56 Table 13 GSM State Transition 57 Table 14 GTSM States and Corresponding Report Priority 58 Table 15 Alpha, Beta and Gamma Values 65 Table 16 Definitions for IMA Frame Synchronization Mechanism 66 Table 17 Priorities of Defect Reports 69 Table 18 IMA Link and Group Anomalies and Defects 74 Table 19 IMA Performance Parameters 74 Table 20 IMA Failure Alarms 76 Table 21 Maximum Differential Delay for Different M Values over various Links 112 Table 22 Maximum Data Rate for a Maximum Link differential Link Delay of 25 msec 112 Table 23 M Implications on PPM 113 Table 24 Maximum Tolerated Frequency Difference between the TRL and the Fastest Link 114 Table 25 Proposed Numbers of IV-IMAs to Trigger SES 126 IMA SYNC (frame by frame) Check incoming link LDS Send LinkActive = 1 Send data One valid ICP cell One invalid or errored/missing ICP cell IMA PRESYNC (frame by frame) IMA HUNT (cell by cell) g consecutive valid ICP cells b consecutive errored ICP cells a consecutive invalid ICP cells Missing ICP Cell Notes: · See both (R-97) and (O-9) for the value of a, b and g. · In brackets: checking scheme in each state (cell by cell or frame by frame checking) · See Table 16 on page 66 for definitions of terms. Optional: Valid ICP cell at unexpected position (with cell by cell hunting) Check incoming link LDS Send LinkActive = 1 Send data Notes: · *: Group state required to be signalled. · Config Aborted State: To avoid a race hazard, the NE GSM should remain in this state for at least one second; this is to allow for at least one round trip of communication between both ends on the IMA virtual links. · Start-up-Ack: The NE GSM should wait for at least one second before moving to Start-up. This return to Start-up occurs if one of the expected signals which would cause the move to Insufficient-Links is not received from the FE GSM. · Sufficient Links transition is defined as: For symmetric operation: at least PTx links Active in both directions, where PTx and PRx are equal. For asymmetric operation: at least PTx transmit links Active and PRx receive links Active. Not Configured Start-up* Group Removed from all states Group Set-up Reject FE parameters while FE=(Start-up or Start-up-Ack) Config-Aborted* NE restarts group, or FE=Start-up with new parameters, or Timeout Start-up-Ack* Accepting group parameters ( M and Symmetry) while FE= (Start-up or Start-up-Ack) Timeout FE = Start-Up-Ack, Insufficient-Links, Blocked or Operational Insufficient-Links* Operational* Blocked* Sufficient Links while not inhibited Not sufficient Links Not sufficient Links No longer Inhibiting Inhibiting Determine links to be set Rx=Usable and report them (2) · Reject links with link defects (3) · Continue procedure with good (no defect) links · Report GSM=Insufficient-Links · Report all accepted links Tx=Usable · Look for incoming ICP cells with Rx=Usable set without LODS set for all Tx links(2) At least PRx links in Rx=Usable? At least PTx links reported Rx=Active by FE? · Report all accepted links Rx=Active (2) · Send Config-Abort signal in ICP cells (Specify reason as defined in Table 2 on page 29) · Stop sending Config Abort At least PRx Links in Rx=Active? · Report links in Tx=Active · Report GSM=Operational Notes: (1) The Insufficient-Links state is entered as defined in Figure 12 on page 54. (2) Should use time-outs accounting for round trip delay. (3) A link defect could be a local or FE link defect. · Start sending ICP/Filler cells over provisioned links · Indicate links in Group in ICP cells · Propose IMA ID and Frame Length in ICP cells · Check status of provisioned incoming/outgoing links Any new links in Rx=Active Is Rx M Supported? Valid symmetrical configuration? Any new links reported FE Rx = Active? Assign new links Determine links to be set Rx=Usable and report them (2) Send "Rx=Active" signal (4) End A Tx/Rx End B Tx/Rx (1) Each link is being assigned a LID. (2) At this point, new links are those that are Usable on both ends. (3) All new links should be reported Tx=Usable at the same time. (4) All new links should be reported Rx=Active at the same time. (5) The new links can be activated in the transmit direction once they all have been recognized Active in the receive direction or after some time-out has expired and some of the links have been recognized Active in the receive direction. All new links should be reported Tx=Active at the same time. Keep Usable links (reject others) Assign new links Send "Tx=Usable" on all accepted links (3) Keep Usable links (reject others) Rx Anomalies Defects Defect Response to FE Rx Link State Tx Link State Persistence (Note 1) Link State Machine (LSM) FE LSM Controlling (Note 2) Performance Monitoring/Failure Reporting (for NE and FE) UM Tx NE Defects FE States FE Defects Impacts on Rx Scheduler Performance Primitives Defects Anomalies Performance Parameter Failure & Failed Storage Threshold Data (Current data) Failure Indication Alert Message Current & historic data Set IMA ID Assign links Set IMA ID Assign links Determine links to be set Rx=Usable and report them (2) Send "Tx=Usable" on all accepted links (3) Send "Rx=Active" signal (4) End A Tx/Rx End B Tx/Rx (1) Each link is assigned a LID (2) At this point, links reported Rx=Usable are those that have been recognized within the IMA group, that do not exhibit any defects and exhibit proper link differential delay. (3) All links are reported Tx=Usable at the same time. (4) All links are reported Rx=Active at the same time. (5) The transmit links can be activated once they all have been recognized Active in the receive direction or after some time-out has expired and P out of N of the receive links have been recognized Active. Links are reported Tx=Active at the same time. Send "Tx=Usable" on all accepted links (3) Keep Usable links (reject others) Determine links to be set Rx=Usable and report them (2) Send "Tx = Active" signal (5) Send "Rx=Active" signal (4) Keep Usable links (reject others) Send "Rx=Active" signal (4) IMA Working State Leaving IMA SYNC state Out of IMA Frame (OIF) anomaly LIF Defect Entering IMA SYNC state Persistence: (g+2) IMA frames Persistence of IMA SYNC for at least 2 IMA frames (differential link delay has to be checked and maybe re-synchronized) IMA-Tx: No FE defect reporting In Link delay Synchronization Cell delineation: Working State = Sync User Plane Functions Layer Management Functions Plane Management Functions ATM Layer Physical Layer IMA Transmission Convergence Sublayer · ATM Cell stream splitting and reconstruction · ICP cells insertion/removal · Cell rate decoupling · IMA Frame Synchronization · Stuffing · Discarding of cells with bad HEC · IMA Connectivity · ICP Cell Errors (OIF, LIF) · LIF/LODS/RDI-IMA defect processing · RDI-IMA alarm generation · Tx/Rx IMA Link State Report · IMA group configuration · Link addition/deletion · ATM cell rate change · IMA group failure notification · IMA statistics Interface Specific Transmission Convergence Sublayer · Cell scrambling/descrambling (if required) · No cell discarding · Cell delineation · Header error correction (if required) · HEC generation/verification · HEC Error Indication · LCD-RDI alarm generation (if required) · LCD failure notification · TC stats Physical Medium Dependent Sublayer · Bit timing · Line coding · Physical Medium · Local alarm processing · RDI alarms generation · Link failure notification · PMD stats Send Test Pattern command Indicate link to test Send Tx Test Pattern Start Test Pattern time-out Receive new Test Link indication Copy Test Link Tx Test Pattern onto Rx Test Pattern field over all links. Test Pattern time-out Keep sending same Tx Test Pattern Verify Rx Test Pattern received over one or more of the other links Keep sending previous test pattern over Rx Test Pattern field End A Tx/Rx End B Tx/Rx Keep sending same Test pattern over Rx Test Pattern field over all links IMA: Working state No LOS, AIS and in-frame OCD anomaly Out of IMA Frame (OIF) anomaly Passing ATM Layer cells to ATM Layer Discarding ATM Layer Cells (Note 1) Check incoming link LDS Send LinkActive = 1 Send data Notes: · *: State required to be signalled to the FE. · The Not In Group state is the starting state. · Tx = Off indicates that the transmit end is not expected to be sending IMA frames. · Tx = Filler indicates that the transmit end is sending IMA frames containing only Filler cells. · Tx = On indicates that the transmit ATM layer cell transfer from the ATM layer has been enabled for that link. · FE Rx = Active is a FE state signalled via ICP cells indicating that FE Rx is Active. · FE Rx Active is a FE state signalled via ICP cells indicating that FE Rx is not Active. · The transition from Unusable to Usable may be delayed due to an ongoing group-wide synchronized start-up or link addition/recovery of links (refer to the group start-up procedure requirement (R-82) and the LASR procedure requirement (R-88)). · The transition from Usable to Active may be delayed due to an ongoing group-wide synchronized start-up or link addition/recovery of links (refer to the group start-up procedure requirement (R-84) and the LASR procedure requirement (R-90)). · Fault: the report of a fault is implementation specific. · See Table 7 on page 47 for detailed definition of transition triggers. FE Rx Active or implementation specific trigger Not In Group from all states Not In Group* In Group (Assign LID and Cell Offset) Unassigned Tx = Off Unusable* Active* Usable* Deleted Tx = Filler Unusable Tx = Filler Active Tx = On Usable Tx = Filler Not Inhibiting and No Tx Fault Inhibiting, or Tx Fault No longer Blocking FE Rx = Active FE Rx Active Inhibiting, or Tx Fault At least PTx links reported Rx=Usable by FE? Check incoming link LDS Send LinkActive = 1 Send data Notes: · There may be a persistence to aggregate changes between these states. This is implementation and application specific. Down Either Local GSM Operational or Remote GSM Operational PHY Unit Management Link Mgmt IMA PHY PHY Source Interface Cell Function Unit Management Link Mgmt IMA PHY PHY Source Interface Cell Function PHY Send "Tx = Active" signal (5) Send "Tx = Active" signal (5) Notes: · No alert is currently defined in this specification. · No historic data is defined in this specification. Any new links without defect? · Reject links with link defects · Continue procedure with good (no defect) links · Check IMA ID over new good links · Ensure proper connectivity over new links · Check LDS for good links (2) · Report new links in Tx=Usable (2) Any new links in Rx=Usable Up Both Local GSM = Operational and Remote GSM = Operational Any new links reported FE Rx = Usable? · Report new links Rx=Active (2) · Start time-out to suspend link addition · Enable link addition capability · Reported new links Tx=Active · Start sending ATM layer cells over them · Allocate unused LIDs to new links · Start sending ICP cells over new links · Indicate new links in Group · Check status of new links PHY: IMA Specific TC Sublayer PHY: Interface Specific TC Sublayer PHY: Lower TC Sublayer and PMD IMA-Tx: FE defect reporting Loss Of Delay Synchronization (LODS) LCD Loss of IMA Frame (LIF) LOS, OOF/LOF, AIS Delay Synchronization (4) ITU-T/ANSI Notes: (1) Fast recovery: ATM layer cells that are received are discarded. When Rx=On, the IMA shall emulate the reception of ATM layer cells by substituting Filler cells. (2) Medium recovery: the receive IMA is waiting for persistent defect. The Rx=On actions is performed until the persistence leads to the entrance of the Rx Failed state. When Rx=On, the IMA shall emulate the reception of ATM layer cells by substituting Filler cells. (3) Slow recovery: Rx Failed occurs. When Rx=On, the IMA shall emulate the reception of ATM layer cells by substituting Filler cells. (4) Differential delay synchronization should be checked and re-synchronized. State transitions: Transition according to Figure 18 on page 66 for leaving IMA SYNC Entering SYNC state according to Figure 18 on page 66. Entering the IMA SYNC state triggers a new delay synchronization for that link. LOS, OOF(DS1)/LOF(E1) or AIS or other lower layer notification is reported at the physical layer. LCD notification is reported at the physical level. Persistence: 2 IMA frames. Loss Of Delay Synchronization (LODS) No LOS, OOF/LOF, AIS, LCD or LIF condition detected No error reporting by IMA protocol, recovery of the link as specified in Section 12.1.3.1 on page 71. LOS or LOF or AIS or LCD or LIF or LODS Sufficient Links while inhibited Check incoming link LDS FE = Start-Up from Insufficient-Link, Blocked, Operational Send LinkActive = 1 Send data Notes: · *: State required to be signalled to the FE. · Not In Group is the starting state. · Rx = Off indicates that no cells are processed by the receive IMA on that link. · Rx = Monitor indicates that the receiver is only processing incoming ICP cells on that link. · Rx = On indicates that the receive ATM layer cell transfer to the ATM layer has been enabled for that link. · FE Tx = Active is a FE state signalled via ICP cells indicating that FE transmit is Active. · The transition from Usable to Active may be delayed due to an ongoing group-wide synchronized start-up or link addition/recovery of links (refer to the group start-up procedure requirement (R-83) and the LASR procedure requirement (R-89)). · FE Tx Active is a FE state signalled via ICP cells indicating that FE transmit is not Active. · Fault: a fault in the link or in the protocol; the meaning of this may be implementation specific. · See Table 7 on page 47 for detailed definition of transition triggers. Not In Group* FE Tx = Active or Usable Unassigned Rx = Off Unusable* Active* Usable* Deleted Rx = On Blocking Rx = On Unusable Rx = Monitor Active Rx = On Usable Rx= Monitor Not in group from Unusable or Usable Not in group Not in group Inhibiting Inhibiting, Rx Failed, or Rx Fault In Group FE Tx Active, or Rx Failed or Rx Fault LID Assigned, Not inhibiting, No Rx Failed, and No Rx Fault FE Tx (Usable or Active) (EQ. 1) FE Tx Active Rx Failed, or Rx Fault Send "Tx=Usable" on all accepted links (3) Starting State Discarding ATM Layer Cells (Note 2) Discarding ATM Layer Cells (Notes 2 and 3) Notes: (1) Only applied when adding links (not for link slow recovery) (2) Should have time-outs accounting for round trip delay NE restarts Group from all states except Not Configured Send "Tx = Active" signal (5) 1. Introduction This is the Inverse Multiplexing for ATM (IMA) specification, the purpose of which is to provide inverse multiplexing of an ATM cell stream over multiple physical links and to retrieve the original stream at the far-end from these links. Multiplexing of the ATM cell stream is performed on a cell by cell basis across the multiple links. This specification is offered for private and public User-to-Network Interfaces (UNI's), Network-to-Network Interfaces (NNI's) and Broadband Inter-Carrier Interfaces (BICI's). It defines a new sublayer located between the Physical Layer Interface Specific Transmission Convergence (TC) sublayer and the ATM layer: the IMA sublayer. This specification also defines modifications to the Interface Specific TC sublayer on which IMA is implemented. It also defines the IMA Management Information Base (MIB) objects. This specification does not deal with ATM layer functions such as UNI/NNI/BICI implementation requirements for signaling, traffic management and OAM. 1.1 Overview of Inverse Multiplexing for ATM A methodology is described which provides a modular bandwidth for user access to ATM networks and for connection between ATM network elements at rates between the traditional order multiplex levels, for instance, between the DS1/E1 and DS3/E3 levels in the asynchronous digital hierarchies. DS3/E3 links are not necessarily readily available throughout a given network and therefore the introduction of ATM Inverse Multiplexers provides an effective method of combining the transport bandwidths of multiple links (e.g., DS1/E1 links) grouped to collectively provide higher intermediate rates. The ATM Inverse Multiplexing technique involves inverse multiplexing and de-multiplexing of ATM cells in a cyclical fashion among links grouped to form a higher bandwidth logical link whose rate is approximately the sum of the link rates. This is referred to as an IMA group. Figure 1 on page 12 provides a simple illustration of the ATM Inverse Multiplexing technique in one direction. The same technique applies in the opposite direction. Figure 1 Inverse Multiplexing and De-multiplexing of ATM Cells via IMA Groups IMA groups terminate at each end of the IMA virtual link. In the transmit direction, the ATM cell stream received from the ATM layer is distributed on a cell by cell basis, across the multiple links within the IMA group. At the far-end, the receiving IMA recombines the cells from each link, on a cell by cell basis, recreating the original ATM cell stream. The aggregate cell stream is then passed to the ATM layer. The transmit IMA periodically transmits special cells that contain information that permit reconstruction of the ATM cell stream at the receiving IMA end after accounting for the link differential delays, smoothing CDV introduced by the control cells, etc. These cells, defined as IMA Control Protocol (ICP) cells, provide the definition of an IMA frame. The transmitter must align the transmission of IMA frames on all links (shown in Figure 2). This allows the receiver to adjust for differential link delays among the constituent physical links. Based on this required behavior, the receiver can detect the differential delays by measuring the arrival times of the IMA frames on each link. At the transmitting end, the cells are transmitted continuously. If there are no ATM layer cells to be sent between ICP cells within an IMA frame, then the transmit IMA sends Filler cells to maintain a continuous stream of cells at the physical layer. The insertion of Filler cells provide cell rate decoupling at the IMA sublayer. The Filler cells should be discarded by the receive IMA. A new OAM cell is defined for use by the IMA protocol. This cell has codes that define it as an ICP or Filler cell. Figure 2 Illustration of IMA Frames 1.2 Terminology This specification uses three levels for indicating the degree of compliance necessary for specific functions, procedures and coding associated with the IMA specification: · Requirement (R-x): functions, procedures and coding necessary for operational compatibility. · Conditional Requirement (CR-y): functions, procedures and coding necessary for operational compatibility if the specified optional function is implemented. · Option (O-z): functions, procedures and coding that may be useful, but are not necessary for operational compatibility. A (R-x) at the beginning of the paragraph shall apply to all the requirements in that paragraph, unless otherwise specified. The x, y, and z represent the order of the requirement, conditional requirement and option as they appear in this specification. 2. Terms and Definitions AAL ATM Adaptation Layer Examples of AALs are AAL1, AAL3, AAL4 and AAL5. Active This is a link state indicating the link is capable to pass ATM layer cell in the specified direction. Anomaly Discrepancy between the actual and desired characteristic of an item. An anomaly may or may not affect the ability of an item to perform a required function (see [3]). Asymmetric Configuration Configuration where the IMA group is not required to configure all links in both the transmit and receive directions. Asymmetric Operation Mode where the IMA group is allowed to carry ATM traffic over links that are not Active in both transmit and receive directions. ATM Asynchronous Transfer Mode ATM Layer Cell Cells that are exchanged between the ATM layer and IMA sublayer. AVCR AVailable Cell Rate B-ISDN Broadband ISDN BICI Broadband Inter-Carrier Interface Blocked This a group state indicating than the group has been inhibited. Blocking This is a transitional state that allows graceful transition into the Unusable without loss of ATM layer cells. CAC Connection Admission Control CBR Constant Bit Rate CDV Cell Delay Variation CID Cell Identification (ICP CID) CLR Cell Loss Ratio Config-Abort This a group state indicating than the group has rejected the group parameters proposed the FE IMA group. CPE Customer Premises Equipment CRC Cyclic Redundancy Check CTC Common Transmit Clock configuration This is a configuration where the transmit clocks of all the links within the IMA group are derived from the same clock source. Data Round-Robin This represents the scheduler transmitting or receiving cells in a round-robin fashion. Defect A defect is a limited interruption in the ability of an item to perform a required function. It may or may not lead to maintenance action depending on the results of additional analysis. Successive anomalies of an item to perform a required function are considered as a defect (see [3]). DSU Data Service Unit DXI Digital eXchange Interface ES Errored Seconds Such as defined in ANSI T1.231[3] Failure A failure is the termination of the ability of an item to perform a required function (see [3]). Fault A Fault is an implementation specific NE event triggered, e.g., due to wrong LSM behavior at the FE. However, Fault does not cover the detection of invalid ICP cell content. FC Failure Count FE Far-End Filler cell This cell is used to fill in the IMA frame when no cells are available at the ATM layer. It is used for performing cell rate decoupling at the IMA sublayer (like Idle cell for single-link interface). GSM Group State Machine State machine defining the behavior of the IMA group. GTSM Group Traffic State Machine This is defined to indicate when traffic is exchanged with the ATM layer. HEC Header Error Check HSSI High Speed Serial Interface ICP cell IMA Control Protocol cell ICO ICP Cell Offset IEC Inter-Exchange Carrier IETF Internet Engineering Task Force IDCC IMA Data Cell Clock IDCR IMA Data Cell Rate This represents the rate at which IMA data cell should be exchanged between the IMA sublayer and the ATM layer. IFSN IMA Frame Sequence Number IMA Inverse Multiplexing for ATM IMA frame The IMA frame is used as the unit of control in the IMA protocol. It is defined as M consecutive cells, numbered 0 to M-1 on each link, across the N links in an IMA group. One of the M cells on each of the N links is an ICP cell that occurs within the frame at the ICP cell offset position (the offset may be different on different links). The IMA frame is aligned on all links. "Aligned" means that it is transmitted "simultaneously". Differential link delay can cause the reception to "misaligned" in time; the alignment is recovered by the link delay synchronization mechanism. M is defined during start-up; N is determined by the UM and the IMA link start-up procedure; and the ICP "stuff" mechanism is a controlled violation of the IMA consecutive frame definition. IMA group Group of links at one end used to establish an IMA virtual link to another end. IMA RR IMA Round Robin This is the distribution or retrieval of ATM layer and Filler on a cell by cell basis, when Tx=On or Rx=On respectively. IMA sublayer Sublayer part of the Physical layer and located between the interface specific Transmission Convergence (TC) sublayer and the ATM layer. IMA virtual link Virtual link established between 2 IMA ends over a number of physical links (IMA group). In Group This is an event indicating that a link has configured within an IMA group. Inhibiting This represents the action to voluntary disable the capacity of the group or the link to carry ATM layer cells reason other than reported problems. Insufficient-Links This a group state indicating than the group has not sufficient links to be in the Operational state. ISDN Integrated Services Digital Network ITC Independent Transmit Clock configuration This is a configuration where there is a transmit clock of at least one link within the IMA group that is not derived from the same clock source as the clock source of any other transmit links. ITU-T International Telecommunication Union - Telecommunication Standardization Sector IV ICP cell Violations LASR Link Addition and Slow Recovery procedure Layer Management Functions The Layer Management functions relate to processing of actions such configuration, fault monitoring, performance monitoring within the layer. LCD Loss of Cell Delineation defect The LCD defect is reported when the OCD anomaly has persisted for the period of time specified in ITU-T Recommendation I.432[41]. The LCD defect is cleared when the OCD anomaly has not been detected for the period of time specified in ITU-T Recommendation I.432. LCD-RDI Loss of Cell Delineation Remote Defect Indicator The LCD-RDI defect is reported to the FE when a link defect is locally detected. The LCD-RDI defect is not always required on link interface. LDS Link Delay Synchronization The LDS is a event indicating that the link is synchronized with the other links within the IMA group with respect to differential link delay. LCR Link Cell Rate Cell rate (cell/sec) over the portion of the link bandwidth available for carrying cells. LID Link IDentifier LIF Loss of IMA Frame defect The LIF defect is the occurrence of persistent OIF anomalies for at least 2 IMA frames. Link Management This function provides direct management of the physical links (e.g., DS1/E1 links). LODS Link Out of Delay Synchronization defect The LODS is a link event indicating that the link is not synchronized with the other links within the IMA group. LOF Loss Of Frame LOS Loss Of Signal LSB Least Significant Bit LSI Link Stuff Indication LSM Link State Machine M IMA Frame Size MIB Management Information Base MSB Most Significant Bit N Number of links configured in an IMA group NE Near-End (local end) Non Number of links passing ATM layer cells in the transmit or receive direction. NMS Network Management System NNI Network-Node Interface Not Configured This is a group state indicating that the group does not exist yet. Not In Group This is used as an event or a state indicating that a link is no longer configured within an IMA group. OAM Operations And Maintenance OCD Out of Cell Delineation anomaly As specified in ITU-T Recommendation I.432[41], an OCD anomaly is reported upon the occurrence of ALPHA consecutive cells with incorrect HEC, and is no longer reported after detecting DELTA consecutive cells with correct HEC. OIF Out of IMA Frame anomaly The OIF is the occurrence of IMA anomalies listed later in this specification. OOF Out Of Frame Operational This a group state indicating than the group has sufficient links on both Tx and Rx directions to carry ATM layer cells. OSI Open System Interconnection PMD Physical Medium Dependent ppm part per million PRC Primary Reference Clock This term is from ITU-T Recommendation G.811[34]. This is a synonym of PRS. PRS Primary Reference Source This term is from ANSI T1.101[1]. This is a synonym of PRC. QoS Quality of Service PTx Minimum number of links required to be Active in the transmit direction for the IMA group to move into the Operational state. PRx Minimum number of links required to be Active in the receive direction for the IMA group to move into the Operational state. RDI Remote Defect Indicator RFC notes Requests For Comments notes RFI Remote Failure Indicator RM cell Resource Management cell PRI Primary Rate Interface Rx Receive (side) Rx=On The receive end is passing received ATM cells to the ATM layer. Rx Failed The Rx Failed condition is entered after a specified persistence of a link defect (e.g., LCD) or an IMA defect (LIF or LODS). It causes the LSM to enter into the Unusable state. The mechanism is implementation specific and could be separated from the failure definition due to a general used Network element-wide mechanism/parameter for failure detection. SAR Segmentation And Reassembly SCCI field Status and Control Change Indication field SES Severely Errored Seconds SICP cell Stuff ICP cell One of the 2 ICP cell comprising a stuff event. Stuff event Repetition of an ICP cell over one IMA link to compensate for timing difference with other links within the IMA group. SMI Structure of Management Information Defined in RFC 1442[19], it is divided into three parts: module definitions, object definitions, and trap definitions. SNMP Simple Network Management Protocol Start-up This a group state indicating than the group is waiting to see the FE in Start-up. Start-up-Ack This a group transitional state, when both groups start-up and the FE group parameters have been accepted. Symmetric Configuration Configuration where the IMA group is required to configure all links in both the transmit and receive directions. Symmetric Operation Mode where the IMA group is required to only carry ATM layer cells on links that are Active in both transmit and receive directions. TC Transmission Convergence TRL Timing Reference Link This is the link selected as the reference to derive the IDCR. TRLCR Timing Reference Link Cell Rate Tx Transmit (side) Tx=On The transmit end is sending ATM cells coming from the ATM layer. UNI User Network Interface Unit Management Entity managing a unit such as an IMA unit. UAS UnAvailable Seconds Such as defined in ANSI T1.231[3]. Unusable This is a link state indicating the link is not in use due to fault, inhibition, etc. Usable This is a link state indicating the link is ready to operate in the specified direction, but it is waiting to move to Active. UUS UnUsable Seconds Seconds where the link state is Unusable. VCI Virtual Connection Identifier VPI Virtual Path Identifier 3. IMA Objectives The main objectives that guided the development of the IMA Specification are listed below. Only the performance objectives applicable to the case where IMA is used over DS1/E1 links have been identified. · Available for private/public UNI's and NNI's and BICI's. · Provide transport of a single ATM cell stream at rates between existing link rates (e.g., between DS1/E1 and DS3/E3 rates) · Applicable over DS1/E1 or other interfaces carrying ATM cells. · Operating on the interfaces operating at the same nominal link cell rate (LCR). · Provide for the provisioning of bandwidth in physical link increments (e.g., DS1/E1 increments). · Provide transparent transport of the ATM layer and higher layer signals (including the preservation of cell order, control of cell delay variation, cell format, etc.). · Use a cell based multiplexing technique for converting a single ATM stream into multiple lower speed ATM streams to be sent over independent links and retrieving the initial ATM cell stream from the links at the far-end. · Maintain compatibility with current ATM Forum Physical Layer specifications (i.e., same transmission convergence sublayer including the relevant transmission MIB). · Detect and reject lines with delay greater than the provisioned maximum differential delay tolerance. · Add/delete links while maintaining the IMA group in service. · Handle link failure and automatic link recovery. · Support the use of leased and dial lines (e.g., ISDN lines) providing the same LCR, including links running in configurations where the transmit clocks of the links in the group are not all derived from the same source. · Support symmetric and asymmetric IMA configurations, and symmetric and asymmetric IMA operations. · Support of all ATM traffic/QoS classes including CBR. · When running over DS1/E1 links, the IMA interface should compensate for link differential delays of at least 25 milliseconds. · When running over DS1/E1 links, the IMA interface should contribute minimal CDV so as to support an end-to-end service objective of 1 millisecond CDV. · When running over DS1/E1 links, the IMA interface should exhibit cell level error performance comparable to an individual DS1/E1 link. The effects of both random and bursty errors should be considered. · Support system easily integrable with current network management system. · Provide IMA status MIB - Management Information Base. · Allow re-use of existing DS1/E1 Physical Layer devices. 4. IMA Reference Models This section provides reference models of different aspects of IMA. 4.1 IMA Sublayer in Layer Reference Model Figure 3 on page 21 illustrates the layer reference model including the Inverse Multiplexing for ATM (IMA) sublayer. It is based on the B-ISDN protocol reference model defined in ITU-T Recommendation I.321[38]. The IMA sublayer is part of the physical layer. It is located between the traditional Transmission Convergence sublayer and the ATM layer. Figure 3 shows the main functions of the IMA sublayer. Figure 3 IMA Sublayer in Layer Reference Model 4.2 Reference Model of Unit Operating IMA This section describes the functions that characterize an unit that supports an IMA interface. Figure 4 on page 22 shows the functional blocks of such unit. This specification only covers the IMA functions and portions of the Link and Unit Management functions required for managing the IMA interface. All others are implementation dependent or defined in other ATM Forum specifications. Figure 4 Functional Blocks of Units Hosting an IMA Interface The following sections describe in more detail the functional blocks of the IMA unit. 4.2.1 Source Interface The Source Interface provides the connection (typically proprietary) to an internal data bus (e.g., an ATM switch, router, computer). The Source Interface might also be a standard interface (e.g., DXI over HSSI). In the first case the IMA is "integrated" into a network element supporting other functions and may therefore provide such (non-standardized) functions as integrated management. In the second case, the IMA is a stand-alone unit. There is no requirement that a particular Source Interface must be supported. The Source Interface choice is vendor specific. There is also no requirement that the Source Interface on one side match the Source Interface on the other (e.g., one side could be a direct interface to a data bus in an ATM switch and the other could be an ATM DSU supporting the IMA function). 4.2.2 Cell Function The Cell Function is dependent upon the Source Interface: · If the Source Interface emits ATM cells, the Cell Function is null (traffic shaping, if any, may be accomplished outside the unit). In this case, OAM cells, RM cells, etc., must be passed transparently through the source interface. · If the Source Interface does not emit ATM cells, the Cell Function must arrange for the output of the source interface to be converted into ATM cells. There is no limitation on the Cell Function other than it must emit ATM cells. This requirement does not preclude the Cell Function implementing traffic shaping, buffering for frames/cells, etc. Support within the cell function is an implementation issue (e.g., OAM cell flows, RM cells, VPI/VCI to frame-level mapping). · There is no requirement that the Cell Function on one side match the Cell Function on the other (e.g., one side could be null, as would be the case with a direct interface to a data bus in an ATM switch, and the other could support full AAL1, AAL3/4, AAL5 SAR functions, as might be the case for an ATM DSU supporting the IMA function). 4.2.3 Inverse Multiplexing The Inverse Multiplexing function controls the distribution of cells onto the group of links made available to the IMA and handles differential delays and actions to be taken when links are added/dropped or when they are failed/restored. In the receive direction, the IMA performs differential delay compensation and recombines the cells into the original cell stream with the original inter-cell spacing or something. In essence, the Inverse Multiplexing function emulates a single UNI/NNI/BICI physical link; the IMA process of splitting and recombining streams is as transparent to the layer above as a traditional single-link physical layer interface. 4.2.4 Link Management This function provides direct management of the physical links (e.g., DS1/E1 links). This may include such functions as establishing those links, for example DS1/E1 links via ISDN PRI signaling over a D channel. Other functions in Link Management include the notification of network management operations upon detection of link defects, collecting Facility Data Link information, instantiating the physical link MIB objects, etc. Link Management functions also relate to the management and establishment of the links available to the IMA function. · When implementing an IMA virtual link over a specific type of links (e.g., DS1/E1 links), the IMA MIB objects should inter-work with the link MIB if specified in an RFC (e.g., RFC 1406 [18] for DS1/E1). · The Link Management function should not preclude the option of using dial-up services (e.g., ISDN service). If such are supported, the Link Management function should perform the connection management (establishment and release). Unit management should determine the establishment and release policies (i.e., when to initiate a new DS1/E1 link, when to release it, etc.). 4.2.5 Unit Management The Unit Management (UM) function provides for the management of all functions of the whole unit. For example, capabilities required by users would include support of MIBs indicating the status of the IMA function, integration of alarms in the IMA, provision of a configuration interface, SNMP access to the unit, etc. The IMA MIBs which allows management of the IMA functions of the unit are specified in Section 15 on page 80 and shall be implemented if the UM is SNMP based. Other unit management functions are for further study. 4.3 Timing Reference Model On a link basis, the unit clocking should comply with the appropriate requirements for the links (e.g., ATM Forum DS1 and E1 specifications[8][9]). On a group basis, the timing may be based on the timing configuration guideline presented in Figure 5 on page 24. Other timing configurations are feasible but are not discussed here. Switch Sw and switches Sw(0) to Sw(N-1) appearing in Figure 5 indicate the possible configurations. The "Tx Clock Unit" may derive its timing from an internal source, an external source or from any incoming link. If loop timing (also referred as slave clocking[33]) is required, Sw(0) to Sw(N-1) could be set to position "1" on the associated link. Loop timing may be used when synchronizing to a digital network on a per link basis. Another example of loop timing would be using one of the incoming links as the source of the "Tx Clock Unit" and have all the link switches set to "0". The term Independent Transmit Clock (ITC) is used for operation where the transmit clock on each link is independently derived from a clock source. An example is illustrated in Figure 5 on page 24 by having at least one of switches Sw(0) to Sw(N-1) being set to position "1". The term Common Transmit Clock (CTC) is used when the same clock is used for all links. An example of this is illustrated in Figure 5 on page 24 by having all switches Sw(0) to Sw(N-1) being set to position "0". Appendix G on page 127 shows application scenarios intended to provide guidance in selecting a timing configuration. Figure 5 IMA Timing Configuration Reference Model 5. Basic IMA Protocol Definitions 5.1 IMA Physical Link Characteristics This section specifies the basic architecture of the IMA interface. (R-1) The IMA interface shall utilize a number (N) of transmission links designated as an IMA group by the unit management (UM). These links shall all operate at the same nominal link cell rate (LCR). (R-2) The IMA interface shall be connected to another IMA interface over clear channel facilities. This implies that all cells generated by the transmit IMA unit shall only be terminated at the receive IMA unit. 5.2 Transmission Convergence Sublayer Specification This section defines: · exceptions to the interface specific transmission convergence functions when IMA sublayer is implemented, and · basic IMA sublayer functions 5.2.1 Exceptions to the Interface Specific Transmission Convergence Sublayer The physical layer HEC generation/verification, cell header correction (if required), cell delineation and cell payload scrambling/descrambling (if required) should be implemented as specified in the appropriate physical layer specification for the links to be used in the IMA group. The following exceptions to the interface specific Transmission Convergence (TC) sublayer shall be met: (R-3) The interface specific TC sublayer shall pass all cells to the IMA sublayer or provide an indication that a cell was received (this includes HEC errored cells). (R-4) Idle cells shall not be used at any time to perform cell rate decoupling. Cell rate decoupling is performed at the IMA sublayer. 5.2.2 IMA Specific Transmission Convergence Sublayer Part 5.2.2.1 IMA General Characteristics (R-5) The transmit IMA shall assign a unique Link Identifier (LID) to each physical link within the IMA group. The LID shall, not be changed while the link is a member of an IMA group. (R-6) The selected LID value shall be between 0 and 31 inclusive. (R-7) The transmit IMA shall distribute ATM cells arriving from the ATM layer (including any unassigned cells) over the N links in a cyclic round robin fashion, and on a cell-by-cell basis. (R-8) The transmit IMA shall distribute the ATM layer cells over the links using an ascending order based on the LID assigned to each link within the IMA group. (R-9) Each end of the IMA virtual link shall use the IMA Control Protocol (ICP) cell format defined in Table 2 on page 29 to convey IMA configuration, synchronization, status and defect information to the far-end (FE). (R-10) The transmitting IMA sublayer shall perform cell rate decoupling by inserting IMA Filler cells between ICP cells when there is no cell available at the ATM layer. (R-11) The receive IMA shall: - accept ATM cells from the N links according to ascending order based on the Link ID (LID) received in the ICP cells on the incoming link, - compensate for differential link delays and re-build the original ATM cell stream, - discard Filler cells, - discard cells with bad HEC, - process and discard ICP cells, - pass the aggregate ATM cell stream to the ATM layer (this includes unassigned cells), and - not mis-order cells. (R-12) The receive IMA shall use the ICP cell to maintain link delay and protocol synchronization and to determine the differential delay between the links in the IMA group. 5.2.2.2 IMA OAM Cell Definition Two IMA OAM cells are defined: · Filler cell · IMA Control Protocol (ICP) cell These cells are defined in Table 1 on page 27 and Table 2 on page 29, respectively. The transmission of the octets is row-by-row, from top to bottom. In each octet, the most-significant bit is transmitted first (MSB = bit 7, LSB = bit 0). The following fields are common to both Filler and ICP cells: · cell header, · OAM label, and · cell identification (R-13) The Filler and ICP cell header is the same and shall contain a fixed combination as specified in Table 1 on page 27 and Table 2 on page 29. (R-14) Octet 6 of Filler and ICP cells shall contain the OAM Label and be set to "0x01", to indicate IMA Version 1.0. (R-15) The Cell Identification (CID) bit, bit 7 of octet 7 of the Filler and ICP cells, shall be used to identify the IMA OAM cell as an ICP or Filler cell. (R-16) Octets 52-53 are defined as specified in ITU-T Recommendation I.610[42], Section 7.1, for octets 52-53 of the F1 and F3 flow OAM cells. The following subsections gives details of the Filler and ICP cells respectively. 5.2.2.2.1 Filler Cell Definition This section defines the Filler cell. This cell is used for performing cell rate decoupling at the IMA sublayer. (R-17) The format of the Filler cell shown in Table 1 on page 27 shall be used. Table 1 Filler Cell Format Octet Label Comments 1 - 5 ATM cell header Octet 1 = 0000 0000, Octet 2 = 0000 0000, Octet 3 = 0000 0000, Octet 4 = 0000 1011, Octet 5 = 0110 0100 (valid HEC) 6 OAM Label bits 7-0: OAM Label value 00000001: IMA Version 1.0 7 Cell ID Link ID Bit 7: IMA OAM Cell Type (0: Filler cell) Bits 6-0: Unused and set to 0 8-51 Unused Set to 0x6A as defined in ITU Recommendation I.432 [41] for unused bytes. 52 - 53 CRC Error Control Bits 15-10: Reserved field for future use - default value coded all zero. Bits 9-0: CRC-10 as specified in ITU Recommendation I.610[42]. The Filler cell can be validated by verifying the value of the header, OAM Label, CID and CRC fields. 5.2.2.2.2 ICP Cell Definition The ICP cell structure is detailed in Table 2 on page 29. The content of the ICP cell has been divided in five classes: · A: Link specific information, transmitted only over the specific link. · B: Group specific information, transmitted over all links in the group. · C: Link specific information, however transmitted over all links in the group. · D: Unused octet · E: End-to-end channel (R-18) The same content of fields appearing under classes B and C shall be transmitted over all links within an IMA group. (R-19) Bits 4-0 of octet 7 shall be used to identify the Link ID (LID) on which the ICP cell is sent. Its range shall be from 0 to 31. The IMA Frame Sequence Number (IFSN) field (octet 8) is used to indicate the sequence number of the IMA frame. The ICP Cell Offset field (octet 9) is used to indicate the location of the ICP cell within the IMA Frame. The use of these is defined in more detail in Section 5.2.2.3 on page 30. The Link Stuff Indication (LSI) fields, bits 2-0 in octet 10, is used to indicate the occurrence of the next stuff event. The use of the LSI field is specified in more detail in Section 7 on page 36. The Status and Control Change Indication (SCCI) field (octet 11) is used to indicate changes over octets 12 to 49 (classes B and C). Its is specified in more detail in Section 5.2.2.4 on page 32. The IMA ID field (octet 12) is used to indicate the ID of the IMA group. The field is set to a value between 0 and 255 inclusive (8 bit value). Its use is specified in more detail in Section 5.2.2.5 on page 33. The Group Status and Control field (octet 13) is used to indicate group status and control information. The use of the Group Status and Control field is explained in more detail in Section 5.2.2.6 on page 33 and Section 10.2 on page 53. The Transmit Timing Information field (octet 14) is used to indicate the synchronization and the timing reference link (TRL) used by the transmit end. The use of the Transmit Timing Information field is explained in more detail in Section 7 on page 36. The Tx Test Control, Tx Test Pattern and Rx Test Pattern fields (octets 15-16-17) are used to implement the test pattern procedure as specified in Section 13 on page 77. The Link Information fields (octets 18 to 49) are used to exchange IMA link specific information between both ends of the IMA virtual link. The detail of the Link Information field is shown in Table 3 on page 30. (R-20) The Link 0 Information field shall be used to exchange information on the transmit link having LID = 0, the Link 1 Information field for transmit link having LID = 1, etc. The use of the Link Information is described in more detail in Section 10.1.6 on page 52 and Section 12.1.2 on page 69. (R-21) Octet 50 within the ICP cell is unused and shall be set to 0x6A as defined for unused octets in ITU-T Recommendation I.432[41]. (R-22) The End-to-End Channel field (octet 51) shall be reserved as a proprietary channel. The field shall be set to "0" if unused. (R-23) The IMA shall not rely on the processing of the End-to-End Channel field for any IMA functionality defined within this specification. (R-24) At the receive end, the HEC and CRC-10 of the ICP cell shall be checked before relying on the fields covered by these two error checks. Table 2 ICP Cell Format Octet Class Label Comments 1 - 5 ATM cell header Octet 1 = 0000 0000, Octet 2 = 0000 0000, Octet 3 = 0000 0000, Octet 4 = 0000 1011, Octet 5 = 0110 0100 (valid HEC) 6 OAM Label bits 7-0: OAM Label value 00000001: IMA Version 1.0 7 A Cell ID and Link ID Bit 7: IMA OAM Cell Type (1: ICP cell) Bits 6-5: Unused and set to 0 Bits 4-0: Logical ID for physical link range (0... 31) 8 A IMA Frame Sequence Number IMA Frame Sequence Number: from 0 to 255 and cycling. 9 A ICP Cell Offset Range (0... M-1): indicates position of ICP cell within the IMA frame. 10 A Link Stuff Indication Bits 7 - 3: Unused and set to 0 Bits 2 - 0: 111 = No imminent stuff event, 100 = Stuff event in 4 ICP cell locations (optional), 011 = Stuff event in 3 ICP cell locations (optional), 010 = Stuff event in 2 ICP cell locations (optional), 001 = Stuff event at the next ICP cell location (mandatory), 000 = This is one out of the 2 ICP cells comprising the stuff event (mandatory). 11 B Status & Control Change Indication Bits 7-0: Status change indication: 0 to 255 and cycling (count to be incremented every change of octets 12-49) 12 B IMA ID Bits 7-0: IMA ID 13 B Group Status & Control Bits 7-4: Group State 0000 = Start-up, 0001 = Start-up-Ack, 0010 = Config-Abort - Unsupported M, 0011 = Config-Abort - Incompatible Symmetry, 01xx = Reserved for other Config Abort reasons, 1000 = Insufficient-Links, 1001 = Blocked, 1010 = Operational, Others: Reserved Bits 3-2: Symmetry of Group 00 = Symmetrical configuration and operation, 01 = Symmetrical configuration and asymmetrical operation (optional), 10 = Asymmetrical configuration and asymmetrical operation (optional), 11 = Reserved Bits 1-0: IMA Frame Length (00: M=32, 01: M=64, 10: M=128, 11: M=256) 14 B Transmit Timing Information Bits 7-6: Unused and set to 0 Bit 5: Transmit Clock Mode: (0: ITC mode, 1: CTC mode) Bits 4-0: Tx LID of the timing reference link (0 to 31) 15 B Tx Test Control Bits 7-6: Unused and set to 0 Bit 5: Test Link Command (0:inactive, 1: active) Bits 4-0: Tx LID of test link (0 to 31) 16 B Tx Test Pattern Bit 7-0: Tx Test Pattern (value from 0 to 255). 17 B Rx test Pattern Bit 7-0: Rx Test Pattern (value from 0 to 255). 18 C Link 0 Information Bits 7-5: Transmit State (see Table 3 on page 30) Bits 4-2: Receive State (see Table 3 on page 30) Bits 1-0: Rx Defect Indicators (see Table 3 on page 30) 19-49 C Link 1-31 Info Status and control of link with LID in the range 1-31. 50 D Unused Set to 0x6A as defined in ITU I.432 for unused bytes. 51 E End-to-end channel Proprietary channel (set to 0 if unused). 52 - 53 CRC Error Control Bits 15-10: Reserved field for future use - default value coded all zero. Bits 9-0: CRC-10 as specified in ITU Recommendation I.610[42]. Table 3 Encoding of the Link Information Fields Bits Encoding 7-5 Tx State State Additional information (see note ) 000 Not In Group 001 Unusable No reason given 100 Unusable Inhibited (vendor specific) 101 Unusable Failed (not currently defined) 010 Unusable Fault (vendor specific) 011 Unusable Mis-connected 110 Usable 111 Active 4-2 Rx State 000 Not In Group 001 Unusable No reason given 100 Unusable Inhibited (vendor specific) 101 Unusable Failed 010 Unusable Fault (vendor specific) 011 Unusable Mis-connected 110 Usable 111 Active 1-0 Rx Defect 00 No defect 01 Physical Link defect (e.g. LOS, OOF/LOF, LCD) 10 LIF 11 LODS 5.2.2.3 IMA Frame Definition The IMA frame is used as the unit of control in the IMA protocol. It is defined as M consecutive cells, numbered 0 to M-1 on each link, across the N links in an IMA group. One of the M cells on each of the N links is an ICP cell that occurs within the frame at the ICP cell offset position (the offset may be different on different links). The IMA frame is aligned on all links. "Aligned" means that it is transmitted "simultaneously". Differential link delay can cause the reception to "misaligned" in time; the alignment is recovered by the link delay synchronization mechanism. M is defined during start-up; N is determined by the UM and the IMA link start-up procedure; and the ICP stuff mechanism, as defined in Section 7 on page 36, is a controlled violation of the IMA consecutive frame definition. (R-25) An IMA Frame shall be composed of M consecutive cells transmitted on each link within the IMA group. (R-26) The ICP cell shall be sent on each link once per IMA frame, hence every M cells. (R-27) The IFSN field in the ICP cell shall be used to indicate the sequence number of the IMA frame. The field shall increment from 0 to 255 and repeat the sequence. (R-28) The IMA Frame Sequence number in the ICP cell shall increment with each IMA frame on a per-link basis, but within an IMA frame, the sequence number contained in the ICP cell of each link is identical. (R-29) The transmit IMA shall align the transmission of IMA frame on all links within an IMA group. Figure 2 on page 13 shows an example of the transmission of IMA frames over three links. On link 0, the ICP cells have their cell offset set to zero (i.e., they are the first cell in each IMA frame). On link 1, the ICP cells have the ICP cell offset set to 3 and on link 2, the ICP cells have their ICP cell offset set to 1. In practice, these ICP cells should be distributed more evenly over the IMA frame but are shown closer for ease of illustration. It should also be noted that within an IMA frame, the ICP cells on all links have the same IMA Frame Sequence number. The ICP cell offset is described in more detail in the next section. Figure 6 Illustration of IMA Frames 5.2.2.3.1 ICP Cell Offset The ICP cell may be located anywhere within the IMA frame (e.g., the ICP cell offset may be any value from 0 to 127 if M = 128). An ICP cell offset of 0 means that the ICP cell is the first cell of the IMA frame on that particular link. An ICP cell offset of M-1 means that the ICP cell is the last cell of the IMA frame on that link. (R-30) The ICP Cell Offset field (octet 9) shall be used to indicate the location of the ICP cell within the IMA Frame. The field shall be set to a value between 0 to M-1 where M is the IMA frame length in cells. (O-1) The transmit IMA may fill the following locations to spread ICP cells: 0, (1/2)M, (1/4)M, (3/4)M, (1/8)M, (3/8)M, (5/8)M, (7/8)M, etc. The transmit end could select the first unused location appearing in the list when adding a new link within the IMA group. (R-31) The offset of the ICP cell sent over any link shall be fixed when the link is assigned a LID and this offset shall remain the same until the link is no longer part of the group. Spreading the ICP cells in the IMA frame from link to link allows faster notification of configuration where the links exhibit the same propagation delay and minimum delay introduction related to the handling of ICP cells. 5.2.2.3.2 IMA Frame Length (M) The IMA Frame Length (M) shall be processed as follows: (R-32) The value of M used by an IMA shall always be carried in the ICP cell within the IMA Frame Length field. (R-33) The IMA interface shall support M = 128. (O-2) The support of M equals to 32, 64, 256 is optional; no other values are supported. (R-34) The value M shall be configured at group start-up time, shall remain fixed thereafter and shall have a default value of 128. Section 10.2 on page 53 describes the group start-up procedure in more detail. Changing the transmitted M value at any other time will impact the IMA Frame Synchronization Mechanism (see Section 11 on page 65). (CR-1) If (O-2) is used, the value of M used by the transmit end shall be as the one configured by the UM. (CR-2) If (O-2) is used, it is not required that both directions of the IMA virtual link use the same M. (CR-3) If (O-2) is used, the receive end shall synchronize its incoming links using the received M value for IMA frame synchronization. (R-35) If the receive end does not support the received M, it shall abort the start-up procedure using the corresponding code defined in the "Group Status and Control" field (see Section 10.2.1.2 on page 55). The value M may be configurable. 5.2.2.4 Processing of the SCCI Field (R-36) The SCCI field shall be set to the previous transmitted SCCI value, incremented modulo 256, to indicate a change on at least one of the fields appearing in octets 12 to 49 in the transmitted ICP cell (see Table 2 on page 29). The monitoring of the ICP cell at the receiving end is implementation dependent. The receiver may select only one or more links to monitor the value of the SCCI field. (R-37) The SCCI field shall be used to identify received ICP cells for processing when ICP cells are monitored on more than one link, or when the monitored link has changed. Fields in octets 12 to 49 shall be processed if the SCCI field has advanced beyond the SCCI value of the last processed ICP cell. 5.2.2.5 IMA ID The IMA ID is used to identify the IMA ID group. (R-38) The IMA ID used by the transmit end shall be carried in the IMA ID field. (R-39) The IMA ID shall be set at group start-up time. Changing the transmitted IMA ID value at any other time will impact the IMA Frame Synchronization Mechanism (see Section 11 on page 65). Both ends of the IMA virtual link can independently select an IMA ID. There is no need to ensure a unique IMA ID on each end. The IMA ID may be configurable. 5.2.2.6 Group Symmetry The IMA protocol is defined to allow symmetric or asymmetric cell rate transfer over the IMA virtual link. The IMA interface can be configured in three modes: · Symmetrical Configuration and Operation: this the default and mandatory mode; in this mode, the IMA interface is required to configure each IMA link in both transmit and receive directions; it is also enforced to only transmit and receive ATM layer cells over links that are Active in both directions. · Symmetrical Configuration and Asymmetrical Operation: in this case, the IMA interface is required to configure each IMA links in both transmit and receive directions; it is permitted to keep transmitting ATM layer cells over a link in the transmit direction while the link is not Active in the receive direction or vice versa. This behavior is described in Appendix C on page 117. · Asymmetrical Configuration and Operation: in this case, the IMA interface is not required to configure all IMA links in both transmit and receive directions; it is also permitted to keep transmitting ATM layer cells over a link in the transmit direction while the link is not Active in the receive direction or vice versa. This behavior is described in Appendix C on page 117. The "Symmetry" field, specified in Table 2 on page 29, is used to indicate the symmetry of the IMA group. (R-40) The symmetry of the group shall be only established or changed at group start-up time. (R-41) The "Symmetrical Configuration and Operation" mode shall be supported by all IMA implementations. (O-3) The use of the "Symmetrical Configuration and Asymmetrical Operation" mode is optional. (O-4) The use of the "Asymmetrical Configuration and Operation" mode is optional. (R-42) If the NE does not support the symmetry mode proposed by the FE, or the proposed symmetry proposed by the FE and the configured symmetry of the NE do not match, the NE shall abort the start-up procedure using the appropriate code defined in the "Group Status and Control" field (Table 2 on page 29). In order to allow a fast recovery when (O-3) or (O-4) is used at the NE and when the FE IMA can only be configured to the "Symmetrical Configuration and Operation" mode, the NE may adjust to the symmetric operation. (R-43) Only the valid combinations of symmetrical configurations specified in Table 4 on page 34 shall be used at each end of the IMA virtual link. The symmetry of the group may be configurable. Table 4 Valid and Invalid Combinations of Different Symmetrical Configurations End B Symmetrical Configuration Asymmetrical Configuration Symmetrical Operation Asymmetrical Operation Asymmetrical Operation End A Symmetrical Configuration Symmetrical Operation Valid Invalid Invalid Asymmetrical Operation Invalid Valid Invalid Asymmetrical Configuration Asymmetrical Operation Invalid Invalid Valid 6. Quality of Service (QoS) Requirements (R-44) The IMA interface shall support all ATM traffic/QoS classes supported at the ATM layer. 7. Support for Common and Independent Transmit Clock Operations In order to accommodate the use of Common Transmit Clock (CTC) and Independent Transmit Clock (ITC) configurations as defined in Section 4 on page 21, this specification defines the insertion of a stuff event to compensate for timing difference between the links within an IMA group. The IMA link transmit interfaces may be locked to one clock source or may be plesiochronous with respect to the other links. When plesiochronous, one of the IMA transmit buffers may become depleted or overflow due to timing differences. The IMA cell stuff mechanism is provided to allow error-free ITC operation. In the CTC mode, stuffing is also inserted on all links at nominal rate specified in Section 8 on page 38. This allows inter-operation between transmitter running the CTC and ITC modes and fixes a single nominal rate for the IMA Data Cell Rate (IDCR) defined in Section 8 on page 38. (R-45) The transmit IMA shall indicate to the far-end (FE) in which transmit clock mode it is running in the "Transmit Clock Mode" field in the ICP cell (see Table 2 on page 29). The transmit IMA is allowed to indicate that it is in the ITC mode even if all the transmit clocks of the links in the group are derived from the same source. (R-46) The transmit IMA shall support the CTC mode. (R-47) The transmit IMA shall only indicate to the FE that it is in the CTC mode when all the transmit clocks of the links in the group are derived from the same source. (O-5) The transmit IMA may also support the ITC mode. (CR-4) If (O-5) is used, the cell stuffing mechanism procedure shall also be invoked to prevent link transmit buffer under-run or over-run. In all cases, the link transmit buffers should not deplete. (R-48) The transmit IMA shall indicate a stuff action in the ICP cell preceding a stuff event using the mandatory Link Stuffing Indication (LSI) codes specified in Table 2 on page 29. (R-49) The transmit IMA shall perform stuffing by repeating the ICP cell containing the Link Stuffing Indication (LSI) code (thus both ICP cells indicate that "this cell is 1 out of the 2 ICP cells comprising the stuff event"). One of the two ICP cells comprising the stuff event is identified as a Stuff ICP (SICP) cell. Either one may be treated as a SICP cell. The insertion of a stuff event is illustrated in Figure 7 on page 37. The three additional indications (010, 011 and 100) may provide greater confidence in detecting a SICP occurrence. (O-6) The transmit IMA may also indicate an incoming stuff event in the forth, third and second ICP cells preceding the stuff event using the optional LSI codes defined in Table 2 on page 29. (R-50) The transmit IMA shall not introduce a stuff event more than once every 5M ICP, Filler and ATM layer cells over any link. Appendix B.4 on page 112 explains why 5M cells has been selected. (R-51) The receiving IMA shall remove one of any two consecutive ICP cells with LSI code indicating that "this cell is 1 out of the 2 ICP cells comprising the stuff event". The removed SICP cell shall not be counted as a cell for the purposes of determining the IMA round-robin sequence. (R-52) The receive IMA shall operate with CTC and ITC transmission modes. (R-53) When the FE IMA transmit mode does not match the NE IMA transmit mode, the NE IMA shall inform the UM of the mismatch. This shall not cause a restart of the group. It is up to the implementer to decide how to process the incoming stuff cell indication codes. It is recommended that the receive IMA rely on at least one ICP cell with a correct CRC-10. Figure 7 on page 37 shows the ICP cells before, during and after the stuff event occurrence. Figure 7 Insertion of a Stuff Event over One Link (Using only Mandatory Advanced Indication) 8. IMA Data Cell Rate Implementation This section defines the requirements of the IMA Data Cell Rate (IDCR) implementation to minimize the introduction of CDV by the IMA virtual link. The IDCR is defined as the rate at which ATM cells should be passed from the ATM layer to the IMA sublayer on transmit and passed from the IMA sublayer to the ATM layer on receive. In order to emulate single-link physical layer interfaces, the IDCR is nominally a constant for any given configuration of links in the Active state. The IDCR is derived from one of the physical links identified as the timing reference link (TRL). The TRL is used to pass synchronization from the transmit to the receive end. The IMA IDCR is derived, at both transmit and receive, according to the following equation: In the transmit direction, Non represents the number of links which currently transmit cells passed from the ATM layer (Tx=On as specified in Section 10.1.3 on page 46). In the receive direction, Non represents the number of links which currently receive ATM layer cells to be passed to the ATM layer (Rx=On as specified in Section 10.1.3 on page 46). TRLCR is the TRL cell rate providing by the TRL in the transmit and receive direction, respectively. M is the IMA frame length in cell units. The "(M-1)/M" factor account for an ICP cell every M cells. The TRLCR is scaled down by "2048/2049" to account for the insertion of one stuff event on the TRL after every 2048 ICP, Filler and ATM layer cells (e.g., every 16 IMA frames if M equals 128). This implies that in the case of ITC mode, the links other than the TRL could be faster or slower than the TRL which would require more or less frequent insertion of a stuff event to prevent transmit buffer underruns/overruns on these links. Appendix B.4.2 on page 113 explains the choice of 2048. 8.1 Behavior of the Transmit End Figure 8 on page 38 shows the behavior of the transmit end. Figure 8 Behavior of the Transmit End (R-54) The actions taken for cell rate decoupling at the IMA transmitter shall not inject a Filler cell if an ATM layer cell is available for scheduling. The IMA transmitter shall perform a check that an ATM Layer cell is available and accept that cell when the Tx IMA Data Cell Clock (IDCC) ticks and only when the Tx IDCC ticks. This means that the IMA interface should emulate the behavior of one physical interface while interacting with the ATM layer. It should also be noted that the IDCR is independently determined by the transmitter at each end of the IMA virtual link. The Rx IDCR is recovered by the receive IMA using the indicated Tx TRL. 8.1.1 Derivation of the Transmit IDCR from the TRL (R-55) The transmit IMA shall derive the Tx IDCR from the selected TRL according to (EQ. 1). 8.1.2 Selection of the TRL (R-56) A link shall be selectable as the TRL if its transmit link state is set to Active (see Section 10 on page 43). (R-57) If there is no link in the Active state, the IMA shall select one of the links in Usable state if any, else one of the links in the Unusable state shall be selected. (R-58) The TRL shall be selected only during IMA start-up by the transmit IMA and changed only when the selected TRL is deleted or no longer satisfies requirement (R-56). (R-59) Once selected, the TRL shall be indicated to the FE over the "Transmit Timing Information" field in the ICP cell (see Table 2 on page 29). As long as requirements (R-56) and (R-58) are met, the criteria for selecting the TRL at the transmit end is vendor specific. 8.1.3 Stuffing on the TRL and Other Links (R-60) When the transmit IMA is operating in the CTC mode, the IMA shall introduce a stuff event every 2048 ICP, Filler and ATM layer cells on all links. (CR-5) If (O-5) is used, the transmit IMA shall introduce a stuff event every 2048 ICP, Filler and ATM layer cells on the TRL. (CR-6) If (O-5) is used, the transmit IMA shall introduce stuff events on links other than the TRL in order to compensate the timing difference between the TRL and the other links. The previous requirements implies that the receive IMA can use a modulo-2049 counter as an additional mean to predict the occurrence of stuff event on the TRL, in the case the transmit is in the ITC mode, or on all links in the case the transmit in the CTC mode, once a stuff event has been detected. 8.2 Behavior of the Receive End This section defines the behavior of the receive IMA through requirements (R-60), (R-61) and (R-62). These requirements may be regarded as not applicable to an implementation if and only if the following conditions both apply: · the IMA receiver is directly built into end equipment that directly terminates the ATM layer (i.e., terminates all ATM connections), and · the system is only capable of carrying services that either do not require CDV control (e.g., some data services), or where the CDV in handled in some other way (e.g., absorbed in a play-out buffer at the ATM layer connection termination). An implementation that satisfies both of the above conditions may conform to these requirements if desired. The IMA receiver should remove the CDV introduced by a transmitter behaving as described in Section 8.1 on page 38. The CDV to be removed is in the form of ICP cells, including Stuff ICP (SICP) cells. Figure 9 on page 40 shows the behavior of the IMA receive end. The CDV introduced due to the emulated single physical interface behavior, as mentioned in Section 8.1 on page 38, cannot be removed. The Rx IDCR should be derived from the incoming IMA link identified as the TRL by the FE IMA transmitter over the "Transmit Timing Information" field in the ICP cell. Figure 9 Behavior of the IMA Receive End (R-61) The CDV attributed to the presence of ICP cells shall be removed by a behavior equivalent to providing a small smoothing buffer into which cells are placed after reordering and after removing ICP cells (including SICP cells), but not Filler cells. If the smoothing buffer is physically realized, the handling of overflow and underflow conditions, if any, are implementation dependent. (R-62) If the TRL is in the Working state (as defined in Figure 20 on page 70), the Rx IDCR made available to the ATM layer of the receiver shall be derived as specified in equation (EQ. 1) using the incoming link indicated by the FE IMA transmitter as the TRL in the "Transmit Timing Information" field in the ICP cell (see Table 2 on page 29). However, the receiver behavior is implementation specific during a short period (up to 100 milliseconds) after receiving the far-end indication of a change of TRL to a different link. If the IMA Frame Synchronization mechanism is not in the Working state, the recovery of the transmit IDCR is implementation specific until the Working state of that link is recovered or another TRL is selected by the transmitter. Appendix B.5 on page 114 gives an example of the recovery of the IDCR at the receive end. (R-63) Zero or one cell only shall be made available to the ATM layer at an IMA data cell clock tick. The behavior of the IMA receiver shall be equivalent to following: when the IMA data cell clock at the receiver ticks, one cell shall be removed from the smoothing buffer. If the cell is a Filler cell, then the Filler cell shall be discarded and nothing passed to the ATM layer. If the cell is not a Filler cell, then it shall be passed to the ATM layer. If there are no cells available (e.g., in the smoothing buffer), then the behavior is implementation dependent. Note that this condition is an anomaly since there should always be a cell available even if it is only a Filler cell. Note that the IMA cell clock rate will change and be re-adjusted to the new TRL if the current TRL fails or is deleted from the IMA group. Note that the abstract behavior described on the above requirements assumes that the cell stream, in the order required by the ATM layer, has been reconstructed in the smoothing buffer. During the addition or deletion of a link into/from the IMA group, the IDCR must be recalculated and the new rate applied. There are dependencies on the time at which the IMA cell rate should actually change. The play-out of data that had been received at the old cell rate and that might not have been transmitted to the ATM layer (in particular the ATM layer and Filler cells that are in the delay compensation buffers) should proceed at the data rate at which they were received. This would affect the CDV during transient phases in a link addition/recovery or deletion procedure. 9. Differential Link Delay on IMA 9.1 Differential Link Delay Requirement on Transmitter (R-64) The transmit IMA shall not introduce more than 2.5 cell times at the physical link rate of differential delay among the constituent links. The choice of 2.5 cell times at the underlying link rate should be sufficient to accommodate the following: · a gap of 1 cell time among the inputs to the constituent physical link interface, · plus 1 cell time to transmit a SICP cell, and · plus 0.5 cell time for processing. The IMA stuffing mechanism should be sufficient to ensure that the frames do not wander from alignment by more than the tolerance. Delay compensation at the receiving end may be performed using the definition of the IMA frame along with ICP cells. 9.2 Differential Link Delay Compensation at Receiver (R-65) The amount of link differential delay tolerated by an IMA implementation shall be up to at least 25 milliseconds when used over DS1/E1 links. (O-7) The amount of link differential delay tolerance may be configured up to the maximum value supported by the IMA implementation. It should be noted that both ends of the IMA virtual link may be configured with different amounts of tolerable differential delay (i.e., say one up to 25 ms and one greater than 25 ms). Appendix A on page 107 provides a detailed example of link differential delay compensation. Appendix B.3 on page 111 describes the limitation of the IMA protocol with respect to link differential delay. 10. IMA Interface Operation This section defines the operation of the IMA individual link and group. 10.1 IMA Link Operation The IMA link operates independently for both the transmit and receive directions at each end of the IMA virtual link. It allows for a smooth introduction of each link in the round-robin. It also allows graceful handle of error conditions and removal of a link. A Link State Machine (LSM) is defined for the transmit and receive directions of each IMA link. 10.1.1 Overview of the Link State Machine Figure 10 on page 44 and Figure 11 on page 45 provide an overview of the link state machine (LSM) in both the transmit and receive directions respectively. A simplified Harel state machine notation [12] is used in Figure 10 and Figure 11. In this notation, the top field of a block identifies the state, while the bottom specifies actions. Arrows denote state transition paths with the event triggering the transition shown as overlaid text. Local events or FE state transitions are used as events. Conditions such as Not In Group and Unusable are locally defined and controlled, no indications received from the FE. One out of 4 states in each direction can be viewed by the FE over the "Link Information" fields defined in Table 3 on page 30: · Not In Group: the link is not configured within an IMA group. · Unusable: link is configured, but not in use due to fault, inhibition, etc. · Usable: link ready to operate, but waiting for the other end to be Usable or Active · Active: link actively passing ATM layer cells from/to the ATM layer The LSM starts in the Not In Group state until the link is configured by the UM. Once configured, the LSM moves out to the Unusable state. From the Unusable state, the LSM provides an operating cycle between the Unusable, Usable and Active states. The Unusable state provides a synchronization point with any vendor-dependent or group level control of link usability. Link error conditions (e.g., physical or IMA errors) and vendor-dependent conditions (e.g., BER over certain limits) can delay the transition of the LSM into the Usable state or may bring the LSM back to the Unusable state from the Usable or Active state. The Unusable state also allows the IMA to voluntary delay the restoration of the link for other reason than detected problems. Later sections will refer to this as the inhibition of the link. The Usable state is an extra state between the Unusable and Active states that allows to coordinate the NE and FE when bringing up the link. It also provides a clear synchronization point before activating the links ready to be set Active. The Unusable and Usable states are also used as synchronization points between the local Tx and Rx LSMs when the IMA group is operated symmetrically. Once the Rx LSM is in the Usable state, it can move into the Active only once the FE is reporting that the Tx LSM is Usable. This transition is also subjected to a group-wide synchronization of link activation. Once the Tx LSM is in the Usable state, it can move into the Active only once the FE is reporting that the Rx LSM is Active. This transition is also subjected to a group-wide synchronization of link activation. The Tx and Rx LSMs also have the Deleted state to provide a graceful deletion of the link without loss of ATM layer cells. The Rx LSM also has the Blocking sub-state which is a transitional state toward the Unusable state to provide a graceful de-activation of a link without loss of ATM layer cells. For symmetrical operation, many of the local events are handled in both Tx and Rx LSMs at the same time. The next section provides more detail on the Tx and Rx LSM requirements. Figure 10 Transmit Link State Machine Overview Figure 11 Receive Link State Machine Overview 10.1.2 Definitions of the Transmit/Receive States and Events 10.1.2.1 Transmit Link States The following four transmit link states are defined: · Not In Group: the link is not configured, there are two sub-states: - Unassigned: no information about the link exists. - Deleted: the link has been removed from the group; this transitional state is to ensure that the other end is still not receiving ATM layer cells before it moves to the Unassigned state. · Unusable: the link is configured but cannot be used. There are many reasons for this state including: - Test failed : mis-connectivity has been found as a result of a test. The Test Pattern procedure defined in Section 13 on page 77 is an example of test that can be used. - Fault: a fault has been detected both on the link and in the link protocol. - Inhibited: operation of the link is blocked for some locally defined application or implementation dependent reason. The link may otherwise be used. · Usable: the link is ready to be used, it is awaiting the FE to activate its receiver before sending any ATM layer cells; IMA frames containing only Filler cells are being transmitted; but the link is not in the data round robin. · Active: the link is transmitting ATM layer cells; it is part of the data round robin. 10.1.2.2 Receive Link States The following four receive link states are defined: · Not In Group: the link is not configured; there are two sub-states: - Unassigned: no information about the link exists. - Deleted: the link has been removed from the group; this transitional state is to ensure that the other end is no longer Active (transmitting ATM layer cells) before it moves to Unassigned sub-state. · Unusable: the link is configured, but cannot be used; there are many reasons for this including: - Idle: insufficient information to start link establishment - Fault: a fault has been detected both on the link and in the link protocol. - Failed: the receiver has failed due to the persistence of a defined defect. Examples of defects are LCD, LIF, and LODS. These are described in more details in Section 12.1 on page 69. - Inhibited: operation of the link is blocked for some locally defined application or implementation dependent reason. The link may otherwise be used. The sub-state "Blocking" has been defined under the Usable to allow graceful transition into the Unusable state without loss of ATM layer cells. · Usable: the link is ready to be used, and it is awaiting the FE Tx to be Usable or Active. · Active: the receive IMA is receiving ATM layer cells on this link; the receive IMA considers this link as part of the data round robin. 10.1.3 Definitions of the Transmit/Receive Link Actions Table 5 on page 46 and Table 6 on page 47 shows the actions that should be performed by the LSM in the transmit and receive directions respectively. Table 5 Actions at the Transmit End Action Meaning Tx = Off Indicates that the transmit end is not expected to be sending IMA frames on that link. Tx = Filler Indicates that the transmit end is sending IMA frames containing only Filler cells on that link. Tx = On Indicates that the transmit ATM layer cell transfer from the ATM layer has been enabled for that link. Table 6 Actions at the Receive End Action Meaning Rx = Off Indicates that no cells are processed by the receive IMA on that link. Rx = Monitor Indicates that the receiver is only processing incoming ICP cells on that link. Rx = On Indicates that the receive ATM layer cell transfer to the ATM layer has been enabled for that link. 10.1.4 Link Events Driving the Link State Machines Table 7 on page 47 defines the local events driving the Tx and Rx LSMs. Depending on the symmetry of the configuration, some events would be input to both Tx and Rx state transitions. Table 7 Local Events Driving the Transmit and Receive State Machines Event Meaning Fully Symmetric Asymmetric Operation Asymmetric Configuration In Group The assignment of a link in an IMA group by the UM. This corresponds to the moment the link is configured. Both Both One only Not in Group The removal of an IMA link from a group by the UM. Both Both One only LID Assigned Sufficient information for the link to begin communication. Rx only Rx only Rx only Rx Failed Condition entered after the persistent detection of a defect at the receiver (see Section 12.1.3 on page 69 and Section B.2 on page 110). The criteria for entering the condition is implementation specific. One only One only One only No longer Rx Failed No longer in the Rx Failed condition. One only One only One only Fault Entering the Fault condition. A fault in the link or in the protocol. The meaning of this may be implementation dependent. Vendor dependent Vendor dependent One only No longer Fault No longer in the Fault condition. Vendor dependent Vendor dependent One only Inhibiting The link is not to be used for some reason (implementation and application specific). An inhibiting action on a link in the Active state is performed without loss of ATM layer cells. Both One only One only No longer inhibiting Inhibiting reason removed. Both One only One only Test related These are possible ways that the testing could be performed. Probably Tx only (see note ) Probably Tx only (see note 1) Probably Tx only (see note 1) The FE LSM states reported over the incoming ICP cells are used to drive the NE LSM. 10.1.5 Link State Transition Tables Table 8 on page 49 and Table 9 on page 51 show the transition from the current to the new LSM state and the corresponding actions to be executed upon the occurrence of any possible events. (R-66) The Tx LSM shall be controlled using the state machine transition illustrated in Table 8 on page 49. (R-67) The Rx LSM shall be controlled using the state machine transition illustrated in Table 9 on page 51. Table 8 on page 49 and Table 9 on page 51 shall be interpreted according to the following rules: · The first row presents the current state of the LSM. The current state shall be signalled to the FE via the ICP cells. · The second row presents the sub-state of the LSM. The sub-states are not signalled, although the corresponding actions shall apply. · The first column presents the events that trigger state transition. Four group of events are defined. Events may appear simultaneously and shall be treated sequentially. The order is implementation specific. Table 8 Detailed Transmit Link State Machine Primary NE Tx State Not In Group Unusable Usable Active Sub-State Unassigned (Tx=Off) Deleted (Tx=Filler) Unusable (Tx=Filler) Usable (Tx=Filler) Active (Tx=On) NE Tx Events (see note ) In group Unusable: Tx = Filler (see note ) -- -- -- -- Not in Group -- (see notes ,) -- Deleted: Tx = Filler Deleted: Tx = Filler Deleted: Tx = Filler Fault N/A (see note ) -- -- Unusable: Tx = Filler Unusable: Tx = Filler No longer Fault N/A -- Unusable or Usable (see note ) N/A N/A Inhibiting -- -- -- Unusable: Tx = Filler Unusable Tx = Filler No longer inhibiting -- -- Unusable or Usable (see note 6) -- -- FE Rx States Received in ICP Cell Not In Group N/A Unassigned: Tx = Off -- -- Usable: Tx = Filler Unusable N/A Unassigned: Tx = Off -- -- Usable: Tx = Filler Usable N/A Unassigned: Tx = Off -- -- Usable: Tx = Filler Active N/A -- -- Active or Usable (see note ) -- NE Rx State (see note ) Not in Group -- -- N/A* N/A* N/A* Unusable N/A* (see note ) N/A* -- -- Usable: Tx = Filler Usable N/A* N/A* -- -- -- Active N/A* N/A* -- -- -- FE Tx State Received in ICP Cell (see note 7) Not in Group -- -- N/A* N/A* N/A* Unusable N/A* N/A* -- -- Usable: Tx = Filler Usable N/A* N/A* -- -- -- Active N/A* N/A* -- -- -- Table 9 Detailed Receive Link State Machine Primary NE Rx State Not In Group Unusable Usable Active Sub-State Unassigned (Rx = Off) Deleted (Rx = On) Unusable (Rx = Monitor) Blocking (Rx = On) Usable (Rx = Monitor) Active (Rx = On) NE Rx Events (see note ) In Group Unusable: Rx = Monitor (see note ) -- -- -- -- -- Not In Group -- (See note ) -- Unassigned Rx = Off Deleted: Rx = On Unassigned: Rx = Off Deleted: Rx = On Failed Condition N/A (see note ) -- -- Unusable: Rx = Monitor Unusable: Rx = Monitor Unusable: Rx = Monitor No longer Failed N/A -- Unusable or Usable (see note ) -- -- -- Fault Condition N/A -- -- Unusable: Rx = Monitor Unusable: Rx = Monitor Unusable: Rx = Monitor No longer Fault N/A -- Unusable or Usable (see note 5) -- -- -- Inhibiting -- -- -- -- Unusable: Rx = Monitor Blocking: Rx = On No longer inhibiting -- -- Unusable or Usable (see note 5) -- -- -- FE Tx States received in ICP cell Not In Group N/A Unassigned: Rx = Off -- Unusable: Rx=Monitor -- Usable: Rx=Monitor Unusable N/A Unassigned: Rx = Off -- Unusable: Rx=Monitor -- Usable: Rx=Monitor Usable N/A Unassigned: Rx = Off -- Unusable: Rx=Monitor Usable or Active (see note ) Active or Usable (see note ) Active N/A -- -- -- N/A -- NE Tx State (see note ) Not in Group -- -- N/A* N/A* N/A* N/A* Unusable N/A* (see note ) N/A* -- -- -- Usable Usable N/A* N/A* -- -- -- -- Active N/A* N/A* -- -- -- -- FE Rx States received in ICP cell (see note 8) Not in Group -- -- N/A* N/A* N/A* N/A* Unusable N/A* N/A* -- -- -- -- Usable N/A* N/A* -- -- -- -- Active N/A* N/A* -- -- -- -- 10.1.6 Processing of the Tx and Rx State Fields (R-68) The encoding of the "Tx State" and "Rx State" fields of the Link Information field (Table 3 on page 30) shall be transmitted according to the link state at the time the ICP cell is constructed. Any change in any link operation status shall be reflected in the ICP cell within the next 2M cells on that link and the SCCI field shall be set for the first ICP cell to reflect a change. Ongoing group-wide synchronized start-up or link addition/recovery of links may enforce to the report of multiple LSMs at the same time. This is covered in more details in Section 10.2.1 on page 53 and Section 10.2.2 on page 62. (R-69) The IMA shall use one of the Unusable encoding when reporting the Unusable state. At a minimum, the "No reason given" shall be used. (O-8) The IMA may optionally use "Inhibited", "Failed", "Fault" or "Mis-connected" as a reason when reporting the Unusable state. (R-70) Each processed incoming ICP cell with new state indication shall cause re-evaluation of the Tx and Rx LSMs operation state. Table 10 on page 52 shows the valid combinations of the Tx and Rx state values for all symmetrical and asymmetrical configurations and operations . (R-71) Each end shall only use the valid combination of Tx and Rx states as specified in Table 10 on page 52. Table 10 Valid Combinations of the Tx and Rx states Tx state Rx state Symmetrical configuration and operation Symmetrical configuration, asymmetrical operation Asymmetrical configuration and operation Not In Group Not In Group Valid Valid Valid Not In Group Unusable Not Valid Not Valid Valid Not In Group Usable Not Valid Not Valid Valid Not In Group Active Not Valid Not Valid Valid Unusable Not In Group Not Valid Not Valid Valid Unusable Unusable Valid Valid Valid Unusable Usable Valid Valid Valid Unusable Active Not Valid Valid Valid Usable Not In Group Not Valid Not Valid Valid Usable Unusable Valid Valid Valid Usable Usable Valid Valid Valid Usable Active Valid Valid Valid Active Not In Group Not Valid Not Valid Valid Active Unusable Not Valid Valid Valid Active Usable Not Valid Valid Valid Active Active Valid Valid Valid Section D on page 119 presents examples of link state exchanges between both ends. 10.2 IMA Group Operation This section defines the operation of the IMA group. The operation of the IMA group is governed by the Group State Machine (GSM), the Group Traffic State Machine (GTSM), and by the Link Addition and Slow Recovery (LASR) procedure. These three items are used to ensure reliable transmission and reception of ATM layer cells across all links in the Active state. This includes the negotiation of group parameters (i.e., symmetry and M values), the bringing up of the IMA group, and the graceful addition/recovery and deletion of links to and from the group. 10.2.1 IMA Group State Machine Definition 10.2.1.1 Overview of the Group State Machine An overview of the GSM is shown in Figure 12 on page 54. The GSM starts in the Not-Configured state from which it goes into the Start-up state. This transition corresponds to the time the UM configures the IMA group. In the Start-up state, the IMA proposes group parameters to the FE and waits to determine if the proposed parameters are accepted by the FE. This is done by monitoring the "Group Status and Control" field in the incoming ICP cells. The FE will indicate if it accepts the proposed group parameters by returning Start-up-Ack. The FE will return Config-Aborted if it rejects the parameters. While in the Start-up state, the local IMA also has to determine if it can accept the group parameters proposed by the FE. If it accepts the proposed parameters it goes into the "Start-up-Ack state. If it rejects the proposed parameters, it goes into the Config-Aborted state. Once in the Start-up-Ack state, the local IMA now waits for one of the signals specified in Figure 12 to move to the "Insufficient-Links" state. At this point, the GSM starts paying attention to the individual LSMs. It stays in the Insufficient-Links state until it gets the amount of links required to be Active. This number is specified in term of PTx and PRx. PTx represents the number of links required to be Active in the transmit direction. PRx represents the number of links required to be Active in the receive direction. PTx and PRx are equal if the group is operating symmetrically. It is required that the GSM receives indications from the individual LSMs about the status of the links. Figure 12 Overview of the Group State Machine Once the group reaches the amount of links required to be Active, it moves into the Operational state if it has not been inhibited. Once in the Operational state, the group is allowed to receive ATM cells and passes them to the ATM layer. It also requires to receive the Operational state signal from the FE before starting transmitting cells passed from the ATM layer. Figure 13 on page 55 illustrates the Group Traffic State Machine (GTSM) that indicates the capability of the group to transmit cells from the ATM layer. ATM layer cells can be only transmitted by the NE when both the NE and FE IMA groups are in the Operational state. The GTSM allows the NE to ensure that both ends have sufficient links before starting transmitting cells to the FE. Figure 13 Group Traffic State Machine Figure 12 on page 54 also shows the presence of 2 time-outs. One time-out is used to allow the GSM to return from the Config-Aborted to the Start-up state to indicate to the FE that it is ready to propose and evaluate new group parameters. A second time-out is used to return from Start-up-Ack to Start-up when the NE is not receiving one of the FE signals required to transition to Insufficient-Links. 10.2.1.2 Detailed Group State Machine Definition This section defines the characteristics of the GSM. Table 11 on page 55 describes the state of the GSM. Table 11 Description of GSM States State Description Not Configured The group does not exist Start-up This end is in start-up, and is waiting to see the FE in start-up. When sufficient communication with the FE is achieved, the Group Parameters (M, Symmetry) are recorded and the group moves to Start-up-Ack. Start-up-Ack This is a transitional state, when both groups start-up, they then move through this state to the Insufficient-Links state. While in this state it ignores an indication from the FE that it is in Start-up. Config-Aborted This state is entered when the FE tries to use unacceptable configuration parameters. Insufficient-Links This state implies that this end does not have "Sufficient Links". There are two definitions of "Sufficient Links" depending on group symmetry. Sufficient Links is defined as: For symmetric operation: at least PTx links are Active in both directions (PTx=PRx). For asymmetrical operation: at least PTx links are Active in the transmit direction and at least PRx links are Active in the receive direction. Blocked The group is blocked (e.g., inhibited by the UM). The group can be blocked for maintenance purposes while sufficient links are Active in both directions. Operational The group is not inhibited and has sufficient links in both the Tx and Rx directions. The IMA has now the capability to receive ATM layer cells and passes to the ATM layer from the IMA sublayer. (R-72) The states listed in Table 11 on page 55, with the exception of the Not Configured state, shall be reported to the FE group using the value defined in the "Group Status and Control" field in Table 2 on page 29 The values PTx, and PRx, mentioned in Table 11 on page 55, are application specific and may be configurable parameters. (R-73) PTx, and PRx shall be greater than 0. (R-74) The transmit end shall send over each link the same value in the "Group Status and Control" field (see Table 2 on page 29) for at least 2 consecutive IMA frames. This is required in order to ensure that the FE is properly informed. (R-75) The GSM shall validate the Rx M and the Rx IMA ID over at least one link before moving the Start-up-Ack state. The validated Rx M and IMA ID shall be used by the IMA Frame Synchronization mechanism defined in Section 11 on page 65. Other group fields in the ICP cells do not have to be validated over all links once the received M and IMA ID have been validated. Table 12 on page 56 lists and describes the local events causing GSM state transitions. Table 12 Local Events Driving the GSM Event Description Group Setup The establishment of the IMA Group by the UM. Group Removed Removal of the IMA Group by the UM. Acceptance of FE Group Parameters All the FE group parameters are acceptable while the FE GSM is either in the Start-up or Start-up-Ack state. Rejection of FE Group Parameters One or more of the FE group parameters are unacceptable. For example the proposed M value is not supported or the requested group symmetries are different. Inhibiting An implementation specific shut down of the group for a reason other than insufficient links (e.g., by the UM). No longer inhibiting Removal of the inhibiting condition. Sufficient Links See the description of the Insufficient-Links state in Table 11 on page 55. Not Sufficient Links See the description of the Insufficient-Links state in Table 11 on page 55. Events that cause a new start-up attempt from Config-Aborted This can be driven by many causes, a new local configuration, a realization that the FE is attempting start-up with a different configuration, or simply a timeout to retry. These are implementation specific. (R-76) If the requested configuration is unacceptable, the IMA shall indicate this using the Config Aborted state for at least 1 second. This is to allow for at least one round trip of communication between the ends (4M cells plus round trip time). (R-77) The IMA shall support the GSM state transitions as defined in Table 13 on page 57. Table 13 shows the state transition of the GSM. The first row lists the current state, and the first column indicates the event triggering state change. Two categories of events (NE events and FE states) are defined. If events occur simultaneously, they shall be treated sequentially. The order is implementation specific. Table 13 GSM State Transition NE State Not Configured (see note ) Start-up Start-up-Ack Config- Aborted Insufficient- Links Blocked Operational NE Events Group Setup Start-up -- -- -- -- -- -- Group Removed (see note ) -- Not Configured Not Configured Not Configured Not Configured Not Configured Not Configured Acceptance of FE Group Parameters -- Start-up or Start-up-Ack (see note ) N/A (see note ) N/A N/A N/A N/A Rejection of FE Group Parameters -- Config-Aborted Config-Aborted -- N/A N/A N/A Inhibiting -- -- -- -- -- -- Blocked Not Inhibiting -- -- -- -- -- Operational -- Sufficient links -- -- -- -- Blocked or Operational (see note ) -- -- Not sufficient links -- -- -- -- -- Insufficient- Links Insufficient- Links Local Restart (see note ) -- Start-up Start-up Start-up Start-up Start-up Start-up Timeout (see note ) -- -- Start-up (see note ) Start-up (see note ) -- -- -- FE State signalled via ICP cell Start-up -- Start-up-Ack or Config-Abort (see note ) -- Start-up or Config-Abort (see note ) Start-up Start-up Start-up Start-up-Ack -- Start-up-Ack or Config-Abort (see note 10) Not Configured -- -- -- -- Config-Aborted -- -- -- -- -- -- -- Insufficient-Links -- -- Insufficient- Links -- -- -- -- Blocked -- -- Insufficient- Links -- -- -- Operational Operational -- -- Insufficient- Links -- -- -- Operational (see note ) (R-78) Each IMA interface shall independently determine whether the group is up or down with respect to carrying traffic as in Figure 13 on page 55 and report the result according to Table 14 on page 58. (R-79) When the GTSM is in the Down state, it shall be reported to the UM and ATM layer management. This shall be the only notification to the ATM layer (management) about Physical Layer defect or failure (other notification to the UM are possible). Table 14 GTSM States and Corresponding Report Priority GTSM State Reasons Report Priority Up Down FE Start-up Most important Down NE Aborted (with given reason) Down FE Aborted (with given reason) Down NE Insufficient Links Down FE Insufficient Links Down NE Blocked Down FE Blocked Least important (R-80) The IMA interface shall not drop any ATM layer cells when adding or recovering links while the GSM is maintained in the Operational state. (R-81) The IMA interface shall not drop any ATM layer cells when deleting or inhibiting links while the GSM is maintained in the Operational state. When links are being deactivating due to link failure or link deletion, the bandwidth of the IMA group decreases. Section B.1 on page 110 explains the possible actions to be performed in this case. 10.2.1.3 Synchronized Link Activation during Group Start-up Procedure This section defines extra requirements to synchronize the activation of the links during the Group Start-up procedure. Once the NE IMA has determined which links exhibit acceptable differential link delay, it is now ready to activate the links in both directions. It is important to activate the links in the receive direction at the same time and then later activate the links in the transmit direction at the same time to minimize the number of bandwidth changes on the IMA virtual link. (R-82) The group start-up procedure shall ensure that all accepted links have their states changed to Tx=Usable over the same advancing of the SCCI field. (R-83) The group start-up procedure shall ensure that all accepted links have their states changed to Rx=Active over the same advancing of the SCCI field. (R-84) The group start-up procedure shall ensure that all accepted links have their states changed to Tx=Active over the same advancing of the SCCI field. (R-85) The GSM shall wait a minimum of one second, unless all the configured links are being reported Tx=Usable by FE, before reporting links Rx=Active. (R-86) The GSM shall wait a minimum of one second, unless all the configured links are being reported Rx=Active by FE, before reporting links Tx=Active. Figure 14 on page 60 illustrates the detailed behavior at each end of the IMA virtual link during group start-up. The flow of the start-up procedure over time is presented in Figure 15 on page 61. The figure highlights the key check points required to be passed before moving further in the process. The links become part of the sequencing round robin (RR) when the transmitting end has allocated them a LID and the receiving end has started synchronizing them (delay compensation for accommodating longest propagation delay links). Appendix C on page 117 details the start-up procedure when using a different value for PTx and PRx in the case of optional asymmetrical operations. Figure 14 Example of Synchronized Link Activation during Group Start-Up Figure 15 Example of Synchronized Link Activation during Group Start-up over Time 10.2.2 Link Addition and Slow Recovery (LASR) Procedure The Link Addition and Slow Recovery (LASR) procedure is defined to synchronize the insertion of new or recovered links within the IMA RR. Figure 16 gives an example of the group and link actions at each end of the IMA virtual link. It is required that each end of the IMA virtual link process the LASR procedure in order to complete the addition and activation of the new link. (R-87) Only one LASR procedure per IMA group shall be executed at any time. The link addition shall be used to add one, or more than one link at the same time. (R-88) The LASR procedure shall ensure that all new or recovered links have their states changed to Tx=Usable over the same advancing of the SCCI field. (R-89) The LASR procedure shall ensure that all new or recovered links have their states changed to Rx=Active over the same advancing of the SCCI field. (R-90) The LASR procedure shall ensure that all new or recovered links have their states changed to Tx=Active over the same advancing of the SCCI field. (R-91) The GSM shall wait a minimum of one second, unless all the new or recovered links are being reported Tx=Usable by FE, before reporting links Rx=Active. (R-92) The GSM shall wait a minimum of one second, unless all the new or recovered links are being reported Rx=Active by FE, before reporting links Tx=Active. The LASR procedure also applies when re-activating a link. (R-93) If the LASR procedure is in progress, the addition of one or more new links triggered by the UM or a possible slow link recovery (as defined in Section 12.1.3 on page 69) shall be delayed until the link addition procedure is completed or aborted (link addition capability is enabled once again as shown in Figure 16 on page 63). (R-94) The execution of the LASR procedure over time is shown in Figure 17 on page 64. Figure 16 Link Addition and Slow Recovery Procedure Example Figure 17 Example of Link Addition Procedure over Time 11. IMA Frame Synchronization Mechanism This section defines the IMA frame synchronization mechanism. It is based on the cell delineation mechanism in ITU-T Recommendation I.432[41] and ANSI T1.646[6]. (R-95) Each IMA link in the group shall provide the IMA frame synchronization mechanism as shown in Figure 18 on page 66. In the standards for the Physical Layer specification like ITU-T Recommendation I.432 or ANSI T1.646 the synchronization mechanism is specified independent of the error/maintenance handling. The synchronization states form a basis for the different error and maintenance states. The same applies for this specification. The IMA frame synchronization mechanism consists of the IMA HUNT, IMA PRESYNC and IMA SYNC states. By analogy with ITU-T Recommendation I.432 and ANSI T1.646 the checking scheme should be Cell-by-Cell in the IMA HUNT state and Frame-by-Frame in the IMA SYNC and IMA PRESYNC states. (R-96) The synchronization mechanism (implemented for each link separately) shall work independently of the other defect conditions and the link delay compensation. (R-97) The default value of Alpha(a), Beta(b) and Gamma(g), variables appearing in Figure 18 on page 66, shall be supported as specified in Table 15 on page 65. (O-9) The support of values of Alpha(a), Beta(b) and Gamma(g) other than the default values, such as specified in Table 15 on page 65, is optional. Table 15 Alpha, Beta and Gamma Values Setting Range Default (Required support) Alpha (a) (consecutive invalid ICP cells) 1-2 2 Beta (b) (consecutive errored ICP cells) 1-5 2 Gamma (g) (consecutive valid ICP cells) 1-5 1 (R-98) Upon the occurrence of HEC/CRC errored cell in the ICP position, the receiving end shall ignore the cell content but shall assume that it was an ICP cell. (O-10) The IMA Frame Synchronization mechanism may also go into the Hunt state when no longer getting cells from the physical layer. Table 16 on page 66 provides the definitions of the terms appearing in Figure 18 on page 66. Figure 18 IMA Frame Synchronization Mechanism Table 16 Definitions for IMA Frame Synchronization Mechanism Term Definition Invalid ICP Cells (see note ) Cell with good HEC&CRC and CID=ICP at expected frame position with (unexpected IMA label) or (unexpected LID) or (unexpected IMA ID) or (received M not equal to expected M of the IMA group) or (unexpected IMA frame number) or (unexpected ICP cell offset) Errored ICP Cell (see note 1) A cell with a HEC or CRC error at expected ICP cell position if it is not a missing cell. Valid ICP Cell (Cell with CID equal to ICP) and (No IMA OAM header, IMA label, HEC or CRC error) and (expected LID) and (expected IMA ID) and (received M equal to expected M of the IMA group) and (expected IMA frame number) and (expected ICP cell offset) Expected/unexpected LID, IMA ID, M, ICP cell offset: expected/unexpected related to value fixed during group start-up or link addition; when in Start-up, any value is to be expected. IMA frame number, stuff indication: related to separate reference counting at Rx side (see note 1). Missing ICP Cell (Cell located at ICP cell location without HEC error and without IMA OAM cell header) or (without HEC error and with IMA OAM cell header and without CID equal to ICP) Consecutive ICP Cells (see note 1) ICP cells sent on the same links in consecutive IMA frames (excepting the SICP cell in a stuff event, and regardless of offset). Thus one consecutive ICP cell is an ICP cell on one link in one IMA frame, two consecutive ICP cells are the cells on the same link in two consecutive IMA frames, etc. 11.1 IMA Frame Synchronization with Stuff Events The IMA should preserve the IMA frame synchronization while receiving stuff events subjected to HEC or CRC errors. Figure 19 on page 68 shows cases when one or more of the ICP cells preceding and comprising the stuff event are HEC or CRC errored. (R-99) The receive IMA shall maintain synchronization for cases 1, 2, 3 and 6 represented in Figure 19 on page 68. (O-11) The receive IMA may optionally maintain synchronization for cases 4, and 5 in Figure 19 on page 68. Case 4 requires the use of cell-by-cell hunting as described in Section 11 on page 65. (O-12) The receive IMA may optionally maintain synchronization for case 7 in Figure 19 on page 68, when passing stuff indication over more than one of the previous ICP cells and when b, as defined in Section 11 on page 65, is greater than 2. Figure 19 Error on ICP Cells Preceding and Comprising a Stuff Event 12. IMA Interface OAM Implementation This section specifies the physical layer OAM functions and procedures required on the IMA interface. 12.1 IMA OAM Functions 12.1.1 IMA Group Maintenance Signals Section 10.2.1 on page 53 specifies the signals to be used for reporting the actual state of the GSM and GTSM. 12.1.2 IMA Link Maintenance Signals Section 10.1.6 on page 52 specifies the signals to be used for reporting the actual transmit and receive link states to the FE. (R-100) The following link remote defect indicators shall be used to report local IMA defects: · Link defects: indicates that a link defect has been detected at the local end (i.e., LOS, OOF/LOF, AIS or LCD). · LIF: indicates that LIF defect has been detected at the local end. · LODS: indicates that LODS defect has been detected at the local end. (R-101) If several defects are detected at the same time, the defect with the highest priority, as listed in Table 17 on page 69, shall be reported. Table 17 Priorities of Defect Reports Priority Rx Defect 1 (highest) Link defect (e.g., LOS, OOF/LOF, AIS or LCD) 2 LIF 3 LODS The IMA defects (LIF or LODS) are defined in Table 18 on page 74. (R-102) The receive IMA shall report Rx defects no later than 2M cells after detection. This is no immediate relationship between any defect reporting and the transmit and receive link states. 12.1.3 IMA Link Error Handling This section defines the procedures to handle IMA link errors. (R-103) Error handling of IMA links shall be as specified in Figure 20 on page 70 and Figure 21 on page 71. Error handling regarding the anomalies, defects and failures are specified based on the IMA frame synchronization mechanism defined in Figure 18 on page 66. Figure 20 on page 70 shows the relationship between states of the IMA frame synchronization mechanism and the error/maintenance states also derived from the cell delineation procedure. The IMA Working state corresponds to the case where the IMA frame synchronization mechanism has been in the IMA SYNC state. The IMA OIF anomaly corresponds to the cases when the IMA frame synchronization mechanism has exited the IMA SYNC state. The IMA LIF defect corresponds to the case where the OIF anomaly has persisted for at least 2 IMA frames. The IMA LIF defect state is exited when the IMA frame synchronization mechanism has been in the IMA SYNC for at least 2 IMA frames. Figure 20 IMA Error/Maintenance State Diagram (R-104) During OCD or OIF anomaly conditions on one link, no ATM layer cells shall be passed to the ATM layer for that link by the receive IMA. Any ATM layer cells accumulated before the occurrence of the OCD or OIF anomaly shall be passed to the ATM layer and only the ATM layer cells received after the anomaly condition has been detected shall be replaced with Filler cells. (R-105) On IMA sublayer backward reporting of an Rx defect shall not be generated until LIF (or LODS) defect state is entered. The reporting shall be as specified in Section 12.1.2 on page 69. The two major states shown as largest boxes in Figure 21 on page 71 are distinguished by whether or not the FE is informed during the error handling. In the case where the FE is not informed, the sub-states are distinguished by whether cells received in the sub-state are passed to the ATM layer or discarded. In general, the detection of failures is based on the persistence of defects and received "FE defect reporting" and is implementation specific. The same applies for the detection of the Rx Failed condition defined in Section 10.1.4 on page 47. The action of maintaining synchronization also means that the IMA receiver passes valid incoming cells to the ATM layer as if the bad link was simply receiving Filler cells. It should be noted that there is only one state in which incoming ATM layer cells can be passed to the ATM layer. Figure 21 IMA Error Handling Overview 12.1.3.1 IMA Link Recovery Mechanisms According to Figure 21 on page 71 three types of link recovery are possible: 1. Fast recovery without entering the defect zone (e.g., going directly from "IMA Out of Frame" anomaly to the IMA Working state as described in Figure 20 on page 70); the FE is not aware of the anomaly and the fast recovery. 2. Medium recovery: a defect is reported and the FE defect reporting is initiated; the FE is aware of the defect and the medium recovery. 3. Slow recovery: a Rx Failed condition is entered due to the persistence of a defect; this triggers the deactivation of that link and the recovery by the IMA protocol as specified in Section 10.1.5 on page 47; the FE is aware of the deactivation of the link and the slow recovery. Examples of the slow recovery are shown in Figure 42 on page 123 and Figure 43 on page 124. The slow recovery mechanism using the IMA protocol is dependent on how the local end processes the defect and declares the Rx Failed condition. The occurrence of the Rx Failed condition will cause the LSM to move to the Unusable state (see Section 10.1.5 on page 47). 12.2 IMA Performance and Failure Alarm Monitoring This section describes the requirements for IMA performance and failure alarm monitoring. Figure 22 on page 72 illustrates the way monitored parameters are used by both the layer management entity, for driving the LSM, and for failure and performance monitoring. NE events (in terms of anomalies, signals, and defects) and FE reports (in terms of anomalies, signals, defects and error conditions) are defined to provide performance monitoring parameters. NE events and (processed) failures are also defined to make up FE reports for the transmitted signal. Figure 22 Structure of anomaly and defect processing 12.2.1 Performance Monitoring Objectives Performance monitoring is the process of continuous collection, analysis and reporting of performance data associated with a transmission entity (such as described in ANSI T1.231[3]). Similar to ITU-T Recommendation G.826[37], the following process is defined: Figure 23 Performance Monitoring Process (based on ANSI T1.231, Figure 4) The IMA Performance Primitives consist of · Anomalies with a. Bit error related events (e.g., errored ICP cells) b. Synchronization related events (e.g., OIF) · Defects with a. IMA Frame error events (e.g., LIF) b. Other defect events (e.g., LODS) · Failure alarm: a failure alarm is the termination of the ability of an item to perform a required function (ANSI T1.231). A failure alarm is declared when the defect (or response FE defect) persists for x seconds (default: 2.5 0.5 seconds). The failure alarm is different than the Failed condition defined in Section 10.1.4 on page 47. · Performance Parameters specified for each sublayer or OAM level separately are based on performance primitives and failures. IMA performance parameters are accumulated in a continuous fashion. Performance parameters are inhibited during seconds when the unavailability of the link or the group has been reported and when the counting of anomaly events is inhibited during defect detection. · The Intermittent defect handling like the hit integration (refer to Appendix B.2 on page 110) is only used for special applications and is not required in ANSI T1.231. 12.2.2 Performance Monitoring Parameters 12.2.2.1 IMA Performance Primitives (R-106) Table 18 on page 74 indicates the performance primitives that shall be detected by the IMA interface. Table 18 IMA Link and Group Anomalies and Defects Performance Primitives Events Definition Anomalies (IMA Specific) Errored ICP cell Same definition as in Figure 18 on page 66. Invalid ICP cell Same definition as in Figure 18 on page 66. Missing ICP cell Same definition as in Figure 18 on page 66. OIF events Leaving the IMA SYNC state. Defects (IMA Specific) LIF Definition as described in Section 12.1.3 on page 69. LODS A LODS defect is reported when the differential link delay between the link and the other links in the group is over the tolerable differential link delay. RDI-IMA One of the available remote defect indicators (including IMA link specific defect) is indicated in the link related "Link Information" field. 12.2.2.2 IMA Performance Parameters The IMA performance parameters are based on principles for the sub-layers of DS1 and E1, e.g. ANSI T.231, ANSI T1.646 and ITU-T Recommendation G.826. Table 19 on page 74 indicates the required and optional IMA performance parameters. Table 19 IMA Performance Parameters (R)/(O) Link/Group Performance Parameter Definition (R-107) Link IV-IMA ICP Violations: count of errored, invalid or missing ICP cells during non-SES-IMA or non-UAS-IMA condition. (R-108) Link SES-IMA Count of one second intervals containing 30% of the ICP cells counted as IV-IMAs (see note ), or one or more link defects (e.g., LOS, OOF/LOF, AIS or LCD), LIF, LODS defects during non-UAS-IMA condition. (R-109) Link SES-IMA-FE Count of one second intervals containing one or more RDI-IMA defects during non-UAS-IMA-FE condition. (R-110) Link UAS-IMA Unavailable seconds: unavailability begins at the onset of 10 contiguous SES-IMA and ends at the onset of 10 contiguous seconds with no SES-IMA. (R-111) Link UAS-IMA-FE Unavailable seconds at FE: unavailability begins at the onset of 10 contiguous SES-IMA-FE and ends at the onset of 10 contiguous seconds with no SES-IMA-FE. (R-112) Link Tx-UUS-IMA Tx Unusable seconds: count of Tx Unusable seconds at the NE LSM. (R-113) Link Rx-UUS-IMA Rx Unusable seconds: count of Rx Unusable seconds at the NE LSM. (R-114) Link Tx-UUS-IMA-FE Tx Unusable seconds at FE: count of seconds with Tx Unusable indications from the FE LSM. (R-115) Link Rx-UUS-IMA-FE Rx Unusable seconds at FE: count of seconds with Rx Unusable indications from the FE LSM. (R-116) Link Tx-FC Count of NE Tx link failure alarm conditions. (R-117) Link Rx-FC Count of NE Rx link failure alarm conditions. (O-13) Link Tx-FC-FE Count of FE Tx link failure alarm conditions. (O-14) Link Rx-FC-FE Count of FE Rx link failure alarm conditions. (O-15) Link OIF-IMA Count of OIF anomalies during non-SES-IMA condition. (O-16) Link Tx-Stuff-IMA Count of Tx stuffing events during non-SES-IMA condition. (O-17) Link Rx-Stuff-IMA Count of Rx stuffing events during non-SES-IMA condition. (R-118) Group GR-UAS-IMA Count of one second intervals where the GTSM is Down. (R-119) Group GR-FC Count of NE group failure conditions. (O-18) Group GR-FC-FE Count of FE group failure conditions. (R-120) Group GR-Timing-Mismatch A possible configuration mismatch has occurred (CTC and CTC modes are not the same at both ends of the IMA virtual links. (O-19) The accumulation of IMA performance parameters over 15 minutes and 24 hours interval is optional. (CR-7) If (O-19) is used, the current/previous and recent data shall be kept. For threshold crossing, the current data set shall be used. 12.2.3 IMA Failure Alarms Table 20 on page 76 presents the IMA failure alarm definitions reported to the UM. Appendix B.2 on page 110 suggests a state machine to be used for processing error conditions. Table 20 IMA Failure Alarms (R)/(O) Link/Group Failure Alarm Definition (R-121) Link LIF Persistence of LIF defect at NE (see note ). (R-122) Link LODS Persistence of LODS defect at NE (see note 1). (R-123) Link Tx-Mis-Connected When the link is detected as mis-connected. This is reported mis-connected when the transmit end has determined the link is not connected to the same FE as the other links in the group. The detection is implementation specific. (R-124) Link RFI-IMA Persistence of RDI-IMA defect at NE (see note 1). (O-20) Link Fault Implementation specific FAULT declared at NE (see note 1). (R-125) Link Tx-Unusable-FE Tx link forced to Unusable due to FE behavior. (R-126) Link Rx-Unusable-FE Rx link forced to Unusable due to FE behavior. (R-127) Group Start-up-FE When the FE is starting-up (see note ). (R-128) Group Config-Abort When the FE tries to use unacceptable configuration parameters. (R-129) Group Config-Abort-FE When the FE reports unacceptable configuration parameters. (R-130) Group Insufficient-Links When less than PTx transmit or PRx receive links are Active. (R-131) Group Insufficient-Links-FE When the FE reports that less than PTx transmit or PRx receive links are Active. (R-132) Group Blocked-FE When the FE reports that it is blocked. (R-133) In the case of the LIF, LODS, RFI-IMA and Fault failure alarms, the IMA shall support 2.5 0.5 seconds as a default persisting checking time to enter a failure alarm condition, and 10 0.5 seconds as a default persisting clearing time to exit the same failure alarm condition. (R-134) The clearing of the Fault Failure Alarm state is implementation dependent, but shall at a minimum require that the error which caused the fault no longer be present. 13. Test Pattern Procedure The test pattern procedure is defined to provide extra supports to verify the connectivity of a link within an IMA group. It is based on the use of a test pattern sent over one link for which verification of the connectivity to the rest of the group is desired. The test pattern is expected to be looped over all the other links in the group at the FE. All the procedure is performed over the ICP cells exchanged between both ends of the IMA virtual links. Figure 24 on page 77 shows an example where a test pattern is originated on one end to verify the connectivity of LID 2 link with the other links already in the group. Figure 24 Example of Looped Test Pattern (O-21) The transmit IMA may optionally use the Test Pattern procedure. The test pattern procedure is made available to ensure proper link connectivity. The following requirements shall be followed in order to exercise the Test Pattern procedure. (CR-8) If (O-21) is used, the IMA interface shall use the Test Pattern command, Test Link and Tx Test Pattern fields in the ICP cell to activate the Test Pattern feature at the FE. It shall also send the same values over the next ICP cells sent over all the links (including test link). It shall specify the test link LID in the Test Link LID field. (CR-9) If (O-21) is used, the IMA interface shall send the same value of the Test Pattern command, Test Link and Tx Test Pattern fields in at least 2 consecutive ICP cells. (CR-10) If (O-21) is used, the IMA interface shall continue to send the new values of the Test Pattern command, Test Link and Tx Test Pattern fields as long as it wants the FE IMA to loop back the test pattern. (R-135) The IMA interface shall monitor to incoming ICP cells on the links already recognized in the group to detect a change of the Test Pattern command. If the Test Pattern command is detected as active, the IMA interface shall monitor the Tx Test Link and Tx Test Pattern fields. It shall also verify that the Test Command bit is set to active on the test link. It shall then copy the Tx Test Pattern received on the test link, indicated by the FE IMA, into the Rx Test Pattern field on every subsequent ICP cell sent over all outgoing links in the group. (R-136) The IMA interface shall keep sending the same Rx Test Pattern until it has been indicated to stop looping the pattern or to loop a new one from the same or another link. (R-137) The IMA interface shall return the 0xff pattern over the Rx Test Pattern field when the incoming test command is inactive or the test link is not detected. (R-138) The IMA interface shall only handle one test pattern per IMA group at any given time. The following text suggests behaviors at the transmit and receive ends. · Once sending the new value of the Tx Test Link and Tx Test Pattern, the IMA interface might have to wait sometime in order to let the pattern be detected by the receive end and to be looped back. The IMA interface should verify that the test pattern is returned over the Rx Test Pattern field over ICP cells received on any other links that have already being recognized part of the group on both ends. · Loopback configuration on a giving link can be detected by verifying that the received Tx Test Pattern value read from the incoming ICP cells is the same as the one inserted in the outgoing ICP cells. · The IMA interface should try several values randomly chosen to ensure that the FE has not been trying the same value at the same time. · At start-up time, the IMA interface sends the 0xff pattern until receiving ICP cells indicating the first Test Pattern command. Figure 25 on page 78 shows the Test Pattern procedure execution over time. Figure 25 Test Pattern Procedure over Time 14. IMA Interaction with Plane Management (R-139) The IMA shall process the following indications from/to Plane Management: · IMA group configuration: this signal is received from Plane Management by the IMA entity and indicates which links are to be assigned to the IMA group. · Link addition/deletion: this signal is received from Plane Management by the IMA entity and indicates that a link is to be added to or deleted from the IMA group. · IMA service operational status change: this signal is sent by the IMA entity to the Plane Management to indicate a change of the operational status of the IMA (e.g., GTSM moving to Down state). · Tx/Rx cell rate change: this signal is sent by the IMA entity to the Plane Management to indicate that the cell rate has changed in the transmit and/or receive directions (a link has been added to or deleted from the IMA group or a link has been inactivated due to a defect or a link recovered from a defect condition). Note 1. Results in Rx Failed as a result of the persistence check (according to Appendix B.2 on page 110) and triggers the LSM (to go to Rx Unusable (Failed) state). Note 2 Optional: the FE can observe the NE persistence behavior and force the NE behavior by changing Tx state to Unusable, thereby forcing the NE out of Active. The FE may do this if, in its estimation, the NE persistence processing is unacceptable. Tx direction cells distributed across links in round robin sequence Rx direction cells recombined into single ATM stream Single ATMCell Stream from ATM Layer Original cell stream passed to ATM Layer Check incoming link LDS Send LinkActive = 1 Send data Failed Start Defect Integration Failed Integrating No longer Failed No defect > y seconds No defect Defect > x seconds Defect present Defect present No defect M = 8 Cells Stuff event MY-1 MY-2 M0 MY-1 Write Ptr 0 Write Ptr 1 Write Ptr 2 IMA Data Cell Clock (see note) Stuff Event Check incoming link LDS Send LinkActive = 1 Send data Tx end of link Rx end of link Tx: Unusable (No action until Tx is set to Usable) Rx: Usable Rx: Unusable Tx: Usable Rx: Active Tx: Active Check incoming link LDS Send LinkActive = 1 Send data Tx end of link Rx end of link Tx: Unusable (No action until link is determined Usable) Rx: Unusable Tx: Usable Tx: Active (When Usable, the link will progress from Unusable to Usable to Active) Rx: Active Note: · IMA Data Cell Clock derived from TRL Tx: Not In Group Rx: Not In Group Check incoming link LDS Send LinkActive = 1 Send data End A Tx/Rx End B Tx/Rx Tx: Unusable Rx: Unusable Tx: Usable Rx: Usable Tx: Usable Rx: Active Tx: Active Rx: Active Tx: Active Rx: Active Tx: Not In Group Rx: Not In Group Tx: Unusable Rx: Unusable Tx: Usable Rx: Usable Tx: Usable Rx: Active Delete link: Tx: Not In Group (Deleted) Rx: Not in Group (Deleted) Check incoming link LDS Send LinkActive = 1 Send data End A Tx/Rx End B Tx/Rx Both directions Active: Tx: Active Rx: Active Both directions Active: Tx: Active Rx: Active Tx: Usable Rx: Usable Unassigned: Tx: Not In group Rx: Not In group Tx: Usable Rx: Unusable (Rx Failed) Tx: Not In Group Rx: Not In Group Check incoming link LDS Send LinkActive = 1 Send data End A Tx/Rx End B Tx/Rx Tx: Usable Rx: Unusable (No action, still Rx: Unusable) Tx: Active Rx: Active Check incoming link LDS Send LinkActive = 1 Send data End A Tx/Rx End B Tx/Rx Operational Tx: Active Rx: Active Tx Fault reported Tx: Unusable Rx: Usable Reacted to Tx Unusable Tx: Usable Rx: Usable Operational Tx: Active Tx: Active Check incoming link LDS Send LinkActive = 1 Send data End A Tx/Rx End B Tx/Rx Operational Tx: Active Rx: Active Tx Fault reported Tx: Unusable Rx: Active Reacted to Tx Unusable Tx: Active Rx: Usable Operational Tx: Active Tx: Active Check incoming link LDS Send LinkActive = 1 Send data End A Tx/Rx End B Tx/Rx Reacted to RFI Tx: Usable Rx: Active Tx: Active Rx: Active Check incoming link LDS Send LinkActive = 1 Send data End A Tx/Rx End B Tx/Rx Tx: Usable Rx: Active Tx: Active Rx: Active (Defect no longer present and receive link ready to be set to Active) (Rx Failed condition entered) Tx: Active Rx: Active Tx: Active Rx: Active Tx: Active Rx: Active Tx: Not In Group (Tx=Filler) Rx: Active Check incoming link LDS Send LinkActive = 1 Send data End A Tx/Rx End B Tx/Rx Both directions Active: Tx: Active Rx: Active Both directions Active: Tx: Active Rx: Active Tx: Active Rx: Usable Tx: Not In Group (Tx=Off) Rx: Active Tx: Active Rx: Unusable Tx: Active Rx: Active Tx: Unusable Rx: Unusable (Defect no longer present and receive link ready to be set to Active) Rx Failed reported Tx: Usable Rx: Unusable Tx: Usable Rx: Active Tx: Active Rx: Active Tx: Active Rx: Active Note: · Only the NE states newly entered and transmitted over the ICP cells are shown. · The transitions to Tx=Usable, Rx=Active and Tx=Active depend on the group wide synchronized addition/slow recovery procedure of links 15. Management Information Base (O-22) The Unit Management (UM) may be SNMP based. (CR-11) If (O-22) is used, the MIBs defined in this section shall be implemented. 15.1 The Network Management Framework IMA management is defined using SNMP MIBs. SNMP [15] is an Internet standard network management framework. The Request For Comment (RFC) documents which are relevant here are · RFC 1213, [17] which defines MIB-II, the core set of managed objects for the Internet suite of protocols · RFC 1442 [19] which defines the Structure of Management Information (SMI), the mechanisms used for describing and naming objects for the purpose of management. · RFCs 1443 through 1452, which define SNMPv2 [20][21][22][23][24][25][26][27][28][29]. · RFC 1573 [30], which defines the evolution of the Interfaces group of MIB-II. 15.2 Overview This MIB provides the objects necessary for configuration, performance, and fault management of the IMA physical layer. If IMA is used over DS1/E1 links, this MIB specification requires the implementation of the DS1 MIB defined in RFC 1406 [18] with a separate instance created for each DS1/E1 used by the IMA. 15.3 IMA Terminology The errors/defects/failures listed in this document pertain to the IMA functionality only. 15.3.1 Error events See Section 12.2.2.1 on page 74. 15.3.2 Defects See Section 12.2.2.1 on page 74. 15.3.3 Performance Monitoring Parameters See Section 12.2.2.2 on page 74. 15.3.4 Failure Alarm States See Section 12.2.3 on page 76. 15.4 MIB-II and RFC 1573 Support All SNMP agents which support IMA must implement MIB-II [19] and the mandatory groups of RFC 1573[30]. The goal of IMA is to present the illusion that a group of one or more links can be treated as a single physical interface of aggregate bandwidth. Real physical interfaces have entries in the MIB-II Interfaces Table. To preserve a consistent management framework, it is highly desirable for each IMA Group to have entries in this table as well. To identify an interface as belonging to an IMA Group, it must be tagged with an ifType constant: atmIma(107). This constant lets a network management application knows that additional information about the interface is available via the IMA MIB. IMA Groups are created and destroyed by network management. So that agents can control IMA ifIndex allocation, IMA Group tables define an object imaGroupIfIndex that represents the ifIndex associated with the IMA interface. Both values are available through table entries: · An imaGroupMappingTable entry converts the IMA ifIndex to an imaGroupIndex. · An imaGroupTable entry contains an imaGroupIfIndex object that identifies the IMA ifIndex The MIB-II interfaces associated with physical links exist independently of the IMA link definition. A physical link is designated to be an IMA link by the creation of a row in the IMA Link Table. 15.4.1 The ifStackTable The relevant portion of the ifStackTable looks like this: ---------------------- ATM Layer ---------------------- IMA Group ---------------------- Physical Interface ---------------------- Note that: · The ATM Layer may multiplex among multiple IMA groups. · The IMA Group may perform inverse multiplexing over multiple physical interfaces. 15.4.2 Interpretations of Interface Tables for IMA Groups The following items defined in the ifTable of RFC 1573 have IMA specific definitions: ifIndex IMA Interface index. ifType atmIma(107) ifMtu Transmission units are ATM cells. The value of ifMtu is 53 octets. ifSpeed The interface speed is represents by the following equation (where Non represents, in the transmit direction, the number of links which currently transmit cells passed from the ATM layer, and in the receive direction, the number of links which currently receive ATM layer cells to be passed to the ATM layer; where TRLCR is the TRL cell rate providing by the TRL in the transmit and receive direction respectively; M is the IMA frame length in cell units): ifPhysAddress A zero-length octet string ifOperStatus This reflects the state of the Group Traffic State Machine. RFC 1573 provides the full descriptions of the status values. For conformance to RFC 1573, the ifGeneralGroup and ifStackGroup are the only mandatory groups. 15.4.3 Interaction with ifAdminStatus Setting the ifAdminStatus of the IMA Group interface to "down" or "testing" will cause the inhibiting condition which affects the Group State Machine. Setting the ifAdminStatus of a link interface to `down' or `testing' will cause the Blocking condition which affects the link's Transmit and Receive State Machines. 15.5 MIB Definition IMA-MIB DEFINITIONS ::= BEGIN IMPORTS ifIndex FROM RFC1213-MIB enterprises FROM RFC1155-SMI MODULE-IDENTITY, OBJECT-TYPE, Integer32, NOTIFICATION-TYPE FROM SNMPv2-SMI MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF TEXTUAL-CONVENTION, DateAndTime, RowStatus FROM SNMPv2-TC; ----------------------------------------------------------------------- -- The implementation of this MIB is mandatory for all network devices -- which have ATM Inverse Multiplexer network interface module. atmfImaMib MODULE-IDENTITY LAST-UPDATED "9701092245Z" ORGANIZATION "ATM Forum" CONTACT-INFO "ATM Forum World Headquarters 2570 West El Camino Real Suite 304 Mountain View, CA 94040-1313 USA Phone: +1 415 949 6700 Fax: +1 415 949 6705 email: info@atmforum.com" DESCRIPTION "The MIB module to describe an ATM Inverse Multiplexer interface" ::= { atmForumNetworkManagement TBD } -- atmForum OBJECT IDENTIFIER ::= { enterprises 353 } atmForumNetworkManagement OBJECT IDENTIFIER ::= { atmForum 12 } atmfImaMibObjects OBJECT IDENTIFIER ::= { atmfImaMib 1} -- This MIB consists of the IMA group subtree. -- The IMA group subtree consists of the number of IMA groups and a -- table of IMA groups. Each entry in the table of IMA groups contains -- information (configuration and status) specific to each group. -- Textual conventions IfIndex ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "ifIndex" SYNTAX Integer32 MilliSeconds ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "Time in milliseconds" SYNTAX Integer32 ImaGroupState ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "State of the IMA group." SYNTAX INTEGER { notConfigured(1), startUp(2), startUpAck(3), configAbortUnsupportedM(4), configAbortIncompatibleSymmetry(5), configAbortOther(6), insufficientLinks(7), blocked(8), operational(9)} ImaGroupFailureStatus ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "Failure reason of an IMA group." SYNTAX INTEGER { noFailure(1), -- unit is up startUpNe(2), startUpFe(3), invalidMValueNe(4), invalidMValueFe(5), failedAssymetricNe(6), failedAssymetricFe(7), insufficientLinksNe(8), insufficientLinksFe(9), blockedNe(10), blockedFe(11), otherFailure(12)} ImaAlarmStatus ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "A qualification of the IMA trap which indicates if the condition causing the trap has been detected (declared) or is no longer present (cleared)." SYNTAX INTEGER { cleared(1), declared(2)} ImaAlarmType ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "An identification of the event that caused the generation of the IMA trap." SYNTAX INTEGER { imaAlarmLinkLif(1), imaAlarmLinkLods(2), imaAlarmLinkTxMisConnect(3), imaAlarmLinkRfi(4), imaAlarmLinkFault(5), imaAlarmLinkTxUnusableFe(6), imaAlarmLinkRxUnusableFe(7), imaAlarmGroupStartupFe(8), imaAlarmGroupCfgAbort(9), imaAlarmGroupCfgAbortFe(10), imaAlarmGroupInsuffLinks(11), imaAlarmGroupInsuffLinksFe(12), imaAlarmGroupBlockedFe(13), imaAlarmGroupTimingSynch(14)} ImaGroupTxClkMode ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "Indicate the transmit clock mode of the IMA group. There are two possible modes: the Common Transmit Clock (CTC) and the Independent Transmit Clock (ITC). The CTC mode corresponds to the case when the transmit clock of all IMA links are derived from the same source. The ITC configuration corresponds to the case where there is at least one IMA link whose transmit clock is derived from a source different than at least another link transmit clock." SYNTAX INTEGER { ctc(1), itc(2)} ImaGroupSymmetry ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "The symmetry mode adjusted during the group start-up." SYNTAX INTEGER { symmetricOperation(1), asymmetricOperation(2), asymmetricConfiguration(3)} ImaFrameLength ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "Length of the IMA frames." SYNTAX INTEGER { m32(32), m64(64), m128(128), m256(256)} ImaLinkState ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "State of a link belonging to an IMA group." SYNTAX INTEGER { notInGroup(1), unusableNoGivenReason(2), unusableFault(3), unusableMisconnected(4), unusableBlocked(5), unusableFailed(6), usable(7), active(8)} ImaLinkFailureStatus ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "Local failure status of a link belonging to an IMA group." SYNTAX INTEGER { noFailure(1), imaLinkFailure(2), lifFailure(3), lodsFailure(4), misConnected(5), blocked(6), fault(7), farEndTxLinkUnusable(8), farEndRxLinkUnusable(9)} ImaTestProcStatus ::= TEXTUAL-CONVENTION STATUS current DESCRIPTION "States of the Test Pattern Procedure." SYNTAX INTEGER { disabled(1), operating(2), linkFail(3)} -- The IMA Group subtree imaGroupNumber OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of IMA groups configured on this system." ::= { atmfImaMibObjects 1} -- IMA Group Table contains configuration and status information imaGroupTable OBJECT-TYPE SYNTAX SEQUENCE OF ImaGroupEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "The IMA Group Configuration table." ::= { atmfImaMibObjects 2 } imaGroupEntry OBJECT-TYPE SYNTAX ImaGroupEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "An entry in the IMA Group table." INDEX { imaGroupIndex } ::= { imaGroupTable 1 } ImaGroupEntry ::= SEQUENCE { imaGroupIndex Integer32, imaGroupRowStatus RowStatus, imaGroupIfIndex IfIndex, imaGroupNeState ImaGroupState, imaGroupFeState ImaGroupState, imaGroupFailureStatus ImaGroupFailureStatus, imaGroupSymmetry ImaGroupSymmetry, imaGroupMinNumTxLinks INTEGER (1..32), imaGroupMinNumRxLinks INTEGER (1..32), imaGroupNeTxClkMode ImaGroupTxClkMode, imaGroupFeTxClkMode ImaGroupTxClkMode, imaGroupTxTimingRefLink IfIndex, imaGroupRxTimingRefLink IfIndex, imaGroupLastChange DateAndTime, imaGroupTxImaId INTEGER (0..255), imaGroupRxImaId INTEGER (0..255), imaGroupTxFrameLength ImaFrameLength, imaGroupRxFrameLength ImaFrameLength, imaGroupDiffDelayMax MilliSeconds, imaGroupLeastDelayLink IfIndex, imaGroupDiffDelayMaxObs MilliSeconds, imaGroupAlphaValue INTEGER (1..2), imaGroupBetaValue INTEGER (1..5), imaGroupGammaValue INTEGER (1..5), imaGroupRunningSecs Integer32, imaGroupUnavailSecs Integer32, imaGroupNeNumFailures Integer32, imaGroupFeNumFailures Integer32, imaGroupTxAvailCellRate Integer32, imaGroupRxAvailCellRate Integer32, imaGroupNumTxCfgLnks Integer32, imaGroupNumRxCfgLnks Integer32, imaGroupNumTxActLnks Integer32, imaGroupNumRxActLnks Integer32, imaGroupTestLinkIfIndex IfIndex, imaGroupTestPattern Integer32, imaGroupTestProcStatus ImaTestProcStatus } imaGroupIndex OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "A unique value for the IMA Group." ::= { imaGroupEntry 1 } imaGroupRowStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The imaGroupRowStatus object allows create and delete operations on imaGroupTable entries. To create a new conceptual row (or instance) of the imaGroupTable, imaGroupRowStatus must be set to 'createAndWait' or 'createAndGo.' A successful set of the following objects must be performed before the row can transition to 'Active' state: imaGroupTxImaId imaGroupTxFrameLength imaGroupMinNumTxLinks and imaGroupMinNumRxLinks To change (modify) an imaGroupTable entry, the imaGroupRowStatus object must be set to 'notInService'. Only then can the conceptual row be changed. To remove (delete) an imaGroupTable entry from this table, set imaGroupRowStatus to 'destroy.' Setting the imaGroupRowStatus to 'Active' has the effect of activating the Group Startup Procedure. The Group Startup Procedure uses provisioned links that have imaLinkRowStatus set to 'Active' an imaLinkGroupIndex set the imaGroupIndex in this conceptual row. When the imaGroupRowStatus is not in 'Active' state, the Group State machine is in its 'Not Configured' state." ::= { imaGroupEntry 2 } imaGroupIfIndex OBJECT-TYPE SYNTAX IfIndex MAX-ACCESS read-only STATUS current DESCRIPTION "This object identifies the logical interface number ('ifIndex') assigned to this IMA group, and is used to identify corresponding rows in the Interfaces MIB. Note that re-initialization of the management agent may cause a client's 'imaGroupIfIndex' to change." ::= { imaGroupEntry 3 } imaGroupNeState OBJECT-TYPE SYNTAX ImaGroupState MAX-ACCESS read-only STATUS current DESCRIPTION "The current operational state of the near-end IMA Group State Machine." ::= { imaGroupEntry 4 } imaGroupFeState OBJECT-TYPE SYNTAX ImaGroupState MAX-ACCESS read-only STATUS current DESCRIPTION "The current operational state of the far-end IMA Group State Machine." ::= { imaGroupEntry 5 } imaGroupFailureStatus OBJECT-TYPE SYNTAX ImaGroupFailureStatus MAX-ACCESS read-only STATUS current DESCRIPTION "The current failure status of the IMA group (the reason why the GTSM is in the down state." ::= { imaGroupEntry 6 } imaGroupSymmetry OBJECT-TYPE SYNTAX ImaGroupSymmetry MAX-ACCESS read-create STATUS current DESCRIPTION "Symmetry of the IMA group." DEFVAL { symmetricOperation } ::= { imaGroupEntry 7 } imaGroupMinNumTxLinks OBJECT-TYPE SYNTAX INTEGER (1..32) MAX-ACCESS read-create STATUS current DESCRIPTION "Minimum number of transmit links required to be Active for the IMA group to be in the Up state." ::= { imaGroupEntry 8 } imaGroupMinNumRxLinks OBJECT-TYPE SYNTAX INTEGER (1..32) MAX-ACCESS read-create STATUS current DESCRIPTION "Minimum number of receive links required to be Active for the IMA group to be in the Up state." ::= { imaGroupEntry 9 } imaGroupNeTxClkMode OBJECT-TYPE SYNTAX ImaGroupTxClkMode MAX-ACCESS read-create STATUS current DESCRIPTION "Transmit clocking mode used by the near-end IMA group." DEFVAL { ctc } ::= { imaGroupEntry 10 } imaGroupFeTxClkMode OBJECT-TYPE SYNTAX ImaGroupTxClkMode MAX-ACCESS read-only STATUS current DESCRIPTION "Transmit clocking mode used by the far-end IMA group." ::= { imaGroupEntry 11 } imaGroupTxTimingRefLink OBJECT-TYPE SYNTAX IfIndex MAX-ACCESS read-only STATUS current DESCRIPTION "The ifIndex of the transmit timing reference link to be used by the near-end for IMA data cell clock recovery from the ATM layer." ::= { imaGroupEntry 12 } imaGroupRxTimingRefLink OBJECT-TYPE SYNTAX IfIndex MAX-ACCESS read-only STATUS current DESCRIPTION "The ifIndex of the receive timing reference link to be used by near-end for IMA data cell clock recovery toward the ATM layer." ::= { imaGroupEntry 13 } imaGroupLastChange OBJECT-TYPE SYNTAX DateAndTime MAX-ACCESS read-only STATUS current DESCRIPTION "The time-of-day the IMA group last changed operational state (i.e., value of imaNeGroupState changed)." ::= { imaGroupEntry 14 } imaGroupTxImaId OBJECT-TYPE SYNTAX INTEGER (0..255) MAX-ACCESS read-create STATUS current DESCRIPTION "The IMA ID currently in use by the near-end IMA function." ::= { imaGroupEntry 15 } imaGroupRxImaId OBJECT-TYPE SYNTAX INTEGER (0..255) MAX-ACCESS read-only STATUS current DESCRIPTION "The IMA ID currently in use by the far-end IMA function." ::= { imaGroupEntry 16 } imaGroupTxFrameLength OBJECT-TYPE SYNTAX ImaFrameLength MAX-ACCESS read-create STATUS current DESCRIPTION "The frame length to be used by the IMA group in the transmit direction. Can only be set when the IMA group is startup." DEFVAL { m128 } ::= { imaGroupEntry 17 } imaGroupRxFrameLength OBJECT-TYPE SYNTAX ImaFrameLength MAX-ACCESS read-only STATUS current DESCRIPTION "Value of IMA frame length as received from remote IMA function." ::= { imaGroupEntry 18 } imaGroupDiffDelayMax OBJECT-TYPE SYNTAX MilliSeconds MAX-ACCESS read-create STATUS current DESCRIPTION "The maximum number of milliseconds of delay differential among the links that will be tolerated on this interface." DEFVAL { 25 } ::= { imaGroupEntry 19 } imaGroupLeastDelayLink OBJECT-TYPE SYNTAX IfIndex MAX-ACCESS read-only STATUS current DESCRIPTION "The ifIndex of the link configured in the IMA group which has the smallest link propagation delay. This value has meaning only if at least 1 link has been configured in the IMA group." ::= { imaGroupEntry 20 } imaGroupDiffDelayMaxObs OBJECT-TYPE SYNTAX MilliSeconds MAX-ACCESS read-only STATUS current DESCRIPTION "The latest maximum differential delay observed (in milliseconds), i.e. between the links having the least and most link propagation delay, among the receive links that are currently configured in the IMA group." ::= { imaGroupEntry 21 } imaGroupAlphaValue OBJECT-TYPE SYNTAX INTEGER (1..2) MAX-ACCESS read-create STATUS current DESCRIPTION "This indicates the 'alpha' value used to specify the number of consecutive invalid ICP cells to be detected before moving to the IMA HUNT state." DEFVAL { 2 } ::= { imaGroupEntry 22 } imaGroupBetaValue OBJECT-TYPE SYNTAX INTEGER (1..5) MAX-ACCESS read-create STATUS current DESCRIPTION "This indicates the 'beta' value used to specify the number of consecutive errored ICP cells to be detected before moving to the IMA HUNT state." DEFVAL { 2 } ::= { imaGroupEntry 23 } imaGroupGammaValue OBJECT-TYPE SYNTAX INTEGER (1..5) MAX-ACCESS read-create STATUS current DESCRIPTION "This indicates the 'gamma' value used to specify the number of consecutive valid ICP cells to be detected before moving to the IMA SYNC state from the PRESYNC state." DEFVAL { 1 } ::= { imaGroupEntry 24 } imaGroupRunningSecs OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The amount of time (in seconds) since this IMA group has been in operation (up or down)." ::= { imaGroupEntry 25 } imaGroupUnavailSecs OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "Count of one second intervals where the IMA Group Traffic State Machine is Down." ::= { imaGroupEntry 26 } imaGroupNeNumFailures OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times a near-end group failure (Config-Abort, Insufficient-Links) has been reported since power-up or reboot." ::= { imaGroupEntry 27 } imaGroupFeNumFailures OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times a far-end group failure (Config-Abort-FE, Insufficient-Links-FE, Blocked-FE) has been reported since power-up or reboot. This is an optional attribute." ::= { imaGroupEntry 28 } imaGroupTxAvailCellRate OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The current cell rate (truncated value in cells per second) provided by this IMA group in the transmit direction, considering all the transmit links in the Active state." ::= { imaGroupEntry 29 } imaGroupRxAvailCellRate OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The current cell rate (truncated value in cells per second) provided by this IMA group in the receive direction, considering all the receive links in the Active state." ::= { imaGroupEntry 30 } -- imaGroupNumTxCfgLnks is used by a network operator to tell how many -- links are configured for transmit in the IMA group. imaGroupNumTxCfgLnks OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of links that are configured to transmit in this IMA group." ::= { imaGroupEntry 31 } -- imaGroupNumRxCfgLnks is used by a network operator to tell how many -- links are configured for receive in the IMA group. imaGroupNumRxCfgLnks OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of links that are configured to receive in this IMA group." ::= { imaGroupEntry 32 } -- imaGroupNumTxActLnks is used by a network operator to tell how many -- links which are configured for transmit are also Active. imaGroupNumTxActLnks OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of links which are configured to transmit and are currently Active in this IMA group." ::= { imaGroupEntry 33 } -- imaGroupNumRxActLnks is used by a network operator to tell how many -- links which are configured for receive are also Active. imaGroupNumRxActLnks OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of links which are configured to receive and are currently Active in this IMA group." ::= { imaGroupEntry 34 } -- -- Test Pattern Procedure control objects. These objects are implemented -- if the IMA implements the Test Pattern Procedure. In this case all -- test pattern procedure related objects must be implemented. Specifically -- these are -- -- imaGroupTestLinkIfIndex -- imaGroupTestPattern -- imaGroupTestProcStatus -- imaLinkTestProcStatus -- imaLinkRxTestPattern -- imaGroupTestLinkIfIndex OBJECT-TYPE SYNTAX IfIndex MAX-ACCESS read-create STATUS current DESCRIPTION "This object is used to designate an interface as the Test Link. A value of -1 specifies that the implementation may choose the Test Link. In this case, the implementation may also choose the value of 'imaGroupTestPattern'." DEFVAL { -1 } ::= { imaGroupEntry 35 } imaGroupTestPattern OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-create STATUS current DESCRIPTION "The value of this object is used to specify the test pattern in an IMA group loopback operation. A value in the range 0 to 255 designates a specific pattern. A value of -1 specifies that the implementation may choose the value. In this case, the implementation may also choose the value of 'imaGroupTestLinkIfIndex'." DEFVAL { -1 } ::= { imaGroupEntry 36 } imaGroupTestProcStatus OBJECT-TYPE SYNTAX ImaTestProcStatus MAX-ACCESS read-create STATUS current DESCRIPTION "This object is used to enable or disable the Test Pattern Procedure, and to note whether at least one link failed the test. The test is started by setting operating(2) status. If any link should fail the test, the IMA will set the status to linkfail(3). The linkfail(3) state will persist until either the disabled(1) state is set or until no instance of imaLinkTestProcStatus has the value linkfail(3). Only the values disabled(1) and operating(2) may be written. Writing the operating(2) value will not cause clearing of the linkfail(3) state." DEFVAL { disabled } ::= { imaGroupEntry 37 } -- -- The IMA Group - ifIndex Mapping Table -- -- Note that the Group Index is different than the ifIndex. -- -- The "ifIndex Mapping" table allows the Unit Management to -- perform easy look-ups (no searches and sorts). imaGroupMappingTable OBJECT-TYPE SYNTAX SEQUENCE OF ImaGroupMappingEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "A table mapping the 'ifIndex' values of 'imaGroupIfIndex' to the 'imaGroupIndex' values of the corresponding IMA group." ::= { atmfImaMibObjects 3 } imaGroupMappingEntry OBJECT-TYPE SYNTAX ImaGroupMappingEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "Each row describes one ifIndex --> imaGroupIndex mapping." INDEX { ifIndex } ::= { imaGroupMappingTable 1 } ImaGroupMappingEntry ::= SEQUENCE { imaGroupMappingIndex Integer32 } imaGroupMappingIndex OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The imaGroupIndex of the IMA Group which implements the specified interface." ::= { imaGroupMappingEntry 1 } -- The IMA link status and configuration table -- Each entry in the table contains status information about a link -- which is part of an IMA group. imaLinkTable OBJECT-TYPE SYNTAX SEQUENCE OF ImaLinkEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "The IMA group Link Status and Configuration table." ::= { atmfImaMibObjects 4 } imaLinkEntry OBJECT-TYPE SYNTAX ImaLinkEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "An entry in the IMA Group Link table." INDEX { imaLinkIfIndex } ::= { imaLinkTable 1 } ImaLinkEntry ::= SEQUENCE { imaLinkIfIndex Integer32, imaLinkRowStatus RowStatus, imaLinkGroupIndex Integer32, imaLinkNeTxState ImaLinkState, imaLinkNeRxState ImaLinkState, imaLinkFeTxState ImaLinkState, imaLinkFeRxState ImaLinkState, imaLinkNeRxFailureStatus ImaLinkFailureStatus, imaLinkFeRxFailureStatus ImaLinkFailureStatus, imaLinkTxLid INTEGER (0..31), imaLinkRxLid INTEGER (0..31), imaLinkRelDelay MilliSeconds, imaLinkImaViolations Integer32, imaLinkOifAnomalies Integer32, imaLinkNeSevErroredSec Integer32, imaLinkFeSevErroredSec Integer32, imaLinkNeUnavailSec Integer32, imaLinkFeUnavailSec Integer32, imaLinkNeTxUnusableSec Integer32, imaLinkNeRxUnusableSec Integer32, imaLinkFeTxUnusableSec Integer32, imaLinkFeRxUnusableSec Integer32, imaLinkNeTxNumFailures Integer32, imaLinkNeRxNumFailures Integer32, imaLinkFeTxNumFailures Integer32, imaLinkFeRxNumFailures Integer32, imaLinkTxStuffs Integer32, imaLinkRxStuffs Integer32, imaLinkRxTestPattern INTEGER (0..255), imaLinkTestProcStatus ImaTestProcStatus } imaLinkIfIndex OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "This corresponds to the 'ifIndex' of the MIB-II interface on which this link is established. This object also corresponds to the logical number ('ifIndex') assigned to this IMA link." ::= { imaLinkEntry 1 } imaLinkRowStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The imaLinkRowStatus object allows create, change and delete operations on imaLinkTable entries. To create a new conceptual row (or instance) of the imaLinkTable, imaLinkRowStatus must be set to 'createAndWait' or 'createAndGo.' A successful set of the object imaLinkGroupIndex must be performed before the RowStatus of this new row can transition to the 'Active' state. The imaLinkGroupIndex provides the association between a physical IMA link to an IMA group. To change (modify) an imaLinkTable entry, the imaLinkRowStatus object must be set to 'notInService'. Only then can the conceptual row be changed. Setting object imaLinkGroupIndex to a different value has the effect of changing the association between a physical IMA link and an IMA group. To place the link 'in group', the imaLinkRowStatus object is set to 'Active'. While the row is not in 'Active' state, both the Transmit and Receive IMA state machines are in the 'Not In Group' state. To remove (delete) an imaLinkTable entry from this table, set this object to 'destroy.' A network manager may elect to perform a delete operation followed immediately by a create operation instead of a modify operation. The net effect of the delete/create is to re-instantiate (reset) agent counters defined in this table." ::= { imaLinkEntry 2 } imaLinkGroupIndex OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-create STATUS current DESCRIPTION "The value which identifies the IMA group (imaGroupIndex) of which this link is a member." ::= { imaLinkEntry 3 } imaLinkNeTxState OBJECT-TYPE SYNTAX ImaLinkState MAX-ACCESS read-only STATUS current DESCRIPTION "The current state of the near-end transmit link." ::= { imaLinkEntry 4 } imaLinkNeRxState OBJECT-TYPE SYNTAX ImaLinkState MAX-ACCESS read-only STATUS current DESCRIPTION "The current state of the near-end receive link." ::= { imaLinkEntry 5 } imaLinkFeTxState OBJECT-TYPE SYNTAX ImaLinkState MAX-ACCESS read-only STATUS current DESCRIPTION "The current state of the far-end transmit link as reported via ICP cells." ::= { imaLinkEntry 6 } imaLinkFeRxState OBJECT-TYPE SYNTAX ImaLinkState MAX-ACCESS read-only STATUS current DESCRIPTION "The current state of the far-end receive link as reported via ICP cells." ::= { imaLinkEntry 7 } imaLinkNeRxFailureStatus OBJECT-TYPE SYNTAX ImaLinkFailureStatus MAX-ACCESS read-only STATUS current DESCRIPTION "The current link failure status of the near-end receive link." ::= { imaLinkEntry 8 } imaLinkFeRxFailureStatus OBJECT-TYPE SYNTAX ImaLinkFailureStatus MAX-ACCESS read-only STATUS current DESCRIPTION "The current link failure status of the far-end receive link as reported via ICP cells." ::= { imaLinkEntry 9 } imaLinkTxLid OBJECT-TYPE SYNTAX INTEGER (0..31) MAX-ACCESS read-only STATUS current DESCRIPTION "The outgoing LID used currently on the link by the local end. This value has meaning only if the link belongs to an IMA group." ::= { imaLinkEntry 10 } imaLinkRxLid OBJECT-TYPE SYNTAX INTEGER (0..31) MAX-ACCESS read-only STATUS current DESCRIPTION "The incoming LID used currently on the link by the remote end as reported via ICP cells. This value has meaning only if the link belongs to an IMA group." ::= { imaLinkEntry 11 } imaLinkRelDelay OBJECT-TYPE SYNTAX MilliSeconds MAX-ACCESS read-only STATUS current DESCRIPTION "The latest measured delay on this link relative to the link, in the same IMA group, with the least delay." ::= { imaLinkEntry 12 } imaLinkImaViolations OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "ICP violations: count of errored, invalid or missing ICP cells during non-SES-IMA condition." ::= { imaLinkEntry 13 } imaLinkOifAnomalies OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of OIF anomalies during non-SES-IMA condition at the near-end. This is an optional attribute." ::= { imaLinkEntry 14 } imaLinkNeSevErroredSec OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "Count of one second intervals containing several IV-IMA, or one or more link defects (e.g., LOS, OOF/LOF, AIS, LCD), LIF, LODS defects during non-UAS-IMA condition." ::= { imaLinkEntry 15 } imaLinkFeSevErroredSec OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "Count of one second intervals containing one or more RDI-IMA defects." ::= { imaLinkEntry 16 } imaLinkNeUnavailSec OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "Count of unavailable seconds at near-end: unavailability begins at the onset of 10 contiguous SES-IMA and ends at the onset of 10 contiguous seconds with no SES-IMA." ::= { imaLinkEntry 17 } imaLinkFeUnavailSec OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "Count of unavailable seconds at far-end: unavailability begins at the onset of 10 contiguous SES-IMA-FE and ends at the onset of 10 contiguous seconds with no SES-IMA-FE." ::= { imaLinkEntry 18 } imaLinkNeTxUnusableSec OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "Tx Unusable seconds: count of Unusable seconds at the near end Tx LSM." ::= { imaLinkEntry 19 } imaLinkNeRxUnusableSec OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "Rx Unusable seconds: count of Unusable seconds at the near end Rx LSM." ::= { imaLinkEntry 20 } imaLinkFeTxUnusableSec OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "Tx Unusable seconds at far-end: count of seconds with Unusable indications from the far-end Tx LSM." ::= { imaLinkEntry 21 } imaLinkFeRxUnusableSec OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "Rx Unusable seconds at far-end: count of seconds with Unusable indications from the far-end Rx LSM." ::= { imaLinkEntry 22 } imaLinkNeTxNumFailures OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times a near-end transmit failure alarm condition has been entered on this link." ::= { imaLinkEntry 23 } imaLinkNeRxNumFailures OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times a near-end receive failure alarm condition has been entered on this link (i.e., LIF, LODS, Mis-Connected, RDI-IMA)." ::= { imaLinkEntry 24 } imaLinkFeTxNumFailures OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times a far-end transmit failure alarm condition has been entered on this link. This is an optional attribute." ::= { imaLinkEntry 25 } imaLinkFeRxNumFailures OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times a far-end receive failure alarm condition has been entered on this link (i.e., LIF, LODS, Mis-Connected, RDI-IMA). This is an optional attribute." ::= { imaLinkEntry 26 } imaLinkTxStuffs OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "Counts of stuff events inserted in the transmit direction. This is an optional attribute." ::= { imaLinkEntry 27 } imaLinkRxStuffs OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION "Counts of stuff events detected in the receive direction. This is an optional attribute." ::= { imaLinkEntry 28 } -- -- Test Pattern Procedure control objects. These objects are implemented -- if the IMA implements the Test Pattern Procedure. In this case all -- test pattern procedure related objects must be implemented. Specifically -- these are -- -- imaGroupTestLinkIfIndex -- imaGroupTestPattern -- imaGroupTestProcStatus -- imaLinkTestProcStatus -- imaLinkRxTestPattern -- imaLinkRxTestPattern OBJECT-TYPE SYNTAX INTEGER (0..255) MAX-ACCESS read-only STATUS current DESCRIPTION "This object identifies the test pattern received in the ICP Cell (octet 17) on the link during the IMA Test Pattern Procedure. This value may then be compared to the transmitted test pattern." ::= { imaLinkEntry 29 } imaLinkTestProcStatus OBJECT-TYPE SYNTAX ImaTestProcStatus MAX-ACCESS read-only STATUS current DESCRIPTION "This value indicates the current state of the Test Pattern Procedure. If the value is disabled(1), the test is not running. A value of operating(2) means the test is running and no error has been found on this interface. A value of linkfail(3) means an error has been detected on this link during the test. Once an error occurs, the linkfail(3) value is latched until either this object is read or until the imaGroupTestProcStatus is moved to disabled(1). Once read, if the error no longer persists, a subsequent read will report the value operating(2)." ::= { imaLinkEntry 30 } -- -- IMA Failure Alarms -- -- Implementation of the imaFailureAlarm Trap is optional. -- imaAlarmStatus OBJECT-TYPE SYNTAX ImaAlarmStatus MAX-ACCESS read-only STATUS current DESCRIPTION "Status of the IMA alarm." ::= { atmfImaMibObjects 5 } imaAlarmType OBJECT-TYPE SYNTAX ImaAlarmType MAX-ACCESS read-only STATUS current DESCRIPTION "The Type of IMA alarm declared or cleared. The value of ImaAlarmType identifies the type of alarm according to the definitions in the IMA specification." ::= { atmfImaMibObjects 6 } imaFailureAlarm NOTIFICATION-TYPE OBJECTS { ifIndex, imaAlarmStatus, imaAlarmType } STATUS current DESCRIPTION "The imaFailureAlarm provides a method for an agent implementing IMA to notify an NMS of an alarm condition." ::= { atmfImaMibObjects 7 } -- Conformance Information atmfImaMibConformance OBJECT IDENTIFIER ::= { atmfImaMib 2 } atmfImaMibGroups OBJECT IDENTIFIER ::= { atmfImaMibConformance 1 } atmfImaMibCompliances OBJECT IDENTIFIER ::= { atmfImaMibConformance 2 } -- Compliance Statements atmfImaMibCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for network elements implementing Inverse Multiplexing for ATM." MODULE IMA-MIB -- Mandatory Part MANDATORY-GROUPS { atmfImaGroupGroup, atmfImaLinkGroup, atmfImaGroupMappingTableGroup } GROUP imaTestPatternGroup DESCRIPTION "This group is mandatory only for implementations that support the Test Pattern Procedure. This group contains objects which control and report on the Test Pattern Procedure." -- Compliance Part OBJECT imaGroupSymmetry MIN-ACCESS read-only DESCRIPTION "Write access is not required." OBJECT imaGroupMinNumTxLinks MIN-ACCESS read-only DESCRIPTION "Write access is not required." OBJECT imaGroupMinNumRxLinks MIN-ACCESS read-only DESCRIPTION "Write access is not required." OBJECT imaGroupTxImaId MIN-ACCESS read-only DESCRIPTION "Write access is not required." OBJECT imaGroupTxFrameLength MIN-ACCESS read-only DESCRIPTION "Write access is not required." OBJECT imaGroupDiffDelayMax MIN-ACCESS read-only DESCRIPTION "Write access is not required." OBJECT imaGroupAlphaValue MIN-ACCESS read-only DESCRIPTION "Write access is not required." OBJECT imaGroupBetaValue MIN-ACCESS read-only DESCRIPTION "Write access is not required." OBJECT imaGroupGammaValue MIN-ACCESS read-only DESCRIPTION "Write access is not required." OBJECT imaGroupTestLinkIfIndex MIN-ACCESS read-only DESCRIPTION "Write access is not required." OBJECT imaGroupTestPattern MIN-ACCESS read-only DESCRIPTION "Write access is not required." ::= { atmfImaMibCompliances 1 } -- Units of Conformance atmfImaGroupGroup OBJECT-GROUP OBJECTS { imaGroupNumber, imaGroupRowStatus, imaGroupIfIndex, imaGroupIndex, imaGroupNeState, imaGroupFeState, imaGroupFailureStatus, imaGroupSymmetry, imaGroupMinNumTxLinks, imaGroupMinNumRxLinks, imaGroupNeTxClkMode, imaGroupFeTxClkMode, imaGroupTxTimingRefLink, imaGroupRxTimingRefLink, imaGroupLastChange, imaGroupTxImaId, imaGroupRxImaId, imaGroupTxFrameLength, imaGroupRxFrameLength, imaGroupDiffDelayMax, imaGroupLeastDelayLink, imaGroupDiffDelayMaxObs, imaGroupAlphaValue, imaGroupBetaValue, imaGroupGammaValue, imaGroupRunningSecs, imaGroupUnavailSecs, imaGroupNeNumFailures, imaGroupFeNumFailures, imaGroupTxAvailCellRate, imaGroupRxAvailCellRate, imaGroupNumTxCfgLnks, imaGroupNumRxCfgLnks, imaGroupNumTxActLnks, imaGroupNumRxActLnks } STATUS current DESCRIPTION "A set of objects providing configuration and status information for an IMA group definition." ::= { atmfImaMibGroups 1 } atmfImaLinkGroup OBJECT-GROUP OBJECTS { imaLinkIfIndex, imaLinkRowStatus, imaLinkGroupIndex, imaLinkNeTxState, imaLinkNeRxState, imaLinkFeTxState, imaLinkFeRxState, imaLinkNeRxFailureStatus, imaLinkFeRxFailureStatus, imaLinkTxLid, imaLinkRxLid, imaLinkRelDelay, imaLinkImaViolations, imaLinkOifAnomalies, imaLinkNeSevErroredSec, imaLinkFeSevErroredSec, imaLinkNeUnavailSec, imaLinkFeUnavailSec, imaLinkNeTxUnusableSec, imaLinkNeRxUnusableSec, imaLinkFeTxUnusableSec, imaLinkFeRxUnusableSec, imaLinkNeTxNumFailures, imaLinkNeRxNumFailures, imaLinkFeTxNumFailures, imaLinkFeRxNumFailures, imaLinkTxStuffs, imaLinkRxStuffs } STATUS current DESCRIPTION "A set of objects providing status information for an IMA link." ::= { atmfImaMibGroups 2 } atmfImaGroupMappingTableGroup OBJECT-GROUP OBJECTS { imaGroupMappingIndex } STATUS current DESCRIPTION "A table mapping the 'ifIndex' values of 'imaGroupIfIndex' to the 'imaGroupIndex' values of the corresponding IMA group." ::= { atmfImaMibGroups 3 } imaTestPatternGroup OBJECT-GROUP OBJECTS { imaGroupTestLinkIfIndex, imaGroupTestPattern, imaGroupTestProcStatus, imaLinkTestProcStatus, imaLinkRxTestPattern } STATUS current DESCRIPTION "Objects in the imaGroupTable and imaLinkTable which control and report on the Test Pattern Procedure. These objects must be implemented if the IMA Test Pattern Procedure is supported." ::= { atmfImaMibGroups 4 } imaAlarmGroup OBJECT-GROUP OBJECTS { imaAlarmStatus, imaAlarmType } STATUS current DESCRIPTION "Objects used in the imaFailureAlarm notification." ::= { atmfImaMibGroups 5 } END 16. References [1] ANSI T1.101-1987 "Synchronization Interface Standards for Digital Networks". [2] ANSI T1.102-1993 "Digital Hierarchy - Electrical Interfaces". [3] ANSI T1.231-1993 "Digital Hierarchy - Layer 1 In-Service Digital Transmission Performance Monitoring". [4] ANSI T1.403-1995 "Network-to-Customer Installation-DS1 Metallic Interface". [5] ANSI T1.408-1990 "Integrated Services Digital Network (ISDN) Primary Rate - Customer Installation Metallic Interfaces Layer 1 Specification. [6] ANSI T1.646-1995, Broadband-ISDN - Physical Layer Specification for User-Network Interfaces Including DS1/ATM, 1995. [7] ATM Forum AF-BICI-0013.003 "B-ISDN Inter Carrier Interface (B-ICI) Specification Version 2.0 (Integrated), December 1995. [8] ATM Forum AF-PHY-0016.000 "DS1 Physical Layer Specification", September, 1994. [9] ATM Forum AF-PHY-0064.000 "E1 Physical Layer Interface Specification", July 1996. [10] ATM Forum AF-PNNI-0055.000 "Private Network-Network Interface Specification Version 1.0", March 1996. [11] ATM Forum User-Network Interface Specification, Version 3.1, May 1994. [12] Harel, D., 1987, "State Charts: A visual formalism for complex systems", Science of Computer Programming, Volume 8. [13] IETF RFC 1155, "Structure and Identification of Management Information for TCP/IP-based Internets", May 1990. [14] IETF RFC 1156, "Management Information Base for Network Management of TCP/IP-based internets", May 1990. [15] IETF RFC 1157, "A Simple Network Management Protocol (SNMP)", May 1990. [16] IETF RFC 1212, "Concise MIB definitions", March 1991. [17] IETF RFC 1213, "Management Information Base for Network Management of TCP/IP-based internets: MIB-II", March 1991. [18] IETF RFC 1406, "Definitions of Managed Objects for the DS1 and E1 interface types", January 1993. [19] IEFT RFC 1442, "Structure of Management Information for version 2 of the Simple Network Management Protocol (SNMPv2)", April 1993. [20] IEFT RFC 1443, "Textual Conventions for version 2 of the Simple Network Management Protocol (SNMPv2)", April 1993. [21] IEFT RFC 1444, "Conformance Statements for version 2 of the Simple Network Management Protocol (SNMPv2)", April 1993. [22] IEFT RFC 1445, "Administrative Model for version 2 of the Simple Network Management Protocol (SNMPv2)", April 1993. [23] IEFT RFC 1446, "Security Protocols for version 2 of the Simple Network Management Protocol (SNMPv2)", April 1993. [24] IEFT RFC 1447, "Party MIB for version 2 of the Simple Network Management Protocol (SNMPv2)", April 1993. [25] IEFT RFC 1448, "Protocol Operations for version 2 of the Simple Network Management Protocol (SNMPv2)", April 1993. [26] IEFT RFC 1449, "Transport Mappings for version 2 of the Simple Network Management Protocol (SNMPv2)", April 1993. [27] IEFT RFC 1450, "Management Information Base for version 2 of the Simple Network Management Protocol (SNMPv2)", April 1993. [28] IEFT RFC 1451, "Manager-to-Manager Management Information Base", April 1993. [29] IEFT RFC 1452, "Coexistence between version 1 and version 2 of the Internet-standard Network Management Framework", April 1993. [30] IETF RFC 1573 "Evolution of the Interfaces Group of MIB-II", January 1994. [31] ISO/IEC 11573.1994(E) "Information technology - Telecommunications and information exchange between systems - Synchronization methods and technical requirements for Private Integrated Service Networks". [32] ITU-T Recommendation G.703 "Physical/Electrical Characteristics of Hierarchical Digital Interfaces", 1991. [33] ITU-T Recommendation G.810, "Considerations on Timing and Synchronization Issues", 1988. [34] ITU-T Recommendation G.811, "Timing Requirements at the Outputs of Primary Reference Clocks Suitable for Plesiochronous Operation of International Digital Links", 1988. [35] ITU-T Recommendation G.823, "The control of jitter and wander within digital networks which are based on the 2048 kbit/s hierarchy, 1988. [36] ITU-T Recommendation G.824, "The control of jitter and wander within digital networks which are based on the 1544 kbit/s hierarchy, 1988. [37] ITU-T Recommendation G.826, "Error performance parameters and objectives for international constant bit rate digital paths at or above the primary rate, 1993. [38] ITU-T Recommendation I.321, "B-ISDN Protocol Reference Model and its applications", March 1993. [39] ITU-T Recommendation I.361, "B-ISDN ATM Layer Specification", March 1993. [40] ITU-T Recommendation I.431 "Primary Rate User-Network Interface - Layer 1 specification", March 1993. [41] ITU-T Recommendation I.432 Series, "B-ISDN User-Network Interface - Physical Layer Specification", April 1996. [42] ITU-T Recommendation I.610, "B-ISDN Operation and Maintenance Principles and Functions", 1995. Appendix A Example of Link Delay Synchronization This section describes an example on how link delay synchronization may be achieved. The delay compensation at the receive end may be done using the IMA framing number and ICP cell offset contained in the incoming ICP cells. Figure 26 on page 107 shows an IMA group with three links called Link 0, Link 1 and Link 2. The link multiplexing order is 0-> 1-> 2-> 0, etc. The ICP cells have been identified according to the LID of the link on which they are sent. The cells other than the ICP cells have been numbered in the order they are sent over the virtual link. Figure 26 Link Delay Compensation example The transmit end has staggered the ICP cells giving them ICP Cell Offset of 1, 0 and 2 for links 0, 1 and 2 respectively. Again, these values are used for illustration purposes only. It is recommended that ICP cell position from link-to-link be spaced out as evenly as possible in an IMA frame. At the receive end, link 0 and link 2 have the same amount of propagation delay but link 1 has a delay one cell time longer than link 0 or link 2. At the receive end, each link has its own circular buffer which should be deep enough to tolerate the maximum link delay variation. Figure 27 on page 108 to Figure 30 on page 109 shows an example of the processing of the incoming cells at the receive end. One Delay Compensation Buffer (DCB) is defined per link. The shaded portions of DCBs on Figure 27 to Figure 30 represent unfilled portions of the buffer allocated for each link. Each section of the buffer represents a single cell buffer. The unshaded portion represents portions filled with cells. Figure 28 to Figure 30 also shows the contents of the three Delay Compensation Buffers (DCB) on the receive end at time t = T1, T2, T3 and T6. The write pointer of each link shows the next location where a cell would be put when received from that link. At time T0, no ICP cells have been received yet on any links so no cells are written to the buffers. Whenever a cell is written into a buffer, the write pointer is incremented. A read (playback) pointer increments as cells are read out of the buffer. Both pointers wrap around when they reach the end of the buffer. Until the first ICP cell is received, no cell is written into the buffer. When the first ICP cell is received, the write pointer is initialized to the value of the IMA frame number plus ICP cell offset contained in that ICP cell. Every cell received after that ICP cell is written into the buffer. All of the delay compensation is done with the adjustment of the write pointers. The read pointers are always aligned and the cells are read out of the buffers in the assigned link multiplexing order. The differential delay between any two links can be simply calculated using the difference between the write pointer values for those two links. Extending this idea to the entire set of links, the maximum differential delay for the link group is simply the difference between the minimum and maximum write pointer values for that group. If we assume the use of DS1 links and given a maximum allowable delay delta of 25 ms, the maximum difference acceptable between the write pointers will be 91cells. The accuracy of this technique is 1 cell time (e.g., 276 microseconds at DS1 rate) which is satisfactory for this application. The process of reading from the buffer is controlled by the IMA cell clock. In round-robin order and at the IMA clock tick, a cell is removed from the DCB (the pointer is advanced). If the cell is an ICP cell, the next link in order is immediately selected (and so on until a cell is found that is not an ICP cell). If the cell is a Filler cell, it is discarded and nothing is passed to the ATM layer. It the cell is not a Filler cell, it is passed to the ATM layer. Figure 27 Snapshot of Buffers at T1 Figure 28 Snapshot of Buffers at T2 Figure 29 Snapshot of Buffers at T3 Figure 30 Snapshot of Buffers at T6 Appendix B Implementation Consideration This section may be used as guidelines for IMA implementers. B.1 Dynamic Changes in ATM Layer Cell Rate This section provides some guidelines to treat dynamic changes of IMA data cell rate (IDCR). The ATM Layer needs to react to dynamic changes in the IDCR, particularly to decreases in the cell rate since decreases in the cell rate are problematic. Connections at the previous (larger) cell rate reserved some quantity of bandwidth (cell rate). If the interface cell rate drops (due to actions within the IMA), then the aggregate reserved cell rate of the connections may exceed the interface cell rate and result in higher Cell Loss Ratio (CLR) and delay than contracted. Dynamic changes can occur in three types of circumstances: (1) a one or more links fail, (2) one or more link are removed administratively, and (3) one or more link are added administratively. In case (1), the IMA interface may or may not experience an increase of CLR and delay on some or all connections due to a decrease of available bandwidth. In some cases, both ends of the virtual links may not release connections and let congestion control discard cells if severe congestion occurs. In other cases, each end may release connections to preserve QoS on the most important connections. The handling of connections upon dynamic bandwidth decrease has been under consideration by several ATM Forum Working Groups (NM, TM, PNNI, and SIG Working Groups). In case (2), the IMA is instructed by the management control plane to drop a link. In this case, the administrative plane function should have taken steps to ensure that the connections on the interface would still pass Connection Admission Control (CAC) at the reduced interface cell rate before instructing the IMA to drop the link. It is conceivable that the administrative function may even preempt connections so those remaining will fall within CAC limits. In any case, close coordination between the CAC and the IMA control functions is necessary if dynamic additions/deletions are to occur. In case (3), the IMA is instructed by the management control plane to add a link. In this case, the administrative plane function should have informed the CAC that additional bandwidth is present. Otherwise new connections will not be admitted, even though more bandwidth is available. The treatment of CAC in the ATM Forum UNI and PNNI specifications [11][10] is implementation dependent. Thus the treatment of CAC under dynamic bandwidth changes is left to the discretion of the ATM interface implementer. B.2 State Machine for De-Bouncing Error Condition Report The Rx Failed condition, described in Section 10.1.4 on page 47, and the link failure alarm, such as defined in Section 12.2.3 on page 76, may be a direct mapping of the defect state machine presented in Figure 20 on page 70, but this may cause lengthening of short errors. Repetitious bursts of errors will also affect the data path if links are brought back in too rapidly. Since there were disparate views as to integration times, a generic state model can be employed, with events loosely defined. Figure 31 on page 111 shows a simplified Rx Failed integration state machine. The integration times can be left as vendor-defined parameters. Another standard technique is the weighted integration into the error condition (e.g., Rx Failed or failure condition). For each sampling period, if a defect is present, a value is added to an integration counter. If no defect is present, a smaller value is subtracted. In this way, errored samples are weighted more heavily. A typical ratio is 10:1. The state machine could also be used for de-bouncing any other error condition report such as "Fault" condition report. The model described above does not apply well to the IMA-specific checks such as IMA framing or link delay synchronization. These take longer to detect than defects, and more latitude may be required. This state machine can be used as an example, leaving X and Y and specific integration techniques to the implementer. Figure 31 Rx Failed State Machine B.3 Maximum Link Differential Delay Limitation This section clarifies an aspect of the IMA baseline text regarding the maximum link differential delay that can be supported by the IMA interface due to the nature of the IMA Frame. Having the following characteristic of the IMA frame and a newly defined IMA super-frame: · IMA frame size: M cells (32, 64, 128 or 256) · IMA frame sequence number (IFSN) range: 0 to 255 · IMA Super-Frame (ISF) definition: starts with IMA frame with sequence number 0 and ends with IMA frame with sequence number 255. · ISF length: 256*M The ISF is defined to illustrate that the IFSN repeats every 256 IMA frames. The IFSN is used by the receiver to compensate for links with longer propagation delay. The receiver then always relies on the IFSN contained in the incoming ICP cells on each links. If the differential delay between the links with the shortest and longest propagation delay is larger than one half of the ISF transmission time, the receiver will not be able to determine which link has the shortest delay. The difference has to be modulo 256, which means that the receiver could think that the difference is either greater or smaller than one half of the ISF. The only way to avoid the confusion is to ensure that the differential link delay between the links with the shortest and the longest propagation delays is never greater than one half of the time to transmit the ISF. Table on page 112 shows the maximum link differential delay that can be supported by the IMA interface in the case DS1/E1 links are used to form an IMA virtual link. Table 21 Maximum Differential Delay for Different M Values over various Links M (cells per IMA Frame) Maximum Differential delay (in milliseconds) DS1 E1 DS3 (Direct Mapping) 32 1130 905 39.3 64 2261 1809 78.6 128 4522 3618 175.1 256 9044 7236 314.3 Although the sizes of the delay listed above is extremely high, it is important to highlight this limitation of the IMA protocol. This would be particularly important if the IMA protocol is implemented over higher speed interfaces. The information can also be expressed another way to give the maximum data rates that can be supported if the required maximum link differential delay is limited to 25 milliseconds. Table 22 on page 112 shows the maximum link rates that may be supported for different M. The data rate is the rate of the cell stream excluding any framing overhead. Table 22 Maximum Data Rate for a Maximum Link differential Link Delay of 25 msec M (cells per IMA Frame) Maximum Data Rate for a maximum link differential delay of 25 msec Bit Rate (Mbps) Cell Rate (kcell/sec) 32 69.5 163.84 64 139 327.68 128 278 655.36 256 555 1310.72 B.4 Clock Variation Tolerance for IMA There are three aspects to be considered for determining the required clock variation tolerance for proper IMA operation: · required number of consecutive ICP cells required for performing stuffing, · periodically stuffing on the timing reference link every 2048 cells, and · maximum insertion rate of stuff event insertion rate B.4.1 Tolerance Due to IMA Stuffing Procedure The specification allows for indication of the stuff action over the previous 4 ICP cells (Section 7 on page 36). This excludes the two ICP cells that comprises the stuff event. This implies a maximum frequency of adjustment of once every 5 ICP cells, or every 5 IMA frames. For an IMA frame with the default value of M=128, 5 IMA frames are 640 cells. This implies that links can have a total variance of 1 cell time out of 640 cell times, or 1/640. Converting this to ppm by multiplying by 106 gives 1562. The frequency variation is then 781 ppm. Table on page 113 gives these calculations for various values of M. Table 23 M Implications on PPM M (cells per IMA Frame) 5M (number of cells) Total variance (ppm) Frequency variation ( ppm) 32 160 6250 3125 64 320 3125 1562 128 640 1562 781 256 1280 781 390 The smallest limit on ppm variation, 390 ppm, is substantially more than that for the one required on DS1/E1 links ( 32 ppm and 50 ppm respectively). Accordingly the IMA stuff procedure does not limit link selection further, and in fact can adjust for differences in link frequencies substantially more than are allowable. Since there is the SICP cell itself, the adjustment period is 5M+1 cells. B.4.2 Tolerance Due to Periodically Stuffing on the Timing Reference Link Equation (EQ. 1) on page 38 requires the insertion of one cell every 2048 ICP, Filler and ATM layer cells transmitted over the timing reference link (TRL). This value, 2048, has been chosen because it is the next binary number (211) that allows to use the optional advanced stuff indication procedure for M equals to 256 (1280 is the minimum required as described in the previous section). In the case the TRL is the faster link in the group, link frequency differences up to 488 ppm can be tolerated between the TRL and the slowest link in the group. This is assuming that this is no need to insert stuff events on the slowest link. B.4.3 Tolerance Due to Maximum Stuff Event Insertion Rate The maximum stuff event insertion rate is defined to be one stuff event every 5M ICP, Filler and ATM layer cells for accommodating configurations using the optional four advanced indications. Enforcing such value also allows to avoid cases where some implementations would not constantly regulate the insertion of the stuff events over time. In the case where the TRL is the slowest link in the group, the choice of 5M where M equals to 128 allows link frequency differences up to 293 ppm between the TRL and the faster link in the group. This value is derived from the fact that there is a frequency difference of 781 ppm between a link on which a stuff event is inserted every 1280 ICP, Filler and ATM layer cells and another link on which there is no stuff event being inserted, and a frequency difference of 488 ppm between the TRL and a link on which there is no stuff event being inserted. The frequency difference between the TRL and the faster link, 293 ppm, is still quite larger than the ppm requirement of most link interfaces. Table 24 on page 114 shows the maximum tolerated frequency difference between the TRL and the fastest link. Table 24 Maximum Tolerated Frequency Difference between the TRL and the Fastest Link M (cells per IMA Frame) 5M (number of cells) Total variance (ppm) Maximum tolerated frequency difference between TRL and faster link 32 160 6250 5762 64 320 3125 2637 128 640 1562 1074 256 1280 781 293 B.5 Example of IMA Data Cell Rate Recovery Implementation This section describes an example of IMA Data Cell Rate (IDCR) recovery mechanism. It suggests that the IMA receive interface to the ATM layer limit itself to specifying the cell order, the IMA data cell rate and aggregate CDV. The actual method to clock an individual cell from the IMA sublayer to the ATM layer is implementation and application specific. Figure 32 on page 115 shows a partial block diagram of the receive IMA. Portions shown are relevant to the IDCR recovery of the IMA group. It consists of the Delay Compensation Buffers (DCB), the IMA Data Cell Clock (IDCC), the Read Pointer Functional Block (RPFB) and the output interface to the ATM layer. The shaded portions of the DCB, in Figure 32, signifies unfilled portions of the buffer allocated for each link. Each section of the buffer represents a single cell buffer. The unshaded portion represents portions filled with cells. The write pointer of each link shows the next location where a cell would be put when received from that link. The read pointer points to the next cell that would be queued to the ATM layer interface. Figure 32 shows the DBC for an IMA group composed of three links 0, 1, 2 (therefore N=3) with M=8 cells. M equal to 8 is used to simplify the figure. Link 0 is the link with the greatest delay with 3 cells in its buffer. Links 0, 1, and 2 have a least 3 cells in their DCB's. When encountering an ICP cell, the RPFB will ignore the cell and will immediately advance to the next link in order without having to wait for the next IDCC tick. When encountering a stuff event, the RPFB will ignore both ICP cells part of the stuff event and will immediately advance to the next link in order. The RPFB is not responsible to examine the ICP cell content. It can be assumed that incoming ICP cells are passed to another functional block of the IMA interface for further processing. When encountering a Filler cell, the RPFB will ignore the cell and wait until the next IDCC tick to advance to the next link in order. Figure 33 on page 116 shows the insertion of stuff cells every "Y" IMA frames on the TRL, where Y is 2048/M, or 256 if this example. Figure 32 Serving Delay Compensation Buffers Figure 33 Insertion of Stuff Cell every Y*M Cells on the TRL Appendix C Asymmetric Operation C.1 Introduction This appendix covers extensions of the IMA specification to the operations and configuration to cover two aspects of asymmetric links. · Asymmetric configuration covers the configuration and static elements of IMA to allow the provision of asymmetric links, for example a group with 3 links in one direction and 2 in the other. · Asymmetric operation treats the operation of the links independently separating the transmit and receive behavior and allowing the IMA to continue to use a link in one direction that has failed in the other. C.2 Transmit and Receive State Transitions The Transmit (Tx) and Receive (Rx) state transitions should operate independently, with independent setting of the Link Information fields in the ICP cells for the Tx and Rx ends. An IMA group set in the asymmetric operation but not supporting asymmetric configuration would always expect the Rx and Tx links to be either both in a group or both out of a group. The NE Tx state transition does not consider the NE Rx state or the FE Tx state when deciding on the state of the NE Tx link (i.e., note 8 in Table 8 on page 49 applies). The NE Rx state transition does not consider the NE Tx state or the FE Rx state when deciding on the state of the NE Rx link (i.e., note 8 in Table 9 on page 51 applies). C.3 Link Start-up There are two cases, one where the receive end is ready first, and a second where the transmit end is ready first. This is shown in Figure 34 on page 118 and Figure 35 on page 118. C.4 Group Start-Up For any group, two values will be provided, PTx and PRx. PTx and PRx as appearing in Figure 14 on page 60, may be different. Figure 34 Exchange of the NE Tx and Rx State during Link Start-up - Rx Ready First Figure 35 Link Start-up - Tx Ready First Appendix D Examples of Link State Exchanges This section presents examples of state exchanges between the two ends of the IMA virtual link based on the LSM defined in Section 10.1 on page 43. The link addition, activation, deletion and de-activation cases are covered. Both symmetrical and asymmetrical configurations are also considered. Figure 37 on page 120 shows the case where a link is added and activated simultaneously at both ends. Overlapping identical handshakes occur in both directions, controlling each direction independently. Figure 36 Link addition with Overlapping Sequence (Symmetrical Operation) Figure 37 on page 120 shows the case when both ends are not overlapping. One end is moving to Usable before the other end. End B may safely skip to the receive Unusable state, and the response is immediate transition to receive Active state at the local end. Full operation is established in a single round-trip. Figure 37 Link addition with Non-Overlapping Sequence (Symmetrical Operation) Figure 38 on page 121 and Figure 39 on page 121 show the state exchange initiated by end A for deleting a link in the transmit direction for both the symmetrical and asymmetrical operations. Note that the receive link remains Active in the case the groups are asymmetrically operated. Figure 38 Transmit Link Deletion at One End (Symmetrical Operational) Figure 39 Transmit Link Deletion at One End (Asymmetrical Operational) Figure 40 on page 122 shows the state exchange in the case of link de-activation in the case of a transmit failure in one direction under symmetrical configuration. Figure 41 on page 122 shows the scenario for the asymmetrical operation. Figure 40 Link De-activation due to Tx Fault (Symmetrical Operation) Figure 41 Link De-activation due to Tx Fault (Symmetrical Operation) Figure 42 on page 123 and Figure 43 on page 124 shows a link de-activation when the Rx Failed condition is entered and the later link re-activation after Rx Failed condition is exited, under symmetrical and asymmetrical operation respectively. Figure 42 Link De-activation/Recovery under Link Failed Condition (Symmetrical Operation) Figure 43 Link De-activation/Recovery under Link Failed Condition (Asymmetrical Operation) Appendix E IMA OAM Behaviors This appendix provides information about the OAM behaviors of the IMA interface. Figure 44 on page 125 shows the OAM behaviors of a single link and an IMA interface. The following can be noted: · A defect is reported at a layer (F1, F2, F3 F4 or F5) once detecting a defect at the same layer or when AIS is reported by the lower layer · Once a defect is detected at a layer, an RDI is reported in the opposite direction · Once a defect is detected at a layer, AIS is reported to the next upper layer Figure 44 Single Link and IMA OAM Behaviors Appendix F Numbers of IV-IMAs to Trigger SES-IMA ITU-T Recommendation G.826 [37] specifies that SES shall be reported for second periods which contain 30% errored blocks. It also specifies that a lesser number may be used in the case the system has not the ability to detect and that value different from 30% may be used and these values may vary with transmission rate. Table 25 on page 126 shows the number of errored ICP cells that could be used to derive SES if we require 30% errored blocks to report SES. This is excluding the presence of Filler and ATM layer cells. The table shows that the values of the SES threshold depends of M and the available LCR. The advantage is to have a threshold adapted to the available LCR. Table 25 Proposed Numbers of IV-IMAs to Trigger SES DS1 (LCR = 3622.6 cells/second) E1 (LCR = 4528.3 cells/second) M ICP cells/second 30% ICP cells/second 30% 32 113 34 142 43 64 56 17 71 22 128 28 9 36 11 256 14 5 18 6 Appendix G Detailed IMA Clocking Configurations This appendix contains detailed information with respect to clocking options that are specific to various IMA link configurations, where the links are DS1 or E1 links. The information contained within this appendix builds upon the details as described within Section 4.3 on page 23 and addresses the scenarios where the transmit clocks of the links within the IMA group may or may not be derived from the same clock source (i.e., CTC or ITC mode), and where the IMA interface is used in public and private network configurations. The respective clocking configuration selected for an IMA application will be determined by the availability and provisioning of link services. It is suggested that, if possible, all the links within the IMA link group use a single source for transmit clock and, if possible, that source be traceable to a Primary Reference Source (PRS). Throughout this appendix the terms Primary Reference Source (PRS)[5], Primary Reference Clock (PRC)[34], and Stratum 1 are synonymous. G.1 IMA Group in CTC Mode This section describes clocking options applicable to the configuration where the IMA interface is running in the Common Transmit Clock (CTC) mode. These clocking options can be categorized into two main sections, namely non-transparent and transparent, as shown in Figure 45 on page 127. The link reference model illustrates the different timing domains [31]. Figure 45 Link Timing Reference Model Transparent is defined within reference [31] as: a link or group of links is transparent if the signal carried is not re-timed from a clock associated with the link(s). The timing of a signal passing across a transparent link may however be altered due to jitter, wander, filtering or error conditions. G.1.1 Non-transparent Links The following section will detail link configurations applicable to a non-transparent relationship. All these configurations are associated with the support of access to a synchronous public network. G.1.1.1 Single Time Domain The single-time domain clocking configuration is applicable to an application where all transmitters are within a single timing domain (e.g., all links from the same local area carrier). An example is given in Figure 46 on page 128. The IMA units will derive their respective transmit clocks from one of their receive clock signals, which will normally be traceable to a Stratum 1. Figure 46 Single Time Domain The DS1 interface will be expected to conform to the ANSI T1.408 [5] specification which imposes the following requirements: · The IMA receiver and transmitted bit streams must be synchronized to the carrier's clock. · In normal operation the bit stream is traceable to a Stratum 1 primary reference, which has a long term bit rate accuracy of 1x10-11. When synchronization by a Stratum 1 clock has been interrupted, the signal delivered by the network to the interface shall have a minimum accuracy of 4.6 x 10-6, Stratum 3 accuracy, as specified in ANSI T1.408[5], Section 5.3.1.1. · For multiple network interfaces (as with an IMA with multiple links), the transmission rate is determined by the signal received across only one link interface, or is derived externally from the carrier's Stratum 1, so that all interfaces are synchronized to the same master clock source. An E1 interface has similar requirements that are specified in ITU-T Recommendations G.703 [32] and I.431 [40]. G.1.1.2 Two or More Timing Domains The two or more timing domains clocking configuration addresses the scenario where the multiple IMA low speed links are obtained from a number of distinct and separate carriers, which have their own synchronization hierarchies (timing domains). This scenario may be quite common as it adds to the diversity and survivability of an IMA application. An example is shown in Figure 47 on page 129. Figure 47 Two or More Timing Domains The configuration will have each link or group of links synchronized to a separate master clock source, which again will normally be traceable to Stratum 1. In practice only one of the carrier master clocks will synchronize the IMA equipment for synchronization, e.g. Carrier A's Stratum 1 reference clock. This may result in virtually error-free traffic performance as the carriers are operating plesiochronously with each other, with average clock rate different by no more than 1 part per 10-11. In this configuration, it is recommended to ensure all carriers use Stratum 1 traceable clocks when subscribing. G.1.1.3 International or Inter Exchange Carrier (IEC) Timing Domains The following configuration, shown in Figure 48 on page 130, can be referred to as the "Classic Plesiochronous" configuration with respect to a synchronous network. The scenario addressed is where the links traverse more than one timing domain. This will occur within international and inter-IEC topologies as well as within many larger networks. Each IMA's internal clock will synchronize to a DS1/E1 received from the host carrier and provide timing to the IMA transmitted signals, so that all the signals in the group of links are normally traceable to one of the carrier's Stratum 1. The inter-working and re-timing of the information stream across the different timing domains will be managed transparently to the application. If timing differences do accumulate then a controlled slip may be introduced by individual DS1/E1 receivers to compensate for the differences. Under fault free conditions the occurrence of a controlled slip will be rare, e.g. in a worst case scenario where the number of carriers (N) is 2, 1 controlled frame slip will occur per 72 days (per DS1/E1). Figure 48 International or Inter IEC Timing Domains G.1.2 Transparent Links The following section details link configurations applicable to a transparent relationship, e.g. private leased lines. These configurations will require the customer premise to provide or act as the master clock source for the transmitted signals. All these configurations should be termed as being asynchronous, which indicates that they are not synchronized to a network wide clock source. Note that the respective local clock source may still be traceable to a network wide PRS but this is not a requirement. G.1.2.1 Master/Master Configuration The master/master configuration is applicable when addressing services which require the customer premise equipment to act as the clock source. In this configuration the transmit clock is not derived from the receive bit stream (see Figure 49 on page 130). The configuration may also be known as a "Transparent" or "Split timing" configuration [31]. The clocks are required to support an accuracy of 1.544Mbps 32 ppm for DS1 configuration [2] and 2.048 Mbps 50 ppm for E1 configuration [32]. Figure 49 Master/Master Configuration Practical configuration options with respect to the clock sources are detailed as follows, refer [31]. (x) and (y) are reference clocks. When (x) and (y) are providing a clock signal, two cases can occur, in addition to the free-running case: 1. (x) and (y) come from the same clock and are therefore synchronous and 2. (x) and (y) are from two different clock sources. G.1.2.2 Master/Slave Configuration The Master/Slave configuration, also referred as looped timing configuration, is the most common configuration with respect to the support of private networking scenarios. An example is represented in Figure 50 on page 131. Figure 50 Master/Slave Configuration As it can be determined from Figure 50, there is a single master clock source. The remote equipment (Slave) will synchronize to the master-provided transmitted signal. The accuracy of the master clock source is expected to be in the range of 1.544Mbps 32 ppm for DS1 configurations [2], and 2.048Mbps 50 ppm for E1 configurations [32]. G.2 Connections to Public ISDN The access DS1/E1s may be either transparent or non-transparent. The ATM switch in the public network will provide timing. The overall effect is as if the links were non-transparent. Figure 46 on page 128 illustrates this case. G.3 IMA Group in ITC Mode Detailed within this section are clocking options applicable to the configuration where the IMA group is running in the Independent Transmit Clock (ITC) mode. This typically results in the scenario where some of the source clock signals are not traceable to a PRS. G.3.1 Two or More Timing Domains - Un-synchronized The clocking configuration, as detailed within Figure 51 on page 132, is similar to the configuration contained within Section G.1.1.2, where the multiple IMA low speed links are supported over a number of distinct and separate carriers in a non-transparent fashion. The main difference in this configuration is that each link within the IMA link group is synchronized via "looped" timing to each of the respective carriers' reference clocks, whereas in the previous configuration (Section G.1.1.2) one of the carriers was selected as the reference. This configuration will result in virtually error-free performance as described in Section G.1.1.2. Figure 51 Two or More Timing Domains - Un-synchronized G.3.2 Non-Transparent/Transparent Mixed Configuration The non-transparent/transparent mixed configuration addresses the scenario where the links within the IMA link group are supported over a combination of transparent and non-transparent facilities. This may be the result of the following conditions where the majority of the links are supported as private leased line connections and additional links are managed/deployed via an on-demand basis by utilizing dialup and/or ISDN facilities. The additional links may be established either as a result of a demand for additional bandwidth or alternatively to address a restoration/survivability scenario. Figure 52 on page 133 shows an example of mixed of transparent/non-transparent configurations. It displays the following configuration mix: · the private leased line links will be supported as transparent links, in this case a master/slave clocking configuration has been selected. · the dialup and/or ISDN lines will be supported as non-transparent links, in this case a master/slave. The non-transparent/transparent mixed configuration, therefore, creates the situation where the links within the IMA link group are supported in a non-synchronous fashion. The private leased line links will be synchronized to a locally derived timing source, which maybe asynchronous to the carrier clock source; and the links supported over the dialup and/or ISDN facilities will be synchronized to the carrier's master clock source. If possible, the timing configuration represented in Figure 52 on page 133 should be avoided. In case this configuration is used, it is recommended to drive timing on the transparent links from one of the PRS traceable sources from a carrier(s) rather than from local sources. This changes the configuration to that covered in section Section G.1.1.1 on page 128 or Section G.1.1.2 on page 128 (depending on the number of independent Primary Reference Sources in the configuration). Figure 52 Non-Transparent/Transparent Mixed Configuration End of the document. Stuff Event M = 8 Y = 256 Note: Only the relevant NE state transitions and exchanges are shown. Tx: Usable Tx: Active Rx: Usable Rx: Active (Rx remains Active) Note: Only the relevant NE state transitions and exchanges are shown. Tx: Usable Rx: Active Tx: Active (Rx remains Active) Note: · Only the NE states newly entered and transmitted over the ICP cells are shown. · The transitions to Tx=Usable, Rx=Active and Tx=Active depend on the group wide synchronized addition/slow recovery procedure of links Note: Only the NE states newly entered and transmitted over the ICP cells are shown. Note: Only the NE states newly entered and transmitted over the ICP cells are shown. Note: Only the NE states newly entered and transmitted over the ICP cells are shown. Note: Only the NE states newly entered and transmitted over the ICP cells are shown. Note: Only the NE states newly entered and transmitted over the ICP cells are shown. Note: Only the NE states newly entered and transmitted over the ICP cells are shown. Tx: Active Rx: Unusable Tx: Usable Rx: Active Single Port OAM Behavior AIS or LOC F1, F2 F3 AIS or LCD AIS AIS F4/F5 RDI (VP/VC RDI) F3 RDI (e.g., P-RDI) F1/F2 RDI (e.g., L-RDI) LOS/LOF defect or AIS F4/F5 (VP/VC) VP/VC-AIS IMA OAM Behavior Down or LOC F1, F2 F3 AIS or LCD IMA Specific AIS F4/F5 RDI (VP/VC RDI) F3 RDI for cell specific part F1/F2 RDI (e.g., L-RDI) LOS/LOF defect or AIS F4/F5 (VP/VC) VP/VC-AIS F3 IMA RDI (link specific) AIS or LIF or LODS AIS Down Rx Tx Rx Tx