International Telegraph and Telephone Document AP IX-61-E Consultative Committee May 1988 (CCITT) Original: English IXth Plenary Assembly This document is the same as COM XV-R 35-E Melbourne, 1988 IXth PLENARY ASSEMBLY - DOCUMENT 61 STUDY GROUP XV - REPORT R 35 ============================ SOURCE: STUDY GROUP XV TITLE: FINAL REPORTS TO THE IXth CCITT PLENARY ASSEMBLY (PART IV - NEW RECOMMENDATIONS/SUPPLEMENTS OF THE G-SERIES) 컴컴컴컴컴 PART IV - NEW RECOMMENDATIONS/SUPPLEMENTS OF THE G-SERIES Add the following section 1.8 to Fascicle III.1 of the Red Book: 1.8 Protection and restoration of transmission systems 1. Recommendation G.180 CHARACTERISTICS OF N+M TYPE DIRECT TRANSMISSION RESTORATION SYSTEMS FOR USE ON DIGITAL SECTIONS, LINKS OR EQUIPMENT (Melbourne, 1988) 1. General Transmission restoration functions are often implemented in the modern telecommunication networks to improve the availability and quality of service, by minimizing the effects or potential effects of a transmission failure, and to make the maintenance operations easier. The terminology and general principles of transmission restoration are described in Recommendation M.495. The functional organization for automatic transmission restoration is described in Recommendation M.496. 2. Object of Recommendation This Recommendation specifies the characteristics of equipment for N+M type direct transmission restoration systems (protection link switching) for digital transmission links (see Recommendation G.701). The general arrangement of a system for N+M direct transmission restoration is shown in Figure 1/G.180. This Recommendation refers to the equipment labelled as RSE and RSCE. This Recommendation is intended also to cover the case where the signals at the interfaces T belong to different hierarchical levels. In this case, each access at one side can be a group of accesses as indicated in the example of Figure 2/G.180. The left part of this figure refers to the particular case where the restored path is not on a complete link but just through a multiplex equipment. Note - The equipment specified in this Recommendation can possibly be used also for N+M automatic or semi-automatic transmission rerouting (Protection Network Switching) but generally this type of restoration function is implemented by different equipment, often incorporating also other functions (such as, for example, Automatic Digital Distribution Frames). This type of equipment is under study. Three types of direct transmission restoration systems are considered by this Recommendation: The first one should permit routing of any one of N normal links on to any one of M restoration links. The second type should permit the interconnection of any of the N accesses to any one of the N+M links. The third one should permit routing of any one of N normal links to a single restoration link (in many cases this type can be considered just a special case of the first type). For all the types two options exist: a) to switch the two directions of transmission independently; and b) to switch the two directions of transmission simultaneously. This Recommendation does not cover the restoration systems fully embedded in transmission systems and the 1+1 systems where the switching occurs at the receive end only (see Recommendation G.181). The hierarchical levels at interfaces T are those specified in Recommendation G.702 (hierarchy levels 1 and up). 3. RSE specifications Two types of RSE are considered by this Recommendation: the "regenerative" and the "non-regenerative" ones. The first type, where the digital signal undergoes a complete process of retiming and reshaping, makes the RSE a digital equipment and it is sometimes considered to be advantageous, e.g. from the station cabling point of view. The second type, where the output signal is proportional to the input signal (except for minor distortion) is considered to be useful in some circumstances, e.g. from a reliability and cost point of view. 3.1 Interfaces 3.1.1 Transmission path interfaces (T) The relevant parameters and the recommended values are listed in the uppermost part of Table 1 for the non-regenerative RSE and in the uppermost part of Table 2 for the regenerative RSE. 3.1.2 Control interfaces The only control interface of the RSE is X. This interface is not at present specified by the CCITT. However in the future, it may be specified as a Q interface (see Recommendation G.771). If the interface X is not standardized, the separation between the RSE and RSCE (and consequently between section 3 and section 4 of this Recommendation) will be somewhat arbitrary. 3.2 Operational aspects 3.2.1 Transfer of the switched signals The relevant parameters and the recommended values are listed in the lower part of Table 1/G.180 for the non-regenerative RSE and in the lower part of Table 2/G.180 for the regenerative RSE. 3.2.2 Response For RSE providing M restoration paths to N normal paths (M=1 included) it is recommended that in response to a RSCE command the RSE should apply the incoming interface signal belonging to a given normal link to the input port of a given restoration link. The signal should not be removed from the input port of the concerned normal link, except that it may be replaced by a test signal. For RSE providing N+M link to N accesses it is recommended that in response to a RSCE command, the RSCE should apply the incoming interface signal belonging to a given access from 1 to N to a given link from 1 to N+M. It is recommended that the time required for the above response actions, that is the "Restoration transfer time", should be less than tx ms. The value for tx is under study. Note - The characteristics necessary to specify the option of detecting in the RSE a failed path and to pass this information to the RSCE are under study. 3.2.3 Other operational aspects A recognized failure of the RSCE or its disconnection from the RSE at interface X (when applicable) should either: a) Cause the RSE to route all the signals on the N normal links. After the failure of the RSCE is cleared or the RSCE is reconnected to the RSE, normal restoration operations will resume. b) Not alter the state of the RSE. The cross-connection pattern of the RSE should be available by interrogation from the RSCE to enable it to update, when the failure is cleared or it is reconnected to the RSE, its own record on the cross-connection pattern. For the restoration systems of the second type (as defined in section 2 of this Recommendation) alternative b) only holds. For the systems of the first and third types both alternatives are applicable. Note - The recommended behaviour of the RSE in case of own power failure is under study. 4. RSCE specifications Interfaces Y, Z and Q of the RSCE (see Figure 1/G.180) are under study, including the bit rate and the tolerable bit error ratio for the Z interface. 4.2 Operational aspects 4.2.1 Responses A switching to a restoration link should be initiated under a request coming from interfaces Y, Z, Q (and X where the faults are detected within the RSE) or on command from the local manual control. When decided in the RSCE the allocation of a restoration link can optionally take place according to defined priority rules based on: - defined priority for each normal link; - request type (low or high priority request). Otherwise the allocation should be specified by the information coming from interfaces Z, Q or local manual control. For the restoration systems providing M restoration links (M=1 included) on N normal links, when a successful restoration request clears, traffic should be returned to the pertinent normal link and the pertinent restoration link should be released. It should be possible from interfaces Z, Q and under local manual control to lock in a working link (e.g. during system maintenance). The time required for the above recommended restoration action is the sum of the "waiting time" and the "restoration procedure time". The two components should remain within the following limits: - waiting time (under study); - restoration procedure time (under study). Note - Values to be recommended may be different for the three types of systems considered under  2 and could depend on the interface over which the information is transferred. No precise proposed value exists at the moment. For a N+1 system, one proposal indicates that the sum of the "restoration procedure time" and of the "restoration transfer time" should not exceed, in 90% of the occasions, 50 ms plus the time required for the communications. 4.2.2 Alarm and status criteria Under study (see Appendix 1 to this Recommendation). 4.2.3 Monitoring and self-test procedures Under study (see Appendix 2 to this Recommendation). Notes to Figure 1/G.180 a) The failing of a section or link can possibly be dectected in the RSE and the information transferred to the RSCE. In this case interface Y may not exist. b) The interworking with the TMN via interface Q is at present beyond the scope of the Recommendation. c) The N+M digital links or sections can be in the same cable or follow different routes. d) Spare link accesses may be used to convey low priority traffic. e) The interface between the RSCE and local manual control is not standardized and it is not covered by this Recommendation. TABLE 1/G.180 Provisionally recommended values for the interface and transfer characteristics of non-regenerative RSE 旼컴컴쩡컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � � Nominal impedance � As stated in Rec. G.703 � � I 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � N � Return loss at the� � � T � input port (with � z dB above the values � � E � the output port � stated in Rec. G.703 � � R � terminated on the � � � F � nominal impedance)� Note 1 � � A � � � � C 쳐컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � E � Accepted levels � The output levels consi- � � � � dered in Rec. G.703 � � � � � 쳐컴컴탠컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � � Transfer function � Y1 dB from any channel � � E � � >Y2 dB multi-channel � � R � Crosstalk attenua-� interference evaluated � � � tion � on a voltage-sum basis. � � � � These values apply up to � � � � a frequency value equal to � � � � the nominal bit-rate � � � � Note 5 � � � � � 읕컴컴좔컴컴컴컴컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� Note 1 - The value for z is under study. A possible value is z=6 dB. Note 2 - As a corresponding requirement is under study to permit the connection of test equipment in protected monitoring points, the relevant specification could alternatively be adopted. Note 3 - The values of x and y are under study. A proposal states: x=10% and y=0.5 dB. Note 4 - A delay limit will be also considered in future if benefit is expected from that. Note 5 - The Y1 and Y2 limits are under study. Y1 = 40 and Y2 = 30 have been proposed as compromise values among different proposals. Different limits could possibly be adopted for RSE having a different configuration (e.g. N+1 or N+M). TABLE 2/G.180 Interface and transfer characteristics recommended for regenerative restoration switching equipment 旼컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴� � General � Nominal bit rate and � As stated in Rec. G.703 � � � tolerance � � 쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴� � � Connecting pairs � � � I � � � � N � Test impedance and return � � � T � loss at the input ports � � � E � � As stated in Rec. G.703 � � R � Pulse shape and levels � � � F � � � � A � Tolerable input jitter � � � C 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴� � E � Intrinsic output jitter � As stated in � � � � Supplement A to Table 2 � 쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴� � � Jitter transfer � As stated in � � T � � Supplement B to Table 2 � � R 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴� � A � Error performance � 99.99% error-free � � N � � seconds Note 3 � � S 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴� � F � � The paths across each � � E � Others � switch shall maintain � � R � Note 1 � bit sequence indepen- � � � � dence and integrity � � � � Note 2 � 읕컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴� Note 1 - A delay limit will also be considered in future if benefit is expected from that. Note 2 - Further study is necessary whether or not the digital signal should be replaced by a signal other than AIS in a restoration switching condition. Note 3 - Evaluated under maximum loading condition and excluding any external source of interference. SUPPLEMENT A (to Table 2/G.180) Maximum permissible intrinsic jitter at output ports of regenerative restoration switching equipment (Values for bit rates of the 1544 kbit/s digital hierarchy are under study) For asynchronous space matrix RSE 旼컴컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴커 � � � Measurement filter bandwidth � � Parameter � Maximum 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 � value � value � Bandpass filter having a � � � � lower cutoff frequency f1 � � Digital � Unit interval � and an upper cutoff � � rate � peak-peak � frequency f4 � � (kbit/s) � 쳐컴컴컴컴컴컫컴컴컴컴컴컴컴컴캑 � � � f1 � f4 � 쳐컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴탠컴컴컴컴컴컵컴컴컴컴컴컴컴컴캑 � 2048 � 0.1 � 20 Hz � 100 kHz � � 8448 � 0.1 � 20 Hz � 400 kHz � � 34368 � 0.075 � 100 Hz � 800 kHz � � 139264 � 0.05 � 200 Hz � 3 500 kHz � 읕컴컴컴컴컴컴컴컴컴컴컨컴컴컴컴컴컴컴컴좔컴컴컴컴컴컨컴컴컴컴컴컴컴컴켸 For synchronous RSE using central timing 旼컴컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴커 � � � Measurement filter bandwidth � � Parameter � Maximum 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 � value � value � Bandpass filter having a � � � � lower cutoff frequency f1 � � Digital � Unit interval � or f3 and an upper cutoff � � rate � peak-peak � frequency f4 � � (kbit/s) 쳐컴컴컴컫컴컴컴컵컴컴컴컴컫컴컴컴컴컫컴컴컴컴컴� � � B1 � B2 � � � � � � (f1�f4 �(f3�f4 � f1 � f3 � f4 � � � filter)쿯ilter)� � � � 쳐컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴탠컴컴컴탠컴컴컴컴탠컴컴컴컴탠컴컴컴컴캑 � 2048 � 0.25 � 0.05 � 20 Hz � 18 kHz � 100 kHz � � � � � � (700 Hz)� � � 8448 � 0.25 � 0.05 � 20 Hz � 3 kHz � 400 kHz � � � � � � (80 kHz)� � � 34368 � 0.35 � 0.05 � 100 Hz � 10 kHz � 800 kHz � � 139264 � under � 0.05 � 200 Hz � 10 kHz �3 500 kHz � � � study � � � � � 읕컴컴컴컴컴컴컴컴컴컴컨컴컴컴컴좔컴컴컴좔컴컴컴컴좔컴컴컴컴좔컴컴컴컴켸 Note 1 - UI = Unit interval for 2048 kbit/s 1 UI = 488 ns for 8448 kbit/s 1 UI = 118 ns for 34368 kbit/s 1 UI = 29.1 ns for 139264 kbit/s 1 UI = 7.18 ns Note 2 - These figures shall be met for any valid signal in the absence of input jitter. The measurement shall be implemented using equipment designed in accordance with CCITT Recommendation 0.171. Note 3 - Recommendation G.823  2 indicates the measurement method. Note 4 - The frequency values in parentheses only apply to certain national interfaces. SUPPLEMENT B (to Table 2/G.180) Jitter transfer characteristics recommended for regenerative restoration switching equipment (Values for the bit rates of the 1544 kbit/s digital hierarchy are under study.) Note 1 - The frequency f0 should be as low as possible (e.g. 10 Hz) taking into account the limitations of measuring equipment. Note 2 - The measuring method should be selective with a bandwidth sufficiently small referred to the relevant measuring frequency, but not wider than 40 Hz. Note 3 - In the f6 to f7 frequency range the jitter gain should be less than y dB, with the exception of spurious responses, which should be suppressed below -6 dB. Note 4 - The frequency values shown in parentheses only apply to certain national interfaces. Note 5 - A value of 0.2 dB has been suggested as technically possible for this type of equipment. This may be useful where large numbers of RSE are employed in the network. Note 1 - The frequency fo should be as low as possible (e.g. 10 Hz) taking into account the limitations of measuring equipment. Note 2 - The measuring method should be selective with a bandwidth sufficiently small referred to the relevant measuring frequency, but not wider than 40 Hz. Note 3 - The need to tolerate spurious responses greater than y dB in the frequency range f6 to f7 is for further study. Appendix 2 (to Recommendation G.180) Proposals for monitoring and self-test procedures (both refer to a N+1 system) 旼컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � � Standby Channel Monitoring � � � � � � The system should include means of monitoring the � � � standby channel continuously for proper operation. � � � � � � Self-check � � � � � � The system should include self-check facilities as � � � follows: � � � � � � a) Communication channel. � � � � � � b) Background-checking of the memory, coaxial � � � relay drive buffer and other hardware. � � � � � � c) Correct programme execution � � � � � � � � � � � � � 쳐컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � � � � � � � � Standby Channel Monitoring � � � � � � The standby channel shall be monitored � � � continuously for proper operation. � � � � � � Switch Exerciser � � � � � � The protective switching system shall provide a � � � switch exerciser meeting the following � � � requirements: � � � � � � The exerciser shall test the complete switch-over � � � procedure up to but excluding the last transfer � � � switch in the direction of transmission. � � � � � � The switching system shall drop the exerciser � � � routine and serve switch requests from failed or � � � deteriorated channels. � � � � � � A facility for including the last switch in the � � � exercise routine may be provided. This feature � � � shall have the capability of being disabled. � 읕컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�