џWPCL ћџ2BJ|xа АH аа АА X агга ХА6p&А6p&Х аеЮ† а Hр аааУ Уб cмˆ4 PŽТ б Fascicle VI.7 Р-Р Rec. Q.701 Ф ФPAGE1У Уб cмˆ4 PŽТ б ЮееЃ† а HH аааб cмˆ4 PŽТ бPAGE20У Уб cмˆ4 PŽТ б Fascicle VI.7 Р-Р Rec. Q.701 Ѓеа HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаа X  аб cмˆ4 PŽТ бAll drawings appearing in this Fascicle have been done in Autocad. ‚У УRecommendation Q.701 аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр8DСб cмˆ4 PŽТ бFUNCTIONAL DESCRIPTION OF THE Ср87Сб cмˆ4 PŽТ бMESSAGE TRANSFER PART (MTP) OF SIGNALLING SYSTEM No. 7 аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б1ТX ТIntroductionФ ФЦЦ 1.1Тh  ТУУGeneralЦЦ а H аФФС СThe Message Transfer Part (MTP) provides the functions that enable User Part significant information passed to the MTP to be transferred across the Signalling System No. 7 network to the required destination. In addition, functions are included in the MTP to enable network and system failures that would affect the transfer of signalling information to be overcome. This constitutes a sequenced connectionless service for the MTP user. а H аС СThe Message Transfer Part together with one of its Р"РusersР"Р, the Signalling Connection Control Part (SCCP), described in Recommendations Q.711Р-Р716, forms the Network Service Part (NSP). а H аС СThe Network Service Part meets the requirement for Layer 3 services as defined in the OSI Р-Р Reference Model CCITT Recommendation X.200. The relationship of the MTP with this model and to other parts of S.S. No. 7 is described in Recommendation Q.700. 1.2Тh  ТУУObjectivesЦЦ а H аФФС СThe overall objectives of the Message Transfer Part are to provide the means for: а Hx аТа ТТ№ ТС€ Сa)СpСthe reliable transport and delivery of Р"РUser PartР"Р signalling information across the S.S. No. 7 network.ЦЦ а H аТа ТТ№ ТС€ Сb)СpСthe ability to react to system and network failures that will affect a), and take the necessary action to ensure that a) is achieved.ЦЦ а H аС СThe Р"РUsersР"Р of MTP are the SCCP, Telephone User Part (TUP) [Recommendation Q.721Р-Р725 Data User Part (DUP) [Recommendation Q.741] and ISDN User Part (ISUP) [Recommendation Q.761Р-Р766]. The MTP Testing User Part is for further study. 1.3Тh  ТУУGeneral characteristicsЦЦ Та ТС€ HСФФ1.3.1С СУУMethod of descriptionЦЦ Та ТФФР-РТ№ Тfunctions provided by each level within the MTPЦЦ Та ТР-РТ№ Тservices provided by the MTPЦЦ Та ТР-РТ№ Тinteraction with the signalling networkЦЦ Та ТР-РТ№ Тinteraction with the MTP Р"РUserР"РЦЦ Та ТТ№ ТС€ СЉСpСthe message transfer capability of the MTPЦЦа HH а а H аС СThe functions of each level of the MTP are performed by means of the level protocol between two systems which provides a Р"Рlevel serviceР"Р to the upper levels, (i.e., Level 1 Signalling Data Link, Level 2 Signalling Link and Level 3 Signalling network) as described in Recommendations Q.702, 703 and 704 respectively. а H аС СThe service interface to the Level 4 Р"РUserР"Р of MTP is described by means of primitives and parameters. Та ТС€ HС1.3.2С СУУPrimitivesЦЦ а H аФФС СPrimitives consist of commands and their respective responses associated with the services requested of the SCCP and of the MTP, see Figure 1/Q.701. The general syntax of a primitive is shown below: б cмˆ4 PŽТ бвЦ„H8(и Ш xhЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚Ср YСааб cмˆ4 PŽТ бX аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјшP И џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр SСGeneric name аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH ˆ№XџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр SСSpecific name Ср UСParameter а hX ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ ˆ№hXџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бˆа HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТТ№ ТЦЦ а H аТа ТР-РТ№ Т"XР"Р designates the functional block providing the service (Р"РMTPР"Р for MTP).ЦЦ а H аТа ТР-РТ№ Т"Generic nameР"Р describes the action that should be performed by the addressed layer.ЦЦ а Hр аТа ТР-РТ№ Т"Specific nameР"Р indicates the direction of the primitive flow.ЦЦ Та ТР-РТ№ Т"ParametersР"Р are the elements of information which are to be transmitted between layers.ЦЦ а HH аС СFour Specific Names exist in general: Та ТР-РТ№ ТrequestЦЦ Та ТР-РТ№ ТindicationЦЦ Та ТР-РТ№ ТresponseУУб cмˆ4 PŽТ б1ж•I а HH а1)б cмˆ4 PŽТ бФФNot all generic names contain all four specific names (Figure 2/Q.701). •ж)ФФб cмˆ4 PŽТ бЦЦ Та ТР-РТ№ ТconfirmationУУб cмˆ4 PŽТ б1)б cмˆ4 PŽТ бФФЦЦ ‚Ср8DСб cмˆ4 PŽТ бFigure 1/Q.701 Љ T1109680Љ88 б cмˆ4 PŽТ бб cмˆ4 PŽТ б Ср8DСFigure 2/Q.701 Љ T1109690Љ88 б cмˆ4 PŽТ б а H аС СPrimitives and parameters of the Messsage Transfer Part service are listed and described in Section 8 of this Recommendation. Та ТС€ HС1.3.3С СУУPeerР-РtoР-Рpeer communicationЦЦ а H аФФС СExchange of information between two peers of the MTP is performed by means of a protocol. The protocol is a set of rules and formats by which the control information and MTP Р"РUserР"Р data is exchanged between the two peers. The protocol caters for Та ТР-РТ№ Тthe transfer of Р"РUserР"Р data in Message Signal Units (MSUs);ЦЦ Та ТР-РТ№ Тlevel 2 control by use of Link Status Signal Units (LSSUs);ЦЦ а H аТа ТР-РТ№ Тtesting and maintenance of signalling links by means of the signalling link test message carried in an MSU.ЦЦ а H аТа ТС€ HС1.3.4С СУУContents of Recommendations Q.701 to Q.707 Series relating to the MTPЦЦ а H аФФС СRecommendation Q.701 contains a functional description and overview of the Message Transfer Part of CCITT S.S. No. 7. а H аТа ТТ№ ТС€ СRecommendation Q.702 details the requirements of a signalling data link to support CCITT S.S. No. 7.ЦЦ Та ТТ№ ТС€ СRecommendation Q.703 describes the signalling link functions.ЦЦ а H аТа ТТ№ ТС€ СRecommendation Q.704 describes signalling network functions and messages.ЦЦ а H аТа ТТ№ ТС€ СRecommendation Q.706 defines and specifies values for MTP performance parameters.ЦЦ а H аТа ТТ№ ТС€ СRecommendation Q.707 describes the testing and maintenance functions applicable to the MTP.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС‚У У2С  Сб cмˆ4 PŽТ бSignalling system structureЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ Ф2.1Тh  ТУУBasic functional divisionЦЦ а Hx ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФС  СThe fundamental principle of the signalling system structure is the division of functions into a common Message Transfer Partй Message Transfer Partйб cмˆ4 PŽТ б (MTP) on one hand and separate User Partsб cмˆ4 PŽТ бй User Partsйб cмˆ4 PŽТ б for different users on the other. This is illustrated in Figure 3/Q.701.аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚б cмˆ4 PŽТ б Ср KСFigure 3/Q.701 Љ CCITT34930 б cмˆ4 PŽТ б С СThe overall function of the Message Transfer Part is to serve as a transport system providing reliable transfer of signalling messages between the locations of communicating user functions. С СThe termУУ userФФ in this context refers to any functional entity that utilizes the transport capability provided by the Message Transfer Part. A User Part comprises those functions of, or related to, a particular type of user that are part of the common channel signalling system, typically because those functions need to be specified in a signalling context. а H аС СThe basic commonality in signalling for different services resulting from this concept is the use of a common transport system, i.e., the Message Transfer Part. Also, a degree of commonality exists between certain User Parts, e.g., the Telephone User Part (TUP) and the Data User Part (DUP). 2.2Тh  ТУУFunctional levelsФФЦЦ Та ТС€ HС2.2.1С СУУGeneralЦЦ а H аФФС СAs a further separation, the necessary elements of the signalling system are specified in accordance with a level concept in which: а H аТа ТР-РТ№ Тthe functions of the Message Transfer Part are separated into three functional levels, andЦЦ а H аТа ТР-РТ№ Тthe User Parts constitute parallel elements at the fourth functional level.ЦЦ а H аС СThe level structure is illustrated in Figure 4/Q.701. The system structure shown in Figure 4/Q.701 is not a specification of an implementation of the system. The functional boundaries B, C and D may or may not exist as interfaces in an implementation. The interactions by means of controls and indications may be direct or via other functions. However, the structure shown in Figure 4/Q.701 may be regarded as a possible model of an implementation. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС2.2.2С јСб cмˆ4 PŽТ бУУSignalling data link functions (level 1)ЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СLevel 1 defines the physical, electrical and functional characteristics of a signalling data link and the means to access it. The level 1 element provides a bearer for a signalling link. а H аС СIn a digital environment, 64Р-Рkbit/s digital paths will normally be used for the signalling data link. The signalling data link may be accessed via a switching function, providing a potential for automatic reconfiguration of signalling links. Other types of data links, such as analogue links with modems, can also be used. С СThe detailed requirements for signalling data links are specified in Recommendation Q.702.‚б cмˆ4 PŽТ б Ср LСFigure 4/Q.701 Љ CCITT34941 б cмˆ4 PŽТ б аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС2.2.3С јСб cмˆ4 PŽТ бУУSignalling link functions (level 2)ЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СLevel 2 defines the functions and procedures for and relating to the transfer of signalling messages over one individual signalling data link. The level 2 functions together with a level 1 signalling data link as a bearer provides a signalling link for reliable transfer of signalling messages between two points. а H аС СA signalling message delivered by the higher levels is transferred over the signalling link in variable lengthУУ signal unitsФФ. For proper operation of the signalling link, the signal unit comprises transfer control information in addition to the information content of the signalling message. С СThe signalling link functions include: Та ТР-РТ№ Тdelimitation of signal unit by means of flags;ЦЦ Та ТР-РТ№ Тflag imitation prevention by bit stuffing;ЦЦ а H аТа ТР-РТ№ Тerror detection by means of check bits included in each signal unit;ЦЦ а H аТа ТР-РТ№ Тerror correction by retransmission and signal unit sequence control by means of explicit sequence numbers in each signal unit and explicit continuous acknowledgements;ЦЦ а H аТа ТР-РТ№ Тsignalling link failure detection by means of signal unit error rate monitoring and signalling link recovery by means of special procedures.ЦЦ а H аС СThe detailed requirements for signalling link functions are given in Recommendation Q.703. Та Т2.2.4Си Сб cмˆ4 PŽТ бУУSignalling network functions (level 3)ЦЦ а H аб cмˆ4 PŽТ бФФС СLevel 3 in principle defines those transport functions and procedures that are common to and independent of the operation of individual signalling links. As illustrated in Figure 4/Q.701 these functions fall into two major categories: а H аТа ТТ№ ТС€ Сa)СpСsignalling message handling functions Р-Р these are functions that, at the actual transfer of a message, direct the message to the proper signalling link or User Part;ЦЦ а H аТа ТТ№ ТС€ Сb)СpСsignalling network management functions Р-Р these are functions that, on the basis of predetermined data and information about the status of the signalling network, control the current message routing and configuration of signalling network facilities. In the event of changes in the status they also control reconfigurations and other actions to preserve or restore the normal message transfer capability.ЦЦ а H аС СThe different level 3 functions interact with each other and with the functions of other levels by means of indications and controls as illustrated in Figure 4/Q.701. This figure also shows that the signalling network management as well as the testing and maintenance actions may include exchange of signalling messages with corresponding functions located at other signalling points. Although not User Parts these parts of level 3 can be seen as serving as Р"РUser Parts of the Message Transfer PartР"Р. As a convention in these specifications, for each description, general references to User Parts as sources or sinks of a signalling message implicitly include these parts of level 3 unless the opposite is evident from the context or explicitly stated. С СA description of the level 3 functions in the context of a signalling network is given in РSР 3 below. The detailed requirements for signalling network functions are given in Recommendation Q.704. Some means for testing and maintenance of the signalling network are provided and the detailed requirements are given in Recommendation Q.707. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС2.2.5С јСб cмˆ4 PŽТ бУУUser Part functions (level 4)ЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СLevel 4 consists of the different User Parts. Each User Part defines the functions and procedures of the signalling system that are particular to a certain type of user of the system. а H аС СThe extent of the User Part functions may differ significantly between different categories of users of the signalling system, such as: а H аТа ТР-РТ№ Тusers for which most user communication functions are defined within the signalling system. Examples are telephone and data call control functions with their corresponding Telephone and Data User Parts;ЦЦ а H аТа ТР-РТ№ Тusers for which most user communication functions are defined outside the signalling system. An example is the use of the signalling system for transfer of information for some management or maintenance purpose. For such an Р"Рexternal userР"Р the User Part may be seen as a Р"РmailboxР"Р type of interface between the external user system and the message transfer function in which, for example, the user information transferred is assembled and disassembled to/from the applicable signalling message formats.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС2.3С   Сб cмˆ4 PŽТ бУУSignalling messageЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СA signalling message is an assembly of information, defined at level 3 or 4, pertaining to a call, management transaction, etc., that is transferred as an entity by the message transfer function. а H аС СEach message containsУУ service informationФФ including aУУ service indicatorФФ identifying the source User Part and possibly additional information such as an indication whether the message relates to international or national application of the User Part. С СTheУУ signalling informationФФ of the message includes the actual user information, such as one or more telephone or data call control signals, management and maintenance information, etc., and information identifying the type and format of the message. It also includes aУУ labelФФ that provides information enabling the message: а H аТа ТР-РТ№ Тto be routed by the level 3 functions and through a signalling network to its destination; andЦЦ а H аТа ТР-РТ№ Тto be directed at the receiving User Part to the particular circuit, call, management or other transaction to which the message is related.ЦЦ а H аС СOn the signalling link, each signalling message is packed into Message Signal Units (MSUs) which also includes transfer control information related to the level 2 functions of the link. 2.4Тh  ТУУFunctional interfaceЦЦ а H аФФС СThe following functional interface between the Message Transfer Part and the User Parts can be seen as a model illustrating the division of а H аfunctions between these parts. The interface (see Figure 5/Q.701) is purely functional and need not appear as such in an implementation of the system. ‚Ср KСб cмˆ4 PŽТ бFigure 5/Q.701 Љ CCITT 34951 б cмˆ4 PŽТ б а H аС СThe main interaction between the Message Transfer Part and the User Parts is the transfer of signalling messages across the interface, each message consisting of service information and signalling information as described above. Message delimitation information is also transferred across the interface with the message. а H аС СIn addition to the transfer of messages and associated information, the interaction may also include flow control information, e.g., an indication from the Message Transfer Part that it is unable to serve a particular destination. а H аС СA description of the characteristics of the Message Transfer Part as seen from the functional interface and the requirements to be met by potential users of the message transfer function is given in РSР 4. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС‚У У3С  Сб cмˆ4 PŽТ бMessage transfer part and the signalling networkЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ Ф3.1Тh  ТУУGeneralЦЦ а H аФФС СSince the Message Transfer Part forms the interface at a node with the rest of the signalling network, the signalling network will have а H аsignificant impact on the MTB. The MTP must however be independent of the signalling network in that it has to be capable of performing its set functions and attaining its objectives no matter what network structure or status prevails. а H аС СThe MTP has therefore to contain the necessary functions to ensure any impact that the network has does not impair MTP performance. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.1.1С јСб cмˆ4 PŽТ бУУSignalling network componentsЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СA full description of signalling network components is contained in Recommendation Q.700, the components that must be considered by the MTP are: Та ТР-РТ№ Тsignalling points (including signalling transfer points);ЦЦ Та ТР-РТ№ Тsignalling relations between two signalling points;ЦЦ Та ТР-РТ№ Тsignalling links;ЦЦ Та ТР-РТ№ Тsignalling link sets (including link groups);ЦЦ Та ТР-РТ№ Тsignalling routes;ЦЦ Та ТР-РТ№ Тsignalling routeР-Рsets.ЦЦ а HH аТа ТС€ HС3.1.2С СУУSignalling modesЦЦ а H№ аФФС СSignalling modes are described in Recommendations Q.700 and Q.705 (signalling network structures). The modes applicable to CCITT S.S. No. 7 MTP are: Та ТР-РТ№ Тassociated mode;ЦЦ Та ТР-РТ№ ТquasiР-Рassociated mode.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.1.3С јСб cмˆ4 PŽТ бУУSignalling point modesЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СA signalling point can be an originating point, a destination point or a signalling transfer point in a signalling relation. All three modes must be considered in the MTP. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.1.4С јСб cмˆ4 PŽТ бУУMessage labellingЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СEach message contains a label. In the standard label the portion that is used for routing is called theУУ routing labelФФ. This routing label includes: а H аТа ТТ№ ТС€ Сa)СpСexplicit indications of destination and originating points of the message, i.e., identification of the signalling relation concerned;д Д-дЦЦŒа H аТа ТТ№ ТС€ Сb)СpСa code used for load sharing which may be the least significant part of a label component that identifies a user transaction at level 4.ЦЦ а Hx аС СThe standard routing label assumes that each signalling point in a signalling network is allocated a code according to a code plan, established for the purpose of labelling, that is unambiguous within its domain. Messages labelled according to international and national code plans are discriminated by means of an indication in the service information octet included in each message. а H аС СThe standard routing label is suitable for national applications also. However, the signalling system includes the possibility for using different routing labels nationally. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.2С   Сб cмˆ4 PŽТ бУУSignalling message handling functionsЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СFigure 6/Q.701 illustrates the signalling message handling functions.‚б cмˆ4 PŽТ б Ср KСFigure 6/Q.701 Љ CCITT 34970 б cмˆ4 PŽТ б аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.2.1С јСб cмˆ4 PŽТ бУУMessage routingЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СУУMessage routingФФ is the process of selecting, for each signalling message to be sent, the signalling link to be used. In general, message routing is based on analysis of the routing label of the message in combination with predetermined routing data at the signalling point concerned. а H аС СMessage routing is destinationР-Рcode dependent with typically an additional loadР-Рsharing element allowing different portions of the signalling traffic to a particular destination to be distributed over two or more signalling links. This traffic distribution may be limited to different links within a link set or applied to links in different link sets. а H аС СEach succession of signalling links that may be used to convey a message from the originating point to the destination point constitutes aУУ message routeФФ. A signalling route is the corresponding concept for a possible path referring to a succession of link sets and signalling transfer points, between a given signalling point and the destination point. а H аС СIn Signalling System No. 7, message routing is made in a manner by which the message route taken by a message with a particular routing label is predetermined and, at a given point in time, fixed. Typically, however, in the event of failures in the signalling network, the routing of messages, previously using the failed message route, is modified in a predetermined manner under control of the signalling traffic management function at level 3. а H аС СAlthough there are in general advantages in using a uniform routing of messages belonging to different User Parts, the service indicator included in each message provides the potential for using different routing plans for different User Parts. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.2.2С јСб cмˆ4 PŽТ бУУMessage distributionЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СУУMessage distributionФФ is the process which, upon receipt of a message at its destination point, determines to which User Part or level 3 function the message is to be delivered. This choice is made on analysis of the service indicator. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.2.3С јСб cмˆ4 PŽТ бУУMessage discriminationЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СУУMessage discriminationФФ is the process which, upon receipt of a message at a signalling point, determines whether or not the point is the destination point of that message. This decision is based on analysis of the destination code in the routing label in the message. If the signalling point is the destination point the message is delivered to the message distribution function. If it is not the destination point, and the signalling point has the transfer capability, the message is delivered to the routing function for further transfer on a signalling link. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.3С   Сб cмˆ4 PŽТ бУУSignalling network management functionsЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СFigure 6/Q.701 illustrates the signalling network management functions. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.3.1С јСб cмˆ4 PŽТ бУУSignalling traffic managementЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СThe tasks of theУУ signalling traffic managementФФ function are: а H аТа ТТ№ ТС€ Сa)СpСto control message routing; this includes modification of message routing to preserve, when required, accessibility of all destination points concerned or to restore normal routing;ЦЦ а H аТа ТТ№ ТС€ Сb)СpСin conjunction with modifications of message routing, to control the resulting transfer of signalling traffic in a manner that avoids irregularities in message flow;ЦЦ Та ТТ№ ТС€ Сc)СpСflow control.ЦЦ а Hh аС СControl of message routing is based on analysis of predetermined information about all allowed potential routing possibilities in combination with information, supplied by theУУ signalling link managementФФ andУУ signalling route managementФФ functions, about the status of the signalling network (i.e., current availability of signalling links and routes). а H аС СChanges in the status of the signalling network typically result in modification of current message routing and thus in transfer of certain portions of the signalling traffic from one signalling link to another. The transfer of signalling traffic is performed in accordance with specific procedures. These procedures Р-РУУ changeover, changeback, forced rerouting and controlled reroutingФФ Р-Р are designed to avoid, as far as the circumstances permit, such irregularities in message transfer as loss, misР-Рsequencing or multiple delivery of messages. а H аС СThe changeover and changeback procedures involve communication with other signalling point(s). For example, in the case of changeover from a failing signalling link, the two ends of the failing link exchange information (via an alternative path) that normally enables retrieval of messages that otherwise would have been lost on the failing link. However, as further explained later, these procedures cannot guarantee regular message transfer in all circumstances. а H аС СA signalling network has to have a signalling traffic capacity that is higher than the normal traffic offered. However, in overload conditions (e.g., due to network failures or extremely high traffic peaks) the signalling traffic management function takes flow control actions to minimize the problem. An example is the provision of an indication to the local user functions concerned that the Message Transfer Part is unable to transport messages to a particular destination in the case of total breakdown of all signalling routes to that destination point. If such a situation occurs at a signalling transfer point, a corresponding indication is given to the signalling route management function for further dissemination to other signalling points in the signalling network. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.3.2С јСб cмˆ4 PŽТ бУУSignalling link managementЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СThe task of the signalling link management function is to control the locally connected link sets. In the event of changes in the availability of а H аa local link set it initiates and controls actions aimed at restoring the normal availability of that link set. а H аС СThe signalling link management function also supplies information about the availability of local links and link sets to the signalling traffic management function. а H аС СThe signalling link management function interacts with the signalling link function at level 2 by receipt of indications of the status of signalling links. It also initiates actions at level 2 such as, for example, initial alignment of an outР-РofР-Рservice link. а H аС СThe signalling system can be applied with different degrees of flexibility in the method of provision of signalling links. A signalling link may for example consist of a permanent combination of a signalling terminal device and a signalling data link. It is also possible to employ an arrangement in which any switched connection to the remote end may be used in combination with any local signalling terminal device. It is the task of the signalling link management function in such arrangements to initiate and control reconfigurations of terminal devices and signalling data links to the extent such reconfigurations are automatic. In particular, this involves interaction, not necessarily direct, with a switching function at level 1. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.3.3С јСб cмˆ4 PŽТ бУУSignalling route managementЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СSignalling route management is a function that relates to the quasiР-Рassociated mode of signalling only. Its task is to transfer information about changes in the availability of signalling routes in the signalling network to enable remote signalling points to take appropriate signalling traffic management actions. Thus a signalling transfer point may, for example, send messages indicating inaccessibility of a particular signalling point via that signalling transfer point, thus enabling other signalling points to stop routing messages to an incomplete route. 3.4Тh  ТУУTesting and maintenance functionsЦЦ ФФС СFigure 6/Q.701 illustrates that the signalling system includes some standard testing and maintenance functions that use level 3 messages. Furthermore, any implementation of the system typically includes various implementationР-Рdependent means for testing and maintenance of equipment concerned with the other levels. 3.5Тh  ТУУUse of the signalling networkЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HСФФ3.5.1С јСб cмˆ4 PŽТ бУУSignalling network structureЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СThe signalling system may be used with different types of signalling network structures. The choice between different types of signalling network structures may be influenced by factors such as the structure of the telecommunication network to be served by the signalling system and administrative aspects. а H аС СIn the case when the provision of the signalling system is planned purely on a perР-Рsignalling relation basis, the likely result is a signalling network largely based on associated signalling, typically supplemented by a limited degree of quasiР-Рassociated signalling for low volume signalling relations. The structure of such a signalling network is mainly determined by the patterns of the signalling relations. International signalling is an example of an application for which this approach is suitable. С СAnother approach is to consider the signalling network as a commonд Д- д resource that should be planned according to the total needs for common а H аchannel signalling. The high capacity of digital signalling links in combination with the need for redundancy for reliability, typically leads to a signalling а H аnetwork based on a high degree of quasiР-Рassociated signalling with some provision for associated signalling for highР-Рvolume signalling relations. The latter approach to signalling network planning is more likely to allow exploitation of the potential of common channel signalling to support network features that require communication for purposes other than the switching of connections. а H аС СFurther considerations about the use of a signalling network are given in Recommendation Q.705. Та ТС€ HС3.5.2С СУУProvision of signalling facilitiesЦЦ ФФС СIn general, the most important factor in the dimensioning of the signalling network is the need for reliability by means of redundancy. Depending on the signalling network structure and the potential for reconfiguration of signalling equipment, the required redundancy may be provided by different combinations of: а Hx аТа ТР-РТ№ Тredundancy in signalling data links (e.g., nominated reserves or switched connections);ЦЦ а H аТа ТР-РТ№ Тredundancy in signalling terminal devices (e.g., a common pool of terminals for the whole signalling point);ЦЦ а H аТа ТР-РТ№ Тredundancy of signalling links within a link set (typically operating with load sharing);ЦЦ а Hh аТа ТР-РТ№ Тredundancy in signalling routes for each destination (possibly operating with load sharing).ЦЦ а H аС СThe loading capacity of a digital signalling link is high in relation to the signalling traffic generated for call control signalling. Therefore, in many typical applications the links will be lightly loaded and signalling traffic volume will be a secondary factor in the dimensioning of the signalling network. However, in high signalling traffic applications or when analogue links with lower speeds are used, it may be necessary to dimension the traffic capacity by provision of additional signalling links. The message routing principles adopted for the signalling system allow partitioning of the total signalling traffic into different portions based on load sharing, destination point code and service information. Such partitioning provides a useful means of controlling the load and dimensioning of the capacity of different sections of a signalling network as it allows distribution of different portions of the signalling traffic. It can also be used to dedicate certain parts of a signalling network to signalling traffic related to a particular user. Та ТС€ HС3.5.3С СУУApplication of signalling network functionsЦЦ а H аФФС СThe signalling network functions provided by the signalling system are designed to cater for a range of signalling network configurations. It is not necessary that all of those functions be present at all signalling points. The necessary functional content at level 3 at a particular signalling point depends for example on what signalling mode(s) are used, whether or not it is a signalling transfer point, what type of signalling equipment redundancy is employed, etc. It is thus feasible to implement level 3 functions with modularity for different capabilities corresponding to different signalling network configurations. As a special case, it is even possible to apply the signalling system without using the level 3 element at all, e.g., in a small exchange or private automatic branch exchange which can only be reached via one primary pulse code modulation system. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС‚У У4С  Сб cмˆ4 PŽТ бMessage transfer capabilityЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ Ф4.1Тh  ТУУGeneralЦЦ ФФС СThe Message Transfer Part recommendations specify methods by which different forms of signalling networks can be established. The requirements а H аfor the Message Transfer Part have been determined primarily by the requirements of call control signalling for the telephone and circuit switched data transmission services. However, the Message Transfer Part is also intended to have the ability to serve as a transport system for other types of information transfer. The following summarises the typical characteristics of the transport service that may be offered by the Message Transfer Part to a potential user of this ability. а H аС СAll information to be transferred by the Message Transfer Part must be assembled into messages. The linking of the source and sink of a message is inherent in the label in combination with the signalling routes existing between the two locations. From a transportation point of view each message is selfР-Рcontained and handled а H аindividually. The nature of the transport service offered by the Message Transfer Part is therefore similar to that offered by a packet switched network. In addition, all messages containing the same label constitute a set of а H аmessages that is handled in a uniform manner by the Message Transfer Part, thus ensuring, in normal circumstances, regular delivery in the correct sequence. 4.2Тh  ТУУUser location in system structureЦЦ а H аФФС СA potential user of the transport service is typically included in the system structure by provision of a separate User Part. This requires allocation of a service indicator code, the specification of which is part of both the Message Transport Part and User Part concerned. С СAs an alternative, a potential user may be catered for, together with other similar users, by an already existing or new User Part. In such a case the discrimination between messages belonging to this potential user and the other similar users is an internal matter within the User Part concerned. It then follows that all messages belonging to such a User Part are necessarily handled, e.g., as regards routing, in a uniform manner by the Message Transfer Part. 4.3Тh  ТУУMessage contentЦЦ Та ТС€ HСФФ4.3.1С СУУCode transparencyЦЦ ФФС СInformation with any code combination generated by a user can be transferred by the Message Transfer Part provided that the message respects the requirements described below. Та ТС€ HС4.3.2С СУУService informationЦЦ а H аФФС СEach message must contain service information coded in accordance with the rules specified in Recommendation Q.704, РSР 14. Та ТС€ HС4.3.3С СУУMessage labelЦЦ а H аФФС СEach message must contain a label consistent with the routing label of the signalling network concerned. See also Recommendation Q.704, РSР 2. Та ТС€ HС4.3.4С СУУMessage lengthЦЦ ФФС СThe information content of a message should be an integral number of octets. а H аС СThe total amount of signalling information transferable in one message is limited by some parameters of the signalling system; the signalling system can accept transfer of user information blocks in the order of 256 octets in single messages. а H аС СDepending on the signalling traffic characteristics of a user and of other users sharing the same signalling facilities, there may be a need to limit message lengths below the system limit based on queueing delay considerations. а H аС СIn the case when information blocks generated by a user function exceed the allowed message length, it is necessary to implement means for segmentation and blocking of such information blocks within the User Part concerned. 4.4Тh  ТУУUser accessibilityЦЦ а H аФФС СThe accessibility of user functions through a signalling network depends on the signalling modes and routing plan employed in that network. а H аС СIn the case when only the associated mode of signalling is employed, only user functions located at adjacent signalling points may be accessed. а H аС СIn the case when quasiР-Рassociated signalling is employed, user functions located at any signalling point may be accessed provided that the corresponding message routing data is present. Та Т4.5СpСУУTransport service performanceЦЦ а Hh аФФС СFurther detailed information is provided in Recommendation Q.706. Та ТС€ HС4.5.1С СУУMessage transfer delayЦЦ а H аФФС СThe normal delay for transfer of messages between user locations depends on factors such as distance, signalling network structure, signalling data link type and bit rate and processing delays. а H аС СA small proportion of messages will be subject to additional delay because of transmission disturbances, network failures, etc. Та ТС€ HС4.5.2С СУУMessage transfer failuresЦЦ ФФС СThe Message Transfer Part has been designed to enable it to transfer messages in a reliable and regular manner even in the presence of network failures. However, inevitably some failures will occur the consequences of which cannot be avoided with economic measures. The types of failures that may occur and some typical probabilities of their occurrence are described below. Recommendation Q.706 provides further detailed information that can be used to estimate failure rates for particular cases. а H аС СIn the case when a potential user function requires a reliability of the transport service that cannot be guaranteed by the Message Transfer Part, the reliability of that user may be enhanced by adoption of appropriate level 4 procedures, possibly including some means of supplementary endР-РtoР-Рend error control. а H аС СThe following types of message transfer failures are possible, and the expected probabilities for such failures in typical applications are indicated (see also Recommendation Q.706). а H аТа ТТ№ ТС€ Сa)СpСUnavailability of the transport service to one or more locations Р-Р the availability of the message transfer capability depends on the redundancy provided in the signalling network; the availability can therefore be dimensioned.ЦЦ а H аТа ТТ№ ТС€ Сb)СpСLoss of messages Р-Р the probability of loss of messages mainly depends on the reliability of signalling equipment; typically it is expected to be lower than 10УУб cмˆ4 PŽТ бР-Р7ФФб cмˆ4 PŽТ б.ЦЦ а Hx аТа ТТ№ ТС€ Сc)СpСMisР-Рsequencing of messages Р-Р may in certain configurations of quasiР-Рassociated signalling occur with rare combinations of independent failures and disturbances. The probability, in such configurations, of a message being delivered outР-РofР-Рsequence depends on many factors but is expected to be lower than 10УУб cмˆ4 PŽТ бР-Р10ФФб cмˆ4 PŽТ б.ЦЦ а H аТа ТТ№ ТС€ Сd)СpСDelivery of false information Р-Р undetected errors may lead to the delivery of false information; the possibility of an error in a message delivered is expected to be lower than 10УУб cмˆ4 PŽТ бР-Р10ФФб cмˆ4 PŽТ б.ЦЦ а HH а‚У У5ТX ТDifferences from the Red BookФ ФЦЦ а H аС СThe ongoing development of the MTP during this study period has resulted in a number of differences occurring between the Recommendations as documented in the Red Book and these current Recommendations (Blue Book). In order to limit interworking problems, a backwards compatibility mechanism is required (see РSР 6). As an initial step towards producing such a mechanism, this section identifies the new items and items changed because of operational considerations, that have been included in the Blue Book. This section does not consider editorial or technical corrections. 5.1Тh  ТУУSignalling Information Field lengthЦЦ а H аФФС СThe maximun length of the Signalling Information Field has been increased to 272 octets. This was previously a National only option. Networks using both signalling terminals with 62 octet maximum SIF length handling capability and signalling terminals with 272 octet maximum SIF length handling capability must ensure that messages with SIFs longer than 62 octets cannot be routed to signalling links that are unable to handle them (see РSР 7). 5.2Тh  ТУУSignalling Point RestartЦЦ а H аФФС СThe Signalling Point Restart procedure (see Q.704 РSР 9) has been included together with a definition of Signalling Point availability. This procedure allows a graceful increase in message traffic at a restarting Signalling Point. 5.3Тh  ТУУManagement BlockingЦЦ а H аФФС СThe Management Blocking procedure for Signalling links has been deleted. No interworking problems are foreseen in networks where some Signalling Points still incorporate this procedure and others are implemented in accordance with the Blue Book. 5.4Тh  ТУУSignalling Link TestЦЦ а H аФФС СThe Signalling Link Test has been enhanced to check that both ends of the link agree as to which signalling link is being tested. No interworking problems are foreseen (see Q.707 РSР 2.2). 5.5Тh  ТУУCompatibility mechanismЦЦ а H аФФС СGeneral principles have been incorporated in the Message Transfer Part that will allow implementations to the Blue Book to be compatible with implementations to Red/Yellow Books and future issues of the Recommendations (see РSР 6). 5.6Тh  ТУУTimer valuesЦЦ а H аФФС СThe values of existing Q.703 and Q.704 Timers have been finalized (see РSР 7). 5.7Тh  ТУУProcessor OutageЦЦ а H аФФС СThe actions related to Processor Outage have been clarified (see Q.703 РSР 8 and Q.704 РSР 4, 5 and 6). No interworking problems are foreseen. 5.8Тh  ТУУUser flow controlЦЦ а H аФФС СProcedures for Message Transfer Part User Flow Control have been adopted for use at a Signalling Point when an MTP user has become unavailable (see Q.704 РSР 11 and Q.701 РSР 7). 5.9Тh  ТУУManagement Inhibiting and Management Inhibiting test procedureЦЦ а H аФФС СThe timeР-Рcontrolled changeover procedure is now used to divert traffic from a management inhibited link. С СTo verify the inhibited status of a link, test procedures have been introduced into management inhibiting (see Q.704 РSР 10 and Q.701 РSР 7). 5.10Т№  ТУУSignalling point/signalling transfer point congestionЦЦ а H аФФС СProcedures to detect and handle signalling point/signalling transfer point congestion have now been identified (see Q.704 РSР 11.2.6). No interworking problems are foreseen. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС‚У У6С  Сб cмˆ4 PŽТ бCompatibility in the message transfer partЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ ФС СTo enable implementations of Signalling System No. 7 to this issue (Blue Book) of the Recommendations to achieve compatibility with implementations to other issues, e.g., Yellow, Red and 1992 Books, a set of appropriate procedures and guidelines has been concluded in Recommendation Q.700. This section identifies the action that is required within the Message Transfer Part to ensure both forward and backwards compatibility. The areas considered are the treatment of spare fields, spare values, lack of acknowledgements and unreasonable information. 6.1Тh  ТУУUnreasonable InformationЦЦ ФФС СThe following actions occur in the MTP when messages are received containing unreasonable information. Та ТС€ HС6.1.1С СУУMessages containing an unallocated SIO valueЦЦ а H аФФС СWhen messages containing an unallocated SIO value are received at either a terminating Signalling Point or an STP that employs message routing based on both DPC and SIO, they should be discarded. If required, a report should be made to management. Та ТС€ HС6.1.2С СУУMessages containing an unallocated H0/H1 codeЦЦ а H аФФС СWhen messages containing an unallocated H0/H1 code are received at the appropriate functional block within the MTP, they are discarded. There should be no impact on any protocol and, if required, a report should be made to management. Та ТС€ HС6.1.3С СУУMessages containing an unallocated value in a recognized fieldЦЦ а H аФФС СWhen massages are received at an owning function within the MTP containing a field with an unallocated value they are discarded and, if required, a report made to management. There should be no impact on any current protocol. а H аС С(An owning function is a function to which a received message pertains.) 6.2Тh  ТУУTreatment of spare fieldsЦЦ а H аФФС СThe MTP will handle spare fields in MTP messages in the following manner:д Д- дŒа H аТа ТТ№ ТС€ Сi)СpСSpare fields are set to zero on message creation, and are not examined on reception at the destination owning function.ЦЦ а H аТа ТТ№ ТС€ Сii)СpСSpare subfields are set to zero on message creation, and are not examined on reception at the destination owning function.ЦЦ а H аТа ТТ№ ТС€ Сiii)Си СImplementations of the STP function should transit all messages unchanged, including spare fields and spare subfields.ЦЦ а HH а6.3Тh  ТУУLack of acknowledgementЦЦ а H аФФС СShould a message that requires an acknowledgement not receive one within a specified time, the message will be repeated, unless the protocol specifies otherwise. However, subsequent failures to receive the acknowledgement should not cause indefinite repeat attempts. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС‚У У7С  Сб cмˆ4 PŽТ бInterworking of Yellow, Red and Blue MTP implementationsЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ ФС СThere have been a number of changes introduced into this issue (Blue Book) of Recommendations Q.701Р-Р707 from the previous issue (Red Book). The changes have been identified in РSР 5 and although in the majority of cases there will be no interworking problems between a Signalling Point/STP implemented to the Red Book and one implemented to a Blue Book, there are some instances where problems will arise. This section gives guidance on the appropriate action that can be taken in the MTP to overcome interworking problems and also considers Yellow to Red Book and Yellow to Blue Book interworking. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС7.1С   Сб cмˆ4 PŽТ бУУYellow Book to Red Book interworkingЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СThere were four areas where changes from the Yellow Book to the Red Book introduced interworking problems: Та ТТ№ ТС€ Сi)СpСLevel 2 flow control, LSSU SIB introduced.ЦЦ а H аТа ТТ№ ТС€ Сii)СpСTransfer Restricted (TRF) and Transfer Controlled (TFC) messages and procedures were introduced into the Red Book.ЦЦ Та ТТ№ ТС€ Сiii)Си СTransfer Allowed (TAA) and Transfer Prohibited (TPA) acknowledgements were deleted from the Red Book.ЦЦ а H аТа ТТ№ ТС€ Сiv)СpСManagement inhibiting procedures were introduced into the Red Book.ЦЦ а H аС СThe suggested action required at the Yellow and/or Red Book SP/STP to enable interworking is contained in the following point items. Та ТС€ HС7.1.1С СУУLevel 2 Flow controlЦЦ а H аФФС СThe Red Book SP/STP should apply normal level 2 flow control action (i.e., acknowledgements are withheld and SIBs sent). The Yellow Book SP/STP should ignore the LSSU SIB when received. It is recognized that although flow control is not performed in this case, interworking is possible. However, a possible option would be to set the congestion threshold at the Red Book SP/STP, such that flow control is not triggered on that signalling relation. Та ТС€ HС7.1.2С СУУTransfer restricted and Transfer controlled proceduresЦЦ а H аФФС СThe Yellow Book SP/STP should ignore TFR and TFC messages when received. Та ТС€ HС7.1.3С СУУTransfer allowed/Transfer prohibited acknowledgementsЦЦ а H аФФС СThe Yellow Book SP/STP should limit the repetition of the TFA/TFP message to once only. The Red Book SP/STP should ignore the acknowledgement messages when they are received. Та ТС€ HС7.1.4С СУУManagement inhibiting procedureЦЦ ФФС СThe Yellow Book SP/STP should ignore the Link Inhibit (LIN) and Link Uninhibit (LUN) messages when received. The Red Book SP/STP should limit the repetition of the LIN/LUN message. 7.2Тh  ТУУRed Book to Blue Book interworkingЦЦ ФФС СThe changes in this issue (Blue Book) from the Red Book Q.701Р-Р707 Recommendations are identified in РSР 5. There are five areas where changes have resulted in interworking problems: а H аТа ТТ№ ТС€ Сi)СpСSignalling Point Restart procedure has introduced the Traffic Restart Allowed (TRA) message.ЦЦ а H аТа ТТ№ ТС€ Сii)СpСTimer values have been confirmed in this issue, previous values were provisional.ЦЦ а Hh аТа ТТ№ ТС€ Сiii)Си СUser Flow Control procedure has introduced the User Part Unavailable (UPU) message.ЦЦ а H аТа ТТ№ ТС€ Сiv)СpСSignalling Information Field length increase will require action to prevent overlength messages being sent on a link that is not capable of handling them.ЦЦ а H аТа ТТ№ ТС€ Сv)СpСManagementР-Рinhibiting test procedure has introduced Link Local inhibit test message (LLT) and Link Remote inhibit test message (LRT).ЦЦ а H аС СThe suggested actions required at the Red and/or Blue Book SP/STP to enable interworking are contained in the following point items. Та ТС€ HС7.2.1С СУУSignalling Point RestartЦЦ а H аФФС СThe Red Book SP/STP should ignore the Traffic Restart Allowed messages when received. Та ТС€ HС7.2.2С СУУQ.703 and Q.704 timer valuesЦЦ а H аФФС СWhere possible, an SP/STP implemented to the Red Book should adopt the timer values specified in the Blue Book when interworking with a Blue Book SP/STP. For timer values (see Q.703 РSР 12 and Q.704 РSР 16). Та ТС€ HС7.2.3С СУУUser flow controlЦЦ а H аФФС СThe Red Book SP/STP should ignore the User Part Unavailable (UPU) message if received. Та ТС€ HС7.2.4С СУУManagement inhibit test procedureЦЦ а H аФФС СThe Red Book SP/STP should ignore the Link Local inhibit test (LLT) and Link Remote inhibit test (LRT) messages. A report to local management should also be made. Та Т7.2.5Си СУУSIF length increaseЦЦ а H аФФС СThe SP/STP with 272 octet SIF length handling capability should prevent overlength messages from being routed over signalling links that only have a 62 octet SIF handling capability. Та ТС€ HС7.2.6С СУУSIF length increase (National networks option)ЦЦ ФФС СIn the international Signalling System No. 7 network, it should be possible to identify signalling links/routes with a limited SIF length handling capability and prevent overlength messages being transmitted over them by administrative action based on the exchange of operational data. However, with some national networks due to the rapid change in status of SP/STP implementation level (e.g., 62 to 272 SIF capability) and the number of SP/STPs in the network, this administrative action and data exchange may not be adequate. In this situation, a mechanism based on the following MTP activities may be more appropriate. а H аТа ТТ№ ТС€ Сi)СpСDetection of a link with 272 SIF capability may be achieved by coding the Р"РDР"Р bit of LSSUs sent during alignment as 1 (with 62 octet SIF links it would be 0). On receipt of this LSSU, a Blue Book SP/STP would mark the link/route as having 272 SIF capability. A Red Book SP/STP would ignore the coding of the Р"РDР"Р bit and treat the LSSU in the normal manner.ЦЦ а H аТа ТТ№ ТС€ Сii)СpСWhen a Blue Book SP/STP receives a message for onward routing, it will check if the message (SIF) is greater than 62 octets. If the SIF is greater than 62 octets, it will verify that the link/route can handle a message of this length. Should the link/route not have the SIF length capability, the message will be discarded and an indication sent to the message origin. A Red Book SP/STP should not receive a message with an SIF > 62 octets.ЦЦ а H аТа ТТ№ ТС€ Сiii)Си СIf the message originator is a local MTP User, an MTP PAUSE primitive will be returned by the MTP in response to an overlength message (see РSР 8). Should the originator be at a remote SP, a TFA coded to indicate that only 62 octet SIF messages can be transferred will be returned by the MTP in response to an overlength message (see Q.704 РSР 15).ЦЦ а H аС СIn national networks using an SIF compatibility mechanism, the two spare bits in the TFA (see Q.704 РSР 15.8.2) may be coded as an SIF compatibility indicator as follows: bitС  СB A Та ТТ№ ТС€ С0 0СpСAllow 62 octet SIFs/Prohibit 272, X and Y octet SIFsЦЦ Та ТТ№ ТС€ С0 1СpСAllow 62 and 272 octet SIFs/Prohibit X and Y octet SIFsЦЦ Та ТТ№ ТС€ С1 0СpСAllow 62, 272 and X octet SIFs Prohibit Y octet SIFs.ЦЦ Та ТТ№ ТС€ С1 1СpСAllow 62, 272, X and Y octet SIFs.ЦЦ а H аТа ТТ№ ТС€ СУУNoteФФ Р-Р 272 < X < Y octets, the values of X and Y are for further study.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС7.3С   Сб cмˆ4 PŽТ бУУYellow Book to Blue Book InterworkingЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СThe changes between Yellow and Blue Books have taken place in two stages: Yellow to Red and Red to Blue. Therefore, to achieve interworking between Yellow and Blue Book implementations, the actions specified in РSРS 7.1 and 7.2 should be applied. In РSР 7.1 Red Book SP/STP should be read as Blue Book SP/STP and in РSР 7.2 Red Book SP/STP should be read as Yellow Book SP/STP. а H аС СThere is one change from the Red Book in the Blue Book that will have an additional impact on interworking with the Yellow Book, and that is the deletion of the blocking procedure. This means that while a Yellow Book implementation can block a signalling link, a Blue Book node can neither inhibit nor block the link in the opposite direction.‚У У Та Т8СpСб cмˆ4 PŽТ бPrimitives and Parameters of the Message Transfer PartЦЦ а HH аб cмˆ4 PŽТ бФ ФС СThe primitives and parameters are shown in Table 1/Q.701. ‚Ср8LСб cмˆ4 PŽТ бTABLE 1/Q.701 Ср8>СУ УMessage transfer part service primitivesФ Ф б cмˆ4 PŽТ бвЦ‚HxhШЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј xџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бPrimitives аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHР(€pШШџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа а hЈ ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџhР(€pШШџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бˆа hЈ аб cмˆ4 PŽТ бвЦƒHши xhШЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи hџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр#TСб cмˆ4 PŽТ бGeneric Name Ср#TСSpecific Name аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџhР(€pШШџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр#UСParameters а hЈ аб cмˆ4 PŽТ бˆа hЈ аб cмˆ4 PŽТ бвЦƒHши xhШЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи hџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бMTPР-РTRANSFER Request Indication а hИ ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџhР(€pШШџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаOPC (see Q.704 РSР 2.2) а hЈ аб cмˆ4 PŽТ бˆа hЈ аб cмˆ4 PŽТ бвЦƒHши xhШЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи hџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б а hИ ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџhР(€pШШџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаDPC (see Q.704 РSР 2.2) а hЈ аб cмˆ4 PŽТ бˆа hЈ аб cмˆ4 PŽТ бвЦƒHши xhШЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи hџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б а h@ ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџhР(€pШШџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаSLS (see Q.704 РSР 2.2) (Note 1) а hЈ аб cмˆ4 PŽТ бˆа hЈ аб cмˆ4 PŽТ бвЦƒHши xhШЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи hџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б а h@ ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџhР(€pШШџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаSIO (see Q.704 РSР 14.2) а hЈ аб cмˆ4 PŽТ бˆа hЈ аб cмˆ4 PŽТ бвЦƒHши xhШЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи hџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б а hШ ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџhР(€pШШџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаUser data (see Q.703 РSР 2.3.8) а hЈ аб cмˆ4 PŽТ бˆа hЈ аб cмˆ4 PŽТ бвЦƒHши xhШЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи hџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бMTPР-РPAUSE (Stop) Indication аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџhР(€pШШџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаAffected DPC а hЈ аб cмˆ4 PŽТ бˆа hЈ аб cмˆ4 PŽТ бвЦƒHши xhШЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи hџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бMTPР-РRESUME (Start) Indication аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџhР(€pШШџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаAffected DPC а hЈ аб cмˆ4 PŽТ бˆа hЈ аб cмˆ4 PŽТ бвЦƒHши xhШЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи hџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бMTPР-РSTATUS Indication а hи ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџhР(€pШШџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаAffected DPC Cause (Note 2) а hЈ аб cмˆ4 PŽТ бˆа €H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ€pи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бУУNote 1ФФ Р-Р The MTP users should take into account that this parameter is used for load sharing by the MTP, therefore, the SLS values should be distributed as equally as possible. The MTP guarantees (to a high degree of probability) an inР-Рsequence delivery of messages which contain the same SLS code. УУNote 2ФФ Р-Р The Cause parameter has, at present, two values: i)Си СУУSignalling network congested (level)ФФ СpСThis parameter value is included if national options with congestion priorities and multiple signalling link states without congestion priorities as in Recommendation Q.704 are implemented. ii)Си СУУRemote User unavailable.ФФ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б8.1Тh  ТУУTransferЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФС  СThe primitive Р"РMTPР-РTRANSFERР"Рй Р"РMTPР-РTRANSFERР"Рйб cмˆ4 PŽТ б is used between level 4 and level 3 (SMH) to provide the MTP message transfer service. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б8.2Тh  ТУУPauseЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФС  СThe primitive Р"РMTPР-РPAUSEР"Рй Р"РMTPР-РPAUSEР"Рйб cмˆ4 PŽТ б indicates to the Р"РUsersР"Р the total inability of providing the MTP service to the specified destination. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б8.3Тh  ТУУResumeЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФС  СThe primitive Р"РMTPР-РRESUMEР"Рй Р"РMTPР-РRESUMEР"Рйб cмˆ4 PŽТ б indicates to the Р"РUserР"Р the total ability of providing the MTP service to the specified destination. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThis primitive corresponds to the destination accessible state as defined in Recommendations Q.704.б cмˆ4 PŽТ б Та Т8.4СpСУУStatusЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФС  СThe primitive Р"РMTPР-РSTATUSР"Рй Р"РMTPР-РSTATUSР"Рйб cмˆ4 PŽТ б indicates to the Р"РUsersР"Р the partial inability of providing the MTP service specified destination. The primitive is also used to indicate to a User that a remote corresponding User is unavailable (see Q.704 РSР 11.2.7). аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СIn the case of national option with congestion priorities or multiple signalling link congestion states without priorities as in Recommendation Q.704 are implemented, this Р"РMTPР-РSTATUSР"Р primitive is also used to indicate a change of congestion level. С СThis primitive corresponds to the destination congested/User Part unavailable state as defined in Recommendation Q.704. б cмˆ4 PŽТ б8.5Тh  ТУУRestartЦЦ а H аФФС СThe MTP indicates to the Р"РUsersР"Р at the restarting SP that the MTP is commencing or ending the signalling point restart procedure (see Recommendation Q.704, РSР 9). С СThe indication may have the following qualifiers: Та ТТ№ ТС€ Сi)СpСBeginЦЦ Та ТТ№ ТС€ Сii)СpСEndЦЦ а H аС СThe qualifier Р"РBeginР"Р indicates to the Р"РUsersР"Р that all destinations should be marked as accessible (but that the resumption of signalling traffic must await the reception of MTPР-РRESUME primitive or MTP restart indication Р"РEndР"Р). а H аС СThe qualifier Р"РEndР"Р indicates to the Р"РUsersР"Р that signalling traffic may be restarted, taking into account any MTPР-РPAUSE primitives previously received. а H аС СThe means of conveying the MTP restart indication to the MTP Р"РUsersР"Р, is for further study.