SIST ETS 300 009-1:1998

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.WRNRODIntegrated Services Digital Network (ISDN); Signalling System No.7; Signalling Connection Control Part (SCCP) (connectionless and connection-oriented class 2) to support international interconnection; Part 1: Protocol specification [ITU-T Recommendations Q.711 to Q.714 and Q.716 (1993), modified]33.080Digitalno omrežje z integriranimi storitvami (ISDN)Integrated Services Digital Network (ISDN)ICS:Ta slovenski standard je istoveten z:ETS 300 009-1 Edition 33SIST ETS 300 009-1:1998en01-IHEUXDU-19983SIST ETS 300 009-1:1998SLOVENSKI
STANDARD



SIST ETS 300 009-1:1998



EUROPEANETS 300 009-1TELECOMMUNICATIONSeptember 1996STANDARDThird EditionSource: ETSI TC-SPSReference: RE/SPS-02018-1ICS:33.080Key words:ISDN, SS7, SCCPIntegrated Services Digital Network (ISDN);Signalling System No.7;Signalling Connection Control Part (SCCP)(connectionless and connection-oriented class 2)to support international interconnection;Part 1: Protocol specification[ITU-T Recommendations Q.711 to Q.714 and Q.716 (1993), modified]ETSIEuropean Telecommunications Standards InstituteETSI SecretariatPostal address: F-06921 Sophia Antipolis CEDEX - FRANCEOffice address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCEX.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: secretariat@etsi.frTel.: +33 92 94 42 00 - Fax: +33 93 65 47 16Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and theforegoing restriction extend to reproduction in all media.© European Telecommunications Standards Institute 1996. All rights reserved.SIST ETS 300 009-1:1998



Page 2ETS 300 009-1: September 1996ForewordThis third edition European Telecommunication Standard (ETS) has been produced by the SignallingProtocols and Switching (SPS) Technical Committee of the European Telecommunications StandardsInstitute (ETSI).The third edition of ETS 300 009 covering the Signalling System No.7 Signalling Connection Control Part(SCCP) to support international interconnection is structured as a multi-part standard (of which this ETSforms part 1) as described below:Part 1:"Protocol specification [ITU-T Recommendations Q.711 to Q.714 and Q.716 (1993),modified]";Part 2:"Protocol Implementation Conformance Statement (PICS) proforma specification";Part 3:"Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for Testing(PIXIT) proforma specification".This ETS implies the existence of a number of functional subsets of the SCCP protocol without, however,explicitly identifying them. Depending on their functional requirements, conforming implementations wouldprobably only implement a subset of the overall functions, e.g. a switch might only implement Class 2embedded, or a GSM basestation might not handle Global Titles. The possibility of having suchimplementations is reflected by the optionality of the corresponding capabilities in the PICS proformaspecification, ETS 300 009-2.Transposition datesDate of adoption of this ETS:6 September 1996Date of latest announcement of this ETS (doa):31 December 1996Date of latest publication of new National Standardor endorsement of this ETS (dop/e):30 June 1997Date of withdrawal of any conflicting National Standard (dow):30 June 1997Endorsement noticeThe text of ITU-T Recommendations Q.711 (1993), Q.712 (1993), Q.713 (1993), Q.714 (1993) andQ.716 (1993) was approved by ETSI as an ETS with agreed modifications as given below.NOTE:New or modified text is indicated using sidebars. In addition, underlining and/orstrikeout are used to highlight detailed modifications where necessary.Whilst every care has been taken in the preparation and publication of this document, errors in content,typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to"ETSI Editing and Committee Support Dept." at the address shown on the title page.SIST ETS 300 009-1:1998



Page 3ETS 300 009-1: September 1996Global modifications to ITU-T Recommendations Q.711 to Q.714 and Q.716Insert the following three clauses (scope, normative references and abbreviations):ScopeThis first part of ETS 300 009 defines the Signalling Connection Control Part (SCCP) signalling protocol ofSignalling System No.7 for use in and between international relay points and gateways and, optionally, inpublic networks.This ETS covers the use of connectionless functions (Class 0 and Class 1) and connection-orientedfunctions (Class 2, including embedded connection setup).NOTE:The SCCP gateway functions are relay functions that bridge two Message TransferPart (MTP) networks.This ETS is applicable to the international network and does not intend to restrict national networks.However, to facilitate SCCP interworking, its adoption within national networks is recommended.Concerning the interconnection of SCCPs, this ETS is based on the assumption that the MessageTransfer Part (MTP) specified in ETS 300 008 [1] supports the SCCP.Normative referencesThis ETS incorporates by dated and undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text and the publications are listedhereafter. For dated references, subsequent amendments to or revisions of any of these publicationsapply to this ETS only when incorporated in it by amendment or revision. For undated references the latestedition of the publication referred to applies.[1]ETS 300 008 (1991): "Signalling System No.7; Message Transfer Part (MTP) tosupport international interconnection".AbbreviationsFor the purposes of this ETS, the following abbreviations apply:CCConnection Confirm messageCRConnection Request messageCREFConnection Refused messageDPCDestination Point CodeERRprotocol data unit Error messageGTGlobal TitleISDNIntegrated Services Digital NetworkISUPISDN User PartITInactivity Test messageMTPMessage Transfer PartOPCOriginating Point CodeRIRouting IndicatorRLCRelease Complete messageRLSDReleased messageSCCPSignalling Connection Control PartSLSSignalling Link SelectionSPCSignalling Point CodeSSSubsystemSSNSubsystem NumberUDTUnitdata messageUDTSUnitdata Service messageUUS3User-to-User Signalling, service 3XUDTExtended Unitdata messageXUDTSExtended Unitdata Service messageSIST ETS 300 009-1:1998



Page 4ETS 300 009-1: September 1996Modifications to ITU-T Recommendation Q.711Page 4, subclause 2Class 3 is not in the scope of this ETS.Page 4, subclause 2.1Permanent signalling connections are not in the scope of this ETS.Page 5, subclause 2.1.1.1.2Sequence control and flow control are not in the scope of this ETS.Page 6, subclause 2.1.1.2.1N-EXPEDITED DATA, N-DATA ACKNOWLEDGE, and N-RESET are not in the scope of this ETS.Page 8, figure 7/Q.711Add the following note to figure 7/Q.711:NOTE:ISUP requests connection setup with the REQUEST Type 1 or REQUEST Type 2interface elements.Page 8, subclause 2.1.1.2.2Negotiation of expedited data is not in the scope of this ETS.Page 9, subclause 2.1.1.2.3N-EXPEDITED DATA, N-DATA ACKNOWLEDGE, and N-RESET are not in the scope of this ETS.Page 13, subclause 2.1.1.3.2Connection establishment interface elements are used by ISUP for the embedded setup of connections.The "receipt confirmation selection" shall be set to false. The "quality of service parameter set" shallindicate Class 2.NOTE:In the international network, the REQUEST Type 1 interface element would normallynot be used. This interface element only applies at the originating node in the nationalnetwork. However, it should be possible that ISUP performs an association ("chaining")of connection sections itself on the user level (see figure 12 of ITU-T RecommendationQ.730 as modified by ETS 300 356-2). This may be necessary if different versions ofSCCP are used in the national and international networks, or if User-to-user data istransported in the national network in another way.Page 14, subclause 2.1.2Delete subclause 2.1.2. Permanent signalling connections are not in the scope of this ETS.Page 15, subclause 2.2.1If the in-sequence delivery is not required (Protocol Class 0), the SCCP shall insert Signalling LinkSelection (SLS) codes with respect to the appropriate load sharing within the signalling network. If thein-sequence delivery is required (Protocol Class 1), the SCCP, at the originating node, while adhering tothe sequence control instruction from the user, shall allocate SLS codes between sequence streams withrespect to appropriate load sharing within the signalling network.As in relay nodes, user sequence control is not available. There shall be a fixed mapping betweenincoming and outgoing SLS code values for Class 1. This mapping may be different for different signallingrelations.SIST ETS 300 009-1:1998



Page 5ETS 300 009-1: September 1996Page 18, subclause 2.3.2.1N-COORD is only needed in nodes that contain local replicated subsystems.Page 19, subclause 2.3.2.3.1N-COORD is only needed in nodes that contain local replicated subsystems.Page 21, table 16/Q.711, note(b)Replace note b) by:b)The Cause parameter in the MTP-STATUS primitive may take the values:"Signalling network congested";"User Part unavailable".For the cause "Signalling network congested", and where an MTP according to ETS 300 008 [1] isused, no congestion levels are reported. MTPs employed in national networks may providecongestion levels.NOTE:The values:-"User Part unavailability: unknown";-"User Part unavailability: unequipped remote user";-"User Part unavailability: inaccessible remote user",occur in ITU-T Recommendation Q.701, clause 8. The first one corresponds to "UserPart unavailable" in ETS 300 008 [1], the latter two are not part of ETS 300 008 [1].Page 21, subclause 3.2.4, first paragraphInsert after the first paragraph:The Cause parameter in the MTP-STATUS primitive may take the values:-"Signalling network congested";-"User Part unavailable".For the cause "Signalling network congested", and where an MTP according to ETS 300 008 [1] is used,no congestion levels are reported. MTPs employed in national networks may provide congestion levels.NOTE:The values:-"User Part unavailability: unknown";-"User Part unavailability: unequipped remote user";-"User Part unavailability: inaccessible remote user",occur in ITU-T Recommendation Q.701, clause 8. The first one corresponds to "UserPart unavailable" in ETS 300 008 [1], the latter two are not part of ETS 300 008 [1].Page 22, subclause 4.1Class 3 functions are not in the scope of this ETS.SIST ETS 300 009-1:1998



Page 6ETS 300 009-1: September 1996Page 22, subclause 4.1.1.2Flow control is not in the scope of this ETS.Expedited data support is not in the scope of this ETS.Missequence detection is not in the scope of this ETS.Reset is not in the scope of this ETS.Receipt confirmation is not in the scope of this ETS.Page 23, subclause 4.1.2Delete subclause 4.1.2. Functions for permanent signalling connections are not in the scope of this ETS.Page 23, subclause 4.3Co-ordinated state change is only needed in nodes that contain local replicated subsystems.Page 23, subclause 4.4The routing and translation function of SCCP does not apply for the embedded method.NOTE:ISUP executes its own routing function. It provides the minimal necessary informationfor SCCP in the MTP-routing label and the Originating Point Code (OPC) field of theembedded request (see subclause 3.15 of ITU-T Recommendation Q.763 as modifiedby ETS 300 356-1).SIST ETS 300 009-1:1998



Page 7ETS 300 009-1: September 1996Modifications to ITU-T Recommendation Q.712Page 1, subclause 1.4Delete subclause 1.4. Data acknowledgement is not in the scope of this ETS.Page 1, subclause 1.6Delete subclause 1.6. Data form 2 is not in the scope of this ETS.Page 1, subclause 1.7Delete subclause 1.7. Expedited data is not in the scope of this ETS.Page 1, subclause 1.8Delete subclause 1.8. Expedited data acknowledgement is not in the scope of this ETS.Page 2, subclause 1.13Delete subclause 1.13. Reset confirm is not in the scope of this ETS.Page 2, subclause 1.14Delete subclause 1.14. Reset request is not in the scope of this ETS.Page 2, subclause 1.16Subsystem-out-of-service-grant is only needed in nodes that contain local replicated subsystems.Page 2, subclause 1.17Subsystem-out-of-service-request is only needed in nodes that contain local replicated subsystems.Page 3, subclause 2.4Delete subclause 2.4. Credit is not in the scope of this ETS.Page 4, subclause 2.6Delete subclause 2.6. Diagnostic is not in the scope of this ETS.Page 4, subclause 2.11Delete subclause 2.11. Receive sequence number is not in the scope of this ETS.Page 4, subclause 2.14Delete subclause 2.14. Reset cause is not in the scope of this ETS.Page 4, subclause 2.17Delete subclause 2.17. Sequencing/segmenting is not in the scope of this ETS.SIST ETS 300 009-1:1998



Page 8ETS 300 009-1: September 1996Modifications to ITU-T Recommendation Q.713Page 6, subclause 3.4.1, third paragraphInsert after the third paragraph, beginning with "A "1" in bit 2 .":On transmission of the called or calling party address, the Subsystem Number (SSN) indicator field shallalways be included and set to 0 if unknown.Page 7, subclause 3.4.1, last paragraphInsert after the last paragraph:Bit 8 (reserved for national use) shall always be coded 0 and is not evaluated.Page 8, subclause 3.4.2.2, list of subsystem numbersReplace all codepoints below 0000 1010 (AUC) by:0000 1011ISS (ISDN Supplementary Services)0000 1100INAP (Intelligent Network Application Protocol)0000 1101üú
toýSpareú1111 1110þ1111 1111Reserved for expansionNOTE:Except for ISUP, there are currently no SCCP users in the international network.Nevertheless, SSNs need to be allocated for all those SCCP subsystems whosemessages may cross network boundaries, so that international agreement is requiredfor the SSNs used. An additional SSN is required for ISDN Supplementary Services(ISS) to identify the services that are based on Transaction Capabilities (TC) (CCBS,Reverse charging, etc.).Page 9, subclause 3.4.2.3.1Global title indicator = 0001 is not in the scope of this ETS.Page 10, subclause 3.4.2.3.2Global title indicator = 0010 is not in the scope of this ETS.Page 11, subclause 3.4.2.3.3Global title indicator = 0011 is not in the scope of this ETS.Page 12, subclause 3.5, last paragraphInsert after the last paragraph:If segmenting/reassembly of connectionless messages or the return option are used, an unambiguous1)identification of the originating SCCP user (possibly complemented by additional MTP information) shallbe supplied in the calling party address.
1)"unambiguous" is used here as defined in ITU-T Recommendation X.650:"A name is unambiguous within a given scope when it identifies one and only one object within that scope. Unambiguity doesnot preclude the existence of synonyms".SIST ETS 300 009-1:1998



Page 9ETS 300 009-1: September 1996Page 13, subclause 3.8Delete subclause 3.8. Receive sequence number is not in the scope of this ETS.Page 14, subclause 3.9Delete subclause 3.9. Sequencing/segmenting is not in the scope of this ETS.Page 14, subclause 3.10Delete subclause 3.10. Credit is not in the scope of this ETS.Page 15, subclause 3.13Delete subclause 3.13. Reset cause is not in the scope of this ETS.Page 21, subclause 4.8Delete subclause 4.8. Data form 2 is not in the scope of this ETS.Page 22, subclause 4.9Delete subclause 4.9. Data acknowledgement is not in the scope of this ETS.Page 23, subclause 4.12Delete subclause 4.12. Expedited data is not in the scope of this ETS.Page 24, subclause 4.13Delete subclause 4.13. Expedited data acknowledgement is not in the scope of this ETS.Page 24, subclause 4.14Delete subclause 4.14. Reset request is not in the scope of this ETS.Page 25, subclause 4.15Delete subclause 4.15. Reset confirm is not in the scope of this ETS.Page 30, annex AAnnex A has the status of a normative annex.SIST ETS 300 009-1:1998



Page 10ETS 300 009-1: September 1996Modifications to ITU-T Recommendation Q.714Page 1, subclause 1.1.2Class 3 procedures are not in the scope of this ETS.Page 2, subclause 1.1.2.2, last paragraphInsert after the last paragraph:The in-sequence delivery not only relies on the properties of the MTP network, but also SCCP shallguarantee the sequential processing of SCCP messages. This excludes e.g. arbitrary parallel processingof Global Title translations in relay nodes.Page 2, subclause 1.1.2.4Delete subclause 1.1.2.4. Protocol Class 3 is not in the scope of this ETS.Page 2, subclause 1.1.3Insert after the last paragraph:NOTE:The ITU-T White Book (1993) leaves the possibility of having relay points withoutcoupling for connection-oriented services for further study because it is not clear how aconnection can be completed (with a Connection Confirm (CC) message) to theoriginator without changing or including the Calling address parameter of theConnection Request (CR) message in relay nodes.For the embedded method, there is in fact the possibility of having no association in anISUP relay point (ISUP would in this case simply pass the embedded request furtheron, without issuing a REQUEST Type 2). This poses no problem, since the OPC of theoriginating node or of the last relay node with coupling is included in the embeddedconnect request of the IAM message. It is therefore always possible to route back theCC message to the correct originator.Page 3, subclause 1.2.1, last paragraphInsert after the last paragraph:When the embedded method is used, ISUP determines whether association of connection sections isrequired or not. If the SCCP receives a REQUEST Type 2 from ISUP, with the "reply bit" set, anassociation of connection sections shall be performed.NOTE:The ITU-T White Book (1993) leaves the possibility of having relay points withoutcoupling for connection-oriented services for further study because it is not clear how aconnection can be completed (with a CC message) to the originator without changingor including the Calling address parameter of the CR message in relay nodes.For the embedded method, there is in fact the possibility of having no association in anISUP relay point (ISUP would in this case simply pass the embedded request furtheron, without issuing a REQUEST Type 2). This poses no problem, since the OPC of theoriginating node or of the last relay node with coupling is included in the embeddedconnect request of the IAM message. It is therefore always possible to route back theCC message to the correct originator.SIST ETS 300 009-1:1998



Page 11ETS 300 009-1: September 1996Page 3, subclause 1.2.2Flow control is not in the scope of this ETS.Expedited data support is not in the scope of this ETS.Missequence detection is not in the scope of this ETS.Reset is not in the scope of this ETS.Receipt confirmation is not in the scope of this ETS.Page 7, subclause 2.2.2, last paragraphInsert after the last paragraph:If an SCCP message is routed across network boundaries, a Global Title shall always be provided in thecalled address. For routing from one network to another passing through the international network, theRouting Indicator (RI) shall always be set to route on Global Title.NOTE:The routing of the embedded connect requests for ISUP is not performed by SCCP butby ISUP itself. The other connection-oriented messages are routed on DestinationPoint Code (DPC) only.Page 11, clause 3Class 3 procedures are not in the scope of this ETS.Page 12, subclause 3.1.3.1, last paragraphInsert after the last paragraph:If a connection request for Protocol Class 3 is received and the node only supports Class 2, the class shallbe lowered to Class 2 in response.Page 12, subclause 3.1.3.2Delete subclause 3.1.3.2. Flow control window negotiation is not in the scope of this ETS.Page 12, subclause 3.1.4.1In the REQUEST Type 1 interface element, the proposed protocol class shall be Class 2. No initial creditshall be indicated.Page 13, subclause 3.1.4.2If the protocol class received in the CC message is higher than the one proposed (i.e. either the class orthe window or both are larger), the connection release procedure shall be initiated on the signallingconnection and the Release cause parameter shall indicate "Inconsistent connection data".Page 13, subclause 3.1.5.1If a connection request for Protocol Class 3 is received and the relay point with coupling does only supportClass 2, the class shall be lowered to Class 2 in response.Page 14, subclause 3.1.5.2If the protocol class received in the CC message is higher than the one proposed (i.e. either the class orthe window or both are larger), the connection refusal procedure shall be initiated (see subclause 3.2.1 ofQ.714 as modified by this ETS).SIST ETS 300 009-1:1998



Page 12ETS 300 009-1: September 1996Page 14, subclause 3.1.6.1If a connection request for Protocol Class 3 is received and the destination node supports only Class 2,the class shall be lowered to Class 2 in response.Page 15, subclause 3.2.1, item(2)(b)Insert after item 2) b):c)the reception of a CC message, with a protocol class higher than the one proposed inthe associated CR message.Page 15, subclause 3.2.1, last paragraphReplace last paragraph by:If the connection refusal procedure is initiated at a relay node due to the reception of a CC message, witha protocol class higher than the one proposed in the associated CR message (see subclause 3.1.5.2 ofITU-T Recommendation Q.714 as modified by this ETS), then the connection release procedure isinitiated on that connection section and a Connection Refused message with refusal cause "Inconsistentconnection data" is transferred on the associated connection section.In either of the above three cases at an intermediate node, if the connection set-up was initiated using aREQUEST interface element, then the SCCP user is informed by invoking the N-DISCONNECT indicationprimitive.Page 18, subclause 3.4Support of supervision of connection by the SCCP user function is not required. The SCCP itself shallperform this supervision. The inactivity test procedure shall apply on all connection sections.Page 19, subclause 3.5.1Only the DT1 message is in the scope of this ETS.Page 19, subclause 3.5.2Delete subclause 3.5.2. Flow control is not in the scope of this ETS.Page 21, subclause 3.6Delete subclause 3.6. Expedited data support is not in the scope of this ETS.Page 22, subclause 3.7Delete subclause 3.7. Reset is not in the scope of this ETSPage 25, subclause 3.8.2.1, item(3)Delete item 3). Permanent signalling connections are not in the scope of this ETS.Page 25, subclause 3.9Permanent signalling connections are not in the scope of this ETS.Page 28, subclause 4.1.1Insert the following note:NOTE:The principle of segmenting/reassembly of connectionless messages is such that noactions are necessary in relay nodes, except for routing the XUDT and XUDTSmessages in the same way as UDT and UDTS messages.SIST ETS 300 009-1:1998



Page 13ETS 300 009-1: September 1996Page 29, subclause 4.1.1.2.3Insert after the last paragraph:The timeout of the reassembly timer shall be considered as one of the errors for which this procedureapplies.Page 32, subclause 5.2.4Additional information for handling MTP level congestion is given in annex ZC of this ETS.Page 35, subclause 5.3.5Insert the following note:NOTE:Co-ordinated state change is only needed in nodes that contain local replicatedsubsystems.Page 36, subclause 5.3.6.6Where an MTP according to ETS 300 008 [1] is used, no congestion levels are reported. MTPs employedin national networks may provide congestion levels.Page 38, annex AAnnex A has the status of a normative annex.Page 43, annex BAnnex B has the status of a normative annex.Page 47, annex CAnnex C has the status of a normative annex.Page 48, clause C.4, timersInsert at the end of clause 4:The following constraint shall be obeyed for the timers:T(guard) ³ T(interval) + T(iar) + D (see note)It may be advantageous to make sure that the inactivity receive timer T(iar) is at least twice the inactivitysend timer T(ias), as used in the nodes at the other side of the connection section. This avoids that theloss of one single Inactivity Test (IT) message (e.g. due to short term MTP congestion) causes theinadvertent release of an otherwise inactive SCCP connection. Loss of more messages (e.g. due to SPCfailures) will, however, still cause the connection to get released.T(iar) ³ 2 × T(ias) + D (see note)NOTE:D is a margin for the inaccuracy of timers at both ends of the connection and for thetransit delay of the IT message. A value of about one minute may be appropriate.Page 91, annex DAnnex D has the status of a normative annex.Page 107, annex EAnnex E has the status of an informative annex.SIST ETS 300 009-1:1998



Page 14ETS 300 009-1: September 1996Modifications to ITU-T Recommendation Q.716No modifications identified.SIST ETS 300 009-1:1998



Page 15ETS 300 009-1: September 1996Annex ZA (normative):Compatibility issuesZA.1Interface to MTPMTP according to the ITU-T White Book (1993) defines separate values for the causes: "User Partunavailability: unknown"; "User Part unavailability: unequipped remote user" and "User Part unavailability:inaccessible remote user". If interworking with a MTP according to the ITU-T White Book is necessary,these values should also be accepted and reacted to by using the SCCP management procedures asdescribed in clause 5 of ITU-T Recommendation Q.714.ZA.2Segmenting/reassembly of connectionless messagesThe mechanism for the connectionless segmenting reassembly are not compatible with the CCITT BlueBook (1988). Two messages had to be introduced in the ITU-T White Book (1993) because the currentUDT and UDTS message did not foresee the possibility of adding optional parameters. There is nocompatibility mechanism foreseen to fallback on use of UDT/UDTS if communication is not successfulusing the XUDT/XUDTS procedures. The introduction of this feature in the network should therefore beexecuted in carefully planned stages:1)before the introduction of any implementations using segmenting/reassembly, all relay nodes thatwill be passed shall be equipped with the ability to accept and route XUDT(S) messages;2)new implementations using segmenting/reassembly are introduced. In this phase, all messagesfrom applications have to be sent as UDT/UDTS messages, as long as they fit within oneUDT/UDTS message. For applications according to CCITT Blue Book (1988), there shall not be anychange in behaviour of SCCP. This maximizes the chances for successful interworking;3)as soon as the network is completely retrofitted according to the second or later editions of thisETS, it is allowed to segment messages that would otherwise fit into an UDT/UDTS message. Thismay be done e.g. to restrict the mean length of the messages sent over the network. In this case,all messages larger than a certain limit (the value "X" from the ITU-T White Book (1993)) aresubjected to segmenting;4)the final goal is the complete replacement of UDT/UDTS messages by XUDT/XUDTS messages.For a certain period of time, it is nevertheless required to be able to receive and relay UDTmessages.It is out of the scope of this ETS to define whether and when each of these stages is to be achieved.ZA.3Embedded methodFailure situations resulting from compatibility problems are covered in annex ZB.ZA.4Introduction of SCCP into national networksThe introduction of SCCP into national networks needs to cope with the fact that in other nationalnetworks capabilities like Class 3 might be already in place. The following text describes the negotiationprocedures that apply in that case to make sure that connections are setup with the maximum availableprotocol class and window. It does not introduce any new requirements, since the procedures are fullycovered by clause 3 of ITU-T Recommendation Q.714 as modified by this ETS.In the originating node, if a N-CONNECT-req primitive is received with Class 3, window = x, and if SCCPdoes not support Class 3, SCCP shall lower the class proposed in the outgoing CR message to Class 2automatically.In a relay point without coupling, if a CR message is received with Class 3, window = x, it shall be passedtransparently (only SCRC routes the message, SCOC procedures are not invoked).In a relay point with coupling, if a CR message is received with Class 3, window = x, and if SCCP does notsupport Class 3, SCCP shall lower the class proposed in the outgoing CR message to Class 2automatically.SIST ETS 300 009-1:1998



Page 16ETS 300 009-1: September 1996In the destination node, if a CR message is received with Class 3, window = x, and if SCCP does notsupport Class 3, SCCP shall lower the class proposed in the N-CONNECT indication primitive to Class 2automatically.If a user in the destination node receives a N-CONNECT indication, it shall check whether the proposedprotocol class is still sufficient to service the connection. If not, the connection shall be refused and a N-DISCONNECT indication shall be returned, otherwise the connection shall be completed withN-CONNECT response.In a relay point with coupling, if a CC message is received, SCCP shall check whether the protocol classis lower than or equal to the one it proposed in its outgoing CR message. If it is not, the connection shallbe refused with a Connection Refused (CREF) message in the backward direction, and the alreadycompleted connection sections shall be released in the forward direction with a Released (RLSD)message.In the originating node, if a CC message is received, SCCP shall check whether the protocol class islower than or equal to the one it proposed in its outgoing CR message. If it is not, the already completedconnection sections shall be released in the forward direction with RLSD.If a user in the originating node receives a N-CONNECT confirmation, it shall check whether the proposedprotocol class is still sufficient to service the connection. If not, the connection shall be r
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