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Content for  TS 29.016  Word version:  16.0.0

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5  Conformance to message transfer part (MTP)

5.1  General

The MTP functions as specified in ITU-T Recommendations Q.702, Q.703, Q.704 and Q.707 for E1 interface and ANSI T1.111 Recommendations for the T1 interface are applicable. However, the following subclauses provide a minimum set of MTP requirements that shall be implemented at a SGSN or VLR to support the functionality required by the BSSAP+ protocol in the Gs interface. The set of exceptions and modifications to those recommendations maintain compatibility with the implementation of a full specification of the MTP. The ITU-T recommendations for E1 interface and ANSI recommendation for T1 interface concerning the MTP shall be taken as requirements unless covered by a statement in the present document.
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5.2  MTP Level 1Word‑p. 8

The MTP level 1 exceptions and modifications to ITU-T Recommendation Q.702 and ANSI T1.111 Recommendation can be found in TS 48.006 subclause 3.2.

5.3  MTP Level 2

5.3.1  MTP Level 2 for E1 Interface

The MTP level 2 exceptions and modifications to ITU-T Recommendation Q.703 are listed below.
  • ITU-T Recommendation Q.703, subclause 1.4:
    • Only the basic error correction protocol is required.
  • ITU-T Recommendation Q.703, clause 6:
    • Not applicable, only basic error correction is required.
  • ITU-T Recommendation Q.703, clause 7:
    • Both the SGSN and the VLR may apply the emergency proving period or the normal proving period in the initial alignment procedure. If all the signalling links between the two entities are unavailable then the SGSN or the VLR shall apply the emergency proving period until one signalling link becomes available.
  • ITU-T Recommendation Q.703, clause 8:
    • The processor outage status indicator shall be recognised at the SGSN and the VLR and the procedures defined in ITU-T Recommendation Q.703 clause 8 supported. The SGSN and the VLR should support the generation of the processor outage indication towards the peer entity if this is appropriate.
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5.3.2  MTP Level 2 for T1 Interface

The MTP level 2 exceptions and modifications to ANSI T1.111.3 are listed below.
  • ANSI T1.111.3, subclause 1.4:
    • Only the basic error correction protocol is required (subclause 1.4.3 is not required).
  • ANSI T1.111.3, clause 6:
    • Not applicable, only basic error correction is required.
  • ANSI T1.111.3, clause 7:
    • Both the SGSN and the VLR may apply the emergency proving period or the normal proving period in the initial alignment procedure. If all the signalling links between the two entities are unavailable the SGSN or the VLR shall apply the emergency proving period until one signalling link becomes available.
  • ANSI T1.111.3, clause 8:
    • The processor outage status indicator shall be recognised at the SGSN and the procedures defined in ANSI T1.111.3 clause 8 supported. The SGSN and the VLR shall support the generation of the processor outage indication towards the peer entity if this is appropriate.
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5.4  MTP Level 3

5.4.1  MTP Level 3 for E1 Interface

The Gs interface may be configured as a point to point interface or may use an intermediate SS7 network. In this last case an SGSN or a VLR may act always as end points of the Gs interface (SP functionality) or may be configured to act as an transfer point between a VLR and an SGSN (SP and STP functionality). The MTP level 3 exceptions and modifications to ITU-T Recommendation Q.704 are listed regarding whether the SGSN and the VLR are connected by a point to point link or are configured to act as SPs in an SS7 network or if they support STP functionality.
Subclause 5.4.1.1 applies to all configurations of the Gs interface. In subclause 5.4.1.2 the exceptions and modifications to ITU-T Recommendation Q.704 are listed depending upon the configuration of the Gs interface, whether it is a point to point interface or the SGSN and VLR act as an SP only or as SP and STP. Subclause 5.4.1.3 provides points of clarification about the ITU-T Recommendation Q.704.
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5.4.1.1  General clausesWord‑p. 9

The MTP level 3 exceptions and modifications to ITU-T Recommendation Q.704 regardless of whether the SGSN supports STP functionality are listed below.
  • ITU-T Recommendation Q.704, subclause 2.3.5:
    • Either of the two methods of congestion control is acceptable. The most appropriate method is dependent on national ITU-T No. 7 implementations.
  • ITU-T Recommendation Q.704, subclause 2.4:
    • The signalling point code for an SGSN may be included in the national signalling point code scheme or in a separate signalling network.
  • ITU-T Recommendation Q.704, subclause 3.8.2:
    • There are two acceptable methods of congestion control defined in ITU-T Recommendation Q.704, in subclauses 3.8.2.1 a) and b). The most appropriate method is dependent on national ITU-T No. 7 implementations. Each administration should specify its congestion threshold setting algorithm and nodal congestion abatement procedures at system procurement.
  • ITU-T Recommendation Q.704, clause 12:
    • Only basic link management procedures are required.
  • ITU-T Recommendation Q.704, subclause 14.2.1:
    • Since all messages are passed using the SCCP, the service indicator for Gs interface operation will be:
        bits  D  C  B  A
              0  0  1  1
      
  • ITU-T Recommendation Q.704, subclause 14.2.2:
    • The sub service field for Gs interface operation will always be set to one of the following values:
        bits  D  C
              1  0  national network
              1  1  local network
      
  • ITU-T Recommendation Q.704, clause 15:
    • The formats and codes listed are only relevant to the messages that are required, i.e. those not excluded in the rest of this recommendation.
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5.4.1.2  Configuration dependent clauses

The MTP level 3 exceptions and modifications to ITU-T Recommendation Q.704 are permitted if the SGSN or the VLR does not support STP functionality are listed below.
  • ITU-T Recommendation Q.704, subclause 1.1.2:
    • If the Gs interface is configured as a point to point interface, then there will be no signalling network management features which need to be considered.
  • ITU-T Recommendation Q.704, clause 2:
    • If STP functionality is not required the discrimination function of the MTP used for GPRS application can be significantly simplified.
  • ITU-T Recommendation Q.704, subclause 2.3:
    • If the implementation of the Gs interface is point to point, load sharing between linksets is not required since there will only be one linkset between SGSN and VLR.
  • ITU-T Recommendation Q.704, subclause 2.4:
    • At an SGSN or VLR that does not implement STP functionality, only messages with a correctly checking DPC will be accepted. Others will be discarded. It is recommended that discarding a message because of an incorrectly set point code causes an incident report to be generated.
  • ITU-T Recommendation Q.704, subclause 3.1.3 c):
    • In a point to point configuration there is no requirement for signalling route management.
  • ITU-T Recommendation Q.704, subclause 3.3.2.3:
    • In a point to point configuration there is no requirement for signalling route management.
  • ITU-T Recommendation Q.704, subclause 3.3.3.3:
    • In a point to point configuration there is no requirement for signalling route management.
  • ITU-T Recommendation Q.704, subclause 3.3.4.3:
    • In a point to point configuration there is no requirement for signalling route management.
  • ITU-T Recommendation Q.704, subclause 3.4.3:
    • Not applicable if no STP functionality is implemented by the SGSN or the VLR.
  • ITU-T Recommendation Q.704, subclause 3.5.3:
    • Not applicable if no STP functionality is implemented by the SGSN or the VLR.
  • ITU-T Recommendation Q.704, subclause 3.8.5.2:
    • The signalling-route-set-congestion-test procedure is not required.
  • ITU-T Recommendation Q.704, subclause 4.1.2:
    • In a point to point configuration signalling routes are not applicable.
  • ITU-T Recommendation Q.704, subclause 4.2:
    • The normal routing situation in a point to point configuration will be that there are 1 or more signalling links available between a SGSN and VLR, these will constitute a link set. They will be run in a load sharing mode and changeover, changeback procedures will be supported between these signalling links.
    • The normal routing situation if more than one route is available between the SGSN and the VLR will be that the load sharing, changeover and changeback procedures would be provided between signalling links within the same signalling linkset and between signalling linksets.
  • ITU-T Recommendation Q.704, subclause 4.3.3:
    • There will be no alternative linkset in a point to point configuration of the Gs interface.
  • ITU-T Recommendation Q.704, subclause 4.4.3:
    • Not applicable in a point to point configuration of the Gs interface.
  • ITU-T Recommendation Q.704, subclause 4.5:
    • Not applicable in a point to point configuration of the Gs interface.
  • ITU-T Recommendation Q.704, subclause 4.6:
    • Not applicable in a point to point configuration of the Gs interface.
  • ITU-T Recommendation Q.704, subclause 4.7:
    • Not applicable in a point to point configuration of the Gs interface.
  • ITU-T Recommendation Q.704, clause 5:
    • Changeover between link sets is not applicable in a point to point configuration of the Gs interface.
  • ITU-T Recommendation Q.704, clause 6:
    • Changeback between link sets is not applicable in a point to point configuration of the Gs interface.
  • ITU-T Recommendation Q.704, clause 7:
    • Forced re-routing is not applicable if there is only one signalling route existing between SGSN and VLR in a point to point configuration of the Gs interface.
  • ITU-T Recommendation Q.704, clause 8:
    • Not applicable if there is only one signalling route existing between SGSN and VLR in a point to point configuration of the Gs interface.
  • ITU-T Recommendation Q.704, subclause 13.2:
    • The transfer prohibited function is not applicable if the SGSN or the VLR does not support STP functionality. At the reception of a TFP message, the SGSN or VLR acting as SP shall process the message.
  • ITU-T Recommendation Q.704, subclause 13.3:
    • The transfer allowed function is not applicable if the SGSN or the VLR does not support STP functionality. At the reception of a TFA-message, the SGSN or VLR acting as SP shall process the message.
  • ITU-T Recommendation Q.704, subclause 13.4:
    • The transfer restricted function is not applicable if the SGSN or the VLR does not support STP functionality. At the reception of the TFR message, the SGSN or VLR acting as SP shall process the message.
  • ITU-T Recommendation Q.704, subclause 13.5:
    • The signalling-route-set-test procedure is not applicable.
  • ITU-T Recommendation Q.704, subclauses 13.6, 13.7 and 13.8:
    • The transfer controlled function is not applicable if the SGSN or the VLR does not support STP functionality. At the reception of TFC message, the SGSN or VLR acting as SP shall process the message.
  • ITU-T Recommendation Q.704, subclause 13.9:
    • The signalling route-set-congestion-test function is not required.
    • At the reception of signalling-route-set-congestion-test message no action is required by the receiving entity.
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5.4.1.3  Informative clausesWord‑p. 11

A list of clarifications to ITU-T Recommendation Q.704 are listed below.
  • ITU-T Recommendation Q.704, subclause 2.3.4:
    • The load sharing procedures shall allow any value of the SLC field in the MTP3 network management messages that are not related to a specific signalling link. This allows compatibility between blue book implementations where only the 0000 value is used and white book implementations where load sharing may be applicable to network management messages
  • ITU-T Recommendation Q.704, subclause 3.4.1:
    • It should be noted that for point to point working, the signalling route will become unavailable when the associated link set fails.
  • ITU-T Recommendation Q.704, subclause 3.4.2:
    • It should be noted that for point to point working, the signalling route will become available when the associated link set is restored.
  • ITU-T Recommendation Q.704, subclause 3.5.1:
    • It should be noted that for point to point working the procedures used in connection with signalling route unavailability will be those specified for signalling route set unavailability in ITU-T Recommendation Q.704 subclause 11.2.1.
  • ITU-T Recommendation Q.704, subclause 3.5.2:
    • It should be noted that for point to point interworking the procedures used in connection with signalling route availability will be those specified for signalling route set availability in ITU-T Recommendation Q.704 subclause 11.2.2.
  • ITU-T Recommendation Q.704, clause 9:
    • The SGSN and the MSC/VLR shall implement the restart procedures specified in ITU T Recommendation Q.704 (03/1993) MTP3. The restart procedure specified in ITU T Recommendation Q.704 (11/1988) MTP3 shall not be used.
  • ITU-T Recommendation Q.704, clause 11:
    • It should be noted that for point to point working the signalling route set will consist of one associated signalling route only.
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5.4.2  MTP Level 3 for T1 InterfaceWord‑p. 12

The Gs interface may be configured as a point to point interface or may use an intermediate SS7 network. In this last case an SGSN or a VLR may act always as end points of the Gs interface (SP functionality) or may be configured to act as an transfer point between a VLR and an SGSN (SP and STP functionality). The MTP level 3 exceptions and modifications to ANSI T1.111.4 are listed regarding whether the SGSN and the VLR are connected by a point to point link or are configured to act as SPs in an SS7 network or if they support STP functionality.
Subclause 5.4.2.1 applies to all configurations of the Gs interface. In subclause 5.4.2.2 the exceptions and modifications to ANSI T1.111.4 are listed depending upon the configuration of the Gs interface, whether it is a point to point interface or the SGSN and VLR act as an SP only or SP and STP. Subclause 5.4.2.3 provides points of clarification about the ANSI T1.111.4.
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5.4.2.1  General clauses

The MTP level 3 exceptions and modifications to ANSI T1.111.4 regardless of whether the SGSN supports STP functionality are listed below.
  • ANSI T1.111.4, subclause 2.3.5:
    • Support of ANSI specific Signalling Link Congestion Control as specified in this subclause is required.
  • ANSI T1.111.4, subclause 2.4:
    • The signalling point code for an SGSN may be included in the national signalling point code scheme or in a separate signalling network.
  • ANSI T1.111.4, subclause 3.8.2:
    • Support of ANSI specific Network Congestion as defined in this subclause is required.
  • ANSI T1.111.4, clause 12:
    • Only basic link management procedures are required.
  • ANSI T1.111.4, subclause 14.2.1:
    • Since all messages are passed using the SCCP, the service indicator for Gs interface operation will be:
          bits  D  C  B  A
                0  0  1  1
      
  • ANSI T1.111.4, subclause 14.2.2:
    • The sub service field for Gs interface operation will always be set to one of the following values:
          bits  D  C
                1  0  national network
      
  • ANSI T1.111.4, clause 15:
    • The formats and codes listed are only relevant to the messages that are required.
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5.4.2.2  Configuration dependent clausesWord‑p. 13

The MTP level 3 exceptions and modifications to ANSI T1.111.4 are permitted if the SGSN or the VLR does not support STP functionality are listed below.
  • ANSI T1.111.4, subclause 1.1.2:
    • If the Gs interface is configured as point to point interface, i.e., it does not support STP function, then the signalling transfer point network management features are not required.
  • ANSI T1.111.4, clause 2:
    • If STP function is not required, then the discrimination functions of the MTP used for GPRS application can be significantly simplified.
  • ANSI T1.1114, subclause 2.3:
    • If the implementation of the Gs interface is point to point, load sharing between linksets is not required since there will only be one linkset between SGSN and VLR.
  • ANSI T1.111.4, subclause 2.4:
    • At the SGSN or VLR that does not implement STP functionality, only messages with a correctly checking DPC will be accepted. Other messages will be discarded. It is recommended that when messages are discarded because of an incorrectly set point code, an incident report should be generated.
  • ANSI T1.111.4, subclause 3.1.3 (3):
    • In a point to point configuration, there is no requirement for signalling route management.
  • ANSI T1.111.4, subclause 3.3.2.3:
    • In a point to point configuration, there is no requirement for signalling route management.
  • ANSI T1.111.4, subclause 3.3.3.3:
    • In a point to point configuration, there is no requirement for signalling route management.
  • ANSI T1.111.4, subclause 3.3.4.3:
    • In a point to point configuration, there is no requirement for signalling route management.
  • ANSI T1.111.4, subclause 3.4.3:
    • Not applicable if no STP functionality is implemented in SGSN or VLR.
  • ANSI T1.111.4, subclause 3.5.3:
    • Not applicable if no STP functionality is implemented in SGSN or VLR.
  • ANSI T1.111.4, subclause 3.8.5.2:
    • The signalling-route-set-congestion-test procedure is not required.
  • ANSI T1.111.4, subclause 4.1.2:
    • In a point to point configuration signalling routes are not applicable.
  • ANSI T1.111.4, subclause 4.2:
    • The normal routing situation in a point to point configuration will be that there are 1 or more signalling links available between a SGSN and VLR, these will constitute a link set. They will run in a load sharing mode and changeover, changeback procedures will be supported between these signalling links.
    • The normal routing situation if more then one route is available between the SGSN and the VLR will be that the load sharing, changeover and changeback procedures would be provided between signalling links within the same signalling linkset and between signalling linksets.
  • ANSI T1.111.4, subclause 4.3.3:
    • There will be no alternative linkset in a point to point configuration of the Gs interface.
  • ANSI T1.111.4, subclause 4.4.3:
    • Not applicable in a point to point configuration of the Gs interface.
  • ANSI T1.111.4, subclause 4.5:
    • Not applicable in a point to point configuration of the Gs interface.
  • ANSI T1.111.4, subclause 4.6:
    • Not applicable in a point to point configuration of the Gs interface.
  • ANSI T1.111.4, subclause 4.7:
    • Not applicable in a point to point configuration of the Gs interface.
  • ANSI T1.111.4, clause 5:
    • Changeover between link sets is not applicable in a point to point configuration of the Gs interface.
  • ANSI T1.111.4, clause 6:
    • Changeback between link sets is not applicable in a point to point configuration of the Gs interface.
  • ANSI T1.111.4, clause 7:
    • Forced re-routing is not applicable since there is only one signalling route existing between SGSN and VLR in a point to point configuration of the Gs interface.
  • ANSI T1.111.4 ,clause 8:
    • Not applicable since there is only one signalling route existing between SGSN and VLR in a point to point configuration of the Gs interface.
  • ANSI T1.111.4, subclause 13.2:
    • The transfer prohibited function is not applicable if the SGSN does not support STP functionality. At the reception of a TFP message, the SGSN or VLR acting as SP shall process the message.
  • ANSI T1.111.4, subclause 13.3:
    • The transfer allowed function is not applicable if the SGSN does not support STP functionality. At the reception of a TFA-message, the SGSN or VLR acting as SP shall process the message.
  • ANSI T1.111.4, subclause 13.4:
    • The transfer restricted function is not applicable if the SGSN does not support STP functionality. At the reception of the TFR message the SGSN or VLR acting as SP shall process the message.
  • ANSI T1.111.4, subclause 13.5:
    • The signalling-route-set-test procedure is not applicable.
  • ANSI T1.111.4, subclauses 13.6, 13.7 and 13.8:
    • The transfer controlled function is not applicable if the SGSN does not support STP functionality. At the reception of TFC message, the SGSN or VLR acting as SP shall process the message.
  • ANSI T1.111.4, subclause 13.9:
    • The signalling route-set-congestion-test function is not applicable. At the reception of signalling-route-set-congestion-test message no action is taken by the receiving entity.
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5.4.2.3  Informative clausesWord‑p. 15

A list of clarifications to ANSI Recommendation T1.111.4 are listed below.
  • ANSI T1.111.4, subclause 2.3.4:
    • The load sharing procedures shall allow any value of the SLS field in the MTP3 network management messages that are not related to a specific signalling link or a default value of 00000000 should be used.
  • ANSI T1.111.4, subclause 3.4.1:
    • For point to point working, the signalling route will become unavailable when the associated link set fails.
  • ANSI T1.111.4, subclause 3.4.2:
    • For point to point working, the signalling route will become available when the associated link set is restored.
  • ANSI T1.111.4, subclause 3.5.1:
    • For point to point working, the procedures used in connection with signalling route unavailability will be those specified for signalling route set unavailability in ANSI Recommendation T1.111.4 subclause 11.2.1.
  • ANSI T1.111.4, subclause 3.5.2:
    • For point to point working, the procedures used in connection with signalling route availability will be those specified for signalling route set availability in ANSI Recommendation T1.111.4 subclause 11.2.2.
  • ANSI T1.111.4, clause 9:
    • The SGSN and the MSC/VLR shall implement the restart procedures specified in ANSI T1.111.4.
  • ANSI T1.111.4, clause 11:
    • For point to point working, the signalling route set will consist of one associated signalling route only.
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