5 Conformance to message transfer part (MTP)

09.163GPPGeneral Packet Radio Service (GPRS)Gs interface network service specificationServing GPRS Support Node (SGSN) - Visitors Location Register (VLR)TS

5.1 General

The MTP functions as specified in CCITT 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 CCITT recommendations for E1 interface and ANSI recommendation for T1 interface concerning the MTP shall be taken as requirements unless covered by a statement in this Technical Specification.

5.2 MTP Level 1

The MTP level 1 exceptions and modifications to ITU-T Recommendation Q.702 and ANSI T1.111 Recommendation can be found in GSM 08.06 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.

5.3.2 MTP Level 2 for T1 Interface

The MTP level 2 exceptions and modifications to ANSI T1.111.3 Recommendation are listed below.

ANSI Recommendation T1.111.3; subclause 1.4

– Only the basic error correction protocol is required. (section 1.4.3 is not required).

ANSI Recommendation T1.111.3; clause 6

– Not applicable, only basic error correction is required.

ANSI Recommendation 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 Recommendation T1.111.3; clause 8

The processor outage status indicator shall be recognised at the SGSN and the procedures defined in ANSI Recommendation 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.

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.

Section 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. Section 5.4.1.3 provides points of clarification about the ITU-T Recommendation Q.704.

5.4.1.1 General clauses

The MTP level 3 exceptions and modifications to ITU-T Recommendation Q.704 regardless of whether the SGSN supports STP functionality are listed below.

– Q.704 subclause 2.3.5.

– Either of the two methods of congestion control is acceptable. The most appropriate method is dependent on national CCITT No. 7 implementations.

– Q.704 subclause 2.4 Message discrimination

– The signalling point code for an SGSN may be included in the national signalling point code scheme or in a separate signalling network.

– 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.

– Q.704 clause 12 Signalling link management

– Only basic link management procedures are required.

– 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

– 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

– 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.

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.

– Q.704 clause 2

– If STP functionality is not required the discrimination function of the MTP used for GPRS application can be significantly simplified.

NOTE: If the implementation of this interface is for point to point application the routing function within the MTP will be present to select the point code appropriate to the parent VLR.

– Q.704 subclause 2.3 Message routing function

– 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.

– Q.704 subclause 2.4 Message discrimination

– 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.

– Q.704 subclause 3.1.3 c)

– In a point to point configuration there is no requirement for signalling route management.

– Q.704 subclause 3.3.2.3

– In a point to point configuration there is no requirement for signalling route management.

– Q.704 subclause 3.3.3.3

– In a point to point configuration there is no requirement for signalling route management.

– Q.704 subclause 3.3.4.3

– In a point to point configuration there is no requirement for signalling route management.

– Q.704 subclause 3.4.3

– Not applicable if no STP functionality is implemented by the SGSN or the VLR.

– Q.704 subclause 3.5.3

– Not applicable if no STP functionality is implemented by the SGSN or the VLR.

– Q.704 subclause 3.8.5.2

– The signalling-route-set-congestion-test procedure is not required

– Q.704 subclause 4.1.2

– In a point to point configuration signalling routes are not applicable

– 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.

– Q.704 subclause 4.3.3.

– There will be no alternative linkset in a point to point configuration of the Gs interface.

– Q.704 subclause 4.4.3.

– Not applicable in a point to point configuration of the Gs interface.

– Q.704 subclause 4.5.

– Not applicable in a point to point configuration of the Gs interface.

– Q.704 subclause 4.6.

– Not applicable in a point to point configuration of the Gs interface.

– Q.704 subclause 4.7

– Not applicable in a point to point configuration of the Gs interface.

– Q.704 clause 5 Changeover

– Changeover between link sets is not applicable in a point to point configuration of the Gs interface.

– Q.704 clause 6 Changeback

– Changeback between link sets is not applicable in a point to point configuration of the Gs interface.

– 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.

– 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.

– Q.704 subclause 13.2 Transfer prohibited

– 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.

– Q.704 subclause 13.3 Transfer allowed

– 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.

– Q.704 subclause 13.4 Transfer restricted

– 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.

– Q.704 subclause 13.5 Signalling-route-set-test

– The signalling-route-set-test procedure is not applicable.

– Q.704 subclauses 13.6, 13.7, 13.8 Transfer controlled

– 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.

– Q.704 subclause 13.9 Signalling route-set-congestion-test

– 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.

5.4.1.3 Informative clauses

A list of clarifications to ITU-T Recommendation Q.704 are listed below.

– 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

– 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.

– 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.

– 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 CCITT Recommendation Q.704 subclause 11.2.1.

– 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 CCITT Recommendation Q.704 subclause 11.2.2.

– Q.704 clause 9

– The SGSN and the MSC/VLR shall implement the restart procedures specified in ITU‑T Q.704 (03/93) MTP3. The restart procedure specified in ITU‑T Q.704 (11/88) MTP3 shall not be used.

– 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.

5.4.2 MTP Level 3 for T1 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 ANSI Recommendation 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.

Section 5.4.2.1 applies to all configurations of the Gs interface. In subclause 5.4.2.2 the exceptions and modifications to ANSI Recommendation 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. Section 5.4.2.3 provides points of clarification about the ANSI Recommendation T1.111.4.

5.4.2.1 General clauses

The MTP level 3 exceptions and modifications to ANSI Recommendation T1.111.4 regardless of whether the SGSN supports STP functionality are listed below.

T1.111.4 subclause 2.3.5.

– Support of ANSI specific Signalling Link Congestion Control as specified in this subclause is required.

T1.111.4 subclause 2.4 Message discrimination

– The signalling point code for an SGSN may be included in the national signalling point code scheme or in a separate signalling network.

T1.111.4 subclause 3.8.2

– Support of ANSI specific Network Congestion as defined in this subclause is required.

T1.111.4 clause 12 Signalling link management

– Only basic link management procedures are required.

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

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

T1.111.4 clause 15

– The formats and codes listed are only relevant to the messages that are required.

5.4.2.2 Configuration dependent clauses

The MTP level 3 exceptions and modifications to ANSI Recommendation T1.111.4 are permitted if the SGSN or the VLR does not support STP functionality are listed below.

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.

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.

NOTE: If the implementation of this interface is for point to point application the routing function within the MTP will be present to select the point code appropriate to the parent VLR.

T1.1114. subclause 2.3 Message routing function

– 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.

T1.111.4 subclause 2.4 Message discrimination

– 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.

T1.111.4 subclause 3.1.3 (3)

– In a point to point configuration, there is no requirement for signalling route management.

T1.111.4 subclause 3.3.2.3

– In a point to point configuration, there is no requirement for signalling route management.

T1.111.4 subclause 3.3.3.3

– In a point to point configuration, there is no requirement for signalling route management.

T1.111.4 subclause 3.3.4.3

– In a point to point configuration, there is no requirement for signalling route management.

T1.111.4 subclause 3.4.3

– Not applicable if no STP functionality is implemented in SGSN or VLR.

T1.111.4 subclause 3.5.3

– Not applicable if no STP functionality is implemented in SGSN or VLR.

T1.111.4 subclause 3.8.5.2

– The signalling-route-set-congestion-test procedure is not required

T1.111.4 subclause 4.1.2

– In a point to point configuration signalling routes are not applicable

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.

T1.111.4 subclause 4.3.3.

– There will be no alternative linkset in a point to point configuration of the Gs interface.

T1.111.4 subclause 4.4.3.

– Not applicable in a point to point configuration of the Gs interface.

T1.111.4 subclause 4.5.

– Not applicable in a point to point configuration of the Gs interface.

T1.111.4 subclause 4.6.

– Not applicable in a point to point configuration of the Gs interface.

T1.111.4 subclause 4.7

– Not applicable in a point to point configuration of the Gs interface.

T1.111.4 clause 5 Changeover

– Changeover between link sets is not applicable in a point to point configuration of the Gs interface.

T1.111.4 clause 6 Changeback

– Changeback between link sets is not applicable in a point to point configuration of the Gs interface.

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.

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.

T1.111.4 subclause 13.2 Transfer prohibited

– 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.

T1.111.4 subclause 13.3 Transfer allowed

– 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.

T1.111.4 subclause 13.4 Transfer restricted

– 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.

T1.111.4 subclause 13.5 Signalling-route-set-test

– The signalling-route-set-test procedure is not applicable.

T1.111.4 subclauses 13.6, 13.7, 13.8 Transfer controlled

– 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.

  • T1.111.4 subclause 13.9 Signalling route-set-congestion-test

– 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.

5.4.2.3 Informative clauses

A list of clarifications to ANSI Recommendation T1.111.4 are listed below.

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.

T1.111.4 subclause 3.4.1

– For point to point working, the signalling route will become unavailable when the associated link set fails.

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.

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.

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.

T1.111.4 clause 9

– The SGSN and the MSC/VLR shall implement the restart procedures specified in ANSI T1.111.4.

T1.111.4 clause 11

– For point to point working, the signalling route set will consist of one associated signalling route only.