3 Message transfer part (MTP) functions

08.063GPPRelease 1999Signalling transport mechanism Specification for the Base Station System - Mobile Services Switching Centre (BSS - MSC) interfaceTS

3.1 General

For E1 links, the MTP functions as specified in CCITT Recommendations Q.702, Q.703, Q.704 and Q.707 are applicable. For T1 links, the MTP functions as specified in ANSI specifications T1.110 section 2, and T1.112 clause 2 are applicable. However, the following exceptions and modifications to those Recommendations may be applied for the MSC to BSS signalling, see clauses 3.2 to 3.4.

Some form of policing could be included at the MSC in order to ensure that no signalling messages received from the BSS can be routed further than the MSC if an administration requires. This is necessary to prevent fraudulent use of the signalling network for implementations of the GSM system. The manner in which this is achieved will be dependent on local agreements or regulation s and system implementations.

Where load sharing is used, all messages to do with a given SCCP connection should be passed down a given link.

3.2 Level 1

3.2.1 E1 link (CCITT Recommendation Q.702)

Q.702 figure 2

These figures should be treated as for information only. For the standard application of GSM, interface point C is appropriate.

Q.702 clause 1.4

The use of analogue circuits to support the signalling link is a national matter.

Q.702 clause 2

A signalling rate of 64kbits/s is assumed. Lower rates (e.g. using analogue bearers) are a national concern.

Q.702 clause 3

Error characteristics and availability are a national concern. Care should be taken as excessive errors could lead to inefficient use of the signalling links.

Q.702 clause 5

The standard arrangement will be to derive the signalling link from a 2048 kbits/s digital path.

Q.702 clause 6

Only digital signalling data links are relevant.

The use of analogue bearers to support this interface is considered a national concern. However it should be noted that there will be potential problems with the following areas:

– the signalling load may exceed that which can be carried by a single low rate analogue link, this may lead to an excessive number of signalling links and more complex changeover/changeback procedures;

– the performance of the analogue lines used to carry the signalling link will have a major impact on the throughput of signalling information that can be achieved;

– message delay may degrade the quality of service.

3.2.2 T1 link (ANSI Specification T1.111.2)

T1.111.2 Figure 2

These figures should be treated as for information only. For the standard application, interface point C is appropriate.

T1.111.2 Clause 1.4 Analogue Signalling Link

The use of analogue circuits to support the signalling link is a service provider option.

T1.111.2 Clause 2 General

A signalling rate of 56/64 kbits/s is assumed. Lower bit rates (e.g. using analogue bearers) are a service provider option.

T1.111.2 Clause 3 Error Characteristics and Availability

Error characteristics and availability are an operator concern. Care should be taken as excessive errors could lead to inefficient use of the signalling link.

T1.111.2 Clause 5 Digital Signalling Data Link

The standard arrangement will be to derive a signalling link from a 1544 kbits/s digital path.

T1.111.2 Clause 6 Analogue Signalling Data Link

Only digital signalling data links are required.

The use of Analogue bearers to support this interface is considered a service provider option. However, it should be noted that there will be potential problems with the following areas:

– the signalling load may exceed that which can be carried by a single low rate Analogue link, which may lead to an excessive number of signalling links and more complex changeover/change back procedures;

– the performance of the Analogue lines used to carry the signalling link will have a major impact on the throughput of signalling information that can be achieved;

– message delay may degrade the quality of service.

3.3 Level 2

3.3.1 E1 link (CCITT Recommendation Q.703)

Q.703 clause 1.4

Only the basic error correction protocol is required.

Q.703 clause 1.7

Only the emergency proving period and status indications should be used by the BSS.

Q.703 clause 6

Not applicable, only basic error correction is required.

Q.703 clause 7

In the initial alignment procedure specified in CCITT Recommendation Q.703, only the emergency proving is applicable for the BSS. Thus, in states 02 and 03 of the initial alignment procedure status indication "N" is not sent from the BSS. The BSS should be capable of recognising status indication "N" if received in order for the alignment procedure to complete.

Q.703 clause 8

The processor outage status indicator shall be recognised at the BSS and the procedures defined in CCITT Recommendation Q.703 clause 8 supported.

The BSS shall support the generation of the processor outage indication towards the MSC if this is appropriate.

Q.703 clause 10

Only the emergency alignment procedures are required.

3.3.2 T1 link (ANSI Specification T1.111.3)

T1.111.3 Clause 1.4 Signal Unit Error Correction

Only the basic error correction protocol is required.

T1.111..3 Clause 1.7

Only the emergency proving period and status indications should be used by the BSS.

T1.111.3 Clause 6 Preventive Cyclic Retransmission Error Correction Method

Only basic error correction is required for the A-Interface.

T1.111.3 Clause 7 Signalling Link Initial Alignment Procedure

In the initial alignment procedure, only the emergency proving is required for the BSS. Thus, in states 02 and 03 of the initial alignment procedure status indication "N" is not sent from the BSS. The BSS should be capable of recognizing status indication "N" if received in order for the alignment procedure to complete.

T1.113 Clause 8

The processor outage status indicator shall be recognised at the BSS and the procedures defined in ANSI standards T1.113 clause 8 supported.

The BSS shall support the generation of the processor outage indication towards the MSC if this is appropriate.

T1.113 Clause 10

Only the emergency alignment procedures are required.

3.4 Level 3

3.4.1 E1 link (CCITT Recommendation Q.704)

Q.704 clause 1.1.2.

If the BSS is only implemented as the end point of a signalling link, IE it does not support STP working, then there will be no signalling transfer point network management features which need to be considered.

Q.704 clause 1.3

Signalling link management is required. Load sharing is required, and changeover/back between links within a single linkset are required.

Q.704 clause 2

Since STP working is not required the discrimination and routing functions of the MTP used for GSM application can be significantly simplified.

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

Q.704 clause 2.2 Routing label

Load sharing will be performed on BSS s with more than one signalling link by means of the signalling link selection field (SLS).

Q.704 clause 2.3 Message routing function

Load sharing between linksets is not required since there will only be one linkset between BSS and MSC.

Q.704 clause 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 clause 2.4 Message discrimination

At the BSS 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.

At an MSC (which has the capability of acting as an STP) an administration may decide that each message received from a BSS signalling link is passed through a "screening function" that checks that the DPC of the message is the same as the SP code of the exchange. If that is the case, the message is sent to the normal MTP message handling functions. Otherwise, the message is discarded and an incident report is made.

The signalling point code for an BSS may be included in the national signalling point code scheme or in a separate signalling network. In the case where the signalling point code is in the national network the MSC need have only one point code, in the case where the signalling point code is in a separate "PLMN" signalling network, the MSC will be required to have two signalling point codes, one for each network.

Q.704 clause 3.1.3 c)

There is no requirement for signalling route management.

Q.704 clause 3.3.1.3

There is no requirement for signalling route management.

Q.704 clause 3.3.2.3

There is no requirement for signalling route management.

Q.704 clause 3.3.3.3

There is no requirement for signalling route management.

Q.704 clause 3.3.4.3

There is no requirement for signalling route management.

Q.704 clause 3.3.5.2

There is no requirement for signalling route management or signalling link blocking initiated by a management system.

Q.704 clause 3.3.6.2

There is no requirement for signalling route management or signalling link unblocking initiated by a management system.

Q.704 clause 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 clause 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 clause 3.4.3

Not applicable.

Q.704 clause 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 clause 10.2.1.

Q.704 clause 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 clause 10.2.2.

Q.704 clause 3.5.3

Not applicable.

Q.704 clause 3.8.2

There are two acceptable methods of congestion control defined in CCITT Recommendation Q.704, in clauses 3.6.2.1 a) and b). The most appropriate method is dependent on national CCITT No. 7 implementations. Each administration should specify its congestion threshold setting algorithm and nodal congestion abatement procedures at system procurement.

Q.704 clause 3.8.5.2

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

Q.704 clause 4.1.2

Signalling routes are not applicable.

Q.704 clause 4.2

The normal routing situation will be that there are 1 or more signalling links available between a BSS and MSC, 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.

Q.704 clause 4.3.3.

There will be no alternative linkset.

Q.704 clause 4.4.3.

Not applicable.

Q.704 clause 4.5.

Not applicable.

Q.704 clause 4.6.

Not applicable.

Q.704 clause 4.7

Not applicable.

Q.704 clause 5 Changeover

Changeover between link sets is not applicable.

Q.704 clause 6 Changeback

Changeback between link sets is not applicable.

Q.704 clause 7

Forced re-routing is not applicable since there is only one signalling route existing between BSS and MSC.

Q.704 clause 8

Not applicable since there is only one signalling route existing between BSS and MSC.

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.

Q.704 clause 12 Signalling link management

Only basic link management procedures are applicable.

Q.704 clause 12.3.4 Link set activation

Link set normal activation defined in clause 11.2.4.1 is not applicable. Link set emergency restart at the BSS is used in all cases.

Q.704 clause 13.2 Transfer prohibited

The transfer prohibited function is not applicable. At the reception of a TFP message, no action should be taken at the BSS.

Q.704 clause 13.3 Transfer allowed

The transfer allowed function is not applicable. At the reception of a TFA-message, no action should be taken at the BSS.

Q.704 clause 13.4 Transfer restricted

The transfer restricted function is not applicable. At the reception of the TFR message no action is taken by the BSS.

Q.704 clause 13.5 Signalling-route-set-test

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

Q.704 clauses 13.6, 13.7, 13.8 Transfer controlled

The transfer controlled function is not applicable. At the reception of TFC message, no action is taken by BSS.

Q.704 clause 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 BSS.

Q.704 clause 14.2.1

Since all messages are passed using the SCCP, the service indicator will be:

bits

D

C

B

A

0

0

1

1

Q.704 clause 14.2.2

The sub service field will always be set to one of the following values:

bits D C

1 0 national network

1 1 local network

Q.704 clause 14.3

This information for SCCP is defined in CCITT Recommendation Q.713.

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.

3.4.2 T1 link (ANSI Specification T1.111.4)

T1.111.4 Clause 1.1.2

Signalling Transfer Point network management procedures are not required on the A-Interface.

T1.111.4 Clause 1.3

Signalling link management is required. Load sharing is required, and changeover/back between links within a single linkset are required.

T1.111.4 Clause 2 Signalling Message Handling

Since STP functionality is not required the discrimination and routing functions of the MTP can be significantly simplified.

NOTE: Since the intent of this interface is point to point routing, the routing function within the MTP will be preset to select the point code appropriate to the parent MSC.

T1.111.4 Clause 2.2 Routing Label

Load sharing will be performed on BSSs with more than one signalling link by means of the Signalling Link Selection (SLS) field.

T1.111.4 Clause 2.3 Message Routing Function

Load sharing between linksets is not required since only one linkset between the BSS and the MSC is required for the A-Interface.

T1.111.4 Clause 2.4 Message Discrimination

It is recommended that discarding a message because of an incorrectly set point code should cause an incident report to be generated.

At a MSC the service provider may decide that each message received from an BSS signalling link is passed through a "screening function" that checks that the DPC of the message is the same as the SP code of the exchange. If that is the case, the message is sent to the normal message handling function. Otherwise, the message is discarded and an incident report is generated.

The signalling point code for an BSS may be included in the national signalling point code scheme or in a separate signalling network. In the case where the signalling point code is in the national network the MSC need have only one point code, in the case where signalling point code is in a separate PLMN signalling network, the MSC will be required to have two signalling point codes, one for each network.

The User Part Unavailable message is not required for the A-Interface.

T1.111.4 Clause 2.3.5.

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

T1.111.4 Clause 3 Signalling Network Management

Since the A-Interface utilizes point to point signalling between the BSS and the MSC, Signalling Route Management, including the status of signalling routes, signalling route restricted, signalling route unavailability and availability, is not required.

T1.111.4 Clause 3.1.3 c)

There is no requirement for signalling route management.

T1.111.4 Clause 3.3.1.3

There is no requirement for signalling route management.

T1.111.4 Clause 3.3.2.3

There is no requirement for signalling route management.

T1.111.4 Clause 3.3.3.3

There is no requirement for signalling route management.

T1.111.4 Clause 3.3.4.3

There is no requirement for signalling route management.

T1.111.4 Clause 3.3.5.2

There is no requirement for signalling route management or signalling link blocking initiated by a management system.

T1.111.4 Clause 3.3.6.2

There is no requirement for signalling route management or signalling link unblocking initiated by a management system.

T1.111.4 Clause 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.

T1.111.4 Clause 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.

T1.111.4 Clause 3.4.3

Not applicable.

T1.111.4 Clause 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 ANSI standard T1.111.4 clause 10.2.1.

T1.111.4 Clause 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 ANSI standard T1.111.4 clause 10.2.2.

T1.111.4 Clause 3.5.3

Not applicable.

T1.111.4 Clause 3.8.2

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

T1.111.4 Clause 3.8.5.2

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

T1.111.4 Clause 4 Signalling Traffic Management

Since the A-Interface utilizes point to point signalling between the BSS and the MSC, the Traffic Management procedures supporting signalling routes, including signalling route restricted, signalling route unavailability and availability, are not required.

T1.111.4 Clause 4.1.2

Signalling routes are not applicable.

T1.111.4 Clause 4.2

The normal routing situation will be that there are one or more signalling links available between the BSS and the MSC, which will constitute a link set. They will be run in a load sharing mode and changeover, change back procedures will be supported between these signalling links.

T1.111.4 Clause 4.3.3

Alternative linksets are not required for the A-Interface.

T1.111.4 Clause 4.4.3

Not Applicable,

T1.111.4 Clause 4.5

Not Applicable,

T1.111.4 Clause 4.6

Not Applicable,

T1.111.4 Clause 4.7

Not Applicable,

T1.111.4 Clause 5 Changeover

The changeover procedure between linksets is not applicable for the A-Interface.

T1.111.4 Clause 6 Changeback

The changeback procedure between linksets is not applicable for the A-Interface.

T1.111.4 Clause 7 Forced Rerouting

Forced rerouting is not applicable for the A-Interface.

T1.111.4 Clause 8 Controlled Rerouting

Controlled rerouting is not applicable for the A-Interface.

T1.111.4 Clause 9. MTP Restart

The MTP Restart procedure is not required for the A-Interface.

T1.111.4 Clause 11 Signalling Traffic Flow Control

The signalling route procedures supporting signalling traffic flow control including signalling-route-unavailability, signalling-route availability and signalling-route-set-congestion are not applicable for the A-Interface.

T1.111.4 Clause 12 Signalling Link Management

Only basic link management procedures are required for the A-Interface.

T1.111.4 Clause 12.3.4 Link set activation

Link set normal activation is not applicable. Link set emergency restart at the BSS is used in all cases.

T1.111.4 Clause 13 Signalling Route Management

Signalling route management is not applicable for the A-Interface since it is a point to point connection. No action is required upon reception of a TFP, TFR, TFA, signalling-route-set-test, signalling-route-set-congestion-test or transfer controlled message.

T1.111.4 Clause 13.3 Transfer allowed

The transfer allowed function is not applicable. At the reception of a TFA-message, no action should be taken at the BSS.

T1.111.4 Clause 13.4 Transfer restricted

The transfer restricted function is not applicable. At the reception of the TFR message no action is taken by the BSS.

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

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

T1.111.4 Clauses 13.6, 13.7, 13.8 Transfer controlled

The transfer controlled function is not applicable. At the reception of TFC message, no action is taken by BSS.

T1.111.4 Clause 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 BSS.

T1.111.4 Clause 14.2.1 Service Indicator

The values for the service indicator shall conform to section 14.2.1

T1.111.4 Clause 14.2.2

The sub-service field will always be set to one of the following values:

bits DC

1 0 national network

1 1 local network

NOTE: local network value is not used for PCS 1900 in North America.

T1.111.4 Clause 14.3

This information for SCCP is defined in ANSI T1.112.3.

T1.111.4 Clause 15

The formats and codes listed are only relevant to the messages that are required for the A-Interface,i.e. those not excluded in the rest of this recommendation.

3.5 Testing and Maintenance

3.5.1 E1 link (CCITT Recommendation Q.707)

Q.707 clause 2.2

The MSC and the BSS shall be capable of responding with an acknowledgement message to a SLTM received at any time as specified in CCITT Recommendation Q.707 clause 2.2.

3.5.2 T1 link (ANSI Specification T1.111.7)

T1.111.7 clause 2.1 Signalling Data Link Test

The signalling data link test is not required for the A-Interface.

T1.111.7 clause 2.2

The generation of a SLTM is not required; however, the MSC and the BSS shall be capable of responding with an acknowledgement message to a SLTM that is received at any time as specified in T1.111.7, clause 2.2.