5 SCCP functions

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

5.1 Overview

The purpose of this section is to identify the subset of the SCCP functions which are necessary to achieve the management of the MS references in the BSS to MSC interface, and to provide addressing facilities. If this subset of SCCP functions is implemented, compatibility with a full CCITT SCCP (ANSI SCCP if T1 links are used) must be maintained for E1 links (T1 links). Only the needs of the BSSAP are taken into account in clause 5: the operations and maintenance requirements about SCCP functions are discussed in clause 7.

These simplifications are applicable to the signalling between BSS and MSC in GSM PLMNs.

In order to limit the complexity of the procedures, a BSS exchanges signalling messages only with its MSC, where a protocol conversion may be needed in some cases. Therefore no SCCP translation function is required in the MSC between the national and the local MTP. The Destination Point Code and Subsystem Number allow direct routing by the local SCCP and MTP within the MSC area. Therefore, no SCCP Global Title Translation (GTT) function is required.

Several functions of the SCCP are not used on the MSC/BSS interface: error detection, receipt confirmation, flow control.

The segmenting/reassembling function shall be used if the total message length exceeds the maximum allowed message length that can be carried by the MTP.

For E1 links, the minimum set of SCCP functions which apply are specified in the Blue Book CCITT Recommendations Q.711, Q.712, Q.713 and Q.714, with the qualifications specified in this Recommendation.

For T1 links, the minimum set of SCCP functions which apply are specified in ANSI T1.112 with the qualifications specified in this Recommendation.

5.2 Primitives

5.2.1 E1 link (CCITT Recommendation Q.711)

Q.711/Table 1

Three primitives of the table 1/Q.711 are not used:

– N-EXPEDITED DATA;

– N-DATA ACKNOWLEDGE;

– N-RESET.

Q.711/Table 2

The following parameters of the N-CONNECT primitive are not used:

– responding address;

– receipt confirmation selection;

– expedited data selection.

Q.711/Table 3

The following parameter of the N-DATA primitive is not used:

– confirmation request.

Q.711/Table 6

The following parameter of the N-DISCONNECT primitive is not used:

– responding address.

Q.711 clause 2.1.2

Permanent signalling connections: not applicable.

Q.711/Table 9

The primitive N-NOTICE is not used.

Q.711/Table 10

The following parameter of the N-UNITDATA is not used:

– return option.

Q.711 clause 4.1.2

Functions for permanent signalling connections: not applicable.

5.2.2 T1 link (ANSI SpecificationT1.112.1)

T1.111.1 Table 1

Two primitives of the table are not used:

– N-INFORM DATA;

– N-RESET.

T1.112.1 Table 2

The following parameters of the N-CONNECT primitive are not used:

– responding address;

– receipt confirmation selection;

– expedited data selection.

T1.112.1 Table 3

The following parameter of the N-DATA primitive is not used:

– confirmation request.

T1.112.1 Table 6

The following parameter of the N-DISCONNECT primitive is not used:

– responding address.

T1.112.1 Paragraph 2.1.2

Permanent signalling connections are not applicable.

T1.112.1 Table 8

The primitive N-NOTICE is not used.

T1.112.1 Table 8A

The following parameter of the N-UNITDATA is not used:

– return option.

T1.112.1 Paragraph 4.1.2

Functions for permanent signalling connections are not applicable.

5.3 SCCP messages

5.3.1 E1 link (CCITT Recommendation Q.712)

Q.712 clause 1.4

The Data Acknowledgement (AK) message is not used.

Q.712 clause 1.6

The Data Form 2 (DT2) message is not used.

Q.712 clause 1.7

The Expedited Data (ED) message is not used.

Q.712 clause 1.8

The Expedited Data Acknowledgement (EA) message is not used.

Q.712 clause 1.10

The Protocol Data Unit Error (ERR) message is not used: the inconsistent messages of the SCCP protocol are discarded.

Q.712 clause 1.13

The Reset Confirm (RSC) message is not used.

Q.712 clause 1.14

The Reset Request (RSR) message is not used.

Q.712 clause 1.16

The Subsystem-Out-Of-Service-Grant (SOG) message is not used.

Q.712 clause 1.17

The Subsystem-Out-Of-Service-Request (SOR) message is not used.

Q.712 clause 1.21

The Unitdata Service (UDTS) message is not used.

Q.712 clause 2.4

The "credit" parameter field is not used for protocol class 2. However the parameter must still be included in the IT message for syntax reasons.

Q.712 clause 2.7

The "error cause" parameter field is not used.

Q.712 clause 2.11

The "receive sequence number" parameter is not used.

Q.712 clause 2.14

The "reset cause" parameter field should not be used.

Q.712 clause 2.16

The "sequencing/segmenting" parameter field is not used for protocol class 2. However the parameter must still be included in the IT message for syntax reasons.

5.3.2 T1 link (ANSI Specification T1.112.2)

T1.112.2 clause 2.4

The Data Acknowledgement (AK) message is not used.

T1.112.2 clause 2.6

The Data Form 2 (DT2) message is not used.

T1.112.2 clause 2.7

The Expedited Data (ED) message is not used.

T1.112.2 clause 2.8

The Expedited Data Acknowledgement (EA) message is not used.

T1.112.2 clause 2.10

The Protocol Data Unit Error (ERR) message is not used. Inconsistent messages of the SCCP protocol are discarded.

T1.112.2 clause 2.13

The Reset Confirm (RSC) message is not used.

T1.112.2 clause 2.14

The Reset Request (RSR) message is not used.

T1.112.2 clause 2.16

The Unitdata Service (UDTS) message is not used.

T1.112.2 clause 3.4

The Subsystem-Out-Of-Service-Request (SOR) message is not used.

T1.112.2 clause 3.5

The Subsystem-Out-Of-Service-Grant (SOG) message is not used.

T1.112.2 clause 4.2

The "credit" parameter field is not used for protocol class 2. However, the parameter must still be included in the Inactivity Test (IT) message for syntax reasons.

T1.112.2 clause 4.6

The "error cause" parameter field is not used.

T1.112.2 clause 4.10

The "receive sequence number" parameter is not used.

T1.112.2 clause 4.13

The "reset cause" parameter field should not be used.

T1.112.2 clause 4.16

The "sequencing/segmenting" parameter field is not used for protocol class 2. However, the parameter must still be included in the IT message for syntax reasons.

5.4 SCCP formats and codes

5.4.1 E1 link (CCITT Recommendation Q.713)

Q.713 clause 3.4

For point-to-point network structures (i.e. direct connections between MSC and BSS) the called party address may consist of the single element:

– sub-system number.

No global title is used. The signalling point code which is coded in the MTP routing label and the subsystem number in the called party address allow the routing of the message.

Then the following encoding of the address indicator may be chosen: X1000010.

If a non point-to-point network structure is used then the global title may be required. This is a national concern.

Q.713 clause 3.4.2.2

The SSN values used on the MSC – BSS interface are specified in 3GPP TS 03.03

Use of alternative values is a national concern.

Q.713 clause 3.4.2.3

Global title: refer to CCITT Recommendation Q.713 clause 3.4.

Q.713 clause 3.6

Protocol class: the classes 1 and 3 are not used.

Q.713 clauses 3.8, 3.9, 3.10, 3.13, 3.14

Parameters not used.

Q.713 clauses 4.8, 4.9, 4.11, 4.12, 4.13, 4.14, 4.15, 4.16

Messages not used.

Q.713 clause 5.1.1

SOR and SOG not needed.

5.4.2 T1 link (ANSI Specification T1.112.3)

T1.112.3 Paragraph 3.4

For point-to-point network structures (i.e., direct connections between the MSC and the BSS) the called party address may consist of the single element:

– subsystem number.

No global title is used. The signalling point code which is coded in the MTP routing label and the subsystem number in the called party address allow the routing of the message. Then the following encoding of the address indicator may be chosen: X1000001.

Separate SSNs are needed to distinguish BSSAP and MAP; the chosen SSNs are network specific and may need to differ from those assigned to other applications (e.g. TCAP applications).

T1.112.3 clause 3.4.2.2

Allocation of the subsystem number is an operator concern.

T1.112.3 clause 3.4.2.3

T1.112.3 clause 3.4

T1.112.3 clause 3.6

Protocol class: the classes 1 and 3 are not used.

T1.112.3 clauses 3.8, 3.9, 3.10, 3.13, 3.14

Parameters are not used

T1.112.3 clauses 4.8, 4.9, 4.11, 4.12, 4.13, 4.14, 4.15, 4.16

Messages are not used

T1.112.3 clause 5.1.1

Subsystem-out-of-service-request (SOR) and Subsystem-out-of-service-grant (SOG) are not needed.

5.5 SCCP procedures

5.5.1 E1 link (CCITT Recommendation Q.714)

Q.714 clauses 1.1.2.2 and 1.1.2.4

Protocol classes 1 and 3 not used.

Q.714 clause 1.1.3

A signalling connection consists of a single connection section. No intermediate nodes are defined in the MSC/BSS protocol.

The use of multiple connection sections is a national concern.

Q.714 clause 1.2.1 (b)

Not applicable for single connections.

Q.714 clause 2.1 (1.)

Global title not used for single connections.

Q.714 clause 2.2.1

Subsystem (SSN) only is present in the called party address for single connections.

Q.714 clause 2.2.2

The addressing information may take the following form in the N-CONNECT request primitive: DPC+SSN (for single connections).

Q.714 clause 2.2.2.2

No SCCP translation function is required for single connections.

Q.714 clause 2.3.1 (3)

Not applicable for single connections.

Q.714 clause 2.3.2 (4)

Not applicable for single connections.

Q.714 clause 3.1.3

Not applicable: no protocol class and flow control negotiations.

Q.714 clause 3.1.5

Not applicable.

Q.714 clause 3.2.2

Not applicable.

Q.714 clause 3.3.4

Not applicable.

Q.714 clause 3.5.1.2

Not applicable.

Q.714 clause 3.5.2

Not applicable.

Q.714 clauses 3.6, 3.7, 3.9, 3.10

Not applicable.

Q.714 clause 4.2

Message return not applicable.

Q.714 clause 5

Only those messages and procedures relating to non-replicated subsystems or nodes are required. At the BSS the concerned point will be the parent MSC. The subsystems involved are the BSSAP and the OMAP.

5.5.2 T1 link (ANSI Specification T1.112.4)

T1.112.4 clauses 1.1.2.2, 1.1.2.4

Protocol classes 1 and 3 are not used.

T1.112.4 clause 1.1.3

A signalling connection consists of a single connection section. No intermediate nodes are defined in the MSC to BSS interface.

The use of multiple connection sections is a operator option.

T1.112.4 clause 1.2.1 (b)

Not applicable for single connections.

T1.112.4 clause 2.1 (1.)

Global title is not used for single connections.

T1.112.4 clause 2.2.1

Subsystem number (SSN) only is present in the called party address for single connections.

T1.112.4 clause 2.2.2

The addressing information may take the following form in the N-CONNECT request primitive: DPC+SSN (for single connections).

T1.112.4 clause 2.2.2.2

No SCCP translation function is required for single connections.

T1.112.4 clause 2.3.1 (3)

Not applicable for single connections.

T1.112.4 clause 2.3.2 (4)

Not applicable for single connections.

T1.112.4 clause 3.1.3

Not applicable. No protocol class and flow control negotiations.

T1.112.4 clause 3.1.5

Not applicable.

T1.112.4 clause 3.2.2

Not applicable.

T1.112.4 clause 3.3.4

Not applicable.

T1.112.4 clause 3.5.1.2

Not applicable.

T1.112.4 clause 3.5.2

Not applicable.

T1.112.4 clauses 3.6, 3.7, 3.9, 3.10

Not applicable.

T1.112.4 clause 4.2

Message return is not applicable.

T1.112.4 clause 5

Only those messages and procedures relating to non-replicated subsystems or nodes are required. At the BSS the concerned point will be the parent MSC. The subsystems involved are the BSSAP and the MAP.