19.2.1 General

29.0023GPPMobile Application Part (MAP) specificationRelease 17TS

In this clause, the term "Inter-MSC handover" is used to denote handover or relocation between different MSCs.

The interfaces involved for Inter-MSC handover are shown in figure 19.2/1. There are two Inter-MSC handover procedures:

1) Basic Inter-MSC handover:

The call is handed over from the controlling MSC(MSC—A) to another MSC(MSC—B) (figure 19.2/1a).

Figure 19.2/2 shows the message flow for a successful handover from MSC‑A to MSC—B, including a request for handover number allocation from MSC‑B to VLR‑B.

2) Subsequent Inter-MSC handover:

After the call has been handed over from MSC‑A to MSC‑B, a further handover either to MSC‑A (figure 19.2/1a) or to a third MSC (MSC‑B’) (figure 19.2/1b) may be necessary in order to continue the call.

Figure 19.2/3 shows the message flow for a successful subsequent handover to MSC‑B’. For a successful subsequent handover to MSC‑A, the messages to and from MSC‑B’ and VLR‑B’ are omitted..

a) Basic handover procedure MSC‑A to MSC‑B
and subsequent handover procedure MSC‑B to MSC‑A.

b) Subsequent handover procedure MSC‑B to MSC‑B’.

Figure 19.2/1: Interface structure for handover

1) MAP_PREPARE_HANDOVER_req/ind

2) MAP_ALLOCATE_HANDOVER_NUMBER_req/ind

3) MAP_SEND_HANDOVER_REPORT_req/ind

4) MAP_PREPARE_HANDOVER_rsp/cnf

5) MAP_SEND_HANDOVER_REPORT_rsp/cnf (Note)

6) MAP_PROCESS_ACCESS_SIGNALLING_req/ind

7) MAP_SEND_END_SIGNAL_req/ind

8) MAP_FORWARD_ACCESS_SIGNALLING_req/ind

9) MAP_PROCESS_ACCESS_SIGNALLING_req/ind

10) MAP_SEND_END_SIGNAL_rsp/cnf

NOTE: This can be sent at any time after the connection between MSC‑A and MSC‑B is established.

Figure 19.2/2: Example of a successful basic handover procedure to MSC‑B

1) MAP_PREPARE_HANDOVER_req/ind

2) MAP_ALLOCATE_HANDOVER_NUMBER_req/ind

3) MAP_SEND_HANDOVER_REPORT_req/ind

4) MAP_PREPARE_HANDOVER_rsp/cnf

5) MAP_SEND_HANDOVER_REPORT_rsp/cnf (Note 1)

6) MAP_PROCESS_ACCESS_SIGNALLING_req/ind

7) MAP_SEND_END_SIGNAL_req/ind

8) MAP_PREPARE_SUBSEQUENT_HANDOVER_req/ind

9) MAP_PREPARE_HANDOVER_req/ind

10) MAP_ALLOCATE_HANDOVER_NUMBER_req/ind

11) MAP_SEND_HANDOVER_REPORT_req/ind

12) MAP_PREPARE_HANDOVER_rsp/cnf

13) MAP_SEND_HANDOVER_REPORT_rsp/cnf (Note 2)

14) MAP_PREPARE_SUBSEQUENT_HANDOVER_rsp/cnf

15) MAP_PROCESS_ACCESS_SIGNALLING_req/ind

16) MAP_SEND_END_SIGNAL_req/ind

17) MAP_SEND_END_SIGNAL_rsp/cnf (Note 3)

NOTE 1: This can be sent at any time after the connection between MSC‑A and MSC‑B is established.

NOTE 2: This can be sent at any time after the connection between MSC‑A and MSC‑B’ is established.

NOTE 3: At this stage, the subsequent handover is complete. Any further interworking between MSC‑A and MSC‑B’ is the same as the interworking between MSC‑A and MSC‑B after basic handover

Figure 19.2/3: Example of a successful subsequent handover to a third MSC

The MAP signalling procedures for inter-MSC handover support the allocation of a handover number or one or more relocation numbers and the transfer of encapsulated BSSAP or RANAP messages.

The minimum application context version for the MAP handover application context shall be:

– version 3 for inter-MSC UTRAN to UTRAN handover;

– version 3 for inter-MSC intersystem handover from GSM BSS to UTRAN;

– version 2 for inter-MSC intersystem handover from UTRAN to GSM BSS.

NOTE: If the MAP handover application context version 2 is used, subsequent handover to UTRAN is not possible.

The minimum application context version for the MAP handover application context should be version 2 for inter-MSC handover from GSM BSS to GSM BSS.

NOTE: If the MAP handover application context version 2 or lower is used, subsequent handover to UTRAN is not possible.

The BSSAP or RANAP messages encapsulated in MAP messages are processed by the Handover Control Application in each MSC. The information in the encapsulated BSSAP or RANAP messages is passed from the Handover Control Application to the MAP process at the sending end; the notation used in the SDL diagrams for the MAP processes is "HO_CA_MESSAGE_ind(Message transfer)". The information in the encapsulated BSSAP or RANAP messages is passed from the MAP process to the Handover Control Application at the sending end; the notation used in the SDL diagrams for the MAP processes is "HO_CA_MESSAGE_req(Message transfer)".

For details of the interworking between the A-interface and MAP procedures or the Iu-interface and MAP procedures, see 3GPP TS 23.009 [21] and 3GPP TS 29.010 [58].