The handover/relocation procedures in this functional unit consist of:

1. signalling between the UE/MS and the 3G_MSC;
2. signalling between the RNS/BSS and the 3G_MSC for access management.

The call control procedures related to handover/relocation in 3G_MSC-A can be divided into two functional entities:

• the first entity is the call control procedure as part of the normal interworking between the PSTN/ISDN and the PLMN/UTRAN; for an UE/MS originating call 3G_MSC-A is the originating exchange, for an UE/MS terminating call 3G_MSC-A is the destination exchange;
• the second entity is the call control procedure for the connection between 3G_MSC-A and 3G_MSC-B in case of a handover/relocation from 3G_MSC-A to 3G_MSC-B. For this call control procedure the following applies.

Call set-up:

• the connection to 3G_MSC-B is set up by procedures relevant to the signalling system used in the PSTN/ISDN to which 3G_MSC-A is connected. The call is set up by using the Handover Number received from 3G_MSC-B as part of the MAP procedure;
• the call set-up direction will always be from 3G_MSC-A to 3G_MSC-B, even when the call was originally established by the UE/MS. Functional unit 2 (see Figure 5) should therefore keep information on call set-up direction in order to be able to interpret correctly any clearing signals (see below);
• the unit should indicate the address complete condition to functional unit 3 and through-connect without awaiting the answer signal from 3G_MSC-B. This applies also to signalling systems where address complete signals are not supported. In such cases an artificial address complete is established by functional unit 2.

Call clearing:

• call clearing consists of two parts: after handover/relocation, clearing of the RNS-UE/MS or BSS-UE/MS connection and clearing of the inter-3G_MSC connection. If a request to release the call is generated by the network while the UE/MS is re-tuning from one RNS/BSS to another RNS/BSS, then 3G_MSC-A shall begin clearing the call to the network and queue the call release to the UE/MS until the UE/MS has resumed communication. This includes the case when 3G_MSC-B and/or 3G_MSC-B' are involved;
• the MAP procedures are used to transfer information between 3G_MSC-B and 3G_MSC-A in order to maintain full call control within 3G_MSC-A. 3G_MSC-A determines, based on information received from 3G_MSC-B, the appropriate signals (according to TS 24.008) to be sent to the UE/MS, and sends this information to 3G_MSC-B;
• when 3G_MSC-A clears the call to the UE/MS it also clears the call control functions in 3G_MSC-B and sends the MAP-SEND-END-SIGNAL response to release the MAP resources in 3G_MSC-B. The clearing of the connection is by procedures relevant to the signalling system in the PSTN/ISDN to which 3G_MSC-A is connected;
• when the Signalling System no 7 ISDN User Part is used, the normal symmetric release procedures apply on both the connection to the fixed network and to 3G_MSC-B;
• when a signalling system is used without a symmetric release possibility, some notice should be given to the clear-forward and clear-back procedures;
• for UE/MS terminating calls the following conditions apply on clear-forward and clear-back:
  • when a clear-forward signal is received on interface B' (see Figure 4), 3G_MSC-A clears the circuit to 3G_MSC-B by normal clear-forward procedures;
  • when a clear-back signal is received from 3G_MSC-B, 3G_MSC-A starts normal clear-back procedures towards the fixed network (interface B') and sends the clear-forward signal on interface B'' in order to clear the connection with 3G_MSC-B.
• for UE/MS originated calls the following applies:
  • when 3G_MSC-A receives a clear-back signal from 3G_MSC-B, this signal must be interpreted as indicating a clear-forward condition. 3G_MSC-A then clears both the connection on interface B' (see Figure 4) and to 3G_MSC-B by normal clear-forward procedures;
  • when 3G_MSC-A receives a clear-back signal on interface B', 3G_MSC-A should distinguish between national and international connections:
    • for international connections where the Q.118 [1] supervision is done in the ISC, 3G_MSC-A sends a clear-forward signal on both interface B' to the fixed network and interface B'' to 3G_MSC-B;
    • for national connections or for international connections where the Q.118 [1] supervision is not done in the ISC, a timer is started according to national practice for clear-back supervision and MSC-A proceeds as follows:
      1. if a clear-back signal is received from 3G_MSC-B, 3G_MSC-A interprets this as indicating a clear-forward condition and proceeds by clearing the connections on interface B' and to 3G_MSC-B by normal clear-forward procedures;
      2. if the timer expires, 3G_MSC-A proceeds by normal clear-forward of the connections on interface B' and to 3G_MSC-B.

The procedures of functional unit 3 are given in terms of SDL diagrams in Figure 43. To easily distinguish the interface concerned the messages received or sent from this unit are prefixed with either 'MAP' for a MAP message, 'A' for an A-Interface message, 'I' for an ISDN/PSTN message or 'Iu' for an Iu-message. The procedures of functional unit 3 include:

1. initiation. The initiation condition is shown by the signal Iu-RELOCATION-REQUIRED or A-HANDOVER-REQUIRED;
   The diagram also includes queuing when there is no channel available. Calls for which handover/relocation has been initiated should be queued with priority higher than normal calls. They should have lower priority than emergency calls.
2. handover/relocation of calls within the area controlled by 3G_MSC-A, i.e. handover/relocation case i);
   In the handover/relocation from RNS-A/BSS-A to RNS-B/BSS-B 3G_MSC-A controls the procedures on both the previous and the new radio channel, using signals Iu-RELOCATION-REQUEST/A-HANDOVER-REQUEST and Iu-RELOCATION-COMMAND/A-HANDOVER-COMMAND. The handover/relocation procedure is completed when Iu-RELOCATION-COMPLETE/A-HANDOVER-COMPLETE is received. If this signal is not received (expiry of timer T102, T302, T502 or T702), the radio path and the connection on interface B' are released.
   For handover/relocation devices with three-party capabilities the device is first set up so that all interfaces Iu'/A', Iu''/A'' and B' are connected (illustrated by the signal 'set up handover device'). This is done when the Relocation Command is sent to serving RNS or Handover Command is sent to the serving BSS. The device is connected in its final position (i.e. Iu''/ A'' to B' for case ii)) (illustrated by the signal 'connect handover device') when Iu-RELOCATION-COMPLETE/A-HANDOVER-COMPLETE is received.
3. relocation to 3G_MSC-B. This procedure is the one described in subclauses 8.3.1 and 8.3.2. For handover/relocation devices with three-party capabilities the device is set-up when 3G_MSC-A sends the Relocation Command to the UE, i.e. the interfaces Iu', B' and B'' are then connected. The device is connected in its final position (i.e. B' to B'') when the successful procedure indication is received from functional unit 4;
4. UMTS to GSM handover to MSC-B. This procedure is the one described in subclauses 8.1.1 and 8.1.2. For handover/relocation devices with three-party capabilities the device is set-up when 3G_MSC-A sends the Relocation Command to the serving RNS, i.e. the interfaces Iu', B' and B'' are then connected. The device is connected in its final position (i.e. B' to B'') when the successful procedure indication is received from functional unit 4;
5. GSM to UMTS handover to 3G_MSC-B. This procedure is the one described in subclauses 8.2.1 and 8.2.2. For handover/relocation devices with three-party capabilities the device is set-up when MSC-A sends the Handover Command to the serving BSS , i.e. the interfaces A', B' and B'' are then connected. The device is connected in its final position (i.e. B' to B'') when the successful procedure indication is received from functional unit 4;
6. subsequent relocation from 3G_MSC-B to 3G_MSC-A. The procedure is described in subclauses 8.3.3.1 and 8.3.4.1. When a relocation to 3G_MSC-A indication is received from functional unit 4, the handover/relocation device is set up so that interfaces B', B'' and Iu' are connected (for devices with three-party capabilities). When Iu-RELOCATION-COMPLETE is received, the device is connected in its final position (i.e. B' to Iu');
   If Iu-RELOCATION-COMPLETE is not received (expiry of timer T704), the handover/relocation device releases interface Iu', B' and B''.
7. subsequent GSM to UMTS handover from MSC-B to 3G_MSC-A. The procedure is described in subclauses 8.2.3.1 and 8.2.4.1. When a handover to 3G_MSC-A indication is received from functional unit 4, the handover device is set up so that interfaces B', B'' and A' are connected (for handover devices with three-party capabilities). When Iu-RELOCATION-COMPLETE is received, the device is connected in its final position (i.e. B' to Iu');
   If Iu-RELOCATION-COMPLETE is not received (expiry of timer T504), the device releases interface Iu', B' and B''.
   viii) subsequent UMTS to GSM handover from 3G_MSC-B to MSC-A. The procedure is described in clauses 8.1.3.1 and 8.1.4.1. When a handover to MSC-A indication is received from functional unit 4, the handover device is set up so that interfaces B', B'' and Iu' are connected (for handover devices with three-party capabilities). When A-HANDOVER-COMPLETE is received, the device is connected in its final position (i.e. B' to A');
   If A-HANDOVER-COMPLETE is not received (expiry of timer T304), the device releases interface A', B' and B''.
8. subsequent relocation from 3G_MSC-B to a third 3G_MSC (3G_MSC-B'). The procedure is described in subclauses 8.3.4.2 and 8.3.5.2. The handover/relocation device is set up in its initial position, (i.e. interconnection of interfaces B', B'' and B''') when the connection to 3G_MSC-B' has been established. 3G_MSC-B is informed via functional unit 4 that the connection has been established and that the procedure on the radio path can be initiated. The device is connected in its final position (i.e. B' to B''') when a successful procedure indication is received from functional unit 4. 3G_MSC-B is informed that all procedures in 3G_MSC-B can be terminated (illustrated by the MAP-SEND-END-SIGNAL response). The device returns to the state where B' and B'' are connected if the subsequent relocation procedure fails;
9. subsequent UMTS to GSM handover from 3G_MSC-B to a third MSC (MSC-B'). The procedure is described in subclauses 8.1.3.2 and 8.1.4.2. The handover/relocation device is set up in its initial position, (i.e. interconnection of interfaces B', B'' and B''') when the connection to MSC-B' has been established. 3G_MSC-B is informed via functional unit 4 that the connection has been established and that the procedure on the radio path can be initiated. The device is connected in its final position (i.e. B' to B''') when a successful procedure indication is received from functional unit 4. 3G_MSC-B is informed that all procedures in 3G_MSC-B can be terminated (illustrated by the MAP-SEND-END-SIGNAL response). The device returns to the state where B' and B'' are connected if the subsequent UMTS to GSM handover procedure fails;
10. subsequent GSM to UMTS handover from MSC-B to a third MSC (3G_MSC-B'). The procedure is described in subclauses 8.2.3.2 and 8.2.4.2. The handover/relocation device is set up in its initial position, (i.e. interconnection of interfaces B', B'' and B''') when the connection to 3G_MSC-B' has been established. MSC-B is informed via functional unit 4 that the connection has been established and that the procedure on the radio path can be initiated. The device is connected in its final position (i.e. B' to B''') when a successful procedure indication is received from functional unit 4. MSC-B is informed that all procedures in MSC-B can be terminated (illustrated by the MAP-SEND-END-SIGNAL response). The device returns to the state where B' and B'' are connected if the subsequent GSM to UMTS handover procedure fails.

Timers in 3G_MSC-A The procedures are supervised by timers in order to avoid a deadlock when responses are not received or the procedures fail. The following timers are defined for SRNS Relocation: The following timers are defined for UMTS to GSM handover: The following timers are defined for GSM to UMTS handover:

The MAP procedures for handover/relocation are defined in TS 29.002. They include:

• procedures for basic handover/relocation;
• procedures for subsequent handover/relocation.

These procedures are as outlined in clause 8.

The interworking between the Handover/Relocation control procedures and the MAP procedures for handover/relocation is defined in TS 29.010. It includes:

• interworking at basic handover/relocation initiation;
• interworking at subsequent handover/relocation completion.

This interworking is not described in the present document.

Interworking with the GSM Phase 1 is not supported.

If the 3G_MSC-A initiates a basic inter-MSC UMTS to GSM handover procedure according to MAP and BSSMAP protocols while using a RANAP protocol towards RNS-A, 3G_MSC-A has to perform the protocol interworking between RANAP on the Iu-Interface and encapsulated BSSMAP on the E-interface. The same holds if 3G_MSC-A accepts a subsequent inter-3G_MSC GSM to UMTS handover back to 3G_MSC-A while using a RANAP protocol towards RNS-B.