13.6.2 Call Hold after Answer, LCLS established

23.2843GPPLocal Call Local Switch (LCLS)Release 17Stage 2TS

13.6.2.1 Hold Request

When the UE makes a request for the hold function for the locally switched call the MSC server shall request a LCLS break procedure described in clause 7.2.1.

The MSC server shall request the MGW to interrupt the communication on the bearer by changing the through-connection of the bearer termination towards the served mobile subscriber to "inactive" or by using the Isolate Bearer Termination Procedure.

If an announcement is to be applied to the held party the MSC shall apply the procedure for non LCLS call defined in 3GPP TS 23.205 [2] clause 14.6 for BICC based CS Core Network and in 3GPP TS 23.231 [3] clause 14.6 for SIP-I based CS Core Network.

If a handover occurs to the UE making the request for the hold function (UE-A) while the party is not intended to be re-connected locally then the MSC Server shall include LCLS-Connection-Status-Control set to "do not establish LCLS" in the HO Request message.

13.6.2.2 Retrieval Request

When the UE makes a request to retrieve a held call the MSC server shall stop an announcement that was applied to the held party. The MSC shall request the MGW to re-establish communication to the held party by changing the through-connection of the bearer termination towards the served mobile subscriber to be both-way through-connected or by using the Join Bearer Termination Procedure.

If the call has been successfully negotiated for LCLS and an LCLS break was triggered by the CN the MSC server shall perform a LCLS re-establishment as described in clause 7.3.1.

NOTE: LCLS re-negotiation can occur while the call is on hold or the held call is connected to a new party (ECT) which may change the LCLS configuration and thus permit or prevent LCLS.

13.6.2.3 Example

13.6.2.3.1 Connection Model

Figure 13.6.2.3.1.1 shows the network model for Call Hold supplementary service when LCLS was established. The MSC-B server seizes one context with two bearer terminations in the MGW-B. The bearer termination T1 is used for the bearer towards the BSS-B and the bearer termination T2 is used for the bearer towards the iMSC selected iMGW. The iMSC server seizes one context with two bearer terminations in the iMGW. The bearer termination T4 is used for the bearer towards the MSC-A server selected MGW-A and the bearer termination T3 is used for the bearer towards the preceding MGW-B. The MSC-A server seizes one context with two bearer terminations in the MGW-A. The bearer termination T5 is used for the bearer towards the iMSC selected iMGW and bearer termination T6 is used for the bearer towards the BSS-A.

Connection Model 1: Before Call Hold, LCLS established and

Connection Model 3: After Retrieval procedure, LCLS established

Connection Model 2: After Hold procedure, LCLS released; Announcement towards held party

Figure 13.6.2.3.1.1: Connection Model for Call Hold

13.6.2.3.2 Basic Sequence

Figure 13.6.2.3.2.1 shows the message sequence example for the Hold procedure with a possible notification to the held party using an announcement. In the example the MSC server requests the MGW to play an announcement towards the held party.

Figure 13.6.2.3.2.1: Hold Request on LCLS call

1. HOLD message is received from the UE-A.

2. The MSC-A server accepts the HOLD request.

3. The MSC-A server requests a LCLS break procedure described in clause 7.2.1.

4. The MSC-A server requests the MGW-A to interrupt the communication on the bearer by changing the through-connection of the bearer termination towards the UE-A to "inactive".

5. The MSC-A server sends the CPG message with the Generic Notification Indicator parameter set to "remote hold" to the iMSC.

6. The iMSC server transfers the CPG message to the MSC-B server.

7. The MSC-B server sends FACILITY message with the call hold notification to the UE-B.

8. The MSC-A server informs the UE-A that call hold is accepted with the HOLD ACKNOWLEDGE message.

9. The MSC-A server requests the MGW-A to play an announcement towards the held party.

Figure 13.6.2.3.2.2 shows the message sequence for the Retrieval procedure.

Figure 13.6.2.3.2.2: Retrieval Request and LCLS re-establishment

1. RETRIEVE message is received from the UE-A.

2. The MSC-A server accepts the RETRIEVE request.

3. The MSC-A server requests the MGW-A to stop an announcement towards the held party.

4. The MSC-A server requests the MGW-A to re-establish communication to the held party by changing the through-connection of the bearer termination towards the UE-A to be both-way through-connected.

5. The MSC-A server sends the CPG message with the Generic Notification Indicator parameter set to "remote retrieval" to the iMSC.

6. The iMSC server transfers the CPG message to the MSC-B server.

7. The MSC-B server sends FACILITY message with the call hold notification to the UE-B.

8. The MSC-A server informs the UE-A that retrieve request is accepted with the RETRIEVE ACKNOWLEDGE message.

9. If the call has been successfully negotiated for LCLS the MSC-A server requests a LCLS re-establishment procedure as described in clause 7.3.1.