7.2.2 Call Clearing received from core network

23.2313GPPRelease 17SIP-I based circuit-switched core networkStage 2TS

7.2.2.1 Procedures towards access side

The MSC server initiates call clearing towards the UE and requests release of the associated radio resources as described in 3GPP TS 23.108[18]. Once the call clearing and the release of the associated radio resources have been completed, the MSC server releases any MGW allocated resources for the access side. If any resources were seized in the MGW, the MSC server uses the Release Termination procedure to requests the MGW to remove the access side bearer termination.

7.2.2.2 Procedures towards network side

7.2.2.2.1 Call Clearing during establishment

7.2.2.2.1.1 Originating MSC-S

If the release indication from the succeeding node is a failure response for the initial INVITE request, the MSC server shall send an ACK for the failure response to the succeeding node.

The MSC server shall then perform the normal bearer release according to 7.2.6.

NOTE: For early dialogue from O-MSC perspective, a BYE can only be received if it overtakes a 2xx response due to out-of-sequence packet delivery which should not be encountered with SCTP transport for SIP, as used on Nc

7.2.2.2.1.2 Terminating MSC-S

If a CANCEL request to initial INVITE is received from the preceding node, the MSC server shall send a 200 OK response for the CANCEL request and the MSC server shall immediately send a 487 Request Terminated response for the initial INVITE request to the preceding node.

NOTE: No final response for the initial INVITE request has previously been sent.

If a BYE request is received from the preceding node, the MSC server shall send a 200 OK response for the BYE request, and immediately send a 487 Request Terminated response for the initial INVITE request to the preceding node.

NOTE: A 487 final response is sent because of a reception of CANCEL/BYE request and does not contain encapsulated REL message.

The MSC sever shall then perform the normal bearer release according to 7.2.6.

7.2.2.2.2 Call Clearing after call established

7.2.2.2.2.1 Originating MSC-S

An MSC server that receives a BYE request from the succeeding node shall send a 200 OK response for the BYE request to the succeeding node. The MSC shall then perform the normal bearer release according to 7.2.6.

7.2.2.2.2.2 Terminating MSC-S

If an MSC server receives a CANCEL request from the preceding node it shall send a 200 OK(CANCEL) final response for the CANCEL request but shall not take further action.

If a BYE request is received from the preceding node, the MSC server shall send a 200 OK response for the BYE request to the preceding node. The MSC server shall then perform the normal bearer release according to 7.2.6.

7.2.2.3 Example Call Flow

Figure 7.2.2.3.1 shows the network model for a network initiated clearing of an established mobile call. The "squared" line represents the call control signalling. The "dotted" line represents the bearer control signalling (not applicable in A/Gb mode for the A-interface) and the bearer. The MSC server seizes one context with two bearer terminations in the MGW. Bearer termination T1 is used for the bearer towards RNC/BSC and bearer termination T2 is used for the bearer towards succeeding MGW.

Figure 7.2.2.3.1: Network Initiated Call Clearing (Network model)

Figure 7.2.2.3.2 shows the message sequence example for the network initiated clearing of an established mobile call. In the example when the call clearing indication is received from the preceding/succeeding node, the MSC server indicates to the preceding/succeeding node that call clearing has been completed and releases the network side bearer termination. The MSC server initiates call clearing towards the UE and requests release of the radio resource. After the response of the radio resource release is received then the MSC server requests release of the access side bearer termination.

Figure 7.2.2.3.2: Network Initiated Call Clearing (message sequence chart)