7.1 Network Initiated

23.2053GPPBearer-independent circuit-switched core networkRelease 17Stage 2TS

The terms "incoming" and "outgoing" in the following text refers to the direction of propagation of the Release message, not to the direction of establishing the original call.

7.1.1 GMSC server

7.1.1.1 Call clearing from the incoming side

Once the Release message has been received from the preceding node, the GMSC server releases any MGW allocated resources for the incoming side. If any resources were seized in the MGW, the GMSC server shall use the Release Bearer and Release Termination procedures to indicate to the MGW to remove the incoming side bearer termination and that the bearer can be released towards the preceding MGW. After the resources in the MGW are released the GMSC server sends the Release Complete message to the preceding node.

7.1.1.2 Call clearing to the outgoing side

The GMSC server sends the Release message to the succeeding node. Once the succeeding node has sent the Release Complete message, the GMSC server releases any MGW allocated resources for the outgoing side. If any resources were seized in the MGW, the GMSC server shall use the Release Bearer and Release Termination procedures to indicate to the MGW to remove the outgoing side bearer termination and that the bearer can be released towards the succeeding MGW.

7.1.2 MSC server

The network initiated call clearing shall be performed in accordance with 3GPP TS 23.108 [18]. The following clauses describe the additional requirements for the bearer independent CS core network.

7.1.2.1 Call clearing from the network side

Once the Release message has been received from the preceding/succeeding node, the MSC server releases any MGW allocated resources for the network side. If any resources were seized in the MGW, the MSC server shall use the Release Bearer and Release Termination procedures to indicate to the MGW to remove the network side bearer termination and that the bearer can be released towards the preceding/succeeding MGW. After the resources in the MGW are released the MSC server sends the Release Complete message to the preceding/succeeding node (bullet 1 in figure 7.2).

7.1.2.2 Call clearing to the UE

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 (bullet 2 or bullet 3 in figure 7.2).

7.1.2.3 Example

Figure 7.1 shows the network model for a network initiated clearing of the 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 7.1: Network Initiated Call Clearing (Network model)

Figure 7.2 shows the message sequence example for the network initiated clearing of a mobile call. In the example the when the call clearing indication is received from the preceding/succeeding node, MSC server indicates that the network bearer can be released and to release the network side bearer termination. After the release of the network side bearer termination the MSC server indicates to the preceding/succeeding node that call clearing has been completed. 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: Network Initiated Call Clearing (message sequence chart)