13.7 Multiparty (MPTY)
23.2053GPPBearer-independent circuit-switched core networkRelease 17Stage 2TS
The procedures specified in 3GPP TS 23.084 [14] for the Multi Party supplementary service shall be followed. The following clauses describe the additional requirements for the bearer independent CS core network. If out-of-band transcoder control is applied for the call, it shall be performed in accordance with 3GPP TS 23.153 [3].
13.7.1 Beginning the Multi Party call
When the served mobile subscriber invokes a Multi Party service the MSC server selects an MGW that provides the Multi Party bridge capabilities. If the selected MGW is different from the MGW that is used for the active call, the MSC server requests the MGW(s) to connect the bearer terminations of the participants to the selected MGW. The bearer terminations are connected together.
13.7.2 Managing an active Multi Party call
When the served mobile subscriber puts the Multi Party call on hold the MSC server requests the MGW to interrupt the connection between the served mobile subscriber and the Multi Party bridge.
When the served mobile subscriber retrieves a held Multi Party call the MSC server requests the MGW to re-establish the connection between the served mobile subscriber and the Multi Party bridge.
When the served mobile subscriber requests private communication with one of the remote parties (e.g. B-party), the MSC server shall request the MGW to interrupt the connection between the served mobile subscriber and the Multi Party bridge, and connection between the remote B party and the Multi Party bridge. The MSC server requests the MGW to connect the bearer termination of the served mobile subscriber to the bearer termination of the remote party (or vice versa) within a same context.
13.7.3 Disconnect
If a remote party is disconnected while other parties still remain the call towards the remote party is disconnected as described in the clause for call clearing.
13.7.4 Failure handling in MSC server
If resources for the Multi Party service cannot be allocated in any of the MGW resources assigned to the MSC server, then the MSC server shall reject the MPTY request.
13.7.5 Example 1 – Multiparty call establishment
Figure 13.19 shows the network model for multi party call. The "squared" line represents the call control signalling. The "dotted" line represents the bearer control signalling and the bearer. Note that for a TDM access there is no separation between the call and bearer control signalling. In the following example it is assumed that each party participating in the Multi Party conference is handled in a separate context representing the call leg between the Multi Party bridge and the Multi Party participant. The Multi Party bridge itself is handled in a separate context. This separation to several contexts is done in order to simplify interactions with other functionality, such as handover, even though other implementation options are not excluded.
Figure 13.19: Multi Party call (Network model)
For the purposes of the information flow diagrams it is assumed that there are only two remote parties. Party A is the subscriber controlling the Multi Party service (served mobile subscriber). Party B is the held party and party C is the active party.
It is assumed that the Multi Party bridge is located in the MGW that has been selected for the served mobile subscriber.
Figure 13.20 shows the message sequence example for the beginning of multi party call. When the served mobile subscriber invokes a Multi Party service the MSC server requests the MGW to create a separate context for the Multi Party bridge. The MSC server seizes a bearer termination for each party in that context. In addition, each call leg is represented by a separate context. Therefore the parties in the active call will be split in separate contexts. The MSC server requests the MGW to create a new context and to move the bearer termination for the served mobile subscriber from the active call context to the new context. To connect the parties to the Multi Party bridge the MSC server requests the MGW to establish internal Nb connections between the bearer terminations in the Multi Party bridge context and the call leg contexts, using the standard external bearer setup procedures. The held party is informed about the retrieval of the held call, and the both remote parties are informed about the multi party call establishment.
Figure 13.20: Information flow for multi party call, internal ATM bearer (message sequence chart)
Figure 13.20a: Information flow for multi party call, internal IP bearer (message sequence chart)
13.7.6 Example 2 – Private call establishment during multiparty call
Figure 13.20b shows the network model for private call. The "squared" line represents the call control signalling. The "dotted" line represents the bearer control signalling and the bearer. Note that for a TDM access there is no separation between the call and bearer control signalling.
Figure 13.20b: Private call (Network model)
Figure 13.20c: Information flow for private call (message sequence chart)
NOTE: The two MOVE commands may be sent in different transactions.
For the purposes of the information flow diagrams it is assumed that there are only two remote parties and the private call is established between the served mobile subscriber (Party A) and the remote C-party.
Figure 13.20c shows the message sequence example for the beginning of private communication between the served mobile subscriber and the remote parties (e.g. C-party).