14.5 OR

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

The procedures specified in 3GPP TS 23.079 [11] for the Optimal Routeing network service shall be followed. The following clauses describe the additional requirements for the bearer independent CS core network.

14.5.1 Optimal routeing for basic mobile-to-mobile calls

The optimally routed call from one mobile subscriber to another mobile subscriber is established as a normal basic call.

14.5.2 Optimal routeing for conditional call forwarding; Early call forwarding

For early call forwarding the same procedures as described for CFU and CFNRc (rerouting by HLR) shall apply.

14.5.3 Optimal routeing for conditional call forwarding; Late call forwarding

14.5.3.1 MSC server

14.5.3.1.1 Resume Call Handling and clearing of connection to GMSC server

When the MSC server determines that the call should be forwarded because the called mobile subscriber is busy (NDUB, UDUB), not reachable or has not replied to the call before the no-reply timer has expired, the MSC server sends a request to resume call handling to the GMSC server.

If the GMSC server determines that the call can be forwarded to the forwarded-to destination it sends a Release message to the MSC server. If no bearer has been established yet the MSC server handles the release only on call control level. If the bearer had been established, the MSC server handles the network side bearer release as described in the clause for the call clearing.

14.5.3.1.2 IU release

When the MSC server determines that the call should be forwarded because the called mobile subscriber is busy (UDUB) or it has not replied to the call before the no-reply call timer has expired, the MSC server shall release the call and bearer connection to the served mobile subscriber as described in the clause for call clearing.

14.5.3.2 GMSC server

14.5.3.2.1 Resume Call Handling and Clearing of Connection to visited MSC server

If the GMSC server determines that the call can be forwarded to the forwarded-to destination it sends a Release message to the MSC server and handles the outgoing side bearer release as described in the clause for call clearing, if the bearer had already been established.

14.5.3.2.2 MGW selection

The GMSC server shall select an MGW for the bearer connection as described for the CFU and CFNRc (in HLR) supplementary services, if not already selected by the mobile terminating call procedures.

14.5.3.2.3 Incoming side bearer establishment

The bearer establishment towards the preceding MGW is handled in the GMSC server as described for the mobile terminating call, if not already established by the mobile terminating call procedures.

14.5.3.2.4 Notification to the Calling Subscriber

The GMSC server sends the possible notification towards the calling subscriber according to the procedures described for the CFU and CFNRc (in HLR) supplementary services.

14.5.3.2.5 Establishment of call and bearer towards the forwarded-to subscriber

The GMSC server establishes the call and bearer towards the forwarded-to subscriber according to the procedures described for the CFU and CFNRc (in HLR) supplementary services.

14.5.3.2.6 Example

Figure 14.7 shows the network model for optimal routeing when no bearer has been established before the invocation of late call forwarding. The "squared" line represents the call control signalling. The "dotted" line represents the bearer control signalling and the bearer. The GMSC server seizes one context with two bearer terminations in the MGW. The bearer termination T_A is used for the bearer towards the preceding MGW (calling subscriber) and the bearer termination T_C is used for the bearer towards the succeeding MGW (forwarded-to subscriber).

Figure 14.7: Optimal routeing; late call forwarding (CFB (NDUB), CFNRc) (Network model)

Figure 14.8 shows the message sequence example for the optimal routeing with late call forwarding without any notification to the calling party. In the example below no bearer has been established for the connection when the MSC server sends the Resume Call Handling request to the GMSC server. After the call towards the visited MSC server has been released the GMSC server establishes the call and the bearer as described for Call Forwarding Unconditional.

Figure 14.8: Information flow for optimal routeing; late call forwarding (CFB (NDUB), CFNRc) (message sequence chart)

Figure 14.9 shows the network model for optimal routeing when a bearer has been established before the invocation of late call forwarding. The "squared" line represents the call control signalling. The "dotted" line represents the bearer control signalling and the bearer. The GMSC server replaces the bearer termination towards the visited MSC server (T_MSC) with the bearer termination for the forwarded-to subscriber (T_C) in an existing context in the MGW. The bearer termination T_A is used for the bearer towards the preceding MGW (calling subscriber).

Figure 14.9: Optimal routeing; late call forwarding (CFB (UDUB), CFNRy, CD) (Network model)

Figure 14.10 shows the message sequence example for the optimal routeing for late call forwarding with a forward bearer release. In the example the MSC server requests the MGW to remove the termination towards the served mobile subscriber after the bearer towards the RNC has been released. At reception of the release message from the GMSC server the MSC server requests the MGW to be prepared for the bearer release. When the GMSC server receives the Release Complete it requests the MGW to release the bearer.

Figure 14.10: Information flow for optimal call routeing; late call forwarding (CFB (UDUB),
CFNRy, CD), forward bearer release (message sequence chart)

Figure 14.11 shows the message sequence example for the optimal routeing for late call forwarding with a backward bearer release. In the example the MSC server requests the MGW to remove the termination towards the served mobile subscriber after the bearer towards the RNC has been released. At reception of the release message from the GMSC server the MSC server requests the MGW to be release the bearer. When the GMSC server receives the Release Complete it requests the MGW to remove the bearer termination.

Figure 14.11: Optimal call routeing; late call forwarding (CFB (UDUB), CFNRy, CD),
backward bearer release (message sequence chart)