13.4.1 Call Forwarding Unconditional (CFU)
23.2053GPPBearer-independent circuit-switched core networkRelease 17Stage 2TS
The procedures specified in 3GPP TS 23.082 [12] for the Call Forwarding Unconditional supplementary service shall be followed. The following clauses describe the additional requirements for the bearer independent CS core network.
13.4.1.1 MGW selection
If in-band information is to be provided to the calling subscriber the GMSC server shall select the MGW before providing the in-band information. The MGW selection can be based on a possibly received MGW-Id from the preceding node.
If in-band information is to not to be provided to the calling subscriber the GMSC server shall select the MGW for the bearer as described for the basic mobile terminating call.
13.4.1.2 Incoming side bearer establishment
The incoming side bearer establishment is handled in the GMSC server as described for the mobile terminating call using either forward or backward bearer establishment.
13.4.1.3 Notification to the Calling Subscriber
If the served mobile subscriber has requested that the calling subscriber shall receive a notification about the call forwarding, a notification is sent to the calling party. If the notification is implemented using intermediate tones or announcements the GMSC server requests the MGW to play an announcement/tone to the calling party, as described in clause 14.6, before establishing the call to the forwarded-to subscriber.
13.4.1.4 Initial addressing
If the incoming call is to be forwarded without being offered to the served mobile subscriber the call towards the forwarded-to subscriber is established as for a basic call. If out-of-band transcoder control is applied for a speech call, it shall be performed in accordance with 3GPP TS 23.153 [3]. After the possible generation of in-band information has been completed the initial addressing towards the forwarded-to subscriber is performed as described for the basic mobile terminating call indicating either forward or backward bearer establishment.
13.4.1.5 Establishment of bearer towards the forwarded-to subscriber
The bearer establishment towards the forwarded-to subscriber is performed as described for the mobile originating call, network side bearer establishment, using either forward or backward bearer establishment. The GMSC server also requests the MGW to both-way through-connect the bearer.
13.4.1.6 Confirmation of bearer establishment
The confirmation of the bearer establishment is handled as described for the basic mobile terminating call.
13.4.1.7 Failure handling in GMSC server
The failures are handled as described for the basic mobile terminating call.
13.4.1.8 Example
Figure 13.3 shows the network model for call forwarding unconditional. 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 TA is used for the bearer towards the preceding MGW (calling subscriber) and the bearer termination TC is used for the bearer towards the succeeding MGW (forwarded-to subscriber).
Figure 13.3: CFU (Network model)
Figure 13.4 shows the message sequence example for the call forwarding unconditional with a possible notification to the calling party using an announcement. In the example the GMSC server optionally requests the MGW to play an announcement and to notify the announcement completion, after the bearer to the incoming side has been established. When the possible announcement has completed the GMSC server requests the establishment of the call and the bearer towards the forward-to subscriber.
Figure 13.4: CFU (message sequence chart)