23.2053GPPBearer-independent circuit-switched core networkRelease 17Stage 2TS
Figure 13.16 shows the network model for the call hold with an establishment of a new call. The "squared" line represents the call control signalling. The "dotted" line represents the bearer control signalling and the bearer. The MSC server isolates the flow connection between the served mobile and the termination in the MGW that is used for the held call. If an announcement is to be played to the held party the MSC Server may seize a new context in the MGW. If a new call is made to C subscriber the MSC server seizes a new context in the MGW if not previously done. The new context is used for the new call and the old context is used for the held call. The bearer termination TA is moved with the bearer towards the RNC (served mobile subscriber) and the bearer termination TC is used for the bearer towards the succeeding MGW (C-party).
NOTE: The main advantage with example 1 is that if B party is connected to a radio access and a handover occurs then the announcement termination is unaffected and therefore there is no break in the announcement. It is also an option to put the B-party on hold using the isolate bearer procedure immediately but this is not shown in this example.
Figure 13.16: Call hold and establishment of a new call (Network model) example 1
Figure 13.17 shows the message sequence for example 1 for the call hold procedure. In the example the MSC server requests the MGW to change the through-connection of the bearer so that it will not be through-connected when the hold request is received from the served mobile subscriber (bullet 2 in figure 13.17). Subsequently if an announcement is to be applied then Termination TA may be isolated from the held party (bullet 3 in figure 13.17) and a new announcement termination TA2 is added to context CTXAB and announcement applied to termination TA2 (bullet 3a in figure 13.17). For setting up a new call to the C-party the termination TA is moved to a new context if not done previously (bullet 4 in figure 13.17) and a new termination TC is reserved (bullet 5 in figure 13.17) and the call shall continue with the appropriate stream mode settings as for a normal call establishment in accordance with Clause 6.1, see figure 6.2.
Figure 13.17: Hold request (message sequence chart) , example 1
Figure 13.18 shows the message sequence for example 1 for the retrieval procedure. In the example the MSC server requests the MGW to move the connection of the bearer back to be both-way through-connected (bullet 3 and 4 in figure 13.18) to the held party, after the held party has been disconnected from an optionally applied announcement (bullet 2 in figure 13.18). The MOVE command (Join Bearer termination procedure) is not required (bullet 3 in figure 13.18) if TA has not previously been moved into the CTXAC. The Change Through-Connection is only required if the retrieval occurs prior to any connection to C-party.
Figure 13.18: Retrieval request (message sequence chart) , example 1