13.6.8 Example 2

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

Figure 13.18a 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. After the request to establish a new call is made the MSC server seizes a new context in the MGW, the new context is used for the new call and the old context is used for the held call. The bearer termination T_A for the bearer towards the RNC (served mobile subscriber) is moved to this context and the bearer termination T_C is used for the bearer towards the succeeding MGW (C-party). In this example the announcement is played directly to Termination T_B.

NOTE: if B party is connected to a radio access and a handover occurs during the announcement then the announcement will be interrupted. It is also possible to put B-party on hold using the isolate bearer termination but if the announcement is still played directly to termination T_B as proposed by this example and a handover occurs then the problem still arises.

Figure 13.18a: Call hold and establishment of a new call (Network model) example 2

Figure 13.18b shows the message sequence for example 2 for the call hold procedure. In the example the MSC server requests the MGW to change the through-connection of the bearer to inactive when the hold request is received from the served mobile subscriber (bullet 2 in figure 13.18b). Subsequently an announcement may be applied to termination T_B (bullet 3 in figure 13.18b). Then the new call is established via a new context with served mobile subscriber termination T_A being moved to this new context (bullet 4 in figure 13.18b) and a new termination T_C is reserved (bullet 5 in figure 13.18b) 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 13.18b: Hold request (message sequence chart), example 2

Figure 13.18c shows the message sequence example for the retrieval procedure. In the example the MSC server moves the served mobile subscriber back to the context with termination T_B and requests the MGW to change the through-connection of the bearer to be both-way through-connected (bullet 3 and 4 in figure 13.18c) after the held party has been disconnected from an optionally applied announcement (bullet 2 in figure 13.18c). The MOVE command (Join Bearer Termination procedure) is not required (bullet 3 in figure 13.18c) if T_A has not been in the CTX_AC. The Change Through-Connection is only required if the retrieval occurs prior to any connection to C-party.

Figure 13.18c: Retrieval request (message sequence chart), example 2