Content for  TS 23.231  Word version:  18.0.0

To initiate the optional "Optimised MGW Selection" procedure, a (G)MSC Server shall seize a MGW as for a normal call and indicate to the succeeding node the identity of the MGW in the initial SDP offer. If the succeeding node receiving the SDP offer supports the "Optimised MGW Selection" option and the SDP offer includes a MGW Identity, and the succeeding node has a Mc H.248 gateway control protocol interface to the indicated MGW, the succeeding node may connect to that MGW. The succeeding node may indicate the MGW Identity in the SDP answer to the preceding node. In the example sequence chart in Figure 4.4.2.2, which assumes the network model in Figure 4.4.2.1, the offerer is a GMSC Server, which has seized a MGW at the network border. The initial offer indicates that a MGW is connected and includes the MGW identity. The answerer is a terminating MSC Server, which is able to connect to the same MGW and seizes a bearer termination in this MGW and returns the user plane connection address in the answer.