8.1.6 Intra-MSC enhanced SRNS Relocation

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

The procedures specified in 3GPP TS 23.009 [8] for "Intra-3G_MSC SRNS Relocation" shall be followed. The following clauses describe the additional requirements for the bearer independent CS core network. The support of the enhanced SRNS Relocation is optional. Enhanced Relocation Complete Request

When the Enhanced Relocation Complete Request message is received, the MSC server requests the MGW to provide a binding reference and a bearer address, using the Prepare Bearer procedure. For speech calls, the MSC server shall provide the MGW with the speech coding information for the bearer. For non-speech calls the MSC server also provides the MGW with the same PLMN Bearer Capability [4] as was provided at the last access bearer assignment. The MSC server uses the Change Flow Direction Procedure to request the MGW to set the Handover Device to initial state. If required the MSC Server shall set-up an interconnection between the "anchor" and the "target" MGW. The MSC server then sends the Enhanced Relocation Complete Response message, containing the bearer address and the binding reference, to RNC-B (bullet 1 in figure 8.1.6/2). Enhanced Relocation Complete Confirm

When the MSC server receives the Enhanced Relocation Complete Confirm message, the MSC server uses the Change Flow Direction procedure to request the MGW to set the Handover Device to intermediate state (bullet 2 in figure 8.1.6/1).

After that the MSC Server requests RNC-A to release the IU. The MSC server also requests the MGW to set the Handover Device to its final state by removing the bearer termination towards RNC‑A, using the Release Termination procedure (bullet 3 in figure 8.1.6/2). Interworking function

The interworking function used by the MGW before relocation will also be used after relocation. Codec handling

The MGW may include a speech transcoder based upon the speech coding information provided to each bearer termination. Voice Processing function

After relocation, the MGW may continue or modify voice-processing function(s) provided to each bearer termination. Handling of multiple bearers (multicall)

If the UE is engaged with multiple bearers all procedures related to the handling of bearers and terminations described for the relocation of a single bearer shall be repeated for each bearer. Failure Handling in MSC server

When a procedure between the MSC server and the MGW fails the MSC server shall send an IU-ENHANCED-RELOCATION-COMPLETE-FAILURE message to RNS-B in accordance with 3GPP TS 23.009 [8] and 3GPP TS 29.010 [23]. If MGW resources have been already seized at the target access side then the resources shall be released using the Release Termination procedure. If the call is to be cleared, then it shall be handled as described in clause 7.3. Example

Figure 8.1.6/1 shows the network model for the Intra-MSC enhanced SRNS Relocation. The "squared" line represents the call control signalling. The "dotted" line represents the bearer control signalling and the bearer. The bearer termination T1 is used for the bearer towards RNC-A, bearer termination T3 is used for the bearer towards RNC-B and the bearer termination T2 is used for the bearer towards the succeeding/preceding MGW.

Before Relocation:

After Relocation:

After release of Source side resources:

Figure 8.1.6/1: Intra-MSC Enhanced SRNS Relocation (network model)

Figure 8.1.6/2 shows the message sequence example for the Intra-MSC enhanced SRNS Relocation.
It is assumed that the Handover Device is located in the MGW, which has been selected for the call establishment by the MSC server. The MSC server controls the call and the mobility management. It is also assumed that only one bearer has been established towards RNC-A.
In the example the MSC server requests seizure of RNC-B side bearer termination with specific flow directions. The MSC server orders the establishment of the bearer by sending Enhanced Relocation Complete Response towards RNC-B. When the MSC server receives an Enhanced Relocation Complete Confirm indication from RNC-B the MSC server requests to change the flow directions between the terminations within the context. MSC Server also orders RNC-A to release the IU. This action causes release of the bearer between the RNC-A and the MGW. Finally the MSC server requests the MGW to release RNC-A side bearer termination.

Figure 8.1.6/2: Intra-MSC Enhanced SRNS Relocation (message sequence chart)