Figure 8.4.5.8.1.1 shows the network model for the Intra-MSC BSS Internal Handover, where the call leg pertinent to the UE-1 is handed over from the serving BSS-1 to BSS-2. BSS-1 is the same as BSS-2 for BSS Internal Handover. The bearer termination T2 is used for the bearer towards BSS-2, which is not affected by this handover. Bearer termination TS is used for the bearer towards BSS-1 and the bearer terminations T1 and TA are used for the bearer towards the succeeding/preceding MGW. Bearer termination TT is for the bearer termination towards the BSS after internal handover. The colours and line types used in the figure are defined differently from
TS 23.205 to indicate LCLS specific issues.
Figure 8.4.5.8.2.1 shows the message sequence example for the BSS Internal Handover that Does Not Modify LCLS Status of a Locally Switched Call.
In the example, the MSC server receives the Internal Handover Required message and requests the MGW to reserve an RTP bearer termination (TT) using the Reserve and Configure RTP Connection Point procedure with specific flow directions.
Step 1 - 2.
Step 3.
The MSC-1 Server determines that local switching is permitted by the core network and sends the Internal Handover Command, optionally including the LCLS-Connection-Control-Status message indicating "Connect".
Step 3a.
BSS-1 may indicate Handover Detected.
Step 4.
BSS-1 sends the Handover Complete message to MSC-1 Server to indicate LCLS-BSS-Status is set to "Call is not locally switched".
Step 5.
The old termination (TS) is removed and the call is normally switched through the Core Network.