Content for  TS 23.284  Word version:  18.0.0

When a call is locally switched through the BSS and an intra-MSC inter-BSS GSM to GSM handover occurs then the LCLS shall be broken and the user plane shall be connected through the core network. The intra-MSC inter BSS GSM to GSM handover procedures specified in TS 23.205 and TS 23.231 shall be followed. The following clauses describe the additional requirements for intra-MSC inter BSS GSM to GSM handovers of LCLS related calls. During a Locally Switched (intra-BSS) Connection when no bicasting occurs there is no data transmission through the core network. In this release the use plane is kept active and therefore does not need to be re-activated when the LCLS is broken due to inter-BSS handover out of LCLS.

When the MSC server receives the Handover Required message from the serving BSS, it requests the MGW to seize a TDM circuit if AoTDM or an IP termination if AoIP for the termination to the Target BSS as for the normal handover procedure. The MSC server shall use the Change Flow Direction procedure to request the MGW to set the Handover Device to the initial state.

The MSC Server may perform the MGW Flow Direction Control in the following ways:

• In accordance with the normal handover case by isolating the termination to the Target BSS (TT) from the termination to the Serving BSS (TS) and configuring the Anchor termination (TA) one-way DL to the Target BSS (TT). Termination to the Serving BSS (TS) is bothway connected to Anchor termination (TA) since it is also receiving UL user data from termination to the Serving BSS (TS).

Or:

• The MSC server may request the MGW to set termination to Target BSS (TT) to bothway connected to Anchor termination (TA) and isolate termination to Serving BSS (TS) completely. This improves the user plane switching and saves a signalling step to the MGW at Handover Detect message. The MSC server sends the Handover Request message to the Target BSS as for the normal case but shall include the GCR IE, the LCLS-Configuration IE and the LCLS-Connection-Status-Control IE set to "Connect".

If the Target BSS supports LCLS feature then it shall include the LCLS-BSS-Status IE in the Handover Request Acknowledge message in order to inform the anchor MSC Server that the BSS supports the LCLS feature, and therefore the MSC Server shall not act upon the status indicated, i.e. no signalling of LCLS-Status IE through the core network. Upon receipt of the Handover Request Acknowledge message the MSC Server shall send to the adjacent call node the LCLS-Status-Change-Request message to indicate "LCLS Disconnection-Preparation-for handover". When the far end MSC server receives the LCLS-Status-Change-Request message indicating LCLS Disconnection preparation-for-handover it shall send to the BSS the LCLS_Connect_Control message with the LCLS-Connection-Status-Control IE indicating "BicastatHandover". When the LCLS_Connect_Control acknowledge message is received from the BSS, the far end MSC server shall return the LCLS Status Change Request Acknowledge message indicating "LCLS Disconnection-Preparation-for-handover" and a Result code indicating LCLS Status Change Request accepted.

When the MSC server sends the Handover Command message or alternatively if it receives the Handover Detect message, if the MSC server followed the MGW control procedures for a non-LCLS call and kept the Termination to the Serving BSS connected then it shall use the Change Flow Direction procedure to requests the MGW to set the Handover Device to intermediate state however if the MSC server isolated TS and set TT to bothway through-connected then no MGW control procedure is required at this point. Upon receipt of the Handover Detect message the MSC Server shall send to the adjacent call node the LCLS-Status-Change-Request message with the LCLS-Status-Change-Request IE set to "Indicate DL data after Handover". When the far end MSC server receives the LCLS-Status-Change-Request message with the LCLS-Status-Change-Request IE set to "Indicate DL data after Handover" it shall send to the BSS the LCLS_Connect_Control message with the LCLS-Connection-Status-Control IE indicating "DL Data_at_Handover" and after reception of the LCLS_Connect_Control acknowledge message from the BSS, return the LCLS-Status-Change-Request-Acknowledge message with "Indicate DL data after Handover" and a Result code indicating LCLS Status Change Request accepted.

When the MSC server receives the Handover Complete message, it releases the A-interface line towards the serving BSS. The MSC server also requests the MGW to set the Handover Device to its final state by removing the bearer termination (TS) towards the serving BSS. The MSC server shall send to the adjacent call node the LCLS-Status-Update message with the LCLS-Status IE indicating the LCLS disconnection. When the serving BSS receives Clear Command it shall release any local switch path. The serving BSS shall inform the far end MSC server that LCLS is broken with the LCLS_Notification message.