Content for TS 23.284 Word version: 18.0.0

1… 4… 4.2… 4.3… 5 6… 6.3… 6.3.2 6.3.3 6.3.4 6.3.5 7… 7.2.4… 7.2.4.2 7.2.4.3 7.2.4.4 7.2.4.5 7.2.4.6 7.3… 7.3.4… 7.3.4.2 7.3.4.3 7.3.4.4 8… 8.2.3 8.3… 8.3.2 8.4… 8.4.1.1.7… 8.4.1.2… 8.4.2… 8.4.2.2… 8.4.5… 8.4.5.6 8.4.5.7 8.4.5.8… 9… 13… 13.4… 13.4.3… 13.4.4… 13.5… 13.6… 13.7… 14… 16… A… A.2…

8.4.2 Inter-MSC GSM to GSM Handover 8.4.2.1 Inter-MSC GSM to GSM Handover that breaks Local Switching
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8.4.2 Inter-MSC GSM to GSM Handover p. 102

8.4.2.1 Inter-MSC GSM to GSM Handover that breaks Local Switching p. 102

8.4.2.1.1 General p. 102

If LCLS is established for a call and an inter-MSC GSM to GSM handover occurs that makes the call not local the LCLS shall be broken in the BSS and the user plane data shall be connected through the core network. The Inter-MSC GSM to GSM handover procedures specified in TS 23.009, TS 23.205 and TS 23.231 shall be followed. The following clauses describe the additional requirements for inter-MSC handovers of LCLS related calls.

8.4.2.1.2 MSC-1 / MGW-1 p. 102

8.4.2.1.2.1 Handover Required p. 102

When MSC-1 Server receives the Handover Required message from the serving BSS and determines that the call shall be handed over to the Target MSC Server, it shall send the GCR of the call, the LCLS-Negotiation Request IE and the LCLS-Configuration-Preference IE to the Target MSC Server in a MAP Prepare-Handover_Request message.

8.4.2.1.2.2 Handover Request Acknowledge p. 102

When MSC-1 Server receives the MAP Prepare_Handover_Response including Handover_Request_Acknowledgement message with a LCLS-BSS-Status IE the Anchor MSC-1 Server shall send to the adjacent call node, MSC-2 Server, the LCLS-Status-Change Request message containing the LCLS-Status-Change-Request IE to signal the change of LCLS status. In the LCLS-Status-Change-Request IE the MSC-1 server shall indicate "LCLS Disconnection-Preparation-for handover".

When the MSC-2 Server receives the LCLS-Status-Change Request message with the LCLS-Status-Change-Request IE that requires LCLS Disconnection preparation-for-handover it shall send to BSS-2 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-2, the MSC-2 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.

8.4.2.1.2.3 Bearer establishment between MGW-1 and Target MGW p. 103

The handling of the bearer establishment between MGW-1 and Target MGW is as described in clause 6.1 for a Basic Mobile Originating Call. The MSC server shall also use the Change Flow Direction procedure to request the MGW-1 to set the Handover Device to the initial state.

8.4.2.1.2.4 MGW Flow Direction Control p. 103

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 in MGW-1 towards the Target MGW (T2) from the termination to the Serving BSS (TS) and configuring the Anchor termination (TA) one-way DL towards the Target MGW termination (T2). Termination to the Serving BSS (TS) is both-way connected to Anchor termination (TA) since it is also receiving UL user data from termination to the Serving BSS (TS). The basic example in clause 8.4.2.1.4 illustrates this type of functionality.

Or:

The MSC-1 Server may request the MGW-1 to set termination towards Target-MGW (T2) to both-way 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-1 at Handover Detect message.

8.4.2.1.2.5 Handover Command/Handover Detect p. 103

When the MSC-1 server sends the Handover Command message or alternatively if it receives the Handover Detect message inside a MAP Process-Access-Signalling request, if the MSC-1 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-1 to set the Handover Device to intermediate state, however if the MSC server-1 isolated TS and set T2 to bothway 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.

8.4.2.1.2.6 Handover Complete p. 103

When the MSC-1 Server receives the Handover Complete message, it releases the A-interface line towards BSS-1. The MSC-1 Server also requests MGW-1 to set the Handover Device to its final state by removing the bearer termination towards the BSS-1.

After the MSC-1 Server receives the Answer message including the LCLS-Status set to LCLS feasible but not yet locally switched, MSC-1 Server shall send to the adjacent call node the LCLS-Status-Update message with the LCLS-Status IE indicating that LCLS is not established.

8.4.2.1.3 Target MSC Server / Target MGW p. 104

8.4.2.1.3.1 Prepare Handover Request message and MGW selection p. 104

The Target MSC server selects the Target MGW when it receives Prepare Handover Request message. The Target 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".

8.4.2.1.3.2 Handover Request Acknowledge p. 104

If the Target BSS supports the LCLS feature it shall include the LCLS-BSS-Status IE in the Handover Request Acknowledge message in order to inform the Target MSC Server that the BSS supports the LCLS feature. The Target MSC Server sends the same information in the MAP Prepare Handover Response message to the MSC-1 Server.

8.4.2.1.3.3 Bearer establishment towards Target BSS p. 104

When the Target MSC Server has selected the Target MGW it requests the Target MGW to seize a TDM circuit if AoTDM using the Reserve Circuit procedure, or an IP termination if AoIP using the reserve Connection Point procedure as for the normal handover procedure. The Target MSC Server sends the Handover Request message to the Target BSS containing the CIC for AoTDM or the IP addresses and UDP ports received from the target MGW if AoIP.

8.4.2.1.3.4 Bearer establishment between MGW-1 and Target MGW p. 104

The handling of the bearer establishment between MGW-1 and Target MGW is as described for basic mobile terminating call in clause 6.2.

8.4.2.1.3.5 LCLS Negotiation in Initial Address message p. 104

If the Target MSC Server receives an Initial Address message that does not include a LCLS-Negotiation Request IE or includes a LCLS-Negotiation Request IE set to LCLS is not permitted, the Target MSC Server shall update the previously sent LCLS-Configuration by sending a LCLS_CONNECT_CONTROL message to BSS with a LCLS-Configuration IE set to LCLS-not allowed and a LCLS_Connection_Status_Control IE set to "do not connect LCLS".

8.4.2.1.4 Example of Inter-MSC Handover that breaks Local Switching p. 104

8.4.2.1.4.1 Connection Model p. 104

Figure 8.4.2.1.4.1.1 shows the network model for the Inter-MSC GSM to GSM Handover, where call leg UE-1 is handed over from BSS-1 to the Target BSS. BSS-1 is the same as BSS-2 when LCLS is established for the call. The BSS-1 is served by the MSC-Server 1, the Target BSS is served by the Target MSC-Server, and MSC-Server 1 is not the same as Target MSC-Server. The bearer termination T2 in MGW-2 is used for the bearer towards BSS-2, which is not affected by this handover. Bearer termination TS in MGW-1 is used for the bearer towards BSS-1 and the bearer terminations TA and T3 in MGW-1, T1 in MGW-2 and T4 in Target-MGW are used for the bearer towards the succeeding/preceding MGW. Bearer termination TT in Target-MGW is for the bearer termination towards the Target BSS.

Copy of original 3GPP image for 3GPP TS 23.284, Fig. 8.4.2.1.4.1.1: Inter-MSC Inter-BSS Handover Connection Model when user plane active

Figure 8.4.2.1.4.1.1: Inter-MSC Inter-BSS Handover Connection Model when user plane active
(⇒ copy of original 3GPP image)

8.4.2.1.4.2 Basic Sequence for Inter-MSC handover that breaks Local Switching p. 107

Figure 8.4.2.1.4.2.1 and Figure 8.4.2.1.4.2.2 show the message sequence example for the basic Inter-MSC GSM to GSM Handover shown in the corresponding network model Figure 8.4.2.1.4.1.1. The Handover Device is located in the MGW-1 selected for the call establishment by the MSC-1 Server, which controls the call and the mobility management. The description is based on TS 23.009, TS 23.205 and TS 23.231.

Copy of original 3GPP image for 3GPP TS 23.284, Fig. 8.4.2.1.4.2.1: Inter-MSC Handover that breaks LCLS when user plane active, initial phase

Figure 8.4.2.1.4.2.1: Inter-MSC Handover that breaks LCLS when user plane active, initial phase
(⇒ copy of original 3GPP image)

Step 1.

The Handover Required message is received from BSS1 requesting an inter-MSC handover. The call is currently locally switched and the MSC-1 server can know that the Inter-MSC handover at one end will break LCLS (the local switch is not broken in the serving BSS (BSS-1) until UE-1 has moved out of the BSS-1 and the MSC-1 server sends the Clear Command message to BSS-1).

Step 2.

The MSC-1 Server determines that inter-MSC handover is required and sends MAP-Prepare-Handover Request to target MSC which includes LCLS Negotiation Request, the LCLS-Configuration-Preference and GCR IEs.

Step 3a, b.

The Target MSC-Server reserves circuit or Connection Point TT towards the Target BSS.

Step 4.

The Target MSC-Server sends the Handover Request message to target BSS with the GCR IE, the LCLS-Configuration IE and the LCLS-Connection-Status-Control IE indicating "connect" to through-connect the local call.

Step 5.

The Target BSS reports in Handover Request Acknowledge message that the call is not possible to be locally switched.

Step 6a, b.

(These signalling steps are only applicable to AoIP) When the Target MSC-Server receives the BSSMAP Handover Request-Ack message, it sends the target BSC IP address and UDP Port number to the target MGW using the Configure RTP Connection Point procedure.

Step 7.

The Target MSC-Server sends the Prepare Handover Response message to the MSC-1 server.

Step 8a.

The Anchor MSC-1 server instructs the far end MSC-2 server to prepare for LCLS disconnection for Handover by sending the LCLS-Status-Change-Request message.

Step 8b.

The far end MSC-2 server requests BSS-2 to start sending data UL with the LCLS_Connect_Control message and the LCLS-Connection-Status-Control IE indicating "BicastatHandover", see Figure 8.4.2.1.4.1.1, Connection Model 3. This triggers the BSS-2 to bicast the user plane data in the same way as the Access MGW-1 would be doing in a non-LCLS inter-BSS handover. At this point the BSS-1 shall send any DL data it receives directly to the served UE.

Step 8c.

The BSS-2 sends the LCLS_Connect_Control_Ack message with the LCLS-BSS-Status IE set to "the call is locally switched with requested LCLS configuration".

Step 8d.

MSC-2 Server sends LCLS-Status-Change-Request-Acknowledge message.

Step 9a, b.

In accordance with normal handover the MSC-1 server requests MGW-1 to isolate the termination towards Target MGW (T3) from the termination to the Serving BSS-1 (TS) and to configure the Anchor termination (TA) one-way DL towards the Target MGW termination (T3).

Step 10.

MSC-Server 1 sends IAM (Initial Address Message) to Target MSC-Server including GCR, the LCLS-Negotiation Request IE and the LCLS-Configuration-Preference IE.

Step 11a, b.

Target-MSC-Server reserves bearer connection T4 towards MGW-1.

Step 12.

After Target MGW has replied with the bearer address and the binding reference, Target MSC-Server returns Bearer and Codec Information (APM) message with selected codec, available codec list, the LCLS-Negotiation Response IE and the LCLS-Configuration-Preference IE.

Copy of original 3GPP image for 3GPP TS 23.284, Fig. 8.4.2.1.4.2.2: Inter-MSC Handover that breaks LCLS when user plane active, completion phase

Figure 8.4.2.1.4.2.2: Inter-MSC Handover that breaks LCLS when user plane active, completion phase
(⇒ copy of original 3GPP image)

Step 13.

The Target MSC-Server sends ACM (Address Complete Message). Target MSC-Server awaits the capturing of the UE-1 on the radio path when the ACM is sent and the Anchor MSC-1 server initiates the handover execution when receiving ACM.

Step 14.

MSC-1 server sends Handover Command message to BSS-1.

Step 15.

BSS-1 sends Handover Command message to UE-1. BSS-1 will discard incoming user plane data send to UE-1 received from CN. If BSS-2 was not instructed to prepare for LCLS related handover in Step 8a, the BSS-2 starts bi-casting UP user plane data generated by UE-2 to local path and A interface and also starts to check whether there is incoming DL user plane data from the core network.

Step 16.

UE-1 is detected at target BSS. But still no UL data can be sent from target BSS to MGW-1 because TA-T3 is one-way DL only. MGW-1 will continue to transmit DL user plane data to the target BSS-1. BSS-2 continues to bi-cast user plane data to both local path and to the A interface.

Step 17.

Target MSC-Server sends MAP-Process-Access-Signal request to the MSC-1 server.

Step 17a.

The MSC-1 Server sends LCLS-Status-Change-Request to indicate that UE-1 has been detected in the target BSS and user data is now being sent through the CN and DL to the distant UE-2

Step 17b.

The MSC-2 Server shall signal to the BSS-2 that DL data received from the CN is now real user data coming from the UE-1.

Step 17c.

The BSS-2 sends the LCLS_Connect_Control_Ack message with the LCLS-BSS-Status IE set to "the call is locally switched with requested LCLS configuration".

Step 17d.

Acknowledgement back through the CN that the indication for DL data after Handover Detect has been delivered.

Step 18a, b.

The MSC-1 server uses the Change Flow Direction procedure to request the MGW-1 to set the Handover Device to intermediate state and TA-T3 to both-way configuration. When BSS-2 finds out there is DL user plane data, BSS-2 will transmit the DL user plane data to UE-2.

Step 19.

Handover Complete message is received from target BSS with LCLS-BSS-status indicating that the call cannot be locally switched.

Step 20.

A Handover-Detect/Complete when received is included in the MAP SendEndSignalling Request message sent to the MSC-1 server.

Step 21.

Target MSC-Server sends ANSWER message with the LCLS-status when a Handover-Detect/Complete is received.

Step 22.

MSC-1 server informs BSS-1 to clear the old call leg.

Step 23.

MSC-1 server sends LCLS Status Update message with LCLS status "LCLS not connected" to MSC-2 server.

Step 24.

Serving BSS-2 informs MSC-2 server that LCLS is broken via LCLS-Notification message.

Step 25.

BSS-1 informs MSC-1 server that the resource for the UE-1 has been released and BSS-2 stops bi-casting.

Step 26a, b.

The MSC-1 server requests MGW-1 to set the Handover Device to its final state by removing the bearer termination TS towards BSC-1 using the Release Termination procedure.