8.4.2 Inter-MSC GSM to GSM Handover

23.2843GPPLocal Call Local Switch (LCLS)Release 17Stage 2TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

8.4.2.1 Inter-MSC GSM to GSM Handover that breaks Local Switching

8.4.2.1.1 General

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 3GPP TS 23.009 [9], 3GPP TS 23.205 [2] and 3GPP TS 23.231 [3] 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

8.4.2.1.2.1 Handover Required

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

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

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

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 (T_S) and configuring the Anchor termination (T_A) one-way DL towards the Target MGW termination (T₂). Termination to the Serving BSS (T_S) is both-way connected to Anchor termination (T_A) since it is also receiving UL user data from termination to the Serving BSS (T_S). 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 (T_A) and isolate termination to Serving BSS (T_S) 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

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 T_S 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.

NOTE: this informs this call leg in the BSS that the other UE has left the BSS and has been detected in the new BSS and as such DL data from the CN is now coming from that UE.

8.4.2.1.2.6 Handover Complete

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

8.4.2.1.3.1 Prepare Handover Request message and MGW selection

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

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

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

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

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

8.4.2.1.4.1 Connection Model

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 T_S in MGW-1 is used for the bearer towards BSS-1 and the bearer terminations T_A 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 T_T in Target-MGW is for the bearer termination towards the Target BSS.

Connection Model 1: Before handover, LCLS is established

Connection Model 2: Before MSC triggers HO command to the BSS, T₃is isolated from T_S, T_A is one-way connected to T₃andT_S is both-way connected to T_A

Connection Model 3: UE-1 not yet detected in Target BSS, BSS-2 bicasts user plane data UL

Connection Model 4: UE-1 connected to Target BSS but Target MSC-S has not received HO Detect

Connection Model 5: MSC-1 instructed MGW-1 to reroute the user plane, T_A is both-way connected to T₃

Connection Model 6: Handover completed, T_S termination was removed

Figure 8.4.2.1.4.1.1: Inter-MSC Inter-BSS Handover Connection Model when user plane active

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

Figures 8.4.2.1.4.2.1 and 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 3GPP TS 23.009 [9], 3GPP TS 23.205 [2] and 3GPP TS 23.231 [3].

Figure 8.4.2.1.4.2.1: Inter-MSC Handover that breaks LCLS when user plane active, initial phase

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).

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.

3a, b. The Target MSC-Server reserves circuit or Connection Point T_T towards the Target BSS.

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.

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

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.

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

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.

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.

NOTE 1: The Serving BSS-1 shall forward the user plane data received locally from UE-1 to UE-2 while the UE-1 is served by the BSS-1. BSS-2 bicasts UL user plane data to both MGW2 and local path and MGW-2 transmits the user plane data to MGW-1 and MGW-1 transmits the user plane data to the Target BSS via the Target MGW. When the UE-1 leaves the serving BSS-1 and begins sending UL data to the Target BSS via the Target MGW, that data will then be received via the A-interface leg at the serving BSS-2.

NOTE 2: Possible bicasting may have been activated earlier when LCLS was established in the BSS-1 /BSS-2 (not shown here) and was indicated with the LCLS-Configuration IE in step 4 and applies to both call legs. If LCLS bicasting was not activated the LCLS-Configuration value is "Connect" (i.e. no bicasting) in step 4, but the value of the LCLS-Connection-Status-Control in step 8b is "BicastatHandover", which applies only for this call leg.

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".

8d. MSC-2 Server sends LCLS-Status-Change-Request-Acknowledge message.

NOTE 3: Handover sequence is independent of the LCLS-Status-Change-Request-Acknowledge message.

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 (T_S) and to configure the Anchor termination (T_A) one-way DL towards the Target MGW termination (T₃).

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.

NOTE 4: Corresponding SIP-I signalling is specified in 3GPP TS 23.231 [3].

11a, b. Target-MSC-Server reserves bearer connection T₄ towards MGW-1.

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.

Figure 8.4.2.1.4.2.2: Inter-MSC Handover that breaks LCLS when user plane active, completion phase

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.

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

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.

NOTE 5: there is no situation where BSS-2 will receive real DL user plane data from the CN at the same time as it receives local data from UE-1 as part of the handover.

16. UE-1 is detected at target BSS. But still no UL data can be sent from target BSS to MGW-1 because T_A-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.17. Target MSC-Server sends MAP-Process-Access-Signal request to the MSC-1 server.

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

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.

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".

17d. Acknowledgement back through the CN that the indication for DL data after Handover Detect has been delivered.

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 T_A-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.

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

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

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

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

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

NOTE 6: When BICC is used as the call control protocol the APM message is sent. When SIP-I is used the INFO request with the encapsulated APM message is sent.

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

NOTE 7: There is no need to send LCLS-Notification message from BSS-1 after receiving the Clear Command message since Clear Complete indicates that LCLS was disconnected.

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

26a, b. The MSC-1 server requests MGW-1 to set the Handover Device to its final state by removing the bearer termination T_S towards BSC-1 using the Release Termination procedure.

8.4.2.2 Inter-MSC GSM to GSM Handover that establishes Local Switching

8.4.2.2.1 General

When LCLS is not established for a call and an inter-MSC handover occurs that makes the call local, the call should be locally switched in the BSS. The Inter-MSC handover procedures specified in 3GPP TS 23.009 [9], 3GPP TS 23.205 [2] and 3GPP TS 23.231 [3] shall be followed. The following clauses describe the additional requirements for inter-MSC handovers that establish LCLS and the differences compared to Inter-MSC handovers that break LCLS are identified.

8.4.2.2.2 MSC-1 / MGW-1

8.4.2.2.2.1 Handover Required

8.4.2.2.2.2 Handover Request Acknowledge

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 configures the bearer terminations in MGW-1 and sends the GCR IE, the LCLS-Negotiation Request IE and the LCLS-Configuration-Preference IE to the target MSC-Server.

8.4.2.2.2.3 Bearer establishment between MGW-1 and Target MGW

8.4.2.2.2.4 MGW Flow Direction Control

In accordance with the normal handover case the MGW-1 isolates the termination towards the Target MGW (T₂) from the termination to the Serving BSS (T_S) and configures the Anchor termination (T₁) one-way DL towards the Target MGW termination (T₂). Termination to the Serving BSS (T_S) is both-way connected to Anchor termination (T₁) since it is also receiving UL user data from termination to the Serving BSS (T_S).

8.4.2.2.2.5 Handover Command/Handover Detect

The MSC-1 Server shall use the Change Flow Direction procedure to requests the MGW-1 to set the Handover Device to intermediate state.

8.4.2.2.2.6 Handover Complete

When LCLS has been established during the handover procedure, the target BSS informs the target MSC-Server that the call has been locally switched in the Handover Complete message,

8.4.2.2.3 Target MSC Server / Target MGW

8.4.2.2.3.1 Prepare Handover Request message and MGW selection

8.4.2.2.3.2 Handover Request Acknowledge

8.4.2.2.3.3 Bearer establishment towards Target BSS

8.4.2.2.3.4 Bearer establishment between MGW-1 and Target MGW

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

8.4.2.2.3.5 LCLS Negotiation in Initial Address message

8.4.2.2.4 Example of Inter-MSC Handover that establishes Local Switching

8.4.2.2.4.1 Connection Model

Figure 8.4.2.2.4.1.1 shows the network model for the Basic Inter-MSC GSM to GSM handover when LCLS is established as a result of the handover. The dashed line in green represents call control signalling and the dashed line in blue represents the user plane connection path via the core network, which should be used if LCLS is not established or after LCLS is broken. The non-dotted lines represent the bearer carrying real user plane data. In MGW-1 the bearer termination T_S is used for the bearer towards BSS-1, bearer termination T_A is used for the bearer towards the succeeding/preceding MGW, that is MGW-2 and bearer termination T₃ is used towards the Target MGW. In MGW-2 the bearer termination T₂ is used for the bearer towards BSS-2 and bearer termination T₁ is used for the bearer towards MGW-1. In Target-MGW the bearer termination T_T is used towards the Target-BSS and bearer termination T₄ is used towards MGW-1.

In this example scenario the Handover Device is located in MGW-1 selected for the call establishment by the MSC-1 server, which controls the call and mobility management.

Before Handover

During Handover, T₃ is isolated from T_S, T_A is one-way connected to T₃

After Handover, LCLS is established and both call legs are in Target BSS (=BSS-2)

Figure 8.4.2.2.4.1.1: Basic Inter-MSC GSM to GSM Handover (network model)

8.4.2.2.4.2 Basic Sequence for Inter-MSC GSM to GSM Handover that establishes Local Switching

Figures 8.4.2.2.4.2.1 and 8.4.2.2.4.2.2 show the message sequence example for the Basic Inter-MSC GSM to GSM Handover shown in the corresponding network model Figure 8.4.2.2.4.1.1. The Handover Device is located in 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 3GPP TS 23.009 [9], 3GPP TS 23.205 [2] and 3GPP TS 23.231 [3].

Figure 8.4.2.2.4.2.1: Initial phase of Inter-MSC Handover establishing Local Switching

1. Handover Required message is received from BSS-1 requesting an inter-MSC handover. The call is currently not locally switched.

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

3a, b. Target-MSC-Server reserves circuit or Connection Point towards the Target-BSS

4. Target MSC-Server sends Handover request message to target BSS with GCR and instructs the BSS to prepare to connect LCLS. The LCLS-Configuration IE can instruct the BSS to bi-cast user plane data, if applicable.

5. Target BSS performs call leg correlation with GCR to find if another call leg is active with same GCR. The BSS reports in Handover Request Acknowledge message that the local call was found but LCLS is not yet established.

5a. The BSS-2 notifies MSC-2 server the LCLS status is changed by sending the LCLS_Notification message with the LCLS-BSS-Status IE set to "Call not yet locally switched".

5b. If the call has been answered and MSC-2 server permits LCLS to be connected, then the MSC-2 server sends to the BSS-2 the LCLS_Connect_Control message with the LCLS-Connection-Status-Control IE set to "connect".

5c. The BSS-2 returns the LCLS_Connect_Control_ACK message with the LCLS-BSS-Status IE set to "Call not yet locally switched".

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 BSC-B IP address and UDP Port number to the MGW-B using the Configure RTP Connection Point procedure.

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

8, 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 (T_S) and to configure the Anchor termination (T_A) one-way DL towards the Target MGW termination (T₃).

9. 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.

NOTE 1: Corresponding SIP-I signalling is specified in 3GPP TS 23.231 [3].

NOTE 2: The LCLS-Negotiation Request IE and the LCLS-Configuration-Preference IE in step 9 can be different from LCLS Negotiation Request IE and the LCLS-Configuration-Preference IE in step 2, because step 9 is BICC signalling and the IE values can be changed by intermediate MSC-Servers.

10a, b. Target MSC-Server reserves bearer connection T₄towards MGW-1.

11. After Target MGW has replied with the bearer address and the binding reference (Step 10b), the Target MSC-Server returns the Bearer and Codec Information (APM) message with selected codec, available codec list and the LCLS-Negotiation Response IE and the LCLS-Configuration-Preference IE.

Figure 8.4.2.2.4.2.2: Completion phase of Inter-MSC Handover establishing Local Switching

12. 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 MSC-1 server initiates the handover execution when receiving ACM.

13 – 18. When the local switching has been established during the handover procedure, the target BSS shall inform the target MSC-Server that the call has been locally switched in Handover Complete message, and the target BSS shall also send a new message LCLS-Notification with LCLS-BSS-Status IE to inform the MSC-2 server that the local switching has been established. In steps 16a and 16b the MSC-1 server configures MGW-1 for the completion of the handover.

19. A Handover-Detect/Complete when received is included in the MAP-Send-End-Signalling request and sent back to the MSC-1 server.

20. Target MSC-Server sends ANSWER message with the LCLS-status when A-HO-DETECT/COMPLETE is received.

21. MSC-Server 1 clears the call in BSS-1.

22. MSC-1 server (Anchor MSC-Server) sends LCLS-Status-Update message to the far end MSC-2 server.

NOTE 3: When BICC is used as the call control protocol the APM message is sent. When SIP-I is used the INFO request with the encapsulated APM message is sent.

23. BSS-1 informs MSC-1 server that the resource for the UE-1 has been released

24a, b. MSC-1 server releases the bearer termination towards BSS-1.

25. Local switching is established in the BSS.

8.4.2.3 Inter-MSC Handover that leaves a not Locally Switched Call unchanged

In this scenario it is assumed that LCLS was not established before the Inter-MSC handover. When one call leg is handed over to another MSC-Server, the call still remains not local. LCLS cannot be established for the call and the LCLS status of the call is not changed.

For the Anchor MSC-1 server and Target MSC server this Inter-MSC handover is similar to the Inter-MSC handover that establishes LCLS as described in clause 8.4.2.2.4.2 until Step 5, but in this case in Step 5 the Target BSS sends the Handover Request ACK message, where the LCLS-BSS-Status IE indicates that the call is not possible to be locally switched since the GCR correlation will indicate that the call is not local. Steps 5a, 5b, 5c will not be triggered. The handover procedure is completed as for a non-local call, LCLS is not established and the LCLS Status in the core network is not changed.