E.2.6 Call release

29.1633GPPInterworking between the IP Multimedia (IM) Core Network (CN) subsystem and Circuit Switched (CS) networksTS

E.2.6.1 Call release initiated from the IM CN subsystem side

When the MGCF has received a BYE message (signal 1 in figure E.2.6.1.1) from the IM CN subsystem side, the MGCF may end the H.245 session between the IM-MGW and the CS network side (signal 3 in figure E.2.6.1.1) firstly.

NOTE: A call release using only ISUP/BICC signalling at the CS side proceeds faster. H.324 terminals can handle situations where they do not receive H.245 call release signalling (see clause 7.5.2 of ITU-T Recommendation H.324 [81]), and this scenario also occurs e.g. at loss of coverage or when a node transporting H.223 transparently releases the call.

The procedure of ending the H.245 session is defined in the clause E.4. After receiving the BYE message, the MGCF shall also send a 200 OK [BYE] message (signal 2 in figure E.2.6.1.1) towards the IM CN subsystem.

After ending the H.245 session, the MGCF shall send a REL message (signal 4 in figure E.2.6.1.1) to the succeeding node. If the IM CN subsystem interworks with ISUP based CS network, the interworking node shall release the resources for the IMS side and the CS network side (signal 6 in figure E.2.6.1.1) after sending the REL message. If the IM CN subsystem interworks with BICC based CS network, the interworking node shall release the resources for the IMS side and the CS network side (signal 6 in figure E.2.6.1.1) upon receiving the RLC message (signal 5 in figure E.2.6.1.1) from the CS network side. The procedures of releasing the resources for the IMS side and the CS network side are specified in the present 3GPP TS in clause 7.

Figure E.2.6.1.1 shows the message sequence chart for the multimedia call release initiated from the IM CN subsystem side.

NOTE: Signal 7 is omitted when IM CN subsystem interworks with BICC based CS network and Signal 5 is omitted when IM CN subsystem interworks with ISUP based CS network.

Figure E.2.6.1.1: Call release initiated from the IM CN subsystem side

E.2.6.2 Call release initiated from the CS network side

If the CS network side initiates the call release, it possibly ends the H.245 session with explicit signalling (signal 1 in figure E.2.6.2.1). The CS network side sends a REL message (signal 2 in figure E.2.6.2.1) towards the IM CN subsystem. The procedure of ending the H.245 session is defined in the clause E.4.

When the MGCF receives a REL message (signal 2 in figure E.2.6.2.1) from the preceding node, the MGCF sends a BYE message (signal 3 in figure E.2.6.2.1) to the IM CN subsystem. After receiving the REL message, the interworking node also releases the resources for the IMS side and the CS network side (signal 4 in figure E.2.6.2.1). The procedure of the releasing the resources for the IMS side and the CS network side are specified in the present 3GPP TS in clause 7. After completion of resource release, the MGCF sends a RLC message (signal 5 in figure E.2.6.2.1) towards the preceding node. Figure E.2.6.2.1 shows the message sequence chart for the multimedia call release initiated from the CS network side.

Figure E.2.6.2.1: Call release initiated from the CS network side

E.2.6.3 Call release initiated from the interworking node

The interworking node may end the H.245 session between the IM-MGW and the CS network side (signal 1 in figure E.2.6.3.1) firstly. The procedure of ending the H.245 session is defined in the clause E.4.

NOTE: A Call Release using only SIP and ISUP/BICC signalling may proceed faster. H.324 terminals can handle situations where they do not receive H.245 call release signalling (see clause 7.5.2 of ITU-T Recommendation H.324 [81]), and this scenario also occurs e.g. at loss of coverage or when a node transporting H.223 transparently releases the call.

To release the call, the MGCF shall send a REL message (signal 2 in figure E.2.6.3.1) to the succeeding node on the CS network side. The MGCF shall also send a BYE message (signal 3 in figure E.2.6.3.1) to the IM CN subsystem side.

If the IM CN subsystem interworks with ISUP based CS network, the interworking node shall release the resources for the IMS side and the CS network side (signal 5 in figure E.2.6.3.1) after sending the REL message. If the IM CN subsystem interworks with BICC based CS network, the interworking node shall release the resources for the IMS side and the CS network side upon receiving the RLC message (signal 4 in figure E.2.6.3.1) from the CS network side. The procedures of releasing the resources for the IMS side and the CS network side are specified in the present 3GPP TS in clause 7. Figure E.2.6.3.1 shows the message sequence chart for the multimedia call release initiated from the interworking node.

NOTE: Signal 6 is omitted when IM CN subsystem interworks with BICC based CS network and Signal 4 is omitted when IM CN subsystem interworks with ISUP based CS network.

Figure E.2.6.3.1: Call release initiated from the interworking node