Method and system for providing voice call continuity
View Patent ↗A method and system for providing circuit-switched to IP Multimedia Subsystem voice call continuity with a single radio are provided. The exemplary embodiment takes advantage of a standard RANAP signaling procedure called “directed retry” to perform a much better coordination between the change in radio mode and the transfer of the media path. With the use of “directed retry”, the transfer of the media path does not begin until the handover procedure is complete, thus significantly reducing the likely amount of media disruption.
1. A method of providing circuit-switched (CS) to IP Multimedia Subsystem (IMS) voice call continuity with a single radio (UE), the method comprising:
detecting that domain transfer is required and sending this information to the UE as well as sending a relocation request to an inter-working function (IWF);
sending a tunneled circuit origination request to the CS CN;
receiving a CS radio access bearer (RAB) assignment request from the CS CN network;
the IWF responding to the CS RAB assignment request with “directed retry” indication to indicate that it will honor the request by initiating a CS RAB handover to a target radio access network (RAN); and
completing the CS RAB handover by directing the UE to the target RAN.
2. The method defined in claim 1 , further comprising:
the CS CN forwarding the handover request to the CS RAN;
the CS RAN assigning resources for the CS RAB and acknowledging the assignment to the CS CN;
the CS CN informing the IWF of CS RAB resource assignment in the CS RAN;
the PS CN directing the UE to re-tune its radio to the CS RAN;
the CS RAN detecting connectivity to the UE 102 ; and
the CS CN propagating the CS origination into the network.
3. The method defined in claim 1 , wherein the PS CN comprises an LTE/SAE (Long Term Evolution/System Architecture Evolution) network.
4. The method defined in claim 1 , further comprising:
transferring PS RABs from the PS CN network to the target RAN to the extent supported by the target RAN.
5. The method defined in claim 1 , further comprising:
the IWF queuing the relocation request until it receives a RAB assignment request from the CS CN to synchronize CS and PS relocation procedures.
6. The method defined in claim 1 , wherein the “directed retry” indication informs the CS CN that the IWF is incapable of assigning a CS RAB at this time but there is a CS RAN candidate to fulfill the CS RAB assignment request and the IWF initiates a CS RAB handover procedure to assign this CS RAB in the CS RAN.
7. The method defined in claim 6 , wherein immediately after the IWF indicates “directed retry” to the CS CN, it initiates a CS RAB handover to the CS RAN via the CS CN.
8. A system for providing circuit-switched (CS) to IP Multimedia Subsystem (IMS) voice call continuity with a single radio (UE), the system comprising:
tunneling means for tunneling CS call control and mobility management messages via a packet-switched core network (PS CN) to a circuit-switched core network (CS CN);
detecting means for detecting that domain transfer is required and sending this information to the UE as well as sending a relocation request to an inter-working function (IWF);
sending means for sending a tunneled circuit origination request to the CS CN;
receiving means for receiving a RAB assignment request from the CS CN network;
an inter-working function (IWF) for responding to the CS RAB assignment request with “directed retry” indication to indicate that it will honor the request by initiating a CS RAB handover to a target radio access network (RAN); and
directing means for completing the CS RAB handover by directing the UE to the target RAN.
9. The system defined in claim 8 , wherein the PS CN comprises an LTE/SAE (Long Term Evolution/System Architecture Evolution) network.
10. The system defined in claim 8 , further comprising:
transferring means for transferring PS RABs from the PS CN network to the target RAN to the extent supported by the target RAN.
11. The system defined in claim 8 , wherein the IWF is operative to queue the relocation request until it receives a RAB assignment request from the CS CN to synchronize CS and PS relocation procedures.
12. The system defined in claim 8 , wherein the “directed retry” indication informs the CS CN that the IWF is incapable of assigning a CS RAB at this time but there is a CS RAN candidate to fulfill the CS RAB assignment request and the IWF initiates a CS RAB handover procedure to assign this CS RAB in the CS RAN.
13. The system defined in claim 12 , wherein the IWF is operative to initiate a CS RAB handover to the CS RAN via the CS CN immediately after the IWF indicates “directed retry” to the CS CN.