System and method for circuit switched fallback in IMS centralized services
A method of performing CSFB in an IMS comprises receiving, at a TAS, an incoming voice call for a UE attached to an EPS; paging the UE by the first ICS GW; receiving, by a second ICS GW associated with a second CS RAN currently connected to the UE, a Location Update message from the UE, the Location Update message containing a first CSFB indicator; transmitting, by the second ICS GW, a Registration message to the TAS, the Registration message containing a second CSFB indicator in response to the first CSFB indicator in the Location Update message; transmitting, by the TAS, a Cancel message to the first ICS GW; and transmitting, by the TAS, an Invite message to the second ICS GW to complete the voice call with the UE.
1. A method of performing Circuit Switched Fallback (CSFB) in an IP Multimedia Subsystem (IMS), comprising:
receiving, at a Telephony Application Server (TAS), an incoming voice call for a User Equipment (UE) attached to an Evolved Packet Subsystem (EPS);
transmitting, by the TAS, an Invite message to a first network node associated with a first Circuit Switched Radio Access Network (CS RAN) connected to the UE;
paging the UE by the first network node;
receiving, by a second network node associated with a second CS RAN currently connected to the UE, a Location Update message from the UE, the Location Update message containing a first CSFB indicator;
transmitting, by the second network node, a Registration message comprising an IMS Registration message to the TAS, the Registration message containing a second CSFB indicator in response to the first CSFB indicator in the Location Update message;
transmitting, by the TAS, a Cancel message to the first network node, after the step of transmitting the Registration message; and
transmitting, by the TAS, an Invite message to the second network node to complete the voice call with the UE.
2. The method of claim 1 , wherein transmitting, by the TAS, an Invite message to a first network node comprises transmitting an Invite message to a ICS GW associated with the first CS RAN.
3. The method of claim 1 , wherein receiving, by a second network node a Location Update message from the UE comprises receiving, by an ICS GW the Location Update message containing the first CSFB indicator from the UE.
4. The method of claim 1 , wherein transmitting, by the second network node, a Registration message to the TAS, comprises transmitting, by an ICS GW, the Registration message containing a second CSFB indicator to the TAS.
5. The method of claim 1 , wherein transmitting a Registration message by the second network node comprises transmitting a Registration message having a unique reg-id to avoid the Registration message from the second network node to overwrite a previous IMS registration from the first network node.
6. The method of claim 1 , wherein transmitting a Registration message comprises transmitting a Registration message having a new SIP header to indicate a CSFB call.
7. The method of claim 1 , wherein transmitting a Registration message comprises transmitting a Registration message having a pre-existing message parameter to indicate a CSFB call.
8. The method of claim 1 , wherein transmitting a Location Update message comprises transmitting a Location Update message having a pre-existing message parameter to indicate a CSFB call.
9. A method of performing Circuit Switched Fallback (CSFB) in an IP Multimedia Subsystem (IMS), comprising:
receiving, at a Telephony Application Server (TAS), an incoming voice call for a User Equipment (UE) attached to an Evolved Packet Subsystem (EPS);
transmitting, by the TAS, an Invite message to a first network node associated with a first Circuit Switched Radio Access Network (CS RAN) connected to the UE;
paging the UE by the first network node;
receiving, by a second network node associated with a second CS RAN currently connected to the UE, a Location Update message from the UE, the Location Update message containing a first CSFB indicator;
transmitting, by the second network node, a Registration message to the TAS, the Registration message containing a second CSFB indicator in response to the first CSFB indicator in the Location Update message;
transmitting, by the TAS, a Cancel message to the first network node; and
transmitting, by the TAS, an Invite message to the second network node to complete the voice call with the UE;
wherein transmitting, by the TAS, an Invite message to a first network node comprises transmitting an Invite message to a MSC/VLR associated with the first CS RAN.
10. A method of performing Circuit Switched Fallback (CSFB) in an IP Multimedia Subsystem (IMS), comprising:
receiving, by a gateway network node associated with a Circuit Switched Radio Access Network (CS RAN) currently connected to a User Equipment (UE), a first message to update its location from the UE containing a first CSFB indicator;
transmitting, by the current gateway network node, a second message comprising an IMS Registration message to register the UE to an application server node handling an incoming voice call for the UE, the second message containing a second CSFB indicator in response to the first CSFB indicator in the first message;
transmitting, by the application server node, a third message to a prior gateway network node associated with a prior CS RAN previously connected to the UE to cancel a prior pending invite request in response to the second CSFB indicator in the second message; and
transmitting, by the application server node, a fourth message to the current gateway network node to complete the voice call with the UE.
11. The method of claim 10 , wherein transmitting an IMS Registration message comprises transmitting an IMS Registration message having a unique reg-id assigned to avoid the IMS Registration message from the current gateway network node to overwrite a previous IMS registration from the prior gateway network node.
12. The method of claim 10 , wherein transmitting an IMS Registration message comprises transmitting an IMS Registration message having a new SIP header.
13. The method of claim 10 , wherein transmitting an IMS Registration message comprises transmitting an IMS Registration message having a pre-existing message parameter to indicate a CSFB call.
14. The method of claim 10 , wherein transmitting a Location Update message comprises transmitting a Location Update message having a pre-existing message parameter to indicate a CSFB call.
15. A non-transitory computer-readable medium having encoded therein a method of performing Circuit Switched Fallback (CSFB) in an IP Multimedia Subsystem (IMS), the method comprising:
receiving, by a first network node associated with a current Circuit Switched Radio Access Network (CS RAN) connected to a User Equipment (UE), a Location Update message from the UE containing a first CSFB indicator;
transmitting, by the first network node, a Registration message comprising an IMS Registration message to a Telephony Application Server (TAS) handling an incoming voice call for the UE, the Registration message containing a second CSFB indicator in response to the first CSFB indicator in the Location Update message;
transmitting, by the TAS, a Cancel message to a second network node associated with a prior CS RAN previously connected to the UE in response to the second CSFB indicator in the Registration message; and
transmitting, by the TAS, an Invite message to the first network node to complete the voice call with the UE.
16. The method of claim 15 , wherein receiving, by a first network node associated with a current Circuit Switched Radio Access Network (CS RAN) connected to a User Equipment (UE), a Location Update message comprises receiving, by a current IMS Centralized Services Gateway (ICS GW) associated with a current Circuit Switched Radio Access Network (CS RAN) connected to a User Equipment (UE), a Location Update message containing the first CSFB indicator from the UE.
17. The method of claim 15 , wherein transmitting, by the first network node, a Registration message to a Telephony Application Server (TAS) comprises transmitting, by a current IMS Centralized Services Gateway (ICS GW), a Registration message to a Telephony Application Server (TAS) handling an incoming voice call for the UE, the Registration message containing a second CSFB indicator in response to the first CSFB indicator in the Location Update message.
18. The method of claim 15 , wherein transmitting, by the TAS, a Cancel message comprises transmitting, by the TAS, a Cancel message to a prior IMS Centralized Services Gateway (ICS GW) associated with a prior CS RAN previously connected to the UE in response to the second CSFB indicator in the Registration message.
19. The method of claim 15 , wherein transmitting a Registration message comprises transmitting a Registration message having a unique reg-id assigned to avoid the Registration message from the first network node to overwrite a previous IMS registration from the second network node.
20. The method of claim 15 , wherein transmitting a Registration message comprises transmitting a Registration message having a new SIP header.
21. The method of claim 15 , wherein transmitting a Registration message comprises transmitting a Registration message having a pre-existing message parameter to indicate a CSFB call.
22. The method of claim 15 , wherein transmitting a Location Update message comprises transmitting a Location Update message having a pre-existing message parameter to indicate a CSFB call.
23. A telecommunication network node configured to coordinate Circuit Switched Fallback (CSFB) in an IP Multimedia Subsystem (IMS), comprising:
receiving, at a Telephony Application Server (TAS), an incoming voice call for a User Equipment (UE) attached to an Evolved Packet Subsystem (EPS);
transmitting, by the TAS, an Invite message to a first network node associated with a first Circuit Switched Radio Access Network (CS RAN) connected to the UE;
receiving, by the TAS, a Registration message comprising an IMS Registration message from a second network node currently associated with a second CS RAN, the Registration message containing a CSFB indicator indicating a CSFB voice call;
transmitting, by the TAS, a Cancel message to the first network node, after receiving the Registration message; and
transmitting, by the TAS, an Invite message to the second network node to complete the voice call with the UE.