Patent ID: 9706446
Date: 2017-07-11
CPC Classifications: H04W

Claim:
1. A method of performing a Single Radio Voice Call Continuity (SRVCC) handover of an emergency call from a Packet Switched (PS) access network to a Circuit Switched (CS) access network and that is routed over an IP Multimedia Subsystem (IMS) network, wherein the emergency call is first transferred from an access network in a first region served by a first Mobility Management Entity (MME) to a second region served by a second MME, the method comprising: sending a first handover request from the first MME to the second MME to transfer the emergency call to the second region, the first handover request including an Emergency Session Transfer Number for the SRVCC (E-STN-SR) identifying an Emergency Access Transfer Function (EATF) in the first region; sending a second handover request for handover to a CS access network, the second handover request being sent from the second MME to a target Mobile Switching Centre (MSC) and including the E-STN-SR identifying the EATF in the first region, wherein the second handover request is sent over an Sv interface between the second MME and the target MSC, wherein the Sv interface has been extended to include an optional E-STN-SR; and handing over the emergency call to the CS access network using the E-STN-SR to route the emergency call via the EATF in the first region, wherein prior to handing over the emergency call to the CS access network, the target MSC initiates a session transfer by sending a message to the IMS network using the E-STN-SR, and wherein the target MSC is preconfigured with an E-STN-SR that identifies an EATF in the second region to which emergency calls that are handed over to the CS access network are routed when the handover request does not include an E-STN-SR of an EATF in another region.