Patent ID: 8848666

Claim:
A method of performing a handover with Single Radio Voice Call Continuity (SRVCC) to a target Packet Switched (PS) access network of an emergency call to a Public safety Access Point (PSAP) from a User Equipment (UE) accessing a Circuit Switched (CS) access network, the method comprising: sending a handover request from the CS access network towards an IP Multimedia Subsystem (IMS) network to transfer the emergency call; sending a CS to PS emergency handover command to the UE, including an authentication token and an emergency Session Transfer Number (STN) identifying an access transfer control function; the UE sending a Session Initiation Protocol (SIP) INVITE to establish an emergency IMS session over the PS access network, wherein the SIP INVITE includes the authentication token and the emergency STN so that the INVITE is routed to the access transfer control function, wherein an unauthenticated IMS emergency procedure is used to set up the emergency IMS session over the PS access network in response to the CS to PS emergency handover; sending a CS to PS emergency handover request to a Mobile Management Entity (MME), the MME allocating resources for the emergency IMS session, wherein an International Mobile Equipment Identity (IMEI) of the UE is included in the CS to PS emergency handover request only in response to the IMS emergency procedure being unauthenticated; operating the MME to inform a Policy and Charging Rules Function (PCRF) of the CS to PS emergency handover request; operating the PCRF to establish an emergency APN and associated emergency bearers; correlating the emergency call sent over the CS access network with the emergency IMS session; and switching the emergency call to the emergency IMS session over the PS access network to complete the handover.