Patent ID: 8811393

Claim:
An apparatus comprising: a processor; a memory coupled to the processor configured for storing state information relating to a session between a mobile node and a remote endpoint on an IP Multimedia Subsystem (IMS) network; a first network interface for communicating with the mobile node via a radio access network; a second network interface for communicating with the IMS network; a back-to-back user agent (B2BUA) module for providing session initiation protocol (SIP) services between the mobile node via the first network interface and the IMS network via the second network interface; a session module configured to receive packet data units (PDUs) from the first network interface and the second network interface and to use an inbound identifier and an outbound identifier with the session; and an interworking module coupled to the first network interface and the second network interface that is configured to interwork between SIP messages that use an IPv4 protocol and SIP messages that use an IPv6 protocol by replacing addresses compatible with the IPv4 protocol in a SIP protocol header with addresses compatible with the IPv6 protocol, and is configured to use at least one of the inbound identifier and the outbound identifier to match an incoming SIP message to the session, thereby enabling interworking between IPv4 and IPv6 SIP messages wherein the apparatus comprises a call session control function (CSCF); and wherein the interworking module is configured to determine whether to perform interworking based on control information stored at the apparatus.