Patent ID: 8644218

Claim:
A method of operating an internet protocol multimedia subsystem (IMS) to control a communication session between a first communication device and a second communication device, the method comprising: in a call session control function, receiving a session initiation protocol (SIP) bye message transferred by the first communication device, wherein the SIP bye message includes a code that indicates a loss of the communication session and that includes an identifier for the second communication device; in the call session control function, subscribing with a home subscriber server for a registration notification for the second communication device in response to the code in the SIP bye message; in the call session control function, receiving the registration notification for the second communication device from the home subscriber server that indicates a network address for the second communication device in response to a SIP registration request transferred by the second communication device after the second communication device reacquires a wireless link; and in the call session control function, transferring SIP invite messages for delivery to the first communication device and to the second communication device to re-establish the communication session in response to the registration notification for the second communication device.