Patent ID: 8908642

Claim:
A mobile communication system comprising: a radio access system employing a first communication scheme not supporting circuit-switched communication; a radio access system employing a second communication scheme supporting the circuit-switched communication; and an IP Multimedia Subsystem (IMS), wherein the mobile communication system is configured to switch between a first communication state and a second communication state, realizing single radio voice call continuity (SRVCC), a first mobile station is in a serving area of the radio access system employing the first communication scheme and is configured to perform voice communication between the first mobile station and a second mobile station in a case of the first communication state, the first mobile station is in a serving area of the radio access system employing the second communication scheme and is configured to perform voice communication between the first mobile station and the second mobile station in a case of the second communication state, and the mobile communication system is configured to switch from paths of a VoIP media signal and a VoIP control signal in the first communication state to paths of a circuit-switched signal, a VoIP media signal, and a VoIP control signal in the second communication state in a serving network of the first mobile station by determining whether the first mobile station has SRVCC capability, wherein the SRVCC-capability of the first mobile station is determined based on a “Tracking Area Update Request” transmitted by the first mobile station to a node of the mobile communication system.