In order to achieve seamless handover for real-time applications in the IP Multimedia Subsystem (IMS) of the next-generation network, a multi-protocol combined handover mechanism is proposed. In this work, we combine SIP (Session Initiation Protocol), FMIP (Fast Mobile IPv6 Protocol) and MIH (Media Independent Handover) protocols by cross-layer design and optimize these protocols' signaling flows to improve vertical handover performance. Theoretical analysis and simulation result illustrate that our proposed mechanism is 1better than the original SIP and MIH combination handover mechanism in service interrupt time and packets loss aspects.