SUMMARYThe services of next generation networks are envisioned to be potentially capable of seamless mobility in spite of the heterogeneity in underlying access technologies. It is undoubted that to accomplish seamless services across heterogeneous networking environments gets harder in case of simultaneous mobility. In this article, we propose a mobile-initiated network-executed (MINE) session initial protocol (SIP)-based handover mechanism to facilitate simultaneous mobility in IP multimedia subsystem over heterogeneous accesses. The novelty of the proposed approach is that no changes are required to the existing network infrastructure since handover decision is fully made by the mobile host (MH) and handover execution is performed by a new-added application server called mobility server (MS). When the MH decides to initiate a handover and obtains a new IP address, it will send a SIP Publish message to trigger the MS to carry out the handover execution. With the network-executed design of the MINE, the MS can perform third-party registration for security re-association and third-party call control for session re-establishment in parallel. Moreover, the Master-Slave Determination procedures derived from H.245 are used in the MS to handle fairly the racing conditions resulting from simultaneous mobility such that redundant message flows are eliminated. Mathematical analyses present that the MINE can shorten the handover latency and reduce power consumption, as observed from a comparison with the integrated solution of an optimized macro-mobility mechanism and a receiver-side simultaneous mobility approach.

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VoIP over WLAN (VoWLAN) gradually has become a popular application with the fast maturing of both WLAN and Voice over IP (VoIP) technology. However, there exists one problem that heavily affects the satisfaction of the users, which is that the mobility of the mobile host (MH) can disrupt or even intermittently disconnect an ongoing real-time session. Therefore, the issue of how to reduce the handover delay gets more and more important. This paper proposes a Network-Initiated SimUltaneouS mobility (NISUS) mechanism to facilitate terminal mobility with the session initiation protocol (SIP) in Voice over 3GPP-WLAN. We design the E2E tunnel state model running on the packet data gateway (PDG) referring to the CAMEL concept. The NISUS is triggered at the PDG by detecting the state transition of the E2E tunnel state model that represents the occurrence of a handover. Then the PDG sends the handover request to notify the Mobility Server (MS) to perform a third party call control (3PCC) and a third party registration on behalf of the MH in parallel for session re-establishment. With the help of the MS, we ensure the lost signaling messages could be correctly re-sent to moving hosts. Moreover, the Master-Slave Determination procedures derived from H.245 are proposed for the MS in order to handle the racing conditions fairly when two MSs involved in a simultaneous mobility issue 3PCC calls respectively at about the same time. We demonstrate the NISUS works well in the simultaneous and non-simultaneous movement cases. Analytical results show that the handover delay can be improved significantly by using the NISUS, compared with the mobile-initiated simultaneous/non-simultaneous mobility.