Network-Initiated Triggering for Mobility in Voice over 3GPP-WLAN

This paper proposes a network-initiated triggering mechanism to facilitate terminal mobility with the session initiation protocol (SIP) in 3GPP voice over WLAN (VoWLAN). We design the E2E tunnel state model running on the packet data gateway (PDG) using the CAMEL concept, and introduce the mobility server to re-establish sessions with third party call control (SPCC). The mobility server is triggered to provide the terminal mobility service from the PDG by detecting the state transition of E2E tunnel state model that represents the occurrence of a handover. This mechanism can advance the time to re-establish sessions. That is, our approach can provide smaller handover delay than SIP mobility; moreover, it can handle mobility without additional support from the mobile host. In addition, the handover missing problem (messages lost) might happen when the MH moves under communication. With the help of the mobility server, the lost messages are re-sent, and the handover missing problem, including simultaneous movement, is therefore solved