ISSN : 1796-2056
Volume : 3    Issue : 2    Date : February 2008

Network-Initiated Terminal Mobility in Voice over 3GPP-WLAN
Wei-Kuo Chiang and Hsin-Fu Huang
Page(s): 1-8
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This paper proposes a network-initiated terminal mobility mechanism (NITM) to facilitate handover
with the session initiation protocol (SIP) in 3GPP Voice over WLAN (3GPP VoWLAN). We design the
E2E tunnel state model running on the packet data gateway (PDG) using the CAMEL concept, and
introduce the mobility server (MS) as a SIP application server to re-establish sessions with third
party call control (3PCC). The MS is triggered to provide the terminal mobility service from the PDG
by detecting the state transition of the 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 mobileinitiated terminal mobility; moreover, it can handle
mobility without additional support from the mobile host (MH). In addition, the handover missing
problem (messages lost) might happen when the MH moves under communication. With the help
of the MS, the lost messages are re-sent, and the handover missing problem, including
simultaneous movement, is therefore solved.

Index Terms
IP multimedia subsystem, WLAN telephony, SIP mobility, handover, IN/CAMEL, mobility server