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In this paper we investigate the problem of voice communications across heterogeneous telephony systems on dual-mode (WiFi and GSM) mobile devices. Since GSM is a circuit-switched telephony system, existing solutions that are based on packet-switched network protocols cannot be used. We show in this paper that an enabling technology for seamless voice(More)
More and more handsets manufactured today are being equipped with WLAN modules, allowing users to access VoIP service whenever they are within the coverage of WLAN service area. One of the greatest challenges for such dual-mode (say GSM and WiFi) handsets to support ubiquitous communication is the ability to maintain session continuity so a phone call(More)
As the popularity of multi-functional communication devices grows, traditional audio conferencing now may involve heterogeneous teleconferencing devices, including POTS phone, VoIP phones, dual-mode smart phones, and so on. During a multi-party audio conference involving heterogeneous devices, it is possible that a video conference is held concurrently(More)
In this paper, we consider a university campus that has an established infrastructure for supporting SIP-based VoIP service through the campus wireless data network. The campus WIAN, however, does not have 100% full coverage , and hence users cannot make untethered VoIP calls anywhere on campus. The goal of this paper is to overcome the limitations of such(More)
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