A Mobility-aware Broadcasting Infrastructure for a Wireless Internet with Hotspots

In this paper, we consider the problem of adaptively delivering live multimedia broadcasts (e.g., for applications such as TV, radio, or e-cinema) to a potentially large number of mobile hosts that roam about in a wireless internet with hotspots. We take a user-oriented approach based on an application-level delivery infrastructure consisting of and managed by (value-added) service providers. The service providers are mobility-aware and offer broadcasts in configurations that are optimized for wireless links and mobile hosts. In hotspots, mobile hosts may be able to simultaneously reach several localized service providers through different interfaces. Within this context, we present the design of a lightweight application-level protocol that enables mobile hosts to select a service provider from which they want to receive a broadcast. Mobile hosts use the protocol to begin receiving a broadcast and to remain connected to the same logical broadcast as they move across subnets. The protocol is independent of the actual stream control protocol (e.g., RTSP) that service providers might use. We show how our protocol can be realized with the existing protocols SIP and SDP. The realization uses SIP in combination with SDP's offer-answer model in a new way.