Push-to-Talk (PTT) is a useful capability for rapidly deployable wireless mesh networks used by first responders. PTT allows several users to speak with each other while using a single, half-duplex, communication channel, such that only one user speaks at a time while all other users listen. Furthermore, enabling regular PSTN phone users (e.g., cell phones) to seamlessly participate in the wireless mesh PTT session is key to supporting the heterogeneous environment commonly found in such settings. This paper presents the architecture and protocol of a robust distributed PTT service for wireless mesh networks. The architecture supports any 802.11 client with SIP-based VoIP software and enables the participation of regular phones. Collectively, the mesh nodes provide the illusion of a single third party call controller, enabling clients to participate via any reachable mesh node. Each PTT group instantiates its own logical floor control manager that is highly available and resilient to mesh connectivity changes such as node crashes and recoveries and network partitions and merges. Experimental results on a fully deployed mesh network consisting of 14 mesh nodes and tens of emulated clients demonstrate the scalability and robustness of the system.

Wireless mesh networks extend the connectivity range of mobile devices by using multiple access points, some of them connected to the Internet, to create a mesh topology and forward packets over multiple wireless hops. However, the quality of service provided by the mesh is impaired by the delays and disconnections caused by handoffs, as clients move within the area covered by multiple access points. We present the architecture and protocols of SMesh, the first transparent wireless mesh system that offers seamless, fast handoff, supporting real-time applications such as interactive VoIP. The handoff and routing logic is done solely by the access points, and therefore connectivity is attainable by any 802.11 device. In SMesh, the entire mesh network is seen by the mobile clients as a single, omnipresent access point, giving the mobile clients the illusion that they are stationary. We use multicast for access points coordination and, during handoff transitions, we use more than one access point to handle the moving client. SMesh provides a hybrid routing protocol that optimizes routes over wireless and wired links in a multihomed environment. Experimental results on a fully deployed mesh network demonstrate the effectiveness of the SMesh architecture and its intra-domain and inter-domain handoff protocols.

This paper presents an architecture and a hybrid routing protocol for multi-homed wireless mesh networks that provide uninterrupted connectivity and fast handoff. Our approach integrates wireless and wired connectivity, using multicast groups to coordinate decisions and seamlessly transfer connections between several Internet gateways as mobile clients move between access points. The protocol optimizes the use of the wireless medium by short-cutting wireless hops through wired connections, paying a very low overhead during handoffs. The paper demonstrates that inter-domain handoffs occur instantaneously, with virtually no loss or delay, for both TCP and UDP connections.

Abstract — This paper presents the architecture and protocols of SMesh, a completely transparent wireless mesh system that offers seamless, fast handoff, supporting VoIP and other real-time application traffic for any unmodified 802.11 device. In SMesh, the entire mesh network is seen by the mobile clients as a single, omnipresent access point. Fast handoff is achieved by ensuring that each client is served by at least one access point at any time. Mobile clients are handled by a single access point during stable connectivity times. During handoff transitions, SMesh uses more than one access point to handle the moving client. Access points continuously monitor the connectivity quality of any client in their range and efficiently share this information with other access points in the vicinity of that client to coordinate which of them should serve the client. Experimental results on a fully deployed mesh network consisting of 14 access points demonstrate the effectiveness of the SMesh architecture and its handoff protocol. I.