Because of the emergence of heterogeneous access devices and diverse wired and wireless networks, and a substantial lack of support for integrating these networks, we are building a communication network and a service infrastructure that provides integrated telephony and data services across these networks. We generalize the basic call service to support communication between two or more call parties using any number of devices through any media. Call setup has already been addressed by protocols such as the session initiation protocol (SIP), so we focus on a missing component: scalable and fault-tolerant call session maintenance and control after call setup. In this paper, we present a new signaling protocol that offers scalability, high availability, robustness, and flexibility in creating new call processing services. The protocol is compatible with existing call setup protocols, but provides lightweight call session management using a completely decentralized, soft-state group control protocol. We show that this approach simplifies the implementation of the basic call service, including multi-device calling and service handoff between diverse access networks. The design of our protocol follows the principle of separation of control (signaling information) from data. The signaling protocol has been implemented in ICEBERG, an IP-based core network testbed with access to heterogeneous networks.
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