A cooperative SIP infrastructure for highly reliable telecommunication services

Voice over IP (VoIP) has been a promising technology for several years. Although it has become very popular, the vision to substitute the "good old" Public Switched Telephone Network (PSTN) is still far from being true. Several issues, such as security, reliability and emergency calls are slowing down the integration of VoIP. Currently, there is a mixture of technologies where VoIP is often used for reducing costs, while still keeping the PSTN if a reliable communication is needed. Peer-to-Peer (P2P) and overlay networks received a large attention in the research community in the last few years. P2P networks provide self-organization and scalability. Recent work involved P2P-based signaling for lookup services for Voice over IP (VoIP) communication based on the Session Initiation Protocol (SIP). The main motivation behind P2P-basd SIP is to support ad hoc communication, to simplify the configuration of SIP networks, to make SIP networks more scalable and to provide services independently of other network components such as DNS. However, pure P2P networks do not have only their advantages. They create also several security threats which are hard to solve. Some of them, for example, the Sybil attack, have been proven to be unsolvable without centralized authorities or an additional out-of-band mechanism. P2P-based SIP may also create a high potential for Spam over IP Telephony (SPIT). In this paper, we present a hybrid solution for telecommunication networks that fills the gap between centralized (and therefore vulnerable to Denial-of-Service (DoS) attacks) telecommunication infrastructures and pure P2P-based telecommunication networks (which are vulnerable to SPIT, Sybil attacks, eclipse attacks, partition attacks, etc.). Our approach works with a SIP server under normal operation, while SIP User Agents (UAs) organize themselves into a P2P network. In the normal case, SIP UAs can profit from the lookup performance provided by the SIP server, which is usually better than the performance provided by the P2P network. In case of a service interruption of the infrastructure, the SIP network will function further due to the interconnection in the P2P network. Since the server and the P2P network cooperate in order to improve reliability, survivability, performance and security, we call this approach Cooperative SIP (CoSIP). We present our prototype implementation of CoSIP and discuss the potential for improvements compared to server-based SIP and P2P-based SIP.