Practical Performance Evaluation of Peer-to-peer Internet Telephony using SIP

Peer-to-peer (P2P) systems have been shown to have excellent scalability and fault tolerance characteristics, mainly due to their distributed nature and the lack of a single point of failure. As a result, P2P technology has been proposed for a wide range of applications. Recently, a number of researchers proposed the use of P2P technology in the context of Voice over IP (VoIP) or Internet Telephony, in particular with the IETF's Session Initiation Protocol (SIP). By replacing the centralised components of the client/server based SIP protocol with a P2P system (P2P-SIP), a higher level of robustness and scalability can be achieved. However this comes at the cost of a higher latency, which might negatively impact on the Quality of Service (QoS) due to increased delays in call establishment. In this paper we provide a practical performance evaluation of a P2P-SIP system via extensive measurements on OpenDHT a large scale, publicly accessible P2P system. The basis of this evaluation is formed by our own implementation of a P2P-SIP system, and standard, SIP-compliant client software. Our results confirm the feasibility of the P2P-SIP approach, since the cost in terms of increased delay in call setup time is quite moderate and well below the recommended value,for traditional telephony defined by the Standardisation Sector of the International Telecommunication Union (ITU-T).