cis Group, LLC Part II TECHNOLOGIES © 2009 by Taylor & Francis Group, LLC P2P SIP: Network Architecture and Resource Location Strategy Guiran Chang, Chuan Zhu, and Wei Ning Northeastern University CONTENTS 9.1 Introduction Peer-to-Peer Network Technologies Early Development of P2P SIP Network Architecture P2P SIP Standardization Protocol Development and Implementation Concluding Remarks References 9.1 Introduction Session Initiation Protocol (SIP) has been widely used in Internet telephony and has been chosen as the protocol for Internet Protocol (IP)-based multi- media call control for third generation (3G) wireless networks. As defined in RFC 3261 [1], SIP is a client server-based control protocol above the trans- port layer for creating, modifying, and terminating sessions between two or more participants. However, SIP-based telephony can be viewed as an appli- cation of peer-to-peer (P2P) architecture where the user agents (UAs) form a self-organizing P2P overlay network to locate and communicate with each other. In consideration of the characteristics of P2P, it is expected to be a perfect method to solve the scalability, robustness, and fault tolerance prob- lems in traditional SIP networks. Skype is a free P2P application based on the Kazaa architecture for Internet telephony and instant messaging [2,3]. The protocol is proprietary and the system has centralized elements for login authentication [2]. Researchers have proposed several pure P2P architectures for SIP-based IP telephony systems [4,5]. The P2P SIP working group has been formed within the Internet Engineering Task Force (IETF) for adapting P2P with features suitable for SIP. © 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security Peer-to-Peer Network Technologies An overlay network is a computer network built on top of another network. Nodes in the overlay are connected by virtual or logical links, each of which corresponds to a path in the underlying network [6]. An example overlay network built on top of anothe