k: Services, Technologies, and Security [12] Jennings, C. and R. Mahy. 2007. Managing Client Initiated Connections in the Session Initiation Protocol (SIP). Internet Draft, November 18, http://tools.ietf.org/html/draft-ietf-sip-outbound-11. [13] Willis, D. and B. Hoeneisen. 2002. Session Initiation Protocol (SIP) Extension Header Field for Registering Non-Adjacent Contacts. RFC 3327, December, http://www.ietf.org/rfc/rfc3327.txt. [14] Baldi, M., L. De Marco, F. Risso, and L. Torrero. 2008. Providing End- to-End Connectivity to SIP User Agents Behind NATs. IEEE Inter- national Conference on Communications (ICC 2008) Advances in Net- workds & Internet Symposium, Beijing (China), May. [15] The OpenWengo project. Available at http://www.openwengo.org. Accessed November 15, 2007. © 2009 by Taylor & Francis Group, LLC Multipoint Extensions for SIP Sureswaran Ramadass and Omar Abouabdalla University of Science, Malaysia CONTENTS 13.1 Introduction 13.2 Multipoint Session Initiation Protocol (MSIP) Entities 13.3 Control Messages 13.4 Messages Flow 13.1 Introduction In the distributed network entities environment, a message-passing distributed algorithm is needed. Session Initiation Protocol (SIP) is point-to-point proto- col. In this chapter, we are going to describe a Multipoint Session Initiation Protocol (MSIP). This protocol is an application-layer control (signaling) pro- tocol for creating, modifying, and terminating sessions with one or more par- ticipants. The protocol is a signaling protocol based on distributed network entities architecture, and the use of the server is mandatory. The server here is the main entity, and it communicates with the other network entities involved in the system (mainly the client entities) using the standard Internet communication protocol (TCP/IP). There are some termi- nologies that are going to be used in this chapter. These terminologies are: MSIP server: is a software that runs on a central machine and its main functions are to control and manage the session. MSIP client: is a s