ion purposes when het- erogeneous SIP user agents are involved in the same SIP session. References 3GPP TR 23.981. 2005. Interworking aspects and migration scenarios for IPv4 based Implementations (release 6). Baugher, M. 2004. The Secure Real-time Transport Protocol (SRTP). RFC 3711. Camarillo, G. 2002. Integration of resource management and session initiation protocol (SIP). RFC 3312. Camarillo, G., and M.A. Garcia-Martin. 2005. The 3G IP multimedia subsystem- merging the internet and the cellular worlds. John Wiley, UK. Camarillo, G., and J. Rosenberg. 2005. The Alternative Network Address Types (ANAT) Semantics for the Session Description Protocol (SDP) Grouping Framework. RFC 4091. Chen, W., Y. Lin, and A. Pang. 2005. An IPv4-IPv6 translation mechanism for SIP overlay network in UMTS all-IP environment. IEEE Journal on Selected Areas in Communications, 23(11): 2152-60. Chen, W., and Q. Wu. 2005. Development and deployment of IPv6-based SIP VoIP networks. Proceedings Symposium on Applications and the Internet Workshops, 76-9. Gurbani, V. 2007. IPv6 Transition in the Session Initiation Protocol (SIP). Draft-ietf-sipping-v6-transition. Gurbani, V., C. Boulton, and R. Sparks. 2007. Session Initiation Protocol (SIP) Torture Test Messages for Internet Protocol Version 6 (IPv6). Draft-ietf-sipping-ipv6-torture-tests Handley, M., and V. Jacobson. 1998. SDP: Session Description Protocol. RFC 2327. ITU-T Recommendation H.323. 1998. SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMS, Infrastructure of audiovisual services - Systems and terminal equipment for audiovisual services, Packet-based multimedia communications systems. Kent, S., and R. Atkinson. 1998. IP Authentication Header. RFC 2402. Kent, S., and R. Atkinson. 1998. IP Encapsulating Security Payload (ESP). RFC 2406. Ono, K., and S. Tachimoto. 2005. Requirements for End-to-Middle Security for the Session Initiation Protocol (SIP). RFC 4189. Ono, K., and S. Tachimoto. 2005. End-to-middle security in the Session Ini- tiation Protocol (SIP). Draft-ietf-sip-e2m-sec-06.