ine. This work extends SO that more presence information can be automatically updated based on calendars and other applications from the network. References Charlton, N., et al., "User Requirements for the Session Initiation Protocol (SIP) in Sup- port of Deaf, Hard of Hearing and Speech-Impaired Individuals," RFC 3351, 2002. Levin, O., and R. Evan, "High Level Requirements for Tightly Coupled SIP Conferenc- ing," IETF Internet-Draft, Work in Progress, April 2003. Rosenberg, J., "A Framework for Conferencing with the Session Initiation Protocol," IETF Internet-Draft, Work in Progress, May 2003. Johnston, A., and O. Levin, "SIP Call Control - Conferencing for User Agents," IETF Internet-Draft, Work in Progress, April 2003. Rosenberg, J., H. Schulzrinne, and P. Kyzivat, "Caller Preferences and Callee Capabilities for the Session Initiation Protocol (SIP)," IETF Internet-Draft, Work in Progress, March 2003. Rosenberg, J., and H. Schulzrinne, "A Session Initiation Protocol (SIP) Event Package for Conference State," IETF Internet-Draft, Work in Progress, June 2002. Peterson, J., "Considerations on the IEPREP Requirements for SIP," IETF Internet- Draft, Work in Progress, April 2003. Future Directions [8] Johnston, A., et al., "Session Initiation Protocol Service Examples," IETF Internet-Draft, Work in Progress, March 2003. Campbell, B., et al., "Instant Message Sessions in SIMPLE," IETF Internet-Draft, Work in Progress, April 2003. Schulzrinne, H., et al., "RPIDS-Rich Presence Information Data Format for Presence Based on the Session Initiation Protocol (SIP)," IETF Internet-Draft, Work in Progress. Appendix A: Changes in the SIP Specification from RFC 2543 to RFC 3261 In late 2001 and early 2002, the base SIP specification RFC 2543 was rewritten and published as RFC 3261. The new RFC was backwards compatible with the old RFC except in areas in which the old RFC was deemed to be broken or buggy. Besides these fixes, the document was also rewritten from the ground up with a new structure and new coauthors to increase th