o contains information about joining the working group e-mail list, which discusses the listed set of Internet-Drafts. Finally, one can search the IETF Internet-Draft archives for documents relating to SIP at http://search.ietf.org. However, be warned: There are many, many documents and most will likely never be published as an RFC-always consult someone familiar with the working group activity before assuming that an Internet-Draft not listed on a working group charter page is likely to ever become an Internet Standard. 11.1 SIP, SIPPING, and SIMPLE Working Group Design Teams From time to time working groups use a design team to work on a particular topic. The teams report regularly to the working group and have a working group chair who provides guidance. The approach has been successful in the past and will likely result in new RFCs being produced by the design teams described in the next sections. SIP: Understanding the Session Initiation Protocol Table 11.1 Latest Status of SIP-Related IETF Work Working Group Web Page URL http://www.ietf.org/html.charters/sip-charter.html SIP protocol extensions SIPPING http://www.ietf.org/html.charters/sipping-charter.html SIP requirements, best current practice documents, and usage SIMPLE http://www.ietf.org/html.charters/simple-charter.html SIP for IM and presence http://www.ietf.org/html.charters/xcon-charter.html Centralized conferencing Some of the referenced Internet-Drafts in this chapter may have become RFCs or have changed. Useful archives of expired Internet-Drafts are available at http://www.softarmor.com/sipwg, http://www.softarmor.com/sipping, http:// www.softarmor.com/simple, http://www.softarmor.com/xcon, and http://www. iptel.org/info/players/ietf. 11.1.1 SIP and Hearing Impairment Design Team This design team is developing requirements, guidelines, and directions for SIP to support the needs of hearing impaired users. The design team has produced a requirements document [1] that includes scenarios and requirements. The work has also produced general require