Network Working Group J. Rosenberg Request for Comments: 3840 dynamicsoft Category: Standards Track H. Schulzrinne Columbia University P. Kyzivat Cisco Systems August 2004 Indicating User Agent Capabilities in the Session Initiation Protocol (SIP) Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2004). Abstract This specification defines mechanisms by which a Session Initiation Protocol (SIP) user agent can convey its capabilities and characteristics to other user agents and to the registrar for its domain. This information is conveyed as parameters of the Contact header field. Rosenberg, et al. Standards Track