This document specifies the Presence Protocol, presence-related extensions to the Session Initiation Protocol (SIP). SIP is used by terminals to establish, modify, and terminate multimedia sessions or calls. The extensions that make up the Presence Protocol are used by the products listed in section 11 to allow users to provide presence-related data to other interested users over SIP.
Sections 1.8, 2, and 3 of this specification are normative and can contain the terms MAY, SHOULD, MUST, MUST NOT, and SHOULD NOT as defined in RFC 2119. Sections 1.5 and 1.9 are also normative but cannot contain those terms. All other sections and examples in this specification are informative.