The Session Description Protocol (SDP) Version 2.0 Extensions protocol specifies a proprietary extension to the Session Description Protocol (SDP) to support audio/video and application sharing calls.
SDP is used to negotiate and establish session characteristics during call setup. Unless explicitly specified, this protocol follows the offer/answer model to represent session characteristics using an SDP to establish a session.
This protocol is used to negotiate audio/video and application sharing call setup and adding video (or audio) to an existing audio (or video) only call.
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 [RFC2119]. Sections 1.5 and 1.9 are also normative but do not contain those terms. All other sections and examples in this specification are informative.