Important Points:

SDP Related

1.   An SDP session description is denoted by the media type  application/sdp".
2.    An SDP session description consists of a number of lines of text of the form: <type>=<value>
3. The "t=" lines specify the start and stop times for a session.      t=<start-time> <stop-time>
4. Currently defined media are "m" = "audio","video", "text", "application", and "message".
5. If an agent receives an offer after having sent one, but before receiving an answer to it, this is considered a "glare"condition. Here, it means both agents have attempted to send an updated offer at the same time.
6. If the answerer has no media formats in common for a particular offered stream, the answerer MUST reject that media stream by setting the port to zero.
7. When issuing an offer that modifies the session,the "o=" line of the new SDP MUST be identical to that in the previous SDP, except that the version in the origin field MUST increment by one from the previous SDP.