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Tuesday, March 15, 2016

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Rules for Generating an SDP Offer and Purpose of SDP

Leke Oyetoke - Tuesday, March 15, 2016

Rules for Generating an SDP Offer
An SDP offer must include all necessary SDP fields (this includes v=, o=, s=, c=, and t=).

It usually includes a media field (m=) but it does not have to. The media lines comprise all codecs listed in preference order. The only exemption to this is if the endpoint supports a huge number of codecs, the most likely to be accepted or most preferred should be listed. Different media types include audio, video, text, MSRP, BFCP, and so forth.

Purpose of SDP
The purpose of SDP is to convey information about media streams in multimedia sessions to help participants join or gather info of a particular session.

1. SDP is a short structured textual description.

2. It conveys the name and purpose of the session, the media, protocols, codec formats, timing and transport information.

3. A tentative participant checks these information and decides whether to join a session and how and when to join a session if it agrees to do so.

4. The format has entries in the form of <type>= <value>, where the <type>defines a unique session parameter and the <value>provides a specific value for that parameter.

5. The normal form of a SDP message is: x=parameter1 parameter2 ... parameterN

6. The line begins with a single lower-case letter, for example, x. There are never any spaces between the letter and the =, and there is exactly one space between each parameter. Each field has a defined number of parameters.


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