What's the meaning of AS for SDP

Question

i can not understand the meaning of as in sdp, i checkout rfc2327 described as below:

AS Application-Specific Maximum: The bandwidth is interpreted to be application-specific, ie, will be the application's concept of maximum bandwidth. Normally this will coincide with what is set on the application's "maximum bandwidth" control if applicable.

My question is how to caculate as in my program?

I looked up a lot of information, but in vain, I wonder if the value of as is the meaning of the codec's bit rate?

Answer 1

The SDP protocol allows an entity taking part in a communications session to provide some information about the session and/or its capabilities for a session it wants to set up or join.

This can include information like the connection type, contact details for the organiser of a conference, timing for a conference or session and media information.

Bandwidth is one of these pieces of information - it allows the organiser or client joining or setting up a session to indicate how much bandwidth they expect to use.

The bandwidth info allows modifiers and one of them is the one you have flagged - this is simply saying that this is the maximum bandwidth that this application is expecting to use for the session.

It's an option piece of information so you may not need it depending on your application.

Note that codec information is usually included in the media and rtp attributes - if you look at some SIP (session initiation protocol used for many VoIP services) you can see examples of codec information being shared - for example for an audio call (between Bob and Alice as is usual in these specs):

   v=0
   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

Lots of of other examples also in the SIP examples RFC: https://datatracker.ietf.org/doc/html/rfc3665