Subject: [Sip] SIP and RTP

From: "Taja Ja" <[email-masked]>
Date: Thu, 18 Jul 2002 13:51:27 -0400

Hi ,

  If someone can help understand how SIP uses RTP.
  (we have two users agent installed on 2 different PCs
   they SIP together but I don't know how to call/use RTP)

  Any help is greatly apperciated.

Thanks for your time.Taher.

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From: "James M. Polk" <[email-masked]>
Date: Mon, 22 Jul 2002 16:30:31 -0500

>   they SIP together but I don't know how to call/use RTP)

Within the INVITE is SDP (capabilities negotiation) for the type of (for
example) RTP session the UAC wants to have with the UAS. The SDP specifies
the payload type/codec and other such details for that proposed session.
Simplistically, if the UAS replies with a 200 OK Response, the session is
created with the SDP parameters specified from the UAC (after the UAC sends
a final ACK to the UAS)

RFC 3264 is a good reference for this explanation in the Offer-Answer Model
where both UAs become aware of the capabilities of each other prior to
session establishment.

>Thanks for your time.Taher.

cheers,
James 

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