Hi Achal,

Offer in INVITE contains the RTP receive ports of Caller. Similarly answer 
contained in 2XX or 1XX contains the RTP receive ports of Callee.

As per RFC 3261, 
- If the initial offer is in an INVITE, the answer MUST be in a reliable 
non-failure message from UAS back to UAC which is correlated to that 
INVITE. For this specification, that is only the final 2xx response to 
that INVITE. That same exact answer MAY also be placed in any provisional 
responses sent prior to the answer. The UAC MUST treat the first session 
description it receives as the answer, and MUST ignore any session 
descriptions in subsequent responses to the initial INVITE.

Hence the UAS MUST send an answer in 2xx either by setting all m-lines to 
zero ( rejecting offer ) or set valid RTP ports in m-lines where it wishes 
to receive media. 

With Regards
Raghu




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04/06/2007 08:42 PM


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Subject
[Sip-implementors] RTP ports






I know the INVITE message contains the inviter's RTP port in the m=audio
field but how is the recipient's RTP port determined when it is not sent 
as
part of the message detail in the 200 OK message?

 

Many thanks.

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