[SIPForum-discussion] Offer-Answer SDP

RAMASAMY, KESAVAN (KESAVAN)** CTR ** kesavan.ramasamy at alcatel-lucent.com
Wed Aug 24 05:04:39 UTC 2011


The session direction value is depends upon the states that the call proceeds.

During session initiation, in INVITE it will be sendrecv. During call hold, UAC will have sendonly & UAS will have recvonly.

In another example where a different unicast address is to be used for a traffic destination than for a traffic source. In such a case, two media descriptions may be use, one sendonly and one recvonly.

Please correct me if I am wrong.

Kesavan R

From: discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of mehmet
Sent: Monday, August 22, 2011 11:56 AM
To: call foreign
Cc: discussion at sipforum.org
Subject: Re: [SIPForum-discussion] Offer-Answer SDP


Sesion could be  established with G729 codec..Also default value of the session direction is a=sendrecv when you can not see it inside the SDP body

2011/8/19 call foreign <callf4rgn at gmail.com<mailto:callf4rgn at gmail.com>>

I need ideas and explanation on this call scenario;

Origination UA sent multiple codecs;

   o=alice 2890844526<tel:2890844526> 2890844526<tel:2890844526> IN IP4 host.anywhere.com<http://host.anywhere.com>
   c=IN IP4 host.anywhere.com<http://host.anywhere.com>
   t=0 0
   m=audio 62986 RTP/AVP 18 4
   a=rtpmap:18 G729/8000
   a=rtpmap:4 G723/8000

Termination UA respond with multiple codecs;

   o=bob 2890844730<tel:2890844730> 2890844731<tel:2890844731> IN IP4 host.example.com<http://host.example.com>
   c=IN IP4 host.example.com<http://host.example.com>
   t=0 0
   m=audio 54344 RTP/AVP 18 4
    a=rtpmap:18 G729/8000
   a=rtpmap:4 G723/8000


What would be the actual media on the session considering that the OFFER-ANSWER has been completed on the signaling with an INVITE-200OK-ACK messages.  Please note the origination has never included attribute "a=inactive" on the initial offer.  In addition, termination side responded with attribute "a=sendrecv" immediately without an update offer from the origination on which codec it choose for the final media stream.

Does this imply that the actual media stream been used on the session is G729 if codec preference is considered?

Please share if you have encountered this scenario.


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