[SIPForum-discussion] proper time to establish stream

[Herve Jourdain]

Hi Nora,

 

As far as I understand, your concern is about when caller can start sending RTP, right ?

If it’s so, then it’s only after receiving the 200 OK.

But the callee can send you “early media” by providing you SDP information in a 18X response – usually 183, but I’ve seen in 180 as well. This can carry “announcements” (tones, voice prompts, etc…).

So I think that the caller can start to “listen” to the “early media” flow as soon as it’s announced by the callee (provided it supports the codec used). But send only after receiving 200 OK (because only then does it know the codecs to use…).

 

Regards,

 

Herve

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From: 雨 陈 [mailto:chen.yu26 at yahoo.com.cn] 
Sent: vendredi 29 août 2008 11:57
To: discussion at sipforum.org; Vivek Batra; Jourdain Herve
Subject: proper time to establish stream

 

Hi,

 

There is another question: What is the real time that the media stream begin to set up?

 

I think in the two common offer/answer models: INVITE/200 and 200/ACK, they can set up the stream after the SDP answer with 200 and ACK respectively, But what is the matter in the reliable response ? I mean the model INVITE/ 180(183). 

 

My 2 cents is even though the 180(183) with SDP answer was accepted by the offer entity , the media stream CAN NOT STRAT until the 200 OK for INVITE is received. Because during the early-dialog, the caller may send a CANCEL to break down the call. 

 

Please correct me if I am wrong. Thanks in advance!

 

Regards

 

Nora :)

 

 

  

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