RE: [Sip-implementors] Offer-answer queries

[Gokul Krishnan]

Also, not negotiating down to one single codec has an advantage: you can change codecs dynamically depending on the type of data or network conditions.

Regards

Gokul

[EMAIL PROTECTED] wrote:

If you want to negotiate things down to 1 and only 1 codec, then you need to send a second offer/answer exchange. In 3GPP, it is done with 3 offer answer exchanges:

 

--INVITE--> offer

<--183-- answer

--PRACK--> offer

<--200-- answer

--UPDATE--> offer

<--200-- answer

 

 

There a also other opportunities for offer/answer. But my question to you is: why do you need to negotiate down to one codec? you can use any of the codecs that were in an answer and look in the RTP packet to find the codec type (just like you stated)

 

Regards,

Hisham

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]On Behalf Of ext Prabha
Sent: 12.December.2003 15:11
To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
Subject: Re: [Sip-implementors] Offer-answer queries

Hi Ranjit,

 Thanks for the response. But i am still not clear.

Here  200 Ok has been sent with codecs 3 and 5. It means to say that he is supporting both 3 and 5.

Now how does an offeror identify the final negotiated codec without seeing the payload type in

RTP header.

 

If 200 OK would have come with one coder, then it is clear fto the offeror regarding the accepted codec

details.

 

Please can you give some more inputs on this.

 

Thanks,

 Prabha N

----- Original Message -----

From: [EMAIL PROTECTED]

To: [EMAIL PROTECTED] ; [EMAIL PROTECTED]

Sent: Friday, December 12, 2003 5:15 PM

Subject: RE: [Sip-implementors] Offer-answer queries

Hi

     The accepted codec gets reflectd in 200 OK. so there is no need to send negotiated codecs in ACK. If no offer is sent in INVITE by caller, then the callee send his offer in 200 OK and the negotiated codec should be sent by caller in ACK

 

 

Thanks & Regards
Ranjit
Wipro Technologies
E-City, Bangalore
Ph: 8520408/16 extn: 2173

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Prabha
Sent: Friday, December 12, 2003 4:42 PM
To: [EMAIL PROTECTED]
Cc: Jonathan Rosenberg
Subject: [Sip-implementors] Offer-answer queries

Hello,

 

I have a question regarding the SDP part of the Invite request.

 

 suppose user agent  "A" wants to talk to user agent "B", he sends a INVITE

 request to B.  the SDP part of the invite request is as follows,

 

 

 v= 0

 o= A 1464112736 1464112736 IN IP4 151.209.33.190

 s=Calling

 c=IN IP4 pgs-477

 t=0 0

 m=audio 2074 RTP/AVP 0 3 5

 a=rtpmap:0 PCMU/8000

 a=rtpmap:3 GSM/4000

 a=rtpmap:5 ADPCM/4000

 

 If user agent accepts the request and agrees to talk to user agent A, he

 sends a OK response with SDP as followed.

 

 v= 0

 o= B1464112736 1464112736 IN IP4 151.209.33.194

 s=Answering the call

 c=IN IP4 pgs-451

 t=0 0

 m=audio 2074 RTP/AVP  3 5

 a=rtpmap:3 GSM/4000

 a=rtpmap:5 ADPCM/4000

 

 now why can't the user agent A send an ACK by selecting one of the coders specified in answer AS

mentioned below ?

 

v= 0

 o= A 1464112736 1464112736 IN IP4 151.209.33.190

 s=Calling

 c=IN IP4 pgs-477

 t=0 0

 m=audio 2074 RTP/AVP  3

a=rtpmap:3 GSM/4000

 

than analyzing the payload type (PT) header field in the RTP Packet.

 

Thanks in advance

Prabha N

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