Subject: RE: [SIP] Changing Codec

From: Pascal Doré <[email-masked]>
Date: Tue, 21 Nov 2000 17:04:22 -0500

(re)Invite with a new session description
 
Pascal Doré

-----Original Message-----
From: Mo Zonoun [mailto:[email-masked]]
Sent: Tuesday, November 21, 2000 1:47 PM
To: IETF SIP (E-mail)
Subject: [SIP] Changing Codec

How do you change codec in a SIP call without disconnecting the established
call? 

Mo Zonoun

---

From: Billy Biggs <[email-masked]>
Date: Tue, 21 Nov 2000 18:43:06 -0600

Pascal Doré ([email-masked]):

> > How do you change codec in a SIP call without disconnecting the
> > established call? 
>

  Actually, it depends on if you are talking about send codec or receive
codec.

  If you want to change the codec you are sending, then as long as the
other end indicated support, you can change any time you like.  For
example, if I send you SDP that says:

   m=audio 8552 RTP/AVP 0 1 2

  Then you can freely switch between sending audio using codec 0, 1 or
2.  If you're feeling cruel, you can use a different codec for every
packet.

  If you want to change which codec you are receiving from the far end,
the best you can do is offer a different set of choices using a
re-INVITE.  So, first maybe you send:

   m=audio 8552 RTP/AVP 0 1 2

  And the far end is sending you codec 1, but you only want to receive
codec 0, then you can always re-INVITE with:

   m=audio 8552 RTP/AVP 0

  And force it to use either codec 0 or nothing.  Be prepared though
that if the remote end can't send codec 0, it might tear down the call
(or at best audio won't flow).

-- 
Billy Biggs, 3Com               Email: [email-masked]
http://www.div8.net/billy/      Phone: [email-masked]

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---

From: "Venkatesh Venkataramanan" <[email-masked]>
Date: Wed, 22 Nov 2000 09:37:33 +0530

But if this (re)INVITE fails, shouldn't the original media agreed upon
prevail ? That's how I understand (re)INVITES(unlike what you mention about
the remote UA tearing down the call). Please clarify.
Venkatesh
----- Original Message -----
From: "Billy Biggs" <[email-masked]>
To: "Pascal Doré" <[email-masked]>
Cc: "Mo Zonoun" <[email-masked]>; "SIP List"
<[email-masked]>
Sent: Wednesday, November 22, 2000 6:13 AM
Subject: Re: [SIP] Changing Codec

   m=audio 8552 RTP/AVP 0