Subject: [MMUSIC] (no subject)

From: "Raman, Sundereshwaran (Sundereshwaran)" <[email-masked]>
Date: Wed, 13 Aug 2003 08:47:14 -0600

I have question related to dynamic payloads. If a session is estblished with a dynamic payload type number mapped to a particular codec, can the number change for the same codec in subsequent offers/answers in the same session? e.g. Lets say a session was established with a dynamic payload type number 96 mapped to telephone-event. Now if a new Re-Invite is sent out, can the response have a different payload type number for the telephone event?

Thanks
Sundi

---

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 13 Aug 2003 16:39:26 -0400

I believe Section 8.3.2 of RFC 3264 directly answers your question:

The list of media formats used in the session MAY be changed.  To do
    this, the offerer creates a new media description, with the list of
    media formats in the "m=" line different from the corresponding media
    stream in the previous SDP.  This list MAY include new formats, and
    MAY remove formats present from the previous SDP.  However, in the
    case of RTP, the mapping from a particular dynamic payload type
    number to a particular codec within that media stream MUST NOT change
    for the duration of a session.  For example, if A generates an offer
    with G.711 assigned to dynamic payload type number 46, payload type
    number 46 MUST refer to G.711 from that point forward in any offers
    or answers for that media stream within the session.  However, it is
    acceptable for multiple payload type numbers to be mapped to the same
    codec, so that an updated offer could also use payload type number 72
    for G.711.

This is true for the answerer as well. Thus, in each direction, once 
PT number is bound to a codec, that PT number can not be used for a 
different codec.

-Jonathan R.

Raman, Sundereshwaran (Sundereshwaran) wrote:

> I have question related to dynamic payloads. If a session is estblished 
> with a dynamic payload type number mapped to a particular codec, can the 
> number change for the same codec in subsequent offers/answers in the 
> same session? e.g. Lets say a session was established with a dynamic 
> payload type number 96 mapped to telephone-event. Now if a new Re-Invite 
> is sent out, can the response have a different payload type number for 
> the telephone event?
> 
> Thanks
> Sundi
> 
> 

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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