Subject: RE: AHG comments on draft-ietf-avt-rtp-mpeg4-es-03 in response to the last call

From: "Luthra, Ajay (SD-EX)" <[email-masked]>
Date: Tue, 12 Sep 2000 19:58:47 -0400

Collin,
   But you said in your previous email, " ... The payload type will have to
be negotiated out of band anyway .. ". And in another email you said, "Yes"
to the question - does one need to work this way in multicast environment
also. And now you are saying it does not need to be negotiated. My
understanding of this subject is not yet excellent. So, I do not understand
these three emails from you which seem to contradict each other. 

Does the payload type need to be negotiated or not?

With regards,
Ajay

-----Original Message-----
From: Colin Perkins [mailto:[email-masked]]
Sent: Tuesday, September 12, 2000 12:11 PM
To: Kris Huber
Cc: Luthra, Ajay (SD-EX); 'Zvi Lifshitz'; [email-masked]';
[email-masked]; [email-masked]
Subject: Re: AHG comments on draft-ietf-avt-rtp-mpeg4-es-03 in response
to the last call

--> Kris Huber writes:
>Hello Colin,
>
>I'm a bit confused.  It seems to me that one or more of these assumptions
>must be wrong:
>- that multicast involves one-way communication from one sender to many
>  receivers
>- 'dynamic negotiation' (of payload type in this case) requires two-way
>  communication.
>
>Perhaps the precise technical definition of 'negotiate' in this case is
what
>I lack.  The definition of the word as generally used seems to require
>two-way communication (A talks to B, B replies to A, A replies back, etc.,
>until they converge to agreement).
>
>Thanks for any clarification,

In the typical "mbone conference" style of multicast, the sender advertises
that a named payload format is using a particular payload type. There's no
negotiation (and none needed, since payload type numbers are local to a 
session).

Colin

---

From: Colin Perkins <[email-masked]>
Date: Wed, 13 Sep 2000 13:23:24 -0400

>Does the payload type need to be negotiated or not?

The payload type is dynamically assigned, and has to be communicated
between the sender and the receiver(s) somehow. RTP does not specify
how that communication is done. In the unicast case it is typical to
negotiate, in the one-to-many multicast case the sender tells the
receivers (i.e. the receiver has no choice, so it can't really be 
called "negotiation"). But there is always out of band signalling.

Colin