Re: [AVT] Final edits to RTP spec and A/V profile

["Spiros Spirou" <spis@intracom.gr>]

Hi,

Please see my comments below.

> In a multimedia session, each medium is carried
> in a separate RTP session with its own RTCP packets.

In this sentence the word "session" is used twice but
with different meanings. Moreover, if you assign a single
meaning to both occurrences then the part before the comma
directly contradicts the part after it due to the mutual
exclusion of the terms "multimedia" and "each medium". I would
suggest a substitution of the first occurrence of "session"
with "communication".

> The distinguishing feature of an RTP session is that each
> defines a distinct space of SSRC identifiers (defined next).

Reading this I got the impression that SSRC identifiers used by
one session cannot be used by another session. Is this the intended
meaning? In this case the reader is left wondering about how a
specific subset of SSRC identifiers is reserved from the set of all
SSRC identifiers. Up to now I thought that the only constraint
for SSRC identifiers was that they should be unique within an RTP
session but the same SSRC identifier can transcend sessions.

> A participant distinguishes multiple RTP sessions by reception
> of different sessions using different pairs of destination
> transport addresses, where a pair of transport addresses
> comprises one network address plus a pair of ports for RTP and RTCP.

> The distinguishing feature of an RTP session is that each
> defines a distinct space of SSRC identifiers (defined next).

> If each participant sends RTCP feedback about data received from
> one other participant only back to that participant, then the
> conference is composed of three separate point-to-point RTP
> sessions.  If each participant provides RTCP feedback about
> its reception of one other participant to both of the other
> participants, then the conference is composed of one
> multi-party RTP session.

Each of the 3 aforementioned experts proposes a different distinguishing
feature for an RTP session. These are a) the destination transport address,
b) the set of SSRC identifiers and c) the scope of RTCP reports
respectively.
I used to think that the common denominator in an RTP session and what
distinguishes from other RTP sessions is only the destination RTP port
number.
In this way, the RTCP port number is implied by the RTP port, both unicast
and multicast cases are covered and the SSRC identifiers are used to
distinguish
among participants of the session. I am now confused as to what constitutes
an RTP session.

Regards,

Spiros Spirou

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