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

[Chuck Harrison <cfharr@erols.com>]

Hi, Steve,

Breaking out the following short definition in section 3 might
help first-time readers:

    Multimedia session: A set of concurrent RTP sessions among a
       common group of participants. For example, a 
       videoconference connection (which is a multimedia session)
       may contain an audio RTP session and a video RTP session.

I remember once finding RFC1889 confusing because there are several
ways "session" is used in the text but only the RTP session had
an explicit definition.

Cheers,
  Chuck


Stephen Casner wrote:
> 
> Attempt number three on the definition of an RTP session.  David Leon
> made some suggestions, and I fixed some typo problems.  Is this clear?
> And even more important, do you agree with what it specifies?
> 
>         RTP session: An association among a set of participants
>              communicating with RTP.  A participant may be involved in
>              multiple RTP sessions at the same time.  In a multimedia
>              session, each medium is carried in a separate RTP session
>              with its own RTCP packets.  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.  All
>              participants in an RTP session may share a common
>              destination transport address pair, as in the case of IP
>              multicast, or the pairs may be different for each
>              participant, as in the case of individual unicast network
>              addresses and port pairs.  In the unicast case, a
>              participant may receive from all other participants using
>              the same pair of ports, or may use a distinct pair of ports
>              for each.
> 
>              The distinguishing feature of an RTP session is that each
>              defines a distinct space of SSRC identifiers (defined
>              next).  The set of participants included in one RTP session
>              consists of those that can receive an SSRC identifier
>              transmitted by any one of the participants either in RTP as
>              the SSRC or a CSRC (also defined below) or in RTCP.  For
>              example, consider a three-party conference implemented
>              using unicast UDP with each participant receiving from the
>              other two on separate port pairs.  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.  The latter case simulates the
>              behavior that would occur with IP multicast communication
>              among the three participants.
> 
>                                                         -- Steve
> 
> _______________________________________________
> Audio/Video Transport Working Group
> avt@ietf.org
> https://www1.ietf.org/mailman/listinfo/avt
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