My comments inline
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-----Original Message-----
From: Tim Chen [mailto:scc@trillium.com]
Sent: Tuesday, May 02, 2000 5:19 PM
To: ITU-SG16@mailbag.cps.intel.com
Cc: 'mbaugher@passedge.com'; 'bill.strahm@intel.com';
'irina@ennovatenetworks.com'; Michael Bird
Subject: Current RTP-MIB definition precludes multi-unicast
RTP session?
Hello,
I see a problem with current "RTP session" definition in RTP MIB
<draft-ietf-avt-rtp-mib-09.txt>.
This MIB definition precludes multi-unicast RTP session which
is clearly
permissible under section 3 of RFC 1889:
RTP session: The association among a set of participants
communicating with
RTP. For each participant, the session is defined by a
particular pair of
destination transport addresses (one network address plus a
port pair for
RTP and RTCP). The destination transport address pair may be
common for all
participants, as in the case of IP multicast, or may be
different for each,
as in the case of individual unicast network addresses plus a
common port
pair.
Hence each participant in an RTP session could have
a different RTP receive address. The only requirement
from the specs is that the RTP and RTCP port pair used by all
participants
has to be the same. For example, I can have the following
RTP session with three participants, each receiving RTP packets
on a different IP address:
participant A : receive RTP on 103.403.25.45 port 6000
participant B : receive RTP on 103.403.33.34 port 6000
participant C : receive RTP on 103.403.25.98 port 6000
So for participant A, he will send to two remote addresses:
103.403.33.34:6000 (that B listens to) and 103.403.25.98:6000
(that C listens to).
However, the current RTP session MIB draft (page 10) has the
following structure:
RtpSessionEntry ::= SEQUENCE {
rtpSessionIndex Integer32,
rtpSessionDomain TDomain,
rtpSessionRemAddr TAddress,
rtpSessionLocAddr TAddress,
rtpSessionIfIndex InterfaceIndex,
rtpSessionSenderJoins Counter32,
rtpSessionReceiverJoins Counter32,
rtpSessionByes Counter32,
rtpSessionStartTime TimeStamp,
rtpSessionMonitor TruthValue,
rtpSessionRowStatus RowStatus
}
This definition allows only a single remote address. This
is contradictory to RFC 1889 which clearly permits
multiple remote addresses in a single RTP session.
Will the authors of this MIB give some clarification? Thanks.
I see each one of these as seperate channels, with different feedback
streams. Therefor participant A would have a RtpSessionEntry for A->B and
A->C, participant B would have B->A and B->C etc. Yes this doesn't scale
very well as you add many participants, but then neither does sending
multiple copies of the same stream, so I think it is a wash.
To clarify. The RtpReceiverEntry needs to have the feedback for just ONE
receiver anyway, so why not model it as multiple unicast flows (since that
is indeed what we have here)
I do not see a problem
Bill Strahm
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