[AG-TECH] Multicast question

Dave Price dap at aber.ac.uk
Tue Jul 19 03:36:52 CDT 2005

Dear All,

natalia at cesga.es said:
> but it  seems to me that it does not influence the tree built to
> deliver traffic  from a source to several receivers (that is probably
> what they network guys  wanna know).

	Unless they have been heavily
patched, I would expect vic and rat to be emitting
RTCP traffic as they normally do.  As this traffic gets placed
on the local LAN, it will be spotted by the designated
router which will then (assuming PIM-SM is being used)
report to the Rendezvous Point that the vic/rat machine is
a new "active source" for the group being used for the RTCP traffic reports.
The port number for the RTCP traffic "should" be an odd number,
one higher than the even number being used for the RTP
transported media traffic.

	Thus, it is my belief, that as the vic/rat receiver
is thus a "source" of RTCP traffic it will effect trees built to others.
They will be receiving the RTCP traffic (from other vic/rat etc)
as well as RTP transported media from the audio/video sources
and thus their designated routers will building first a shared
tree to the RP, but as RTPC traffic arrives, shortest path trees
back to the other vic/rat machines that are emitting RTCP.

Dave Price

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