[AG-TECH] IGMPv3, Source Specific Multicast, fully supported in Windows XP

Ivan R. Judson judson at mcs.anl.gov
Fri Aug 16 13:31:28 CDT 2002

> >I've recently been wondering if for AG-like scenarios we need to use 
> >two IP addresses, one for "shared" traffic like RTCP SDES 
> notifications 
> >and another for "filtered" traffic like SSM filtered RTP 
> streams (see 
> >my message to the IETF AVT alias on this if you're interested).
> Consider going beyond only two multicast group addresses.
> One group address could be used to discover active sources.
> Each active source would transmit to (say) three additional groups.
>   - One could be low-rate, postage-stamp size suitable for node ops
>     to select from.
>   - One would be medium-rate, QCIF size, suitable for putting up on
>     the AG display in a "Brady Bunch" scenario.
>   - One would be high-rate, 30 fps CIF size, suitable for enlarging
>     on the AG display to full size (think view of speaker).

This is something that I have a hard time thinking about.  My concern is
mostly based around the fact that these seem to be things that AG
Nodes/Users need to have in the technology portfolio.  Ie, can the user
send more than one stream?  What format? What quality?  If not, who's
doing it for them?  Is this a network service?  Does it need to be

None of these questions say, "The Venue needs to know about lots of
addresses", to me.  The venue might have a passing interest at some
point, or it might be where all of these are stored, we have to figure
all that out.

Another argument in my head (I don't know how this plays out in the real
world) but the specs already allow what's described above, check out the
SDP spec it allows multiple address to be specified.


Ivan R. Judson .~. http://www.mcs.anl.gov/~judson
Futures Laboratory .~.  630 252 0920
Argonne National Laboratory .~. 630 252 6424 Fax

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