Subject: Minimum bandwidth for MBONE

From: John Roberts <[email-masked]>
Date: Fri, 11 Apr 1997 13:34:07 -0400

I've heard discussions of MBONE over ISDN, Frame Relay etc..

What is the minimum bandwidth/connectivity method to get the full effect of
MBONE?

A T1 is the simple answer but will a 512k frame connection perform?  Or
would there be degradation (over a T1) even at those speeds?

Thanks,

-John
[email-masked]

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From: "John M. Zwiebel" <[email-masked]>
Date: Fri, 11 Apr 1997 11:22:40 -0700

I think I heard you say....

    

It all depends on your application.  I'm listing to vat over 2B channels right
now that is using PCM encoding.  I'm also running a number of emacs windows
and wb and sdr.  We have some folks at the end of 56K frame-relay links that 
find vat useful with dvi (subjectively better with gsm if the link is busy).

Cisco routers can sniff sdr announcements and limit the bandwidth used
by video streams so that the audio keeps working.

    [no] ip multicast rate-limit in | out [video] | [whiteboard]
                                 [group-list <acl>] [source-list <acl>] <kbps>

    [no] ip sdr listen 

We have had some folks using audio over 28.8 modems.  So, the answer is that
is "all depends".  Especially if you have multiple sessions traveling your
link or lots of unicast traffic.

------------------------------------------------------------------------------
	John Zwiebel                       Phone: 408-526-5303
	Cisco Systems Inc.                 Fax:   
	Multimedia Group                   Email: [email-masked]

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From: Mark Handley <[email-masked]>
Date: Fri, 11 Apr 1997 15:56:28 -0400

>would there be degradation (over a T1) even at those speeds?

There isn't a simple single answer to this question.  It depends on
the sessions you want to participate in.

Typically a session such as the IETF or WWW conference may push out
128Kbps video, 32 or 64Kbps audio and variable rate whiteboard data.
So to receive such a session without being concerned about local loss,
you'd get away with a 256Kbps link assuming not too much overhead from
routing and periodic traffic bursts which get pruned.  In fact many
people get away with 128Kbps of ISDN and use mrouted's prioritisation
to preferentially throw away some of the video when the link gets
saturated.

There are good low rate codecs for audio and video available these
days and I expect a lot of lower rate sessions to start appearing in
the near future.  Mbone access over modems hasn't been a priority in
the past, but a part of the market will go that way in the future,
especially as RTP header compression starts to get deployed.  In
addition, as workstations get faster, expect to see higher bandwidth,
higher quality sessions appear too.

If you're feeding more than one user, they will probably want to watch
different sessions simultaneously.  The Mbone used to be engineered
for 512Kbps traffic loads, but these restrictions are no longer in
place, and transit sites often see significantly in excess of 512Kbps
these days.  I expect this to grow significantly as multicast moves
from being a Unix-only experiment into being generally available.

Of course any answer also depends greatly upon what other traffic your
multicast traffic would share your access link with.

Mark