Re: Restrictions on transimssion rates if isdn used with cuseeeme?

John Ingham (
Mon, 10 Feb 1997 17:35:26 +0930

Ed Haynsworth asked...

>If I use an ISDN channel and CUseeme, are there restrictions placed on how
>fast I may Transmit my video conference data?
>If so, is this restriction an internet restriction, a CUseeme software
>restriction or a common sense restriction since most users have 28.8 baud

I think you've just put your finger on the major restriction - the fact
that most users have 28.8 baud modems. It is my understanding that if you
were connected to your ISP via (say) a clear-channel 128 kbs ISDN service
(ie 2 x 64K "B"channels aggregated), when looking at a reflector you might
expect to be able to see 4 or 5 CU-SeeMe windows each running as fast as a
single CU-SeeMe window connected via a 28,800 modem.

But if you wanted to be sure that all the 28,800 viewers presently
connected to that reflector got a good picture from you, you'd have to cap
your CU-SeeMe transmit data to 28 kbs or less. Remember, just because a
person's modem connects to their ISP at 28,800 bsp doesn't mean that they
have a clear 28,800 bps path through the Internet to you. Reports are
legendary of Internet Grid-block.

FWIW it is my opinion that many CU-SeeMe users fortunate enough to be
connected to the Internet by a T1 or E1 service set their Transmit cap to
200 kbs, which is fine IF they are talking with a similarly connected
CU-SeeMe user. But the majority of other Reflector users (ie the modem
connected ones) see a badly broken up picture from them because of the
large number of lost packets.

Those who are lucky enough to have a T1 or E1 connection are a bit like
CBers with a Power Booster - they think they can blast their way through to
a better picture than the modem-connected "plebs". The last laugh is on
them though, because they are the ones whose picture looks the worst to the

One of the ironies of videoconferencing is that you never know what your
own picture/sound is like. Even if you connect to a loopback reflector,
you still don't know how others receive you because you don't experience
their connection bandwidth! My suggestion to anyone looking for better
quality reports is to throttle your system back by initially setting your
Tx cap LOW (say) 10 or 15 kbs. Only once you have made contact with
another person of comparable connection (ie T1 or E1) can you crank up your

John Ingham
Supervisor, Technical Operations, CALS (Centre for Applied Learning Systems)
Adelaide Institute of TAFE (Training and Further Education)
GPO Box 1872 Adelaide South Australia 5001
Ph: +61 8 8207 8550 Fax: +61 8 8207 8552
Web Site: