Re: Videoboard with PowerMa

Richard Cogger (R.Cogger@cornell.edu)
Wed, 28 Sep 1994 11:47:40 -0400


Much of what you ask is answered in the readme and FAQ files, ftp'able from
cu-seeme.cornell.edu (and alias for gated.cornell.edu) /pub/video. Here
are some answers for what may not be covered there:

At 12:13 AM 9/28/94, Dick Ivan wrote:
> Reply to: RE>>Videoboard with PowerMac 7100/66
>
>I am going to configure 2 Macintosh systems to be used for executive video
>conferencing over a provite ethernet network between San Fransisico and San
>Diego and have several performance related quesions. Reliability and high
>quality video and audio performance are more important than price.
>(1)Should I order a 7100 or 8100 Power Mac?

If cost no object, get 8100, of course.

>(2)Should I use the AV version or use the SuperMac video Spigot?

The spigot may work just as well or better with the small images. But with
upcoming still-image capture/transmission facilities, the AV has higher res
and produces better looking stills. Other capture boards in future may be
better still.

>(3)How can I keep the microphone on continuously without pushing the mouse
>butin down al the time?

Set the tick-mark for squelch near the bottom in non-PTT mode.

>(4)What can I do to reduce the annoying feedback which occurs on my local
>Mac. Does the other end hear the eco I hear in my office? Is the Jabra
>microphone useful in this situation and how good is the quality of the audio
>under CuSeeMe?

What's a Jabra mic? Feedback: for now, keep speaker away from mic, use
headphones... In a future version, we'll offer some "speakerphone" features
so that mic is muted when receiving from net or vice versa. Also, plan to
experiment with using high-quality full-duplex speakerphone, but need to
figure out hookup.

>(5)Can both parties talk at the same time in duplex mode?

Well, as of right now, the delay is a little high to make that workable.
Users need to learn to pause a little to let the speaker stop before
starting. In the future, as networks improve, etc. we'll come closer to
telephone spec delays, but for now, folks need to adapt. Or use the phone.

>(6)What are the individual Audio CuSeeMe buttons used for?
>(7)What is the difference between the grey microphone icon background with
>the purple dot and the same icon with a white background?
See Readme's.

>(8)Has anyone compiled a list of compression and transmission settings for
>different Macintosh computer configurations which result in the same video
>and audio performance in a controlled enviornment?

Can't be done. Video performance is dependent on many things, but
importantly on the cpu power available for compression. There are no
settings that make a CI work like a PM8100. If everyone has a powerful
machine and you have no limit on net bw, set Max to 300Kbps and let 'er
rip. But don't do it on the Internet.

>(10)What is the best reflector configuration for 8 way conferencing? Should I
>dedicate a SUN server to be a reflector? Why are multiple reflectors, one in
>San Fransisco and one in San Diego, desireable?

The main thing you want is reflectors with bandwidth and cpu (same old
story). We get real good results from an RS-6000 with an FDDI interface.
To get bad results, just put a feeble machine on an overloaded ethernet.
Multiple reflectors reduce the number of duplicate copies sent on the links
between them. Consider: 8 participants on one reflector, 4 in SF, 4 in SD.
If each sends at 100Kbps, that's 8 streams in x 100 = 800Kbps in. Plus 7
out to each is 7 x 100 x 8 = 5600Kbps. Total in and out = 6.4Mbps which is
probably into the collision realm on an ethernet all by itself. In
addition, say the single reflector is in SD: you have 4 streams coming down
from SF and *3 copies of each* going back plus 4 copies of each of the SD
streams. If you have two reflectors, each one receives 4 streams locally
and 4 from the remote reflector but sends only 3 x 4 locally plus 4
remotely for a total of 800K in (same) and 1600 out or 2.4Mbps total. And
the Wan link has only 400k each way instead of 400 one way and 4 x 7 x 100
= 2800kbps the other way. It's really just simple arithmetic.
>
>Please respond soon! I need to order this equipment this week and set it up
>as quickly as possible! I have been using CuSeeMe for several weeks but still
>don't have all the answers I need. We have been getting pretty good
>performance on our dedicated ethernet network linking the San Fransisco
>office to San Diego. I am very impressed overall with CuSeeMe and I want to
>thank Cornell for developing and making available this product to everyone.
>
Welcome. Let us know how it all works out. -Dick