Re: Win Audio via dialup

Ian Carr-de Avelon (
Wed, 30 Aug 1995 10:14:10 +0200

Dear All,
After poor experience with PC CU-SeeMe with audio I have decided to
try it next during the weekend when the net is a lot quieter, but I have
been thinking a little about where the problems may lie. I suspect that the
problem may lie with UDP. I don't want to resurrect the whole UDP vs TCP
argument, but .... There is a difference between bits of the video going
missing and bits of audio getting lost. We have heard a lot about how
CU-SeeMe backs off if packets are being dropped, but I can't see that a main
router looks to see how many datagrams are passing to a certain user. If 10%
of packets are being lost on a link, 10% will be lost however slowly you
send. This means that greater compression may not be better, I have read
that model based systems eg. vocoders can transmit recognisable speach
(although you can't recognise the speaker) with 1K bits per second, but if
a packet of that is lost, you have lost a sentence.
Does anybody know anything about the compression techniques which
CU-SeeMe is using? How does it recover from a lost packet? How big is an
audio packet? Are there likely to be clashes between interups when the:
packet card, audio card, and video card all need CPU time?

At 17:59 29-08-95 -0400, Don Johnson wrote:
>>On Tue, 29 Aug 1995, Roger Lee Boston wrote:
>>> Reading the below explanation got me to wondering ... WHY is it hard for
>>> CuSeeMe to do voice and video in a 14.4 data bandwidth via a network,
>>> when a point-to-point modem connection via SV3000 gives superb full
>>> duplex audio, a white board, -AND- a few frames/second in color at that
>>> same speed? What is the network (or CuSeeMe) demanding that a
>>> point-to-point connection via POTS does not?
>>> Roger Boston
>>> HCCS Distance learning,
>>The system you describe has the benefit of specific hardware (the
>>expansion card) doing all the work... primarily compressing the bee-geezus
>>out of the outgoing data (and uncompressing the incoming stream). There
>>is a lot you can do when you build an expensive card to do it :)
>Yeah, and it's relatively independent of the CPU! Did you hear about the
>new system that gets 15-20 FPS over ISDN? The product is called Virtual Desk
>PC and the company is Imagelink, Inc. They also claim 4000 installations in
>Europe. I'm excited, I'm waiting to get info. But I've been disappointed
>before! We'll see!
>Their number is 800-420-1110.
>Now, back to Cu-Seeme.
* Ian Carr-de Avelon *
* *
* *
* dept. of Physics Education *
* University of Amsterdam *
* Netherlands *