SLIP and Cu-SeeMe cont'd

Geoff Rehn (
Tue, 2 Aug 1994 22:58:41 -0400

At 5:26 PM 8/2/94 -0400, Jim B. Krone wrote:
>>I have been told that a SLIP connection is too slow for an application
>>like CuSeeMe. Is this true?
>I am using SLIP from home on a 14.4Kbps raw connection (38.4Kbps using=
> compression) and find that CuSeeMe works on my Centris 650. It is video=
> only. Some sound comes through but it is too chopy to be understood. The=
> video updates fairly well but nothing like my network connection at work.

What frame rates can you report?

I was just then doing a one-to-one connection via SLIP at 14k4, running
from my PC at home, to a Mac at work. I achieved fairly consistent rate of
about 5 - 7 fps. I never get this when connecting to a reflector though...
BTW, you can _forget_ audio over a dialup connection (at this stage). IT
simply WON'T work...

I found that if the Sender sets a CAP of about 10kps, the frame rate and
refresh rate seems pretty good. If the CAP is higher (eg. 30kps) too much
data seems to get lost and the video received doesn't update too well.

I am still undecided as to whether or not to use:
1. Compressed SLIP (ie. CSLIP) (ie. header compression)
2. Compressed data ie. MNP-5 or V42bis data compression.

I don't think using data compression would help at all, as I imagine (in my
naive understanding) that the video data is of course already compressed,
and my understanding of modem comms is that using data compression can
actually slow down the transer rates of already compressed data.

But on CSLIP for header compression, I don't know.
I guess not. Does CU-SeeMe video data have headers, Cornell?

But I think no CSLIP and no MNP5 or V42bis might give the best results.

I only just then a few minutes ago used CU-SeeMe in video phone mode
connecting to my University, Murdoch, from home, and it does work
tolerably. (Two phone lines; one for data, one for normal telephone voice).
It (using SLIP) would be best suited for still image transmission, as in
using a desktop camera to send documents, still images, etc.

But a one-to-one using SLIP works pleasingly well.
Not so good for higher CAP transmissions across multiple hops though.

And then it depends on the network traffic and the time of day connecting
to a reflector.

Cornell, any comments on the best SLIP/PPP settings?
Use compressed or uncompressed data?
Use CSLIP or not?

BTW, I am using an MTU (maximum transmission unit) of 290, as I'm using
Tattam's Trumpet WinSock with its internal SLIP driver.

One last point:
To the original poster of the "SLIP connection is too slow" query.

It sounds like you have command-line access only to the Internet (ie.
interactive login, some call it).
You can't get CUSM or any WinSock working over unix command line access
(ie. plain serial access). You will need some kind of TCP/IP access such as
SLIP, PPP or ARA (or ARNS too).

(Cornell, some advice on the SLIP questions might be useful, as there seem
to be a few SLIP/PPP users out there).

best wishes
Geoff R.

(This email cross-posted to

Geoff Rehn
Academic Services Unit    Murdoch University