Fast SLIP on slow lines

Ian Carr-de Avelon (
Thu, 30 Nov 1995 10:35:03 +0100

Dear All,
This is just a train of thought which I had this morning, does
anyone know if it makes sense?
I am thinking about providing Internet services in Poland. One of
the big problems there is that the phone lines are poor, 28.8kb modems
usually won't work. The question which formed in my mind is: what happens if
you are on the border line? some data is received correctly but some not.
The obvious answer is that the transmition protocol takes care of it by
resending the corrupt data. So the modem stays sending signals at 28.8kb,
but the real throughput is, say, 20kb (still better than 14.5kb) but the
data received is the data transmited.
Now what happens if the data is UDP packets? I assume that any
corrupt packets are ignored. In that case people using CU-See-Me through
such a connection will appear to have (extra) lost packets. If CU-See-Me
responds by backing off, the rate of the (extra) lost packets will remain
the same, so it backs off further etc.
Is why we get such varied reports from people using 28.8 kb modems?
a perfect connection gives video and audio, but just a little noise and
you're finished, although the same modem gives maybe 25 kb of throughput for
web browsing.
Anyone know SLIP internally?

* Ian Carr-de Avelon *
* *
* *
* dept. of Physics Education *
* University of Amsterdam *
* Netherlands *