[ILUG] Subscription ISDN ISPs

[Karl Jeacle]

On Fri 25 Jan 02, 13:17:19 +0000, Niall O Broin wrote:
> Modem protocols are asynchronous so even if you get a
> claimed 50Kbits/s connection your data transmission rate = 5KBytes/s
> (because every 8 bits of data are preceded by a start and stop bit hence
> 25% of the bits transmitted are pure waste from the point of view of

That's not strictly true because only the computer<->modem link is async.
The modem<->modem link uses LAP-M framing, which has a smaller overhead.
So while you are wasting bits locally on your serial link (which you can
afford to waste), you aren't wasting quite so many between the modems.

http://www.cisco.com/warp/public/793/access_dial/async_lapm_framing.html

Karl