From: Leo Talbot (leo at domain maths.tcd.ie)
Date: Tue 29 Feb 2000 - 10:05:14 GMT
On Tue, 29 Feb 2000, John Allen wrote:
[SNIP Modems use compression]
> I see clearly now
> But I still don't understand why my home phone line is dead reliable at 33k
> but quite flaky at 56k. If it were only compression that was producing the
> increased bandwidth, then surely the reliability should be consistent?
It's not all compression you see. Back in the old days baud == bps, because
one signal change gave one bit. The signal change could be anyone of phase,
frequency, or amplitude. As new modems came in, these signal change methods
were combined, and non-binary signalling came in....so for a 32kbps modem,
one signal change can transmit 16 (I think) bits. As you squeeze more and
more bandwidth out of the phone line, the distinction between different
signals becomes closer and closer, so if the phone line isn't good, at
56kbps info may be lost, and the modem will automatically switch down to 33.
Ah, the joys of 3rd Year networking lectures...zzzzzz.....zzzzz....
-- I've got green eyes, red hair, and I'm left handed. A hundred years ago, I'd have been considered in league with the Devil. http://www.cs.tcd.ie/Leo.Talbot PGP: RSA 1024 0x341E0EBD fp=79940BEB A9F22827 E524F100 9C83D34A
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