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....
Leo Talbot
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