> > They are half-duplex.
>
> I have to aknowledge being wrong.
>
> That leaves the poor peformance of a 28.8 dialup compared to half that
> of a 56k line unexplained. Modem turnaround time is the explanation I
> have often seen given.
It's the latency introduced via. what, in reality, is a 2400 baud connection.
Even a 28.8Kbps is 2400 *baud*. An analog line can't switch states
faster than 2400 times per second. You get 12 bits/baud by using 12
distinct signaling frequencies.
The fastest a bit of information can make a round trip is 2 * 1/2400 seconds.
A 56Kbps connection is 56000 baud. A bit takes 2 * 1/56000 seconds
theoretical minimum round trip time.
- Matt
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