Not only that, but many systems encode the clock into the signal by
toggling the smallest bit every byte, giving us (tada!) 56,000 bits per
second.  That the modem's today can characterize the miles of wire,
devices, and codec such that they can use even 85% of that bandwidth
(for 48k) is neat, when you think about all the digital signal
processing that that sort of thing takes.

Only ISDN/T1/etc is able to achieve the full channel bandwidth.  I
assume they have built in clock encoding and regeneration.

-Adam

Sean H. Breheny wrote:

> Well, the biggest problem I have with the idea that a 56k modem could go
> faster than 56k (truly faster, not just on compressible data) is that
> AFAIK, the codecs in the phone system which digitize the analog signal
> only
> do so at a 64kbps rate (8000 8bit samples per second), unless that has
> been
> changed (and even then it would be strange that the 56k modem would have
> the ability to take advantage of that and they would not advertise such a
> great capability!).
>
> Sean

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