Re: [OT} Wnat does bandwidth mean these days?

[ant <blowback@xxxxxxxxx>]

On Thu, 01 Jul 2004 16:42:59 +0100, Pete Shew <ukha_d@xxxxxxx> wrote:
>
> The meaning of the term "bandwidth" seems to have undergone
a shift.
> I think bandwidth started as a radio communications term where the
width of the radio band, that is the spread of used frequencies, is related
to the capacity to send information.

Yes, bandwidth is formally the range of frequencies which can be
conveyed by a channel. For a channel of bandwidth B, the maximum rate
at which the signal may change is 2B, governed by the Nyquist-Shannon
law. This is sometimes called the maximum information rate.

The theoretical rate at which information passes error-three through a
bandwidth-constrained limited-power channel in the presence of
Gaussian noise is called the Channel Capacity, and is found from the
Hartley-Shannon Law C=B log2 (1 + (S/N)) bits/second.  (S/N is the
signal to noise ratio).

This is a theoretical maximum; real channels do not achieve this. The
maximum 'signal rate', 'bit rate', 'information rate' or whatever you
want to call it is lower than the channel capacity by a factor called
the channel bit error rate (BER).

So, as you say, the terms "bandwidth" and "capacity"
are mis-used by telcos ;)

ant