Re: how fast are Mod 170 comm ports

[Douglas Handy <dhandy1@xxxxxxxxxxxxx>]

Pat,

>I know I'll never find it again, but a few years back some engineer
>type from one of the modem companies wrote an article 

In News/400, November 1995, John Enck wrote both an article and a
sidebar.  The sidebar was titled "The Analog Roadblock" and said, in
part:

        "Shannon's Law defines the maximum throughput a modem can
achieve given the construction and operating parameters of analog
phone lines. Shannon's Law is expressed as the formula

C = BW log2 (1 + S/N)

where C is the throughput capacity (measured in bps), BW is the
bandwidth (measured in hertz), and S/N is the signal-to-noise ratio.
        Let's not get bogged down in the mathematical details of the
formula. The important point is the result: Based on the parameters
associated with most analog voice circuits, the maximum possible
throughput we can achieve through modem technology is 30,000 bps (for
the U.S. phone system, BW is 3 KHz and S/N is 1000/1). So, with
today's 28.8 Kbps modems, we're at the end of the line for analog
modem speed.
 
... Digital lines offer higher throughput (they start at 56 Kbps)
because data is not converted into an analog format by a modem, so
Shannon's Law doesn't apply. ... "

Doug  (CD magazine archives are great for searching...)
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