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Note from a satisfied customer
W. Curtiss Priest wrote in a message to Mike Bilow:
WCP> ISDN is simply another form of analog transmission.
* * *
WCP> At each "step" from 0 to 1 we have a transition of a voltage
WCP> or phase angle or whatever that makes a transition in zero
WCP> time. This is a true digital step function. But if you
WCP> check your communications handbook you find it takes
WCP> infinite bandwidth to send a step function in zero time.
This is a pointless argument. Let me remove the "technical" issue and try to
explain digital communications by example.
Consider two people who need to communicate, one named Sender and the other
Receiver. They are within earshot of each other, so they agree on the
following "analog" communications protocol:
Sender shouts floating point numbers to Receiver in sequence. Each number
is between 0 and 1. Receiver writes them down.
It is possible to send a lot of information in each data packet, because each
data packet can have one of an infinite number of states. Suppose, however,
that this high bandwidth channel proves unnecessary or unsuited to the kind of
data being sent, and they decide to use instead the following "digital"
Exactly the same as Protocol A, except that all numbers less than 0.5 are
written down as "0" and all numbers greater than or equal to 0.5 are
written down as "1".
Obviously, our new digital Protocol D uses exactly the same transmission method
as our analog Protocol A, and the interesting point is that they are perfectly
indistinguishable from the point of view of an outside observer. It is only
the meaning attached to the data which makes the protocol digital instead of