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W. Curtiss Priest wrote in a message to Mike Bilow:
WCP> The POTS local loop connects to some 'device' at the CO that
WCP> converts analog to digital. An ISDN line connects to a
WCP> different 'device'. converting a different analog signal to
ISDN is not analog; it is digital. Because of this, the "device" to which you
refer has sufficient knowledge about the internal structure of the information
to extract only the real information, eliminating analog noise that may have
crept into the analog representation of the digital information as it travels
on its copper wire pair.
With POTS, the "device" in question knows nothing about whether the circuit it
is maintaining is a V.34 modem connection, two humans talking, or dead air. It
cannot tell what information is real data and what is noise that has been
introduced along the way, so it must simply attempt to relay the whole
conglomeration as faithfully as possible.
WCP> My question is: for the purposes of digital communications
WCP> (i.e. digitized data emminating from a PC, etc.) is the
WCP> first device more or less expensive than the second device?
The ISDN tap may be functionally simpler, even if more expensive. The real
costs here are determined by many complicated factors.