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FW: satisfied customer
W. Curtis Priest Said:
WCP> Nonetheless, I gather there is agreement that 28.8 Kbps modems
WCP> are as "digital" as ISDN "modems."
No, not really.
WCP> There was an argument that ISDN traffic moved by a digital network
WCP> between COs while voice traveled by an analog route -- but given
WCP> the statements that almost all inter-office voice is handled by
WCP> the "digital network", this distinction, apparently, does not
WCP> So when we compare 28.8 to ISDN we really are talking about
WCP> comparing an unconditioned local line with a conditioned local line
WCP> with repeaters (if necessary). Once at the CO both data travel
This is not true. Once at the CO it is possible to have the information digitized and transmitted digitally, however that is irrelevant unless you're comparing voice communication. For data communication the only time that the actual data being transmitted between two computers with a 28.8k modem is between the computer's serial port and the modem itself. The modem modulates the information into an analog carrier. This is a completely analog carrier and isn't simply the square rise and fall of a voltage level. An "ISDN Modem" is not a modem at all. It is a terminal adapter. It doesn't do any modulation at all. It simply translates digital information coming in one pipe so it may travel through a different one. An analog modem, simply put, translates the data into an audio stream. At no point is ISDN data converted to audio.
WCP> Does anyone know if there are inherent advantages, efficiencies in
WCP> using ISDN vis a vis a 28.8 modem where the connection is made
WCP> at the CO?
At the CO? Yes, since (in most cases) the connection signalling is done out-of-band... on a separate channel compared to analog where it is done along with the conversation. Thera are also efficiencies at the customer end. There are transmission delays inherent in a 28.8k analog modem. These delays are associate with the process of modulating and