Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: john@bovine.ati.com (John Higdon) Newsgroups: comp.dcom.telecom Subject: Re: Data Access Lines Message-ID: <8371@accuvax.nwu.edu> Date: 28 May 90 20:21:35 GMT Sender: news@accuvax.nwu.edu Reply-To: John Higdon Organization: Green Hills and Cows Lines: 29 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 394, Message 6 of 10 Mike Riddle writes: > My understanding is that a 9600 bps modem actually operates at 2400 baud, > with 4 levels, creating a 9600 bps signal. This method was used > precisely because of the inherent bandwidth of a "normal" voice line. > It seems to me that whoever told him 9600 wouldn't work on a "normal" > line either didn't understand 9600 bps methodology or was trying to > sell up. I don't have the reference in front of my and can't give a detailed explanation of PEP (Packetized Ensemble Protocol), but it is somewhat more complex than that. PEP (I don't know anything at all about the theory of v.32) tries for as many as 512 separate carriers (each operating very slowly) over the line. During training and negotiation, carriers that are unusable because of line quality are locked out. This is why PEP can be so variable in terms of throughput. If line conditions change significantly, the modems will renegotiate. 1200 and 2400 bps modems don't operate at 1200 and 2400 baud, respectively, but rather at a slower baud rate and carry 4 or 8 bits per baud. This is accomplished by introducing a phase (and in the case of 2400, amplitude) component. BTW, most people don't understand 9600 bps methodology. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !