Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!olivea!uunet!hayes!tnixon From: tnixon@hayes.uucp Newsgroups: comp.dcom.modems Subject: Re: Best modem protocol summary? (Correct me if I'm wrong) Message-ID: <4036.28673077@hayes.uucp> Date: 25 Jun 91 12:00:55 GMT References: Organization: Hayes Microcomputer Products, Norcross, GA Lines: 35 In article , clemon@lemsys.UUCP (Craig Lemon) writes: > [W]hat is the bis on V.32? The 14400 carrier instead of 9600? Yes. The difference between V.32bis and V.32 is that V.32bis supports, in addition to V.32's 4800 and 9600 speeds, 7200, 12000, and 14400 bps. V.32bis also supports "rate renegotiation", which allows the modems to rapidly (1/10th of a second) change speeds in response to changing line conditions, without going through a full retrain as required in V.32 (5 seconds or more). > Also again, will the "throughput upto" value for a V.32bis/V.42bis > modem be the 38400 number that I've seen floating around. Of course, that > would be a manufacturer's statement, I realize that real throughput doesn't > get that high. Most of the V.32bis/V.42bis modems I've seen so far still have a maximum DTE interface speed of 38400. This is adequate for nearly all applications. The main benefit of V.32bis is in being able to achieve 38400 on more different types of data, since it only needs to get about 2.2-to-1 compression (38400/14400/1.22) instead of 3.3-to-1 (38400/9600/1.22). [The 1.22 factor is the improvement achieved by the error control protocol itself through stripping of start and stop bits, less protocol framing overhead.] It's possible for text data, which is compressible at around 3.3-to-1, to achieve 57600bps on a V.32bis/V.42bis modem, but I've only heard of one modem that supports that rate (AT&T Paradyne). -- Toby Nixon, Principal Engineer | Voice +1-404-840-9200 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet tnixon%hayes@uunet.uu.net