Path: utzoo!mnetor!tmsoft!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!uunet!hayes!tnixon From: tnixon@hayes.uucp Newsgroups: comp.dcom.modems Subject: Re: HST implementation of V.32/V.32bis Message-ID: <3761.27aae893@hayes.uucp> Date: 2 Feb 91 16:28:03 GMT References: <59490@aurs01.UUCP> Distribution: na Organization: Hayes Microcomputer Products, Norcross, GA Lines: 57 In article <59490@aurs01.UUCP>, whitcomb@aurs01.uucp (Jonathan Whitcomb) writes: > 1. Does HST high speed channel use V.32 modulation specs for > constellation mapping and Trellis decode algorithms? Yes. The HST modulation, like Hayes' fast-turnaround ping-pong modulation in the V-series Smartmodem 9600, uses the constellation and trellis coding of V.32 at 4800 and 9600; the HST uses the same constellation and trellis coding as V.32bis at 7200, 12000, and 14400 (in fact, the text describing these modulations that was used in the V.32bis standard was taken from the old "V.asym" draft asymmetrical modem standard, which had been submitted by US Robotics). > 2. What are the specifics of the low speed channel? I assume that > it is an FSK channel, and if so, what are the mark and space frequencies? > Is it correct that the 9600 uses a 300 baud channel and the 12000 uses > a 450 baud channel? Do both have the same mark and space frequencies? No, it is not FSK, but PSK. The 450bps reverse channel is 150 baud using 8 phase states to send 3 bits per baud. The carrier frequency is 375 +/- 1 Hz. The 9600 did use a 300bps reverse channel; I think it was 100 baud, 8 phase. > 3. Are there any other modem manufacturers that are implementing > pseudo-CCITT implementations of V.32/V.32bis? It seems like folks > are jumping through all kinds of hoops to avoid echo cancellation and > Trellis code implementations. As I mentioned above, the Hayes V-series Smartmodem 9600 uses a fast-turnaround ping-pong half-duplex modulation scheme that uses the same constellation and trellis coding as V.32. These two are the only non-standard high-speed modems I'm aware of that have even this in common with V.32. When these modems were designed, real V.32 modems cost $2,500+, due to the extreme high cost of implementing an echo canceller with technology that existed then. Since then, the cost of implementing echo cancellation has plummeted, and I doubt that you'll see many new modems being developed that are non-standard. The HST and V-series will continue to be sold for at least a while, particularly in "dual standard" implementations such as the Ultra 96, for customers who require backward compatibility with their installed base of non-standard modems. > 4. Is the HST modem popular enough to worry about, or will it vanish > once V.32/V.32bis catch on? "Vanish" is a strong word, but I suspect you'll see fewer and fewer non-standard high-speed modems of all types being sold in the future. It just makes so much more sense to stick with a real international standard. -- Toby Nixon, Principal Engineer | Voice +1-404-449-8791 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 hayes!tnixon@uunet.uu.net