Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!motcid!wallach From: wallach@motcid.UUCP (Cliff H. Wallach) Newsgroups: comp.dcom.modems Subject: Re: HST implementation of V.32/V.32bis Keywords: echo cancellation, constellations, Trellis Message-ID: <4540@avocado5.UUCP> Date: 1 Feb 91 21:57:51 GMT References: <59490@aurs01.UUCP> Distribution: na Organization: Motorola Inc. - Cellular Infrastructure Div., Arlington Heights, IL 60004 Lines: 60 In article <59490@aurs01.UUCP> whitcomb@aurs01.uucp (Jonathan Whitcomb) writes: -I am trying to understand the differences between HST and the -V.32/V.32bis standards. I understand that HST does not have -echo cancellation, and instead uses a low speed channel for -full duplex operation. I also gather that HST can change the -high speed channel from the caller to receiver by retraining. - -I am still fuzzy on the following: - -1. Does HST high speed channel use V.32 modulation specs for -constellation mapping and Trellis decode algorithms? Yes. - -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? The low speed channel uses phase shift keying, with 3 bits/baud. The earliest HST had a 300 bps backchannel. After a year the 450 bps backchannel was added to the 9600 HST. backchannel 300 450 ----------- --- --- baud rate 100 150 carrier freq 350 375 (I may be off here) - -3. Are there any other modem manufacturers that are implementing -pseudo-CCITT implementations of V.32/V.32bis? Yes. - It seems like folks -are jumping through all kinds of hoops to avoid echo cancellation and -Trellis code implementations. The echo cancellation requires a lot of DSP time. This translates into an extra DSP chip. - -4. Is the HST modem popular enough to worry about, or will it vanish -once V.32/V.32bis catch on? Over 100k are out there. Sales have steadily increased. Only recently have V22bis modems surpassed Bell 212a modems in volume. - -Thanks. You are welcome. Cliff Wallach ...uunet!motcid!wallach