Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!think.com!spool2.mu.edu!uunet!hayes!tnixon
From: tnixon@hayes.uucp
Newsgroups: comp.dcom.modems
Subject: Re: V32bis
Message-ID: <3722.278c7fbc@hayes.uucp>
Date: 10 Jan 91 14:52:43 GMT
References: <19700002@inmet> <3713.27832d53@hayes.uucp> <87110@tut.cis.ohio-state.edu>
Organization: Hayes Microcomputer Products, Norcross, GA
Lines: 37

In article <87110@tut.cis.ohio-state.edu>,
bsmith@rose.cis.ohio-state.edu (brentley r smith) writes: 

> How does V.32bis compare to "HST", U.S. Robotics' proprietary protocol?
> Are teh mechanics of the protocols similar?  Is the (theoretical) 
> throughput similar?

V.32bis, like V.32, is a duplex modulation scheme -- it transmits 
and receives in both directions simultaneously at the same rate, 
using echo cancellation techniques so that both modems can transmit 
on the same frequencies.

HST is "asymmetrical".  One modem is transmitting at high speed (up 
to 14400), while the other is transmitting at low speed (300 or 450 
bps).  No echo cancellation is used; each modem transmits on a 
different frequency.  Thus, it is incompatible with and quite 
different from V.32bis.

The "constellation" (method of encoding bits into analog signal 
states) of V.32bis is similar to the HST high-speed modulation.  The 
handshaking and other procedures are quite different.

If you only transmit in one direction, the theoretical throughput of 
V.32bis and HST are identical.  The sharp band-edge filters needed 
to make an asymmetrical modem work do make the HST more susceptible 
to certain line impairments, but this is traded off against the 
potentially damaging effects of echo path impairments in V.32bis.  
Of course, the performance of V.32bis is vastly superior to HST when 
transmitting in both directions simultaneously, which is required in 
many high-speed applications.  Full-duplex modems are much more 
flexible in terms of the applications which can be supported.

-- 
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