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From: wunder@hpcea.UUCP
Newsgroups: comp.dcom.modems
Subject: Re: Looking for a fast modem < $1000.
Message-ID: <490001@hpcea.CE.HP.COM>
Date: Sun, 6-Dec-87 20:30:53 EST
Article-I.D.: hpcea.490001
Posted: Sun Dec  6 20:30:53 1987
Date-Received: Sat, 12-Dec-87 09:05:18 EST
References: 
Organization: HP Corporate Engineering - Palo Alto, CA
Lines: 37

> I seem to recall that the proposed standards ( e.g., from ISO ) suck.
> They do things like fall back from 9600 to 4800 if there is too much
> line noise.  The Trailblazer is much better.
> -- 
> Tim Smith, Knowledgian				tim@ism780c.isc.com

Well, you recall wrong.  The V.32 standard is for full-duplex (no
turnaround needed), synchronous traffic.  This is not what you want
for async login or UUCP, but it works great for IBM stuff, or HDLC
between IP gateways.  We use them for emergency backup between X.25
switches and gateways.

They are also great for demos, trade shows, etc.  HP had an IP
connection from the trade show at Usenix last winter back to Palo
Alto.  We used a 56Kbit satellite link and a V.32 modem in parallel.
We ran a similar link from Geneva for Telecom '87.

The fall back is in increments of 2400 bits/sec, and doesn't cause any
problem if your synchrous equipment uses external clock (the modem
will clock you at 9600, 7200, whatever).  Trailblazer falls back, too, 
but in smaller increments.

So, V.32 doesn't suck, it is just different.  Trailblazer (PEP) and
V.32 use different (but equally effective) advanced singal processing
magic, and they have comparable performance (PEP is 18Kbits in one
direction, V.32 is 9600 in two directions).

PEP is spread spectrum with packets and retransmission, while V.32
uses signal cancelling and forward error correction (Trellis
encoding) without retransmission.  Different modem karma, as I said.

There is a CCITT 2400 baud standard that uses some of the V.32 tricks
and is more noise-resistant than the 1200 baud modems, but it didn't
catch on, alas.  It cost more, and the market went for the more
fragile 2400 baud modems that we all use.

wunder