Path: utzoo!utgpu!water!watmath!onfcanim!dave
From: dave@onfcanim.UUCP (Dave Martindale)
Newsgroups: comp.dcom.modems
Subject: Re:  hayes 9600 vs. trailblazer
Message-ID: <15612@onfcanim.UUCP>
Date: 11 Apr 88 22:33:55 GMT
References: <8804110136.AA16978@ucbvax.Berkeley.EDU>
Reply-To: dave@onfcanim.UUCP (Dave Martindale)
Organization: National Film Board / Office national du film, Montreal
Lines: 39

In article <8804110136.AA16978@ucbvax.Berkeley.EDU> RAF@NIHCU.BITNET ("Roger Fajman") writes:
>Why restrict your choice to the Hayes 9600 and the Trailblazer?  You
>might want to consider V.32 modems.  They are truly 9600 bps full
>duplex, rather than pseudo full duplex like the Hayes 9600 and the
>Trailblazer or asymetric like the USR Courier 9600.

But remember, the Trailblazer is 18000 bps half-duplex, with about 14000 bps
left over after protocol overhead.  The V.32 modems are presumably capable
of 19200 bps total throughput, but you must take some out of that for
error-checking protocol in any real file-transfer application.

In an environment where most of the data is travelling in one direction,
the Trailblazer will approach 14000 bps throughput, while a V.32 or any
of the other modems are restricted to 9600 maximum.

(I know that some modems, including the Trailblazer, can get higher
effective throughput by compression.  But news is usually already
compressed (it actually saves host CPU time to do the compression
on the host) and doing compression in the modem is counterproductive).

A V.32 modem could get equal or better total throughput than a Trailblazer
only if the amount of traffic in each direction is roughly balanced AND
you have a communications protocol that sends data in both directions
at once (uucico doesn't, SLIP does).

The Trailblazer seems to extract about the same data bandwidth from a
telephone line that the V.32 modems do, but does a better job of allocating
it depending on need.  Thus, it should do about as well as V.32 in the
worst case, and considerably better in the best case.

Also, all of the above assumes that the phone line is good enough to
get full data rate.  When the line is noisy or its frequency response
is poor, the Trailblazer uses as much bandwidth and S/N as it finds,
with the effect that the data rate throttles back in increments of
perhaps 16 bps as the line gets worse.  The V.32 fallback steps are
much larger.

The Trailblazer seems like the better choice unless the V.32 modem is
substantially cheaper, even if you don't need protocol spoofing.