Path: utzoo!utgpu!watmath!onfcanim!dave
From: dave@onfcanim.UUCP (Dave Martindale)
Newsgroups: comp.dcom.modems
Subject: Re: Which is best?
Message-ID: <16715@onfcanim.UUCP>
Date: 14 Nov 88 05:41:11 GMT
References: <9515@conexch.UUCP> <1125@vsi1.UUCP> <299@telebit.UUCP> <10711@cup.portal.com> <654@hscfvax.harvard.edu> <16680@onfcanim.UUCP> <610@pcrat.UUCP>
Reply-To: dave@onfcanim.UUCP (Dave Martindale)
Distribution: na
Organization: National Film Board / Office national du film, Montreal
Lines: 30

In article <610@pcrat.UUCP> rick@pcrat.UUCP (Rick Richardson) writes:
>In article <16680@onfcanim.UUCP> dave@onfcanim.UUCP (Dave Martindale) writes:
>>They have apparently already demonstrated 28000 bps on a voice channel,
>>using a more powerful signal processor than is in current Trailblazers.
>
>It was easy to cost justify the `blazer, non-standard and all, when
>the older technology was 2400 and the blazer promised up to 18000.
>Nobody gets that, of course, (I see around 12000 using AT&T into UUNET,
>*much* less if I use SPRINT).

Rick misunderstands the theoretical maximum throughput of current
Trailblazers.  Telebit says that the current modulation technique gives
just over 18000 bps total (on a clean line0, but some of that bandwidth
is used up for protocol and error-control information passed between
the modems.  Telebit quotes an actual throughput of user data of 14000
bps, after all overhead is subtracted.  So not even Telebit claims that
you will see more than 1400 cps.  1200 cps is a pretty respectable
portion of 1400.

(Note that the UUCP packet overhead does not get accounted for here,
since with UUCP spoofing the packet overhead won't get transmitted
between the modems.  Thus the 1400 cps theoretical throughput is all
available for real data.  *However*, to get 1400 cps through the modem,
the host has to send or receive characters at 1400 * 70/64 = 1531
cps).


Anyway, I assumed that the Telebit rep was talking about 28000 bps of
user data, exactly twice the current rate.  Thus, real throughput
should also double, if the host can keep up.