Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!apple!netcomsv!gandrews
From: gandrews@netcom.COM (Greg Andrews)
Newsgroups: comp.dcom.modems
Subject: Re: help wrt UUCP between 3B1 OBM and TB
Summary: Not intended for speedup purposes
Message-ID: <1991May9.071349.1377@netcom.COM>
Date: 9 May 91 07:13:49 GMT
References: <29.28280170@zswamp.uucp>
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In article <29.28280170@zswamp.uucp> root@zswamp.uucp (Geoffrey Welsh) writes:
>In a letter to All, Greg Andrews (gandrews@netcom.COM ) wrote:
>
> >However:  Stop bit deletion is allowed in the 'specification'
> >(actually the correct term is recommendation) for V.22bis,
>
>   Hmmm, delete the stop bit every 8th character and you have a 1.3% 
>throughput improvement... hardly seems worth the hassle.
>

It wasn't included for the purpose of pushing the link to higher speeds.
It was done because the modem may need to contend with a terminal (or a
computer) which has a baud rate clock that's running faster than a true
1200 bps.  Or the modem's baud rate clock is running slower than a true
1200 bps (or whatever the modulation rate is).

If the modem is receiving data nonstop from a DTE device that's running a
bit fast, then it may need to drop a bit out of the modulation every so
often in order to keep the pace.  (remember that the modulation specs must
assume the worst - the modem has no means of flow control)  Dropping 1 bit 
out of every 80 bits (8 bytes) could compensate for up to a 1.25% speed 
difference.  Dropping 1 bit out of every 40 bits could compensate for up 
to 2.5%.  There's a complementary allowance for inserting extra stop bits 
if the DTE is running more slowly than the modem modulation.

I pulled this from the V.14 recommendation, which the V.22bis and V.22
recommendations reference as their async-to-sync-and-back converter spec.  
I haven't found the Bell 212 stuff yet.  Will summarize when I get it all 
together.

>Geoffrey Welsh - Operator, Izot's Swamp BBS (FidoNet 1:221/171)

-- 
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 |  Greg Andrews   |       UUCP: {apple,amdahl,claris}!netcom!gandrews    |
 |                 |   Internet: gandrews@netcom.COM                      |
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