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From: rick@pcrat.UUCP (Rick Richardson)
Newsgroups: comp.dcom.modems,comp.mail.uucp
Subject: Re: UUCP over X25 [Was Re: Telebits and uucp g-protocol]
Keywords: Telebit Trailblazers, g-protocol, uucp
Message-ID: <782@pcrat.UUCP>
Date: 24 Jun 89 11:18:55 GMT
References: <335@nixtor.UUCP> <10391@smoke.BRL.MIL> <1989Jun12.185746.7217@eci386.uucp> <193@cat.Fulcrum.BT.CO.UK> <1989Jun22.154318.25599@
Reply-To: rick@pcrat.UUCP (Rick Richardson)
Organization: PC Research, Inc., Tinton Falls, NJ
Lines: 40

In article <1989Jun22.154318.25599@eci386.uucp> clewis@eci386.UUCP (Chris Lewis) writes:
>
>With "g", you can send your three packet window not too badly, but
>remember, you have to wait for the "transmit timeout" (minimum 50ms
>on our pad) before the last bit of it actually gets sent.  
>[Well, depends on X.25 packet size etc. etc. etc.]
>
>As well, you also have to wait for the transmit timeout before the acks get
>sent back.  So, think of basic X.25 "g" speed as: "time to send
>three packets at rated link speed" *plus* two "transmit timeouts".

If you are lucky (?) enough to have ISDN capable lines, you can
use an AT&T 750x series voice/data phone to transmit X.25.  The
PAD in these phones has (in addition to the usual 50ms idle timer),
a feature we called "minimum timer".  This option automatically
determines whether or not file transfer or interactive typing
is going on, and forwards packets within a couple RS232 character
times, while at the same time it avoids sending wasteful short packets.
I.E. file transfer packets fill up and get forwarded immediately,
the partial packet at the end of a file transfer block burst gets
forwarded within a couple RS-232 character times, and single keystrokes
go out as one character packets.

Of course, since the ACKs also get delayed, it is best to have
this scheme running on both ends of the connection.  These days,
thats pretty unlikely, since there are only a few areas which
are served by ISDN. Sigh.

The scheme works wonderfully for all kinds of protocols, not just
UUCP g.  It was, in fact, developed to solve the abysmal performance
of X and Y -MODEM protocols when layered on top of X.25, as well as
the noticeable echoplexing delay when the conventional 50 msec idle
timer is used.  And the best part is, you just set the mode once
when you install the phone and forget it.  No hacking PAD parameters.

-- 
Rick Richardson | JetRoff "di"-troff to LaserJet Postprocessor|uunet!pcrat!dry2
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