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000089_news@columbia.edu_Thu Jun 8 07:09:32 1995.msg
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From: jrd@cc.usu.edu (Joe Doupnik)
Newsgroups: comp.protocols.kermit.misc
Subject: Re: Xon-Xoff and modem buffers help
Message-Id: <1995Jun8.130932.53660@cc.usu.edu>
Date: 8 Jun 95 13:09:32 MDT
References: <1995Jun8.114735.1048@gems.vcu.edu>
Organization: Utah State University
Lines: 43
Apparently-To: kermit.misc@watsun.cc.columbia.edu
In article <1995Jun8.114735.1048@gems.vcu.edu>, agnew@gems.vcu.edu (Brainwave Surfer) writes:
> Dear Net people and Kermit hackers ( in the old sense of the word,
> please! ),
>
> I am in a quandary...
>
> If i set my pratical periperals modems to factory defualts, and then
> use x-on xoff flow control as demanded by VMS's hacker ( ok, new sense
> ! ) evasion, then all is very nice, no errors, but if I xoff and try
> to stop the flow of data to the screen, there is a humongous buffer in
> the modems somewhere of data already in the pipeline that will not
> respond to the xoff..
>
> On the other hand, if i take all error corrections off and make the
> modem try to be a direct wire, i can xoff and xon nicely, but errors
> abound as in Psalm 19:12 "Who can discern his errors? ... " 8-)
>
> So, after downloading a 200 page paper from Practical Periperials,
> I'm throughtly confused... Should I enable all error corrections, and
> then enable pass-thru xon xoff via the Q commands??? Or am I still
> talking moonshine?
>
> My Old setup was 19.2 Kbaud ports on the DECserver, 1.44 pp modems,
> and generic whatever to dial in, testing with pp modems.. I'm open
> to change/ideas.
---------------
You can bypass much of the problem by defining a convenient key
as keyboard verb \Kholdscrn and then relying upon point to point flow
control of hardware or software kinds to handle the comms link. The
holdscreen operation blocks reading of the comms buffer which drives the
terminal emulator; it does not touch the comms link itself but rather
lets the receive buffer fill to the high water mark.
Since VAXen are not normally RTS/CTS flow control devices you
are better off using specific flow control at each point in the link, to
minimize propagation/buffer queue delays inherent in sending a bare
XON/XOFF end to end to the remote VAX host to act upon. Please do ask
someone to look carefully at the DECserver box to ascertain how it wishes
to be treated.
If you try only end to end flow control then parts in the middle
are highly vunerable to being overrun. Generally RTS/CTS between your PC
and your modem is the most desirable configuration, and let your modem
deal with the other modem, et seq.
Joe D.