Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!lll-winken!gauss.llnl.gov!casey
From: casey@gauss.llnl.gov (Casey Leedom)
Newsgroups: comp.dcom.modems
Subject: Re: Modem control lines
Summary: Which modem/modem protocols support flow control?
Keywords: flow control, full duplex RS232 (RTS, CTS), modem/modem protocols
Message-ID: <36214@lll-winken.LLNL.GOV>
Date: 19 Oct 89 17:10:41 GMT
References: <1180@srhqla.SR.COM> <2532@cs.yale.edu> <1989Oct17.170047.18468@utzoo.uucp>
Sender: usenet@lll-winken.LLNL.GOV
Reply-To: casey@lll-crg.llnl.gov (Casey Leedom)
Organization: Lawrence Livermore National Laboratory
Lines: 30

| From: henry@utzoo.uucp (Henry Spencer)
| 
| > From: Owens-Christopher@cs.yale.edu (Christopher Owens)
| > 
| > ... Now, presumably, the modem's internal buffer is going to fill up
| > pretty fast, at which point it is going to want to send some kind of
| > signal to the other modem to tell it to stop sending data down the
| > communications line...
| 
| It wants to.  However, it can't, in most of the standard modem protocols,
| because there is no such signal.  If you can't accept data as fast as the
| other end sends it, you lose some of it.  Simple as that. ... I think
| Telebit's PEP will do it, but that's a very different story from the rest
| of the modem world.

  This is a question I've been needing to deal with for a bit now and
just haven't gotten around to it.  I assumed that Telebit's PEP and
Microcom's MNP would both have flow control provisions in the protocols
because they're error controlling protocols, but Henry's letter calls
that assumption into question.

  Does anyone know if two MNP modems (say running MNP5) have any way of
throttling each other?  It would be most inconvenient if they don't ...
I'm running a GraphOn Optimax 200 X terminal at home over a pair of
Telebit T2500s.  The T2500s can overrun the GraphOn fairly easily.  (I've
been told there are new PROMs coming out for the Optimax 200 that speed
up character drawing to about 22KCPS - it's currently somewhere around
16KCPS.  I don't know if anything else will be faster.)

Casey