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000308_news@newsmaster….columbia.edu _Sun Sep 7 19:12:19 1997.msg
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From: fdc@watsun.cc.columbia.edu (Frank da Cruz)
Newsgroups: comp.protocols.kermit.misc
Subject: Re: AT command question
Date: 7 Sep 1997 23:12:15 GMT
Organization: Columbia University
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In article <5uv02o$5q6@newslink.runet.edu>, I l y a <ibelooze@runet.edu> wrote:
: My AT command manual says that at&Q6N0S37=n will make the modem connect
: at a certain speed.
:
: n=9 for 9600, 6 for 2400, 5 for 1200, 1 for 300 bps. What values of n
: stand for higher speeds?
:
Such commands are not standardized at all. We can't answer your question
unless (a) we know what kind of modem you have, and (b) we have a copy of
the manual too. But even if we did...
: The reason I am asking this is because I connect without any problems at
: 19200 but experience data loss at 38400bps.
:
: OS: Ultrix 4.4 on DEC5000/20
:
We have been through this before. It is almost certainly not a modem issue.
It *is* an issue with Ultrix. Ultrix does not support any method of flow
control that is effective enough to be used with high serial speeds.
To put it another way, even if the DECstation port supports (say) 38400 bps,
the DECstation itself can not keep up with incoming data at that speed. So
it needs a way of controlling the flow of incoming data to prevent data
loss. But RTS/CTS hardware flow control is not supported in Ultrix, and
Xon/Xoff has enough latency as to be relatively ineffective at high speeds.
You need to either learn to live with 19200 bps, or switch to a different
operating system that supports RTS/CTS on the serial port. DEC supported
OSF/1 on the DECstation for a while, but then gave up on it. Other posters
have suggested other operating systems to you as well.
- Frank