Columbia Kermit/kermit.zip/newsgroups/misc.19950329-19950528/[e-mail]_Thu Apr 27 13:00:32 1995.msg

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From: [e-mail] (Frank da Cruz)
Newsgroups: comp.protocols.kermit.misc
Subject: Re: Setting modem speed
Date: 27 Apr 1995 13:00:32 GMT
Organization: Columbia University
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In article <3nmpig$[e-mail]>, Alan McConnell <[e-mail]> wrote:
>Hi, everybody!  I have a fine US-Robotics modem whose maximum speed
>is 14400 -- which it is capable of when I run minicom under Linux.
>But when I run C-Kermit, I get a message just after the two modems
>have negotiated: "Can't change speed to 14400", and it turns out
>they've negotiated to 9600.  What I want to know is: what do I have
>to change in the C-Kermit source(I have just grabbed C-Kermit190)
>so that I can run C-Kermit at 14400?  This must surely be a FAQ,
>but I can't find the answer in the only Kermit FAQ available to me.
>
It is indeed an FAQ, and the answer is indeed in the Kermit FAQ,
which you can find at:

  ftp://kermit.columbia.edu/kermit/faq.txt
  http://www.columbia.edu/kermit/moreinfo.html

And of course, the answer is also in the manual.   Quoting from the FAQ:

  15. Q: WHEN C-KERMIT DIALS MY V.32bis (OR V.34) MODEM, I GET THE ERROR
         "CAN'T CHANGE SPEED TO 14400 (OR 28800)"
         A: Tell C-Kermit to SET DIAL SPEED-MATCHING OFF; explained below.

Dialing is covered in Chapter 3 and Appendix II of "Using C-Kermit".  To
recapitulate very briefly: older modems, like the Hayes 1200 and 2400,
that did not do error correction or compression, but that could negotiate
their modulation speed, would report the modulation speed upon successful
connection, and change their interface speed to match.  Thus, the
communication software would also have to change its own interface speed,
or else the user would see only garbage.

Modern modems have two different speeds: the interface speed and the
modulation speed.  The interface speed can be kept constant even though
the modulation speed changes.  Or not, depending on how the modem is
configured.

Kermit has no way of knowing whether your modem is set up to lock its
interface speed, or to change it to match the modulation speed, and
therefore it has no way of knowing whether to believe the "CONNECT 28800"
(or whatever) message.  By default, for compatibility with the huge
installed base of older modems, it does believe, and therefore changes
its interface speed according to the CONNECT message.

So if your modem's interface speed is locked (which it SHOULD be if it is
an error-correcting, data-compressing modem), you must tell Kermit NOT to
change its interface speed by giving it the command:

  SET DIAL SPEED-MATCHING OFF

Now to complicate matters, some of the newer modulations report speeds
that are not commonly supported by the host operating system, such as
14400 and 28800.  Hence the message "Can't change speed to 14400" (or
28800).  But even if these speeds were supported, you would not want
Kermit changing to them if the modem's interface speed was locked.  You
would still see only garbage, but you would not get the "Can't change
speed" message.

See pages 60-61 of "Using C-Kermit" for additional detail.