joel@wam.umd.edu (Joel M. Hoffman) writes:

quoted text
>For many many hours now I've been trying to connect a serial terminal
>(actually, a 286 PC) to Linux via a null modem cable.  Alas, I have
>failed.  No matter what I try, I can't get h/w flow control to work,
>and so I get overrun errors on the DOS end.

quoted text
>So my question is this: If I install ka9q (or kq9a, or whatever it's
>called) on my DOS machine, can I telnet into Linux?

While I haven't used it this way, it should be possible to connect
from DOS to Linux using KA9Q on Linux and KA9Q on DOS (although I
think you'd prefer CUTCP on DOS -- the user interface is nicer,
particularly for telnet).  Yes, TCP will compute checksums and
retransmit.  So if you've got a connection with a bit of noise, using
SLIP over it should clean things up.  Whether it will help you depends
upon exactly what your problem is.

If your problem is overrunning your software's ability to take input
characters, hardware flow control probably won't help.  Hardware flow
control is normally used to match differing speeds, e.g. when you want
to talk to a v.32 compressing modem using a line that's higher speed
than the modem connection (which you need to do in order to take
advantage of compression).  If the software is simply dropping
characters, I don't think flow control is going to help.  Flow control
is normally combined with buffering.  When the buffer is nearly full,
you toggle flow control to tell the other end to stop.  If your system
is dropping characters, it would have to predict he circumstances
under which it would drop a character, and give the other end enough
warning to stop it.  I think that's sort of unlikely.  I'd start by
moving to DOS software that can handle high speed lines reliably.
MSDOS Kermit would probably be my first choice.  If that doesn't
work, I'd suspect a hardware problem of some sort.

If for some reason you can't get rid of the errors, and they are only
occasional, SLIP might actually fix things up.  TCP uses checksums and
packet length checks, so it should retransmit if a character is
dropped.  But I think something odd is going on with your system, and
wonder whether SLIP might make it worse...

If you're going to use SLIP primarily to log in, I suggest using CUTCP
on DOS rather than KA9Q.  It's got a much nicer user interface for
telnet sessions.

With a hardwired line directly between two machines, I don't see any
way that it would make sense to turn on flow control for SLIP.