Error-correcting modems & uucp

[Steve Nuchia]

In article <963 at frcs.UUCP> paul at frcs.UUCP (Paul Nash) writes:
>However, when I use the Telebit with non-PEP modems (v22bis, say)
>should I lock the interface at 19200 and use hardware flow control for
>the speed conversion, or should I let the port change speeds down to
>2400 bps or whatever?

Run with the speed locked at 19200 and NO flow control, unless it
gives you problems with specific neighbors.  The uucp protocol
has a limited send-ahead window, and there is enough memory
in the modem to buffer it.  But the modem doesn't know that,
and will jiggle with the flow control if it is enabled, slowing
the whole process down noticably.

The (one?) problem that comes up when doing this is that there
is a feature in the modem protocol specs that says they can
drop the stop bit from every eight byte when the interface is
running faster than the analog link.  I believe that the spec
should enable this only when *both* digital links are fast,
but telebit does it all the time.  Most 2400 and even 1200
bps modems can receive this properly, but some can't.  If you
have a neighbor who can't cope with it, it will show up as
abysmal throughput or connections timing out, and you will
have to arrange to run your digital link at the connection speed
when talking to that site.

>In addition, I have a pair of v22bis MNP4-compatible modems. At present
>I run them as dumb modems (AT&E0), and would like to know whether there
>are advantages or disadvantages to using MNP on top of (under?) uucp.

It depends on the quality of the line and the kind of traffic.
MNP error correction slows down the link slightly, but takes
less time to deal with a bad error than the timeouts in uucico
do, so on a lousy line it might be a win.  MNP compression is
a win only if you are sending uncompressed files; if you
precompress your traffic it is best to run the modems without
compression.

>Should I lock the interface at 9600 and use RTS/CTS flow control, or is
...
>Just what is the optimal setup for this, and for the modem when left
>for dial-in work?

Depends on how hard it is to reconfigure for uucp.  I'd make it
as easy to use for humans as possible, then make uucp cope with
it as best it can.  That is an administrative, not a technical, opinion.