7300 and 9600 baud modems (VT220 suggestion, and question)

[Bill Mayhew]

I don't have any problems with my Trailblzer on my 3b1.  I've been
using a TB since 11/1987.  I started with one of the old version
3.1 TBs and then switched to the white-cased TB+.

The problem of over-runs happens when you use in-band signaling
with xon/xoff.  There is a ~30K byte buffer in the TB, and it can
take a couple of seconds for the host on the other end to see your
xoff.  The Unix PC can use the RTS/CTS leads for signaling flow
control, and the TB modem can be used to send the RTS/CTS lead
status outside of the serial data stream when it is talking in PEP
fast mode.  This works great when you have two Unix PCs talking
together, but you have to make sure that both Unix PCs and
Trailblazers are set up correctly, obviously :-).  The Unix PC
won't do RTS/CTS signaling until you turn it on with /etc/hfc.
When you have hfc on, you don't get xon/xoff recognition.  The
problem of over-runs really isn't the fault of the Unix PC, but
rather the delays cuased as in-band signally ripples through the
buffers at each end.  The Unix PC seems to be able to keep up with
a 9600 baud input as long as you aren't trying to view the result
on /dev/w* on the console.  At 19.2K port speed, you can get actual
throughputs of around 11,400 buad before the system starts to get
behind.

When I talk to the Vax at work, I have to settle for xon/xoff, and
I occasionally get over-runs when catting some immense file. But
no problem for stuff like more and kermit that are essentially
self-regulating or limit blobs of transmission to less than 30K at
a time.  Feeding from the Vax at 9600 to my Unix PC at 19.2K and
letting the Trailblazer packetization handle the float, I can do a
~%take in cu and not lose anything.  Obviously a ~%put doesn't work
to the Vax, but does work between Unix PCs.  Uucp is no problem
since the Trailblazer does the protocol spoofing.

You would have to be very persuasive to get me to give up my
Trailblazer; I think I'd listen if you had a loaded Colt .45 or
something like that, I suppose.

'nuff said.

Bill
wtm at neoucom.edu