From: walrus@wam.umd.edu (Udo K Schuermann)
Newsgroups: comp.sys.amiga.datacomm,comp.sys.amiga.hardware
Subject: Re: How do I get LIGHTNING on my SupraFAX?
Date: 22 Jul 92 19:24:18 GMT
Distribution: comp
Organization: University of Maryland, College Park

In article <1992Jul22.085505.13897@vax5.cit.cornell.edu> blyy@vax5.cit.cornell.edu writes:
>Big Question - 
>
>I'm something of a novice at telecommunications, and I've recently purcahsed
>a Supra FAXModem V.32bis. I'd like to maximize my transfer speed as much
>as possible and would like any advice anyone has on the matter. So far, I've
>been able to get approx. 100k per second using Jr-Comm 1.2, a 19200 connect
>setting, and Ymodem-G protocal. Can anyone reccomend anything else I can
>do to get the fastest throughput I can? Would connecting at 38400 help?
>What about using XON/XOFF or CTS/RTS?  Screen colors/depth? Protocol?
>
>P.S. THe Supra has a max baud rate of 14400. The manual, though, advises
>connecting at 57600 to get the maximum connection. Is this okay?

100k per second?  "You lucky, lucky, b......!"  :-)

Well, here's my bit of advise on how to maximize your throughput with high
speed modems.  I'm basing this on my SupraFAX V.32bis modem but it should
apply to similar modems as well:

1. Read the documentation on your modem to let it select the best connect
   speed.  There are a lot of options available but loading the factory-
   settings #2 (at&f2, I believe) has worked quite well for me.

2. Avoid XON/XOFF.  Set your serial-preferences to CTS/RTS, which allows
   the modem and the computer to do handshaking via dedicated hardware
   lines.

3. Use the highest speed between your modem and your computer that doesn't
   cause you loss of data.  Rough rule of thumb:  KS1.3/68000: 19200 baud.
   KS2.04/68000: double that; accellerated machines: use 57600.

   The modem will stop your computer via CTS/RTS if your computer goes too
   fast, and if stuff comes in from the other system slower than your
   actual connection between modem and computer, then your computer will
   simply not get things as quickly as it is able to.

4. Video modes:  watch the modem receive light.  If the light goes off and
   your screen is still scrolling text, then your display is lagging behind.
   Your choices are to increase the pre-scroll (VLT has it, I don't know
   about other software), reduce the number of bitplanes/colors of your
   terminal.

5. Protocol: use streaming protocols, such as zmodem.  Zmodem transmits
   without having to stop until the other end complains because of errors
   or whatever.  This means that there is no "transmit-ACK/NAK" cycle and
   transfer is as fast as reading and writing the information to disk
   allows.  I don't know how Ymodem-G and other protocols work, but I
   suspect it's more a features thing from there on, rather than
   performance.


Miscellaneous tidbits:

Because of error-correction protocols being handled in hardware,
transmission errors are less frequent with V.42bis/MNP modems.

I run VLT at a priority of 2 to make sure the process is never blocked by
any of the things that *I* do.  This reduces the chance of more stuff
coming in on the modem side than the computer can swallow at once.


I hope the above is helpful to others who are curious or wondering how to
get the most out of their fast modem.  If anyone has anything to add to
this, please let us hear it.

 ._.  Udo Schuermann     "If I went around calling myself emperor just because
 ( )  walrus@wam.umd.edu  some moistened bint lobbed a scimitar at me, they'd
 Seeking virtual memory   put me away!"         -- Monty Python's "Holy Grail"
Newsgroups: comp.sys.amiga.datacomm