> According to Jake Messinger <jake@ams.com>:
> >On Wed, 20 May 1998, Brantley Jones wrote:
> >
> >> Would there be any point in this, though? Would you get that much better
> >> compression ratios out of STAC as opposed to V.42 bis?
> >
> >Think about it. V.42 bis compression is a function of the processor in a
> >modem. Stac compression would be a function of your processor on your main
> >board, in some cases, a 400 Mhz Pentium II. Plus stac is newer
> >algorhithms. What do you think? Ive heard a 20% average increase in
> >performance.
>
> Also, you are now putting fewer bits through your serial ports, so you
> have fewer interrupts occuring. I would bet that a computer with a few
> CPU cycles to spare would run better spending them on compression than
> on serial port interrupt handling. You can set your serial port speed
> back down to 38400 or 57600, instead of pushing it to 115200 or beyond.
With V.42 bis compression and a line speed of 115200 you can get a maximum
of 14400 bytes per second over a 33.6 modem. I have seen sustained 10500
bytes per second on uncompressed text. The limiting factor with using
modem based compression schemes is the speed of the serial interface that
connects the computer and the modem. Stac is done outside of that and
with uncompressed text you can probably get speeds 2 or 3 times greater
than with modem based compression methods.
The real thing you have to understand is the stuff you badly want to move
over the link faster is not going to improve in performance at all. I
mean images, sound, video. Stuff that is already compressed as much as
the technology allows. Those move at the link speed. Typically 3000
bytes per second for 28.8 and 33.6 and 4500 bytes per second for K56Flex.
Doug Ingraham The best defense against logic is ignorance.
Rapid City, SD
USA
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