Re: Slow downloading

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <1995Jul21.220845.4818@news.etc.bc.ca>,
Robin Prest <rprest@cln.etc.bc.ca> wrote:
> 
> 	If my modem's rated at 14.4 k/s, then why does it only sustain a 
> file transfer rate of about 40k/m.  Shouldn't it be receiving data at a 
> rate more around 3 or 4 hundred k per minute?

With error correction and data compression are enabled, I get about
1650 characters per second for most file transfers (compressed files).
This works out to about 100k per minute.

With error correction and data compression disabled, the maximum
transfer rate (assuming ZModem) would be about 1400 characters per
second (84k per minute).

If you are using a simpler protocol such as YModem, XModem-1k, or
XModem-128, the transfer rate will be much slower, as the sender has
to wait for an acknowledgement for each block it sends.

I would expect plain XModem to manage about 40k per minute with a
14400 modem.  XModem-1k or YModem should be able to manage more like
60k to 80k per minute.


Another possibility is that you aren't actually connecting at 14400.
Your modem should have commands for displaying as much information as
possible about the communication speed and protocol being used.  For
example, I can use ATX5 with my ZyXEL, and it tells me the protocol
(speed) and error correction/data compression protocols.

Rockwell-based modems have an S-register (S95) that can be used to
enable "COMPRESSION", "PROTOCOL" and "CARRIER" messages that give more
information.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand