US Robotics 56K x2 modem ... lousy compressed file throughput

US Robotics 56K x2 modem ... lousy compressed file throughput

Post by Doug Hair » Sat, 07 Feb 1998 04:00:00

>I've had a US Robotics 56K x2 internal modem for about a month now.
>I've noticed that I get lousy transfer rates with highly compressed
>files (gz, mp2, etc.). I'm talking 3.3 KB/s from a machine on our local
>network, which works out to roughly 26000 bps. Don't newer modems
>generally disable compression on the fly these days when sensing
>compressed data? Also, even with compression on shouldn't I get at
>nearly the negotiation speed? I ususaly connect at 45333 or 48000, and
>my serial port rate is set at 115200.

What are the final rates? Do the modems stay in the mid to upper 40's?
Look at the ATI6 after you disconnect and examine the various parameters
measured. Pay close attention to Link Naks, Blers, and the like. You
should get better rates on compressed files for those connect rates if
you are able to stay at them throughout the transfers. Don't ignore the
possibility of slowdowns and bottlenecks on the LAN

Quote:>I was using the default modem settings for a while over a ppp
>(Pentium 233 MMX, Linux kernel 2.0.32 #13 i586 unknown, RedHat 5.0,
>xisp, pppd) and recently tried new settings, which seemed to have sped
>things up. I stole these from the modem dialer on my NT partition:

>AT &F1 E0 Q0 V1 &C1 &D2 S0=0 S7=55 S19=0 L0 &M4 &K1 &H1 &R2 &I0 B0 X4

M0      -----------------------------------------------************-----


The items underlined with "---" are defaults under &F1 and the ones
underlined with "***" have no affect on connection rates or performance.
You can look them up in your manual or through the Help display screens.

Theyat init string should have made absolutely no difference in
performance unless you didn't set up your modem correctly in the first


>What's weird is as far as I can tell, nothing in that init sequence
>anything significantly different than the powerup default. But I really
>notice faster transfer rates when websurfing, for instance, especially
>with images. But highly compressed files are still not moving very
>and NT performance is identical.

So, turn off compression entirely and see if *that* improves speed on
those files. If it does, you can work from there.

Quote:>I notice when downloading compressed files that the modem lights (as
>evident from the 'virtual' asmodem) blink a lot as opposed to being on
>solid for uncompressed data.

Don't you think it might be a problem with the other end of the
connection, based on the above

Quote:>I know compression is working because I got over 12 KB/s with a file
>that was all 1's ;)

>Any insight would be appreciated, thanks in advance.

Have you tried calling into other hosts, such as local ISPs? You could
also try an LD connection to USR's BBS (847-982-5092) and download some
files from there for comparison.

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