On Sat, 01 Jan 2011 00:17:13 -0800, David Nebenzahl
wrote:

On 1/1/2011 12:11 AM Jeff Liebermann spake thus:

On Fri, 31 Dec 2010 23:10:51 -0800, David Nebenzahl
wrote:

On 12/31/2010 10:54 PM John Tserkezis spake thus:

David Nebenzahl wrote:

http://s786.photobucket.com/albums/y...speed44-59.gif

Phew. Finally; yes, that's what I'm talking about, the "little"
fluctuations (between ~4K and ~5K in that second snapshot).

Methinks you're looking at the effects of roundoff error. There are
not enough packets used for the download test, so the graph is
rounding off the result to the nearest convenient significant figure.
A running average, with larger time slices, would yield a much
smoother and more realistic curve.

But as I watch the display during a download, I can see the rate *very
regularly* alternating between two definite speeds (like 4.4 and 5.9 K).

Toss a coin. From the pattern of heads and tails, I can see a very
regular pattern of randomly alternating heads and tails. OK, bad
analogy, but I thought it was cute. It might be doing 5.75Kbits/sec
and alternately rounding off to the nearest convenient value. Most
speed test software these daze is made for DSL or cable modem speeds.
They use fairly short sampling times, because with the higher speeds,
it's a fair assumption that there will be a sufficient number of bytes
downloaded to get a reasonable value. However, the same software at
dialup speeds is going to see far fewer bytes of traffic, and
therefore generate a more granular result.

As you can see, the pattern is visible, at least according to this
display. Doesn't that tell us something about how the transfer is taking
place? Or is this just a regularly repeating roundoff error?

I think this would be a good time for you to disclose how you're
running this test and what hardware, OS, and software you're using. I
don't like guessing (even though I do it quite often).

In fact, I can tell when the transfer rate is faster or slower, based on
the display: it'll bounce between the same two speeds--that never
changes--but the "flats" on the upper part of the line will be longer,
meaning it's spending more time at the faster speed. The difference is
actually noticeable, in the time it takes to render web pages and such.

It really depends on what your mystery application is doing and how
large or long a sample it takes. If the sample is too short, you'll
get roundoff error. Looking at your usenet news header,
User-Agent: Thunderbird 2.0.0.4 (Windows/20070604)
it appears that you're using an older copy of Windoze, possibly Win98,
and a 3.5 year old out of date copy of Thunderbird. Therefore, I
won't suggest you use the XP performance monitor to get a better
picture.

Incidentally, if you want to do useful performance measuring, with
clues as to what's going on behind the magic curtain, I suggest you
look at IPerf and JPerf.
http://openmaniak.com/iperf.php
http://code.google.com/p/xjperf/
You may have to update your version of Windoze and Java in order for
it to run properly. You'll find a few IPerf servers available on the
internet, but they're usually reserved for specific users in order to
avoid overload.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558