On 24 Sep 2005 at 9:49, Carol wrote:

> Here's probably a dumb question, but is the connection speed the same as the
> speed you see in the window when the download is happening?  I see it as
> 'kbps' when I'm downloading, (in the little window), but you're talking
> about just 'k'.  The other day when I was trying to download O.O., it
> started out at about 25 kbps, but within a few minutes was down to 4.92
> kbps, which is less than when I had dialup.  (I have 256k DSL now.)  I gave
> up the download, because it was going to take over 4 hours at 4.92 kbps.  I
> tried it later that night and managed to download it in a little over an
> hour at a range between 18-22 kbps, fairly consistent.  So, I guess it has
> something to do with phone line usuage/time of day.  But, is 22 kbps slow
> for 256k DSL?  Am I talking about apples and oranges here with the 'k' vs.
> 'kbps'?
> Carol Hanson
>
> >  A larger MTU size reduces some overhead, but increases the impact of line
> > noise.  If you're consistently getting 44K connection speeds, this may
> > help
> > you.  [Those of you on broadband or LAN connections are almost certainly
> > already at the maximum; this only applies to dial-up.]

  The effective speed of a download is going to reflect several factors.

  First of all, your 256k DSL connection is to your ISP.  But the server
you're downloading from isn't at your ISP -- it's somewhere else in the
Internet.  Generally, the various bits of the Internet will try to find a
reasonable route between your machine and there -- although there's
absolutely no grarantee that packets from your machine to the download host
take the same path as packets coming the other way....

  Each packet will be passed from router to router over links set up by the
various ISPs.  Each link has a maximum capacity, which you're sharing with
everyone else whose packets are using that link.  So the path in either
direction may include some links with low capacity, and some links with
heavy usage -- effectively, only a little capacity is available for your
traffic.  (Odds are that all of the customers of your ISP share a handful of
high-capacity links to other ISPs -- and that if you all try to use your
full 256k at once, you'll far exceed the capacity of those links and will
each get only a trickle.)

  So the capacity of the path is basically the available cpapcity of the
link with the least available capacity.  And then there is overhead, use of
some of the bits in each packet to manage the packet and the file transfer
process.  [Since some of this is per packet, a larger packet size (MTU)
means those items are repeated less often.]  So if nobody else -- including
other programs running on your machine -- was using any of the path between
you and the server, and your DSL connection was the slowest link in the
chain, you might possibly see around 200kbps as your effective download
speed.  (However, the download window *might* be showing the speed in kBps --
 bytes rather than bits per second -- in which case 22 is pretty close to
this ideal.)

  So:  if you're only seeing 5kbps, your download is probably competing with
other traffic -- for your DSL line (check your machine for spyware and
viruses!), for the server's Internet connection (you have to rely on the
server owners to address this), or for your ISP's gateways to adjoining ISPs
(your ISP might be trying to hard to save money),

David Gillett

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