FWIW, Comcast has a technology called 'powerboost' which can give you an
initial speed cap increase at the start of a download, network permitting.
http://www.comcast.com/

With a connection like this, it would be hard to find the optimal download
pipe size unless you used the low end of the connection's capability.
Shaping would be a nightmare since there is no real 'set' pipe speed. My
cable ISP is consistently around 4Mbit so it was easy in my case.

On 1/31/07, David W. Hess <dwhess at banishedsouls dot org> wrote:
>
> On Tue, 30 Jan 2007 23:25:34 -0500, "Chris Buechler" <cbuechler at gmail dot com>
> wrote:
>
> >Cable modems have a fixed speed cap. Whether or not you can actually
> >utilize that to its full capacity depends mainly upon congestion in
> >any portion of your ISP's network and the speed of the remote server
> >(or the connection between the remote server and your ISP). It's
> >unlikely, unless your ISP's network is severely mismanaged, that your
> >actual connection is varying from 4-11 Mb. The reality is likely that
> >whatever you're connecting to can only reach that speed at that given
> >time. Another possibility is traffic shaping of some sort on your
> >ISP's network.
>
> I would not put it past a broadband ISP to have these types of problems
> but they
> do seem rare.  Back when I had cable, I had similar issues where we
> verified
> limited throughput below the link speed which varied over a 24 hour period
> caused by congestion close on the ISP side but at the time I was not in a
> position to do traffic shaping anyway outside of what the applications I
> was
> using supported.
>
> >You should be able to set that to the actual cap and be fine. If your
> >ISP's network routinely gets bogged down and you can't actually reach
> >your cap, there isn't anything you can do about it. It would be
> >theoretically possible, though difficult, to write something to detect
> >changes in your actual maximum achievable throughput in near real time
> >and change pipes accordingly, but I don't know of anything that
> >permits something of that nature.
>
> I have not had an occasion to try it yet but several people have setup the
> BSD
> or Linux traffic shaping facilities with a monitoring script or program
> that
> measures latency to a close router on the ISP side of the DSL or Cable
> link and
> adjusts the maximum traffic shaper throughput accordingly.  I suspect this
> would
> work rather poorly in some circumstances without sophisticated tuning
> unless the
> ISP enforced some type of equal sharing at the point of congestion.
>
>
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