Re: Download Accelerator

from "Joseph M. Reagle Jr." <[email protected]>, Thu, 14 Sep 2000 09:03:23 -0400

Replies:

hugo

Parents:

At 10:01 9/14/2000 +0200, Hugo Haas wrote:
>Every browser speaking HTTP/1.1 could use this feature to do the same. I
>am not sure why they don't do it, but in my opinion, download
>accelerators are anti-social because they use several connections

Browsers will now open multiple connections for multiple resources. But I
think it's 1-to-1, and for big files I think you answered your own question!

>I woud like to know the number of people using such programs. I
>occasionally see them in my logs, but not very often.

I installed it just to play around with, and it is convenient for large
downloads. One of the things that surprise me with a cable modem is that
usually my bandwidth is not the limiting factor on my interactions. (The
reason I say cable modem is I'm not usually downloading movies and mp3s at
work, so I wouldn't notice this there.) Frequently, when using scour (I
don't use napster anymore) I'll pull out those folks with stated T1
connections and ping<50 and still only get a 30Kbps average. I once got 80
on scour, so maybe that was someone on my local subnet! Regardless (and I'm
sure there is an answer) where is most of the congestion/hold-up? It isn't
my pipe, and I'd be surprised if it's the servers.

But then again, if this accelerator really does work that means the
intermediary pipes can handle the bits (otherwise I wouldn't see a
difference) AND the server can as well. So was the previous "inefficiency"
arbitrary; or am I benefiting at the expense of my network peers?
__
Regards, http://www.mit.edu/~reagle/
Joseph Reagle E0 D5 B2 05 B6 12 DA 65 BE 4D E3 C1 6A 66 25 4E
MIT LCS Research Engineer at the World Wide Web Consortium.

* This email is from an independent academic account and is
not necessarily representative of my affiliations.

Re: Download Accelerator

from Hugo Haas <[email protected]>, Thu, 14 Sep 2000 16:44:34 +0200

Replies:

None.

Parents:

On Thu, Sep 14, 2000, Gerald Oskoboiny wrote:
> For a single large file, I don't really see how this would speed
> things up, unless the multiple connections are just getting
> around some kind of artificial limit per connection or something.
> (shouldn't a single download be enough to saturate whatever
> bandwidth you have available?)

On Thu, Sep 14, 2000, Joseph M. Reagle Jr. wrote:
> But then again, if this accelerator really does work that means the
> intermediary pipes can handle the bits (otherwise I wouldn't see a
> difference) AND the server can as well. So was the previous "inefficiency"
> arbitrary; or am I benefiting at the expense of my network peers?

This is actually a very interesting question: what is the bottleneck for
a TCP connection between two hosts?

I guess that the answer is simple: at some point along the route between
the source and the destination, there is a congestion.

Being very simplistic:

If we imagine that there are 100 TCP connections at this particular
point, and that this is the only problem along the way, the bandwidth
you get with this connection would be 1/100th of the available
bandwidth.

If all things are equal and you open 4 extra connections, you will get
5/104th of the bandwidth, i.e. that you will download your large file
4.8 times faster.

Again, this is very simplistic and I'm not even sure that it would work
that well, but I guess that it is the idea.

And if everybody starts using download accelerators, a user will end up
with 5/500th of the bandwidth, i.e. the same as the beginning, except
that there will be 5 times as many TCP control packets as there were
with only one connection, which means that this increased overhead will
make the user lose bandwidth used for the actual transfer.

--
Hugo Haas <[email protected]> - http://larve.net/people/hugo/
I would kill everyone in this room for a drop of sweet beer. -- Homer
J. Simpson