Re: [core-dev] Bandwidth drop-off in Limewire 4.2.6 (test results)

Brian,

I didn't notice in this email but were any of those firewalled transfers?  I
guess not but there is a wastage there of uplink capacity due to ACKing that we
are going to take care of shortly.

Otherwise, it sounds very fishy.  Not having followed the earlier conversation
totally, I would suggest neutralizing any bandwidth throttles that are used and
turning off the 1/2 second delay that we add in to allow other TCP traffic to
get through for browsers, etc and see what happen.  I think Sam and Zlatty can
point those areas out.

Thanks
-greg
Quoting Brian Fall <[email protected]>:
> Hello everyone, I've finished testing Limewire 4.2.6 to
> determine if the bandwidth drop-off that I reported
> earlier is fundamental to the magnet links (my original
> testing method) or is independent of magnet links. In my
> earlier tests with earlier versions of Limewire 4.2.x I used
> magnet links with multiple sources (using the as and xt
> attributes), each of which are my own servers. That is,
> the magnet link sources pointed to my own servers so that
> I could monitor bandwidth during the upload from those
> servers to the client that clicked on the magnet links.
>
> What I observed was very surprising: with each new source
> the bandwidth for ongoing uploads dropped. For example,
> if I used just one of my servers I got the download at
> full speed, but when two were used both of those sources
> only uploaded at about half-speed -- it was no faster to
> upload from two sources than one because of the upload
> speed drop-off. Things got worse with each new source;
> with a handful of sources or more my own two servers
> dropped off  to just a fraction of the bandwidth they
> had available. As a result, most of the available
> bandwidth on my servers was not used despite the fact
> that the client actually started with them (that is,
> my two servers are the first sources that the client
> starts with and they have ample bandwidth, but as the client
> starts to connect with other clients on the Gnutella
> network the upload/download speed between the client and
> my servers drops off to the point where only a fraction
> of the available bandwidth is used).
>
> With Limewire 4.2.6 I decided to eliminate the magnet links
> from the equation entirely, and provide a testing method
> that is easy enough for anyone to try. If you do the same
> and get the same results we can then assume that there is
> a fundamental upload/download issue with Limewire and that
> magnet links have nothing to do with it. I ran these new
> tests and had the same result as previously; with each new
> source the upload/download speed drops off until eventually
> only a fraction of the available bandwidth on my own servers
> is used. Following are the steps I took for these new tests:
>
>  1) Using a personal file that I know isn't available on the Gnutella
>     network I tested the upload/download speed on my own servers.
>     Because the file isn't available on the larger network I didn't
>     have to worry about the client finding new sources; I got full
>     speed downloads from each of my servers with this test when only
>     one of them was used by the client. But, when both were used the
>     drop-off occured as previously (each server used only about half
>     of their bandwidth when both servers were used, yet transferred at
>     full speed when only one for the transfer).
>
>
>  2) Using popular files on the Gnutalla networks (movies, music files, etc.)
>     that have a large number of sources) I was able to determine that the
>     download speed drops-off as more sources are found. To observe this I
>     would download the file onto my servers using Limewire, so that my
> servers
>     had the files *and* retained any alternate sources associated with the
> files.
>     Then, using my client, I established a direction connection to my server
> and
>     manually downloaded the media file. This would start the download at full
>     speed (one source - my server), and within a minute or so the client
> would
>     also start downloading from the alternate sources associated with that
> file
>     (multiple sources on the Gnutella network). That's when the drop-off
> started...
>
> As I observed previously when conducting tests with magnet links the upload/
> download bandwidth for my own server began to drop-off as the client adds
> more sources; this drop-off continues to the point where only a fraction of
> the available bandwidth my server has is actually used. In other words,
> the exact same behavior occurred when magnet links weren't involved,
> indicating that the problem is isolated withing the core upload/download
> code in Limewire.
>
> Can others replicate the drop-off in bandwidth? The test is rather simple,
> and you can do it as long as you have two computer (one to act as the source,
> the other the client). Merely share a private file that isn't on the larger
> Gnutella network and record how fast the upload/download happens, and then
> do the same for a popular file available on the Gnutella network -- download
> it first to your server, then direct connect to your server from the client
> and manually start the download. The download starts at full speed, and
> should
> drop-off in speed as the alternate sources are found and added.
>
> Unless my particular test results are unique to me it seems like a big
> problem that limits Limewire's overall effectiveness since it
> loses speed with each new source added to the download (in order to get
> decent speed a lot of sources are needed to compensate for the drop-off).
> In my case it's faster to have the download from my own server than to
> swarm it from a few (2-3) sources (in which case a standard Web server
> would be better to transfer the files since users only need a Web
> browser to get the files at the same speed as Limewire offers). If I have
> enough sources however, with ample bandwidth available from each, the
> drop-off in bandwidth is overcome. This means that more sources are tapped
> just to overcome the problem, which in turn means more traffic on the
> network and more resources consumed than needed.
>
> But if the swarming didn't drop-off in speed it would offer a
> tremendous advantage for such file transfers. We're looking at
> Limewire's potential as a file transfer tool for companies, but
> so far it seems like the bandwidth drop-off makes it on par with
> traditional file sharing. But it could just be my setup, so I wonder:
>
>   Can anyone confirm that this happens to them as well?
>
> Brian
>
> --
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