Re: [tlug] Bittorrent Newbie

["Stephen J. Turnbull" <stephen@example.com>]

>>>>> "Edward" == Edward Middleton <edward@example.com> writes:

    Edward> Stephen J. Turnbull wrote:

Please include attributions for recursively quoted material (unless I
screwed that up, sometimes I do).

    Scott> Oddly enough, though it's supposed to be faster, I've
    Scott> always found it slower than standard downloads of ISOs.

    >> No, it's *supposed* to be slower,

    Edward> It is supposed to be less bandwidth efficient, not slower.

No, it's supposed be more bandwidth efficient (ie, it uses unsaturated
bandwidth, which---except for packet-metered connections---is free),
and slower.

    Edward> If you are using ftp to download a file your download
    Edward> bandwidth is limited by the servers bandwidth.

Which may or may not be the bottleneck; typically it is not for
servers that offer FTP.  It is true that bittorrent allows servers
with piss-poor connectivity to serve larger files than they could by
FTP, but by that very token you're unlikely to actually observe them
in reality.  This will increase the perception that torrents are
slower, and much of the time they are likely to be slower on the same
hardware.

    Edward> If you are downloading with bittorrent the bandwidth is
    Edward> limited by the number of seeding (I think that is the
    Edward> correct terminology) nodes.

Assuming (as you implicitly do) an infinitely large file or a random
and growing distribution of active nodes on the Internet, and that you
are "close" to the backbone, it's limited by the minimum of the sum of
the bandwidths of the active nodes and the minimum of your upload and
download bandwidths.  In other words, torrents are going to be slower
on ADSL.

NB, the special characteristic of a seed node is that it starts with
the whole file but nevertheless it stays active until the torrent is
deactivated.

    Edward> This assumes that you are also uploading.  If there is
    Edward> only one seed your download bandwidth will be a bit less
    Edward> then ftp, if there are many it will be greater.

This assumes that you join the torrent while it is young.  If you join
it when it is old, you start with bad karma and you stay that way,
because nobody wants to play with you.  The negotiations required to
get blocks when you have bad karma induce inter-block latency.

On the whole, downloads are going to be slower, but you will have
much lower latency to getting connected to the server with a torrent
on popular downloads.  Also, there will be many more servers because
they can be implemented more cheaply.


-- 
School of Systems and Information Engineering http://turnbull.sk.tsukuba.ac.jp
University of Tsukuba                    Tennodai 1-1-1 Tsukuba 305-8573 JAPAN
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