<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">In practice, BT prefers the fattest pipes irrespective of distance. It’s basically a scheme that trades bandwidth for content. <br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Feb 26, 2019, at 3:08 PM, Jack Haverty <<a href="mailto:jack@3kitty.org" class="">jack@3kitty.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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<div text="#000000" bgcolor="#FFFFFF" class=""><p class="">If I create a file and put it on BT here in California, someone
in Europe might download it. The full contents of the file have
to travel from CA to EU. If subsequently someone in EU attempts
to download that same file, and the first EU downloader is still
online and has the file, the file will hopefully be transferred
from the first EU site to the second.</p><p class="">In that scenario, there is no need to transfer the same data
across the US and Atlantic a second, or third, etc. time. It's
already in EU. Those redundant 10,000 mile transfers are
eliminated. The more players, the better it presumably gets.<br class="">
</p><p class="">I think that's what Miles means by "effectively multicast".
It's the characteristic that makes BT attractive for things like
distributing DVD-scale ISO files of Linux distributions.<br class="">
</p><p class="">/Jack<br class="">
</p>
<div class="moz-cite-prefix">On 2/26/19 1:24 PM, Richard Bennett
wrote:<br class="">
</div>
<blockquote type="cite" cite="mid:E9C7302A-9628-4968-A6B1-342385CAF705@bennett.com" class="">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" class="">
Miles made the claim that BT is “more efficient” than unicast
because it somehow becomes "EFFECTIVELY multicast - avoiding
redundant traffic when more than one destination is downloading
the same file, at the same time.” I don’t believe this is true.
<div class=""><br class="">
</div>
<div class="">BT is a UDP-based protocol that senses queuing
delays and defers more aggressively than TCP when they happen.
Here’s the protocol spec: <a href="http://www.bittorrent.org/beps/bep_0003.html" class="" moz-do-not-send="true">http://www.bittorrent.org/beps/bep_0003.html</a>,
if you can find any redundancy reduction in it please point it
out.
<div class=""><br class="">
</div>
<div class="">RB<br class="">
<div class=""><br class="">
<blockquote type="cite" class="">
<div class="">On Feb 26, 2019, at 2:16 PM, Guy Almes <<a href="mailto:galmes@tamu.edu" class="" moz-do-not-send="true">galmes@tamu.edu</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div class="">Richard,<br class="">
If you do multicast at the network layer, you get IP
multicast, Steve Deering's thesis project that escaped
from the lab and has challenged network engineers ever
since.<br class="">
But if you do multicast at the application layer, you
get lots of (IP) unicast traffic, but with some of the
properties of IP multicast and also with some of the
advantages of TCP and without the challenging routing
issues of IP multicast. Examples include BitTorrent,
Unidata's LDM/IDD software, and the USENET netnews
utility.<br class="">
Oh, and you can also do multicast at the Ethernet
level. Historically, it was the multicast feature of
the then-new 10Mb/s Ethernet that triggered Deering's
considering the possibility of multicast at the
network layer.<br class="">
<br class="">
So IMHO the term multicast can be used appropriately
without necessarily referring to network-layer IP
multicast.<br class="">
<br class="">
Back to the primary topic,<br class="">
<span class="Apple-tab-span" style="white-space:pre"> </span>--
Guy<br class="">
<br class="">
On 2/26/19 15:35, Richard Bennett wrote:<br class="">
<blockquote type="cite" class="">Perhaps you can
explain that the term "EFFECTIVELY multicast” means
to you, and how it applies to BitTorrent. Every time
I’ve looked at it in Wireshark I see nothing but
unicast.<br class="">
RB<br class="">
<blockquote type="cite" class="">On Feb 26, 2019, at
10:01 AM, Miles Fidelman <<a href="mailto:mfidelman@meetinghouse.net" class="" moz-do-not-send="true">mfidelman@meetinghouse.net</a>
<<a href="mailto:mfidelman@meetinghouse.net" class="" moz-do-not-send="true">mailto:mfidelman@meetinghouse.net</a>>>
wrote:<br class="">
<br class="">
Well, that's not how it's supposed to work. Or
claimed to work.<br class="">
<br class="">
On 2/25/19 8:27 PM, Richard Bennett wrote:<br class="">
<blockquote type="cite" class="">Naw, it’s all
unicast with plenty of redundant traffic moving
along long routes.<br class="">
<br class="">
<blockquote type="cite" class="">On Feb 25,
2019, at 5:49 PM, Miles Fidelman <<a href="mailto:mfidelman@meetinghouse.net" class="" moz-do-not-send="true">mfidelman@meetinghouse.net</a>
<<a href="mailto:mfidelman@meetinghouse.net" class="" moz-do-not-send="true">mailto:mfidelman@meetinghouse.net</a>>>
wrote:<br class="">
<br class="">
That's not what anybody said. It's
EFFECTIVELY multicast - avoiding redundant
traffic when more than one destination is
downloading the same file, at the same time.
That's its whole point. (Or as someone else
put it, it's a caching mechanism.)<br class="">
<br class="">
Miles<br class="">
<br class="">
On 2/25/19 4:24 PM, Richard Bennett wrote:<br class="">
<blockquote type="cite" class="">Bittorrent
doesn’t use multicast.<br class="">
<br class="">
<blockquote type="cite" class="">On Feb 25,
2019, at 1:42 PM, Miles Fidelman <<a href="mailto:mfidelman@meetinghouse.net" class="" moz-do-not-send="true">mfidelman@meetinghouse.net</a>
<<a href="mailto:mfidelman@meetinghouse.net" class="" moz-do-not-send="true">mailto:mfidelman@meetinghouse.net</a>>>
wrote:<br class="">
<br class="">
Well yes, but torrent is a distribution
mechanism - it's not an infrastructure for
maintaining or mirroring files. It's
essentially another, sometimes more
efficient, option for click-to-download
(e.g., ftp, http, bittorrent). And it's
only more efficient if multiple people are
downloading at the same time.<br class="">
<br class="">
Miles<br class="">
<br class="">
On 2/25/19 12:28 PM, Richard Bennett
wrote:<br class="">
<blockquote type="cite" class="">No,
Bittorrent uses DHTs and accesses as
many copies of a given file as users
choose to share. It has to be running to
serve files, however.<br class="">
<br class="">
RB<br class="">
<br class="">
<blockquote type="cite" class="">On Feb
25, 2019, at 9:59 AM, Miles Fidelman
<<a href="mailto:mfidelman@meetinghouse.net" class="" moz-do-not-send="true">mfidelman@meetinghouse.net</a>
<<a href="mailto:mfidelman@meetinghouse.net" class="" moz-do-not-send="true">mailto:mfidelman@meetinghouse.net</a>>>
wrote:<br class="">
<br class="">
On 2/24/19 9:53 PM, John Levine wrote:<br class="">
<br class="">
<blockquote type="cite" class="">
<blockquote type="cite" class="">That's
what I find intriguing about my
Benevolent BotNet notion. Rather<br class="">
than depending on finding an
institution interested in,
competent at,<br class="">
and willing to save history, and
hoping that it has longevity, you
rely<br class="">
on a network of volunteers to
provide that survivable
infrastructure by<br class="">
volunteering their excess
computing resources.<br class="">
</blockquote>
Hi again. Please look at Bittorrent
and tell us how it is different<br class="">
from what you're proposing.<br class="">
<br class="">
Bittorrent has the advantage of
already existing and being deployed<br class="">
all over the world. It's notorious
for pirated music but it's also<br class="">
widely used for sharing linux
distributions and the like.<br class="">
<br class="">
</blockquote>
Bit torrent is transient. It's more
like an ad-hoc multi-cast<br class="">
streaming. When nobody is
downloading, there may be only one
copy of<br class="">
the file.<br class="">
<br class="">
Now gnutella, and some of the other
P2P file sharing systems - that<br class="">
replicate copies, or distribute files
across a distributed hash table -<br class="">
that's another story entirely.<br class="">
<br class="">
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<div style="word-wrap: break-word; -webkit-nbsp-mode:
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<a href="http://hightechforum.org/" class="" moz-do-not-send="true">High Tech Forum</a> Founder</div>
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