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wmf
You said Luby, so prepare to be vaporized.

On the technical side, theoretically this should only be a few percent faster than BitTorrent but requires significant complexity.

andrewcooke
why vaporized?

also, why faster? does bittorrent duplicate some traffic?

wmf
BitTorrent has overhead from control traffic (have messages etc.) that can theoretically be eliminated using rateless coding. The extra decoding makes it a wash IMO.
evgen
FWIW, when building the second version of the core tech from which BT was of forked we did license the tornado codecs from digital fountain to try to get a better reliability rate and it ended up being worse than a wash; setting aside the additional complexity it adds to the system it completely screws with internal block verification based on hashes. The blocks are also not structured compared to other FEC codecs (e.g. Rizzo) so you lose any hope of streaming. Long sorry short, unless you are trying to get around nasty packet loss there are better encoding schemes for this sort of data distribution task.
andrewcooke
this is all new to me and i'm struggling to find a friendly, simple introduction to the field. does anyone have a good link to, say, an introductory article on fountain codes? i'm starting to get a feel for the idea from reading various wikipedia pages, paper abstracts, powerpoints, etc, but a good "layman's" article would be great...

[update] huh. just after posting i started searching for "fountain codes" and found this - http://blog.notdot.net/2012/01/Damn-Cool-Algorithms-Fountain... (previously had been searching for luby, raptor, etc).

kenko
Change test-client.py to end:

  print client.fetch(1000)
  print client.fetch(1)
And when you run it, you get the same thing twice (whatever file was specified as the first argument to test-server.py on the commandline). On the other hand, change it to end

  print client.fetch(1)
  print client.fetch(1000)
and you get "Hello World!" twice.

At one point the server process also gave me this:

  Server(s) started. Press enter to stop.
  Exception in thread Thread-1:
  Traceback (most recent call last):
    File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 552, in __bootstrap_inner
      self.run()
    File "/Users/wolfson/src/others/pouring-rain/LT/Server.py", line 84, in run
      self.streams[ entry[1] ].discard( entry[0] )
  NameError: global name 'entry' is not defined
mgronhol
Thanks, just noticed a small initialization issue there, fixibg that soon :)
[deleted]
(comment deleted)
kilburn
I fail to see how is this _exponentially_ faster. "Transfer time T(K) = 1.25/K where K = number of servers" seems pretty linear to me...
mgronhol
Linearity: function's derivative is constant w.r.t. the parameter discussed. dT(K)/dK = -1.25/K^2 and this most certainly is not constant.
kilburn
To clarify, the original title said that this was a method for _exponentially faster_ data transfer. That said, you got me in that it is not linear. As you have shown, that function is quadratically decreasing (which is _worse_ than linear). The title has been corrected since then, so I kind of got my point through.