[BitTorrent] Plans for Multicast?

Nick Johnson arachnid at notdot.net
Tue Jan 18 17:09:32 EST 2005

Bill Cox wrote:

>On Mon, 2005-01-17 at 16:45 +0000, Justin Cormack wrote:
>I took a quick tour of the multi-cast tutorial at:
>>From my point of view, it would be ideal if multicast simply allowed me
>to specify multiple addresses for a message to be sent to.  AFAIK, it
>doesn't.  Instead it is a very complex mechanism designed for
>distributing real time video signals, rather than BitTorrent packets.
>Also, since much of the core of the internet has multicast disabled, it
>probably wouldn't help much in the near-term, except possibly on local
>nets where it's value is less.  The situation for multicast seems to me
>to be the same for IPv4 and IPv6.
>But what the heck, it's still fun to talk about how we might use it if
>it were widely available...  I'm not recommending we take action on any
>of these ideas.  There just ideas:
If you're interested in this sort of thing, you might like to look into 
Digital Fountain Algorithms and Tornado Codes. It's a very cool system 
that allows one or more sources to distribute (multicast) files via 
broadcast in such a way that listeners can reassemble the file after 
recieving enough data, even with arbitary gaps (packetloss etc) in the 
source data. The overhead for doing this is about 5% over the original 

Actually, I've been pondering its application to non-broadcast (BT like) 
systems myself lately. I think it could alleviate problems 
(particularaly at the start and end of getting a torrent) where two 
connected peers can't both offer something of interest to each other.

-Nick Johnson

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