[bittorrent] Encryption, Azureus Extended Messaging and reserved bits...

David P. Mott dpmott at sep.com
Mon Sep 11 14:17:49 EDT 2006

I was suprised when I read that there was not a place on the WIKI for 
people to document their use of the reserved bits.  I guess when I 
originally put that page together, I was thinking that Bram would do more 
with it, and didn't want to encourage others to step on his toes by 
grabbing bits for their own use.

If you *do* get some information and decide to update the WIKI, I'd like 
to suggest that you organize it in a way that:
1. Provides a title for the feature
2. Provides a description of the feature
3. Defines the bit that is most commonly used/accepted for the feature
4. Provides a place to list the bittorrent clients that implement this

Hopefully the last part will be (or become) redundant identical 
information, but if there *are* clients out there that just randomly used 
a bit for something, then we'd probably like to know about it and have a 
place to document it.

Also, an old Yahoo post from Bram suggested that the LSB bits be used 
first, so that MSB bits could "override" their meaning.  So, for example, 
if bit #3 represents "ZIP compression", but bit #5 overrides this to mean 
"SHA link encryption + compression", then clients should list *all* of the 
bits that *could* affect the meaning of bit #3, and what they need to be 
set to to get the feature described for "ZIP compression".  Under the 
heading of "SHA link encryption", it might mention that #3 would enable 
compression on the SHA link when bit #5 is in use.

Sorry for the corny example, I couldn't think of anything better off the 
top of my head.


> ------------------------------
> Message: 4
> Date: Mon, 11 Sep 2006 16:21:27 +0100
> From: "Alan McGovern" <alan.mcgovern at gmail.com>
> Subject: Re: [bittorrent] Encryption,	Azureus Extended Messaging and
> 	reserved bits...
> To: bittorrent at lists.ibiblio.org
> Message-ID:
> 	<117799f00609110821w1f4d7701u9cb29aa6fe760c01 at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
> [sorry for posting this twice, i didn't reply to the list the first time]
> If i do get any information, i will update the
> wiki.theory.org/BitTorrentSpecification page and give the list a mail to let
> ye know of the updates.
> As it stands for using the reserved bits, there doesn't seem to be any
> formal listing *anywhere*, or even an informal one. What i'm going to do (in
> the next day or two) is expand the above mentioned BitTorrent page with the
> 2 reserved bits that i know of (Fast Peers Extendsion and Azureus Extended
> Messaging). So hopefully anyone else here that knows of other reserved bits,
> what they're used for (and hopefully a link for implementing what they're
> used for) could be put there aswell.
> Thanks,
> Alan

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