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| 28 | <!-- ### Begin Content ### --> |
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| 29 | <div id="second"> |
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| 30 | |
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| 31 | |
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| 32 | |
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| 33 | <table class="rfc2822 docutils field-list" frame="void" rules="none"> |
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| 34 | <col class="field-name" /> |
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| 35 | <col class="field-body" /> |
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| 36 | <tbody valign="top"> |
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| 37 | <tr class="field"><th class="field-name">BEP:</th><td class="field-body">26</td> |
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| 38 | </tr> |
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| 39 | <tr class="field"><th class="field-name">Title:</th><td class="field-body">Zeroconf Peer Advertising and Discovery</td> |
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| 40 | </tr> |
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| 41 | <tr class="field"><th class="field-name">Version:</th><td class="field-body">11105</td> |
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| 42 | </tr> |
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| 43 | <tr class="field"><th class="field-name">Last-Modified:</th><td class="field-body"><a class="reference external" href="http://bittorrent.org/trac/browser/dotorg/trunk/html/beps/bep_0026.rst">2008-05-27 20:57:09 -0700 (Tue, 27 May 2008)</a></td> |
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| 44 | </tr> |
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| 45 | <tr class="field"><th class="field-name">Author:</th><td class="field-body">Robin Perkins <robin DOT perkins AT internode DOT on DOT net></td> |
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| 46 | </tr> |
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| 47 | <tr class="field"><th class="field-name">Status:</th><td class="field-body">Draft</td> |
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| 48 | </tr> |
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| 49 | <tr class="field"><th class="field-name">Type:</th><td class="field-body">Standards Track</td> |
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| 50 | </tr> |
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| 51 | <tr class="field"><th class="field-name">Content-Type:</th><td class="field-body"><a class="reference external" href="http://www.bittorrent.org/beps/bep-0012">text/x-rst</a></td> |
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| 52 | </tr> |
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| 53 | <tr class="field"><th class="field-name">Created:</th><td class="field-body">10-May-2008</td> |
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| 54 | </tr> |
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| 55 | <tr class="field"><th class="field-name">Post-History:</th><td class="field-body"></td> |
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| 56 | </tr> |
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| 57 | </tbody> |
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| 58 | </table> |
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| 59 | <hr /> |
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| 60 | <div class="contents topic" id="contents"> |
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| 61 | <p class="topic-title first">Contents</p> |
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| 62 | <ul class="simple"> |
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| 63 | <li><a class="reference internal" href="#abstract" id="id16">Abstract</a></li> |
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| 64 | <li><a class="reference internal" href="#rationale" id="id17">Rationale</a></li> |
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| 65 | <li><a class="reference internal" href="#requirements" id="id18">Requirements</a></li> |
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| 66 | <li><a class="reference internal" href="#method" id="id19">Method</a></li> |
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| 67 | <li><a class="reference internal" href="#considerations" id="id20">Considerations</a></li> |
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| 68 | <li><a class="reference internal" href="#thoughts" id="id21">Thoughts</a></li> |
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| 69 | <li><a class="reference internal" href="#references" id="id22">References</a></li> |
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| 70 | <li><a class="reference internal" href="#copyright" id="id23">Copyright</a></li> |
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| 71 | </ul> |
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| 72 | </div> |
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| 73 | <div class="section" id="abstract"> |
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| 74 | <h1>Abstract</h1> |
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| 75 | <p><a class="reference external" href="ZeroConfigurationNetworking(Zeroconf)http://www.zeroconf.org">Zeroconf</a> <a class="footnote-reference" href="#id1" id="id2">[1]</a> is a collection of protocols including ipv4 link local |
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| 76 | networking, <a class="reference external" href="MulticastDomainNameSystem(mDNS)http://www.multicastdns.org">mDNS</a> <a class="footnote-reference" href="#id3" id="id4">[2]</a>, and <a class="reference external" href="DNSservice-discovery(DNS-SD)http://www.dns-sd.org">DNS service-discovery</a> <a class="footnote-reference" href="#id5" id="id6">[3]</a>. This document aims |
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| 77 | to outline an extension for BitTorrent clients to allow them to find |
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| 78 | peers on a local-link network using the zeroconf <a class="reference external" href="DNSservice-discovery(DNS-SD)http://www.dns-sd.org">DNS |
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| 79 | service-discovery</a> <a class="footnote-reference" href="#id5" id="id7">[3]</a> system. It was written in the hope that clients |
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| 80 | could standardise the way in which they found peers on the local-link |
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| 81 | in order to maximize the functionality of the BitTorrent protocol.</p> |
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| 82 | </div> |
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| 83 | <div class="section" id="rationale"> |
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| 84 | <h1>Rationale</h1> |
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| 85 | <p>Many networks today consist of computers that have a fast network |
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| 86 | connection (tens or hundreds of megabits/s) to a local area network, |
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| 87 | in addition to a relatively slower (hundreds of kilobits/s or a few |
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| 88 | megabits/s) connection to the wider internet. Such networks exist in |
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| 89 | places such as university colleges, defence barracks and community |
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| 90 | wifi networks. If two hosts on the same (fast) local-link network |
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| 91 | wish to download the same torrent at the moment they only share |
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| 92 | packets across their slow internet connection. The BitTorrent Zeroconf |
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| 93 | Peer Advertising and Discovery Extension will allow automatic |
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| 94 | discovery of these peers to each other so that packets can be quickly |
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| 95 | transfered across the fast local network as opposed to across their |
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| 96 | slow internet connections. Effectively the effort of downloading the |
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| 97 | torrent can now be distributed between the hosts on a local-link |
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| 98 | network.</p> |
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| 99 | </div> |
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| 100 | <div class="section" id="requirements"> |
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| 101 | <h1>Requirements</h1> |
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| 102 | <p>In order to facilitate the BitTorrent Zeroconf Peer Advertising and |
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| 103 | Discovery Extension each host is going to be required to run a |
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| 104 | zeroconf service discovery daemon. This is relatively trivial as there |
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| 105 | are many available for free but two particularly good zeroconf |
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| 106 | implementations are:</p> |
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| 107 | <ol class="arabic simple"> |
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| 108 | <li>Apple's <a class="reference external" href="Apple'sBonjourhttp://developer.apple.com/networking/bonjour/">Bonjour</a> <a class="footnote-reference" href="#id11" id="id12">[5]</a> for Mac OS X (included by default), Windows and POSIX systems</li> |
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| 109 | <li><a class="reference external" href="Avahihttp://www.avahi.org">Avahi</a> <a class="footnote-reference" href="#id8" id="id9">[4]</a> recommended for Linux and BSD clients and already available in many Linux and BSD distributions.</li> |
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| 110 | </ol> |
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| 111 | <p>Note that you can only run one zeroconf instance per host due to it |
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| 112 | binding to specific ports on your network interfaces, so it is <strong>not</strong> |
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| 113 | recommended to build the whole zeroconf daemon/server into your |
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| 114 | client. It is much better plug into a system wide service using the |
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| 115 | API's: it cuts down your code and allows other services e.g. http, ftp |
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| 116 | to advertise themselves using the same daemon.</p> |
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| 117 | </div> |
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| 118 | <div class="section" id="method"> |
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| 119 | <h1>Method</h1> |
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| 120 | <p>Each host will be required to publish (via zeroconf) the service type |
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| 121 | _bittorrent._tcp. with the instance name as the torrent peer-id (in |
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| 122 | hex).</p> |
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| 123 | <p><tt class="docutils literal"><span class="pre"><peer-id>._bittorrent._tcp.</span></tt></p> |
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| 124 | <p>Then clients need publish a subservice that is the torrent info hash (in hex). The result will be something in the form of:</p> |
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| 125 | <p><tt class="docutils literal"><span class="pre"><peer-id>._<info-hash>._sub._bittorrent._tcp.</span></tt> |
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| 126 | e.g. |
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| 127 | <tt class="docutils literal"><span class="pre">4d336d342d312d2d343834616435313564343437._32f17bbf96bdc77de85bb91ff8d56f124e817c0a._sub._bittorrent._tcp.</span></tt></p> |
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| 128 | <p>The above-mentioned zeroconf implementations provide good |
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| 129 | documentation for developers on how to do this. If the client uses the |
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| 130 | same peer-id for all torrents it has loaded, then for each additional |
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| 131 | torrent file, only the subservice needs to be added. If the client |
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| 132 | uses a different peer-id for each torrent then a |
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| 133 | _bittorrent._tcp. service will have to be added for each torrent file |
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| 134 | with the respective subservice. This is also true if each torrent uses |
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| 135 | a different port.</p> |
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| 136 | <p>In simple terms you can publish subtypes using the Apple Bonjour API |
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| 137 | by passing them as a comma separated list after the service type (you |
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| 138 | don't need to pass in the "_sub" label, since mDNSResponder will |
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| 139 | automatically add it for you).</p> |
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| 140 | <p><tt class="docutils literal"><span class="pre">"_bittorrent._tcp,_info-hash1,_info-hash2,_info-hash3"</span></tt></p> |
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| 141 | <p>For the Avahi C API use the function |
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| 142 | <tt class="docutils literal"><span class="pre">avahi_entry_group_add_service()</span></tt> to establish the parent |
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| 143 | _bittorrent._tcp service and |
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| 144 | <tt class="docutils literal"><span class="pre">avahi_entry_group_add_service_subtype()</span></tt> with |
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| 145 | <tt class="docutils literal"><span class="pre">_<info-hash>._sub._bittorrent._tcp.</span></tt> as the 'type' parameter to |
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| 146 | establish the subservices. For both functions the <peer-id> should be |
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| 147 | used for the 'name' parameter.</p> |
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| 148 | <p>Clients will need to browse for _<info-hash>._sub._bittorrent._tcp in |
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| 149 | order to discover peers participating in the same torrent. Once again |
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| 150 | good documentation is provided on how to browse for zeroconf services |
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| 151 | in the above implementations. The replies will be in the form of |
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| 152 | <peer-id>._bittorrent._tcp. Note: Some Macintosh official bittorrent |
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| 153 | clients have a zeroconf implementation built in that publishes its |
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| 154 | services in the form of:</p> |
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| 155 | <p><tt class="docutils literal"><span class="pre">_bittorrent-<info-hash>._tcp.</span></tt> |
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| 156 | i.e. |
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| 157 | <tt class="docutils literal"><span class="pre">_bittorrent-32f17bbf96bdc77de85bb91ff8d56f124e817c0a._tcp.</span></tt></p> |
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| 158 | <p>However this does not comply with <a class="reference external" href="http://www.faqs.org/rfcs/rfc2782.html">RFC 2782</a> as the service name needs |
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| 159 | to be 14 characters or less in addition to the fact that it is not a |
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| 160 | service type but in fact a service instance it is advertising. Clients |
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| 161 | may choose to also browse for these services for backwards |
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| 162 | compatibility purposes (minimal effect - only one client is known to |
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| 163 | do this) however they should not publish in this format.</p> |
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| 164 | </div> |
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| 165 | <div class="section" id="considerations"> |
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| 166 | <h1>Considerations</h1> |
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| 167 | <p>Clients should consider a couple of options when implementing the |
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| 168 | BitTorrent Zeroconf Peer Advertising and Discovery Extension |
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| 169 | specifically:</p> |
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| 170 | <ul class="simple"> |
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| 171 | <li>an option to not advertise torrents via zeroconf</li> |
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| 172 | <li>an option not to upload limit local-link peers (or possibly have a separate rule).</li> |
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| 173 | </ul> |
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| 174 | </div> |
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| 175 | <div class="section" id="thoughts"> |
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| 176 | <h1>Thoughts</h1> |
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| 177 | <ul class="simple"> |
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| 178 | <li>I suspect the published peer-id need not be the hexed string as I |
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| 179 | have it now. A simple unique string may be all that is required |
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| 180 | (i.e. a hostname or a human readable computer name) with any |
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| 181 | uniqueness conflicts handled by zeroconf automatically. We |
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| 182 | ultimately only need to know what is on offer (as denoted by the |
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| 183 | info-hash) and where to get it (the resolved IP address).</li> |
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| 184 | <li>The mainline client and others may like to examine |
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| 185 | <a class="reference external" href="pybonjourhttp://o2s.csail.mit.edu/o2s-wiki/pybonjour">pybonjour</a> <a class="footnote-reference" href="#id14" id="id15">[6]</a>. pybonjour provides a pure-Python interface to Apple |
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| 186 | <a class="reference external" href="Apple'sBonjourhttp://developer.apple.com/networking/bonjour/">Bonjour</a> <a class="footnote-reference" href="#id11" id="id13">[5]</a> and compatible DNS-SD libraries (such as <a class="reference external" href="Avahihttp://www.avahi.org">Avahi</a> <a class="footnote-reference" href="#id8" id="id10">[4]</a>).</li> |
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| 187 | <li>Newer zeroconf implementations such as Bonjour include support for |
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| 188 | wide area service discovery. (Avahi can browse but not publish these |
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| 189 | yet). This may be another consideration in support of this BEP.</li> |
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| 190 | <li>May make a nice companion to BEP 9.</li> |
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| 191 | </ul> |
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| 192 | </div> |
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| 193 | <div class="section" id="references"> |
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| 194 | <h1>References</h1> |
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| 195 | <table class="docutils footnote" frame="void" id="id1" rules="none"> |
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| 196 | <colgroup><col class="label" /><col /></colgroup> |
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| 197 | <tbody valign="top"> |
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| 198 | <tr><td class="label"><a class="fn-backref" href="#id2">[1]</a></td><td><a class="reference external" href="ZeroConfigurationNetworking(Zeroconf)http://www.zeroconf.org">ZeroConfigurationNetworking(Zeroconf)http://www.zeroconf.org</a></td></tr> |
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| 199 | </tbody> |
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| 200 | </table> |
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| 201 | <table class="docutils footnote" frame="void" id="id3" rules="none"> |
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| 202 | <colgroup><col class="label" /><col /></colgroup> |
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| 203 | <tbody valign="top"> |
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| 204 | <tr><td class="label"><a class="fn-backref" href="#id4">[2]</a></td><td><a class="reference external" href="MulticastDomainNameSystem(mDNS)http://www.multicastdns.org">MulticastDomainNameSystem(mDNS)http://www.multicastdns.org</a></td></tr> |
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| 205 | </tbody> |
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| 206 | </table> |
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| 207 | <table class="docutils footnote" frame="void" id="id5" rules="none"> |
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| 208 | <colgroup><col class="label" /><col /></colgroup> |
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| 209 | <tbody valign="top"> |
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| 210 | <tr><td class="label">[3]</td><td><em>(<a class="fn-backref" href="#id6">1</a>, <a class="fn-backref" href="#id7">2</a>)</em> <a class="reference external" href="DNSservice-discovery(DNS-SD)http://www.dns-sd.org">DNSservice-discovery(DNS-SD)http://www.dns-sd.org</a></td></tr> |
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| 211 | </tbody> |
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| 212 | </table> |
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| 213 | <table class="docutils footnote" frame="void" id="id8" rules="none"> |
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| 214 | <colgroup><col class="label" /><col /></colgroup> |
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| 215 | <tbody valign="top"> |
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| 216 | <tr><td class="label">[4]</td><td><em>(<a class="fn-backref" href="#id9">1</a>, <a class="fn-backref" href="#id10">2</a>)</em> <a class="reference external" href="Avahihttp://www.avahi.org">Avahihttp://www.avahi.org</a></td></tr> |
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| 217 | </tbody> |
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| 218 | </table> |
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| 219 | <table class="docutils footnote" frame="void" id="id11" rules="none"> |
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| 220 | <colgroup><col class="label" /><col /></colgroup> |
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| 221 | <tbody valign="top"> |
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| 222 | <tr><td class="label">[5]</td><td><em>(<a class="fn-backref" href="#id12">1</a>, <a class="fn-backref" href="#id13">2</a>)</em> <a class="reference external" href="Apple'sBonjourhttp://developer.apple.com/networking/bonjour/">Apple'sBonjourhttp://developer.apple.com/networking/bonjour/</a></td></tr> |
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| 223 | </tbody> |
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| 224 | </table> |
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| 225 | <table class="docutils footnote" frame="void" id="id14" rules="none"> |
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| 226 | <colgroup><col class="label" /><col /></colgroup> |
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| 227 | <tbody valign="top"> |
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| 228 | <tr><td class="label"><a class="fn-backref" href="#id15">[6]</a></td><td><a class="reference external" href="pybonjourhttp://o2s.csail.mit.edu/o2s-wiki/pybonjour">pybonjourhttp://o2s.csail.mit.edu/o2s-wiki/pybonjour</a></td></tr> |
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| 229 | </tbody> |
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| 230 | </table> |
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| 231 | </div> |
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| 232 | <div class="section" id="copyright"> |
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| 233 | <h1>Copyright</h1> |
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| 234 | <p>This document has been placed in the public domain.</p> |
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| 235 | <!-- Local Variables: |
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| 240 | coding: utf-8 |
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| 241 | End: --> |
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| 252 | </html> |
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