Changeset 11110

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Timestamp:
06/16/2008 05:34:48 PM (2 months ago)
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dave
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regenerated html.

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  • dotorg/trunk/html/beps/bep_0022.html

    r11107 r11110  
    3737<tr class="field"><th class="field-name">BEP:</th><td class="field-body">22</td> 
    3838</tr> 
    39 <tr class="field"><th class="field-name">Title:</th><td class="field-body">BitTorrent Cache Discovery Protocol</td> 
    40 </tr> 
    41 <tr class="field"><th class="field-name">Version:</th><td class="field-body">11101</td> 
    42 </tr> 
    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_0022.rst">2008-05-27 19:02:55 -0700 (Tue, 27 May 2008)</a></td> 
     39<tr class="field"><th class="field-name">Title:</th><td class="field-body">BitTorrent Tracker Discovery Protocol</td> 
     40</tr> 
     41<tr class="field"><th class="field-name">Version:</th><td class="field-body">11109</td> 
     42</tr> 
     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_0022.rst">2008-06-16 17:33:22 -0700 (Mon, 16 Jun 2008)</a></td> 
    4444</tr> 
    4545<tr class="field"><th class="field-name">Author:</th><td class="field-body">David Harrison &lt;dave&#32;&#97;t&#32;bittorrent.com&gt;, Stanislav Shalunov &lt;shalunov&#32;&#97;t&#32;bittorrent.com&gt;, Greg Hazel &lt;greg&#32;&#97;t&#32;bittorrent.com&gt;</td> 
    … …  
    7272<div class="section" id="motivation"> 
    7373<h1>Motivation</h1> 
    74 <p>Some Internet Service Providers (ISPs) may be interested in deploying 
    75 BitTorrent caches to lower transit costs, reduce internal traffic, and 
    76 improve user experience by speeding up downloads.</p> 
    77 <p>A cache is simply a fast peer in the middle of the network. It might 
    78 also have substantial disk space. The client communicates with a cache 
    79 using the normal BitTorrent protocol.</p> 
    80 <p>With this extension, BitTorrent clients are able to discover caches 
    81 nearby on the network.  When a cache is present, the user benefits 
    82 from having a high capacity peer from which the user's client 
    83 downloads and to which it can delegate seeding.  When a cache inside 
    84 the user's ISP network seeds on behalf of the client, it frees 
    85 upstream capacity in the user's access network benefiting the user and 
    86 those that share the access network.  When subsequent peers transfer 
    87 from their ISP's cache, the ISP experiences less transit traffic.</p> 
     74<p>Some Internet Service Providers (ISPs) may wish to localize traffic 
     75to reduce transit costs, reduce internal traffic, and improve user 
     76experience by speeding up downloads.</p> 
     77<p>With this extension, BitTorrent clients are able to discover a tracker 
     78nearby on the network, and via this tracker discover nearby caches or 
     79peers.  A cache is simply a fast peer in the middle of the network. It 
     80might also have substantial disk space. The client communicates with a 
     81cache using the normal BitTorrent protocol.</p> 
     82<p>When a cache is present, the user benefits from having a high capacity 
     83peer from which the user's client downloads and to which it can 
     84delegate seeding.  When a cache inside the user's ISP network seeds on 
     85behalf of the client, it frees upstream capacity in the user's access 
     86network benefiting the user and those that share the access network. 
     87When subsequent peers transfer from their ISP's cache, the ISP 
     88experiences less transit traffic.</p> 
    8889<p>The key words &quot;MUST&quot;, &quot;MUST NOT&quot;, &quot;REQUIRED&quot;, &quot;SHALL&quot;, &quot;SHALL 
    8990NOT&quot;, &quot;SHOULD&quot;, &quot;SHOULD NOT&quot;, &quot;RECOMMENDED&quot;,  &quot;MAY&quot;, and 
    … …  
    9394<div class="section" id="the-discovery-mechanism"> 
    9495<h1>The Discovery Mechanism</h1> 
    95 <p>To find the caches for its ISP, a BitTorrent client performs a reverse 
     96<p>To find the tracker for its ISP, a BitTorrent client performs a reverse 
    9697DNS lookup on its external IP address and then obtains the BitTorrent 
    9798SRV resource record associated with the host's domain name.  For 
    … …  
    115116<p>The target field in each returned SRV resource record contains the 
    116117domain name of a tracker and the port on which the tracker runs.  This 
    117 tracker is called a <em>cache tracker</em>, but the protocol to talk to this 
     118tracker is called a <em>local tracker</em>, but the protocol to talk to this 
    118119tracker is no different from the standard BitTorrent tracker protocol 
    119120described in <a class="footnote-reference" href="#bep-3" id="id2">[1]</a>.</p> 
    120121<p>When the BitTorrent client joins a swarm it announces to one or more 
    121122of the trackers referenced in the .torrent file and announces to the 
    122 cache tracker.  The cache tracker returns peers which may be caches or 
    123 other peers that announced the same file to the cache tracker.</p> 
    124 <p>A cache is a BitTorrent peer.  A client MAY treat it preferentially.</p> 
     123local tracker.  The local tracker returns peers which may be caches or 
     124other peers that announced the same file to the local tracker.</p> 
     125<p>A client MAY treat nearby peers or caches preferentially.</p> 
    125126<p>Reverse DNS lookups are described in <a class="reference external" href="http://www.faqs.org/rfcs/rfc1034.html">RFC 1034</a> <a class="footnote-reference" href="#rfc-1034" id="id3">[4]</a>. 
    126127The SRV resource record type is described in <a class="reference external" href="http://www.faqs.org/rfcs/rfc2782.html">RFC 2782</a> <a class="footnote-reference" href="#rfc-2782" id="id4">[6]</a>.</p> 
    … …  
    210211<h1>Example</h1> 
    211212<p>In our example, we use AT&amp;T's PacBell network.  AT&amp;T could implement 
    212 cache discovery by adding the following lines to the zone file for 
     213tracker discovery by adding the following lines to the zone file for 
    213214pacbell.net,</p> 
    214215<pre class="literal-block"> 
    … …  
    216217_bittorrent-tracker._tcp.pacbell.net. 600  IN  SRV 5   0      6969 tracker 
    217218</pre> 
    218 <p>Now when a client performs cache discovery, it performs three DNS 
     219<p>Now when a client performs tracker discovery, it performs three DNS 
    219220queries removing labels before reaching the domain name pacbell.net, 
    220221at which point the SRV record is returned and the client queries 
    221222tracker.pacbell.net to obtain the domain names of caches.</p> 
    222 <p>In Python, the cache tracker's port and domain can be obtained using 
     223<p>In Python, the local tracker's port and domain can be obtained using 
    223224PyDNS using the following code:</p> 
    224225<pre class="literal-block">