You are reading:
Under the Surface of Azeroth:
A Network Baseline and Security Analysis
of Blizzard's World of Warcraft
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If there are problems with the BitTorrent-based file transfer process, the patch download is a very straightforward transfer using HTTP over the default TCP port 80. If the BitTorrent protocol can operate properly, the download process is much more interesting, and usually much more efficient.
BitTorrent protocol problems can occur when the Blizzard Downloader is behind a firewall or router. Blizzard has created a technical support document that addresses many of the most common (and some not so common) problems:
http://www.blizzard.com/support/wow/?id=aww01154p
Now that the Blizzard Downloader has obtained a list of swarm participants from the tracker, TCP connections can be created to the other IP addresses in the swarm. The Blizzard Downloader methodically builds sessions to other peers and transfers small sections of the patch between hosts. If a remote swarm member has part of the patch that we need, the Blizzard Downloader sends a request for that small segment to a remote host. If we have downloaded a portion of the patch, we may receive requests to upload a section of the patch to another eager swarm participant. Because the Blizzard Downloader is downloading information while also providing information for others, the Downloader is acting as both a client and a server.
The Blizzard Downloader includes a monitor that provides extensive connection information, regardless of the download method employed. To get the comprehensive details, select the "View" pull-down menu in the Blizzard Downloader and choose "Connection Info."
The connection information shows the file transfer summary information across the top, including the Peer ID, Download Hash and a graphical representation of exactly which pieces of the file have been downloaded. The lower section of the screen is a summary of the open connections to other systems listed by IP address, port number, the time connected, and upload and download metrics.
Notice that the Blizzard Downloader is constantly uploading and downloading portions of the file to other World of Warcraft players around the Internet. Doesn't it make you feel good to share with your fellow gamers?
