BitTorrent

BitTorrent offloads some of the file tracking work to a central server denoted as tracker.

Uses a principle called tit-for-tat.

• To receive files, you have to give them.

• Solves the problem of leaching.

Enables fast downloading for large files using minimum internet bandwidth.

.torrent: a pointer file that directs the computer to the file it wants to download.

Swarm: a group of computers simultaneously downloading or uploading the same file.

Tracker: server that manages the BitTorrent file transfer process.

BitTorrent client software communicates with a tracker to find other computers running BitTorrent that have the complete file (seeders), or that have a portion of the file (currently downloading the file).

The tracker identifies the swarm: this group of computers.

The tracker helps the client software to trade pieces of the file with other computers in the swarm.

The computer receives multiple pieces of the file simultaneously.

While running the BitTorrent software after the download is complete, others can receive the .torrent file from this computer.

• Ranked higher in the tit-for-tat system.

Trackers: keep track of the number of seeds/peers; responsible for helping downloaders find each other, using a simple protocol on top of HTTP.

Downloader sends status info to trackers, which reply with lists of contact information for peers which are downloading the same file.

Web servers do not have information about the content location.

• Only store metadata files describing the objects (length, name, etc.) and associate each of them with the URL of a tracker.

Network architecture: Hybrid unstructured.

Algorithm: Centralized Directory Model (CDM).

"trackerless" torrents through a system called the "distributed database”, through DHT (Distributed Hash Tables).