Posted On June 28, 2009 at 3:43 pm in BitTorrent, uTorrent information
BitTorrent (literally, pp. «Bitstream») – peer-to-peer (P2P) network protocol Cohen for the cooperative exchange of files over the Internet.
The files are transmitted in parts, each torrent-client, receiving (downloading) of these parts, at the same time preference (downloads) to other customers, which reduces the burden and dependence on the source of each client and provides data redundancy.
The first torrent-client «BitTorrent» Bram Cohen created the Python 4 April 2001, launching the first version was held on 2 July 2001.
There are many other programs customers to exchange files from BitTorrent.
The operating principle of the protocol
How it works BitTorrent: load on the distributor of the file is reduced due to the fact that customers are beginning to share data immediately, even if the file does not dokachan them to the end.
Before you start downloading the client connects to the tracker, he said his address and the hash sum of the requested file, which in response the customer receives the addresses of other clients to download or distributing the same file. The client periodically informs the tracker about the process and obtain an updated list of addresses.
Customers are connected with each other and exchange segments of files without the direct involvement of tracker, which is only regularly updates information on the contracts for the exchange of clients and other statistical information. An effective network BitTorrent necessary that as many customers have been able to accept incoming connections. Incorrect changes to the NAT or firewall can prevent this.
When connecting clients directly exchange information on their segments. Clients wishing to download segment, sends a request and if the second client is ready to give, receive the segment. The client then verifies the checksum for the segment and notifies all connected peers about having him in this segment.
Each client is able to temporarily block the return to another client (eng. choke). This is done to make better use of the channel output. In addition, if you choose – one to unlock preferred piram, which are transferred to this client a lot of segments. Thus, the feasts with good impact velocities encourage each other on the principle of «you – I, I – you».
Exchange of segments is on a «you – I, I – you» symmetrically in two directions and in random order. Clients periodically communicate with each other on their segments. Data transfer starts when both parties are interested in it, that is, each side has segments, which have no other. The number of transferred segments are calculated, and if one party discovers that sends on average more than taking it to block (engl. choke) returns. Thus, the protocol provided protection against licherov.
Upon receipt of the full file, the client goes into a special mode of operation, in which he pays only the data (becomes Sid).
Clients periodically inform the tracker on the changes in the status of the download and update the lists of IP-addresses.
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Posted On June 27, 2009 at 3:47 pm in BitTorrent, bitTorrent tracker, uTorrent description, uTorrent information
BitTorrent-Tracker – a web server, which coordinates BitTorrent-Client.
Coordination of client
The main function of BitTorrent-tracker – handling customer queries.
Each time a client calls with a request to the tracker, which indicated:
* Unique hash sum torrent file;
* TCP-port, where the client is waiting for connections from other clients;
* The amount of data that the client had time to share with other clients;
* And some other information.
This treatment is a normal HTTP-request, which information is encrypted using a special protocol Bencode (en: Bencode).
If the BitTorrent-client open more than one active torrent file, then each use a separate request, in no way connected with others. The intervals between requests for each individual torrent settings depend on the client, and usually range from 30 to 60 minutes.
BitTorrent-tracker, using the hash value as a unique identifier file that lists of IP-addresses and ports involved in the distribution of each individual customer. Every client in response to another request tracker returns a list, and the client uses it to establish connections with other clients.
Role tracker
Thus, the tracker «associates» clients with each other, but is not directly involved in the exchange of distributed data files. Moreover, in principle tracker can work without having any information about these files, as customers have reported to him just the hash sum file.
Tracker regarded as «weak» place of BitTorrent, because when the device is disconnected, new customers just can not mutually «find». This has already been involved in the distribution of customers may continue to file for some time, gradually losing those who are disabled or who has changed the dynamic IP-address.
To resolve this problem, can be used stand-trackers or special protocol such as DHT.
Additional features
Most implementations trackers, except for the coordination of clients also have additional features available to users with browsers through a regular Web server, often with a different address or port than the interface for the client.
Thus, virtually all trackers statistics show the distribution, ie the number of sidov and peers in each hand, the overall volume of data transferred between clients and other information available to them.
Most trackers are used to store the torrent files, and their descriptions.
Private (private) trackers
Private (English private) tracker – this tracker, limiting access to users, usually requiring the registration of the account and demand the maintenance of «ranking», at a certain level.
One of the reasons for the emergence of private trackers is the asymmetry of user access channels to the Internet. Average user during download torrent manages to give other users a small amount of data, many users after receiving a file is closed immediately torrent client. As a result of reduced availability of torrent, and the original distributors of the file falls unduly heavy workload.
As a rule, private trackers record statistics (top) of each user by the number of «downloaded» and «given» to other users, and require the maintenance of a minimum ratio of these two variables. As a result, the availability and speed of downloading torrent on a private tracker is usually higher than in the open.
To identify a specific client tracker uses an IP-address of the user, or a unique key for each user (called user key and pass key), add trackers in the torrent file when downloading it yourself.
A rating system is, and the negative side: discrimination of users with a narrow channel of impact. Most of the impact that user does not, the reason for that – other people who have more upload-channel, and give much more and faster. This user is very difficult to restore your rating, especially if it deals with malovostrebovannymi files. In the end, stay at a private tracker turns out for him a constant headache on how to maintain the rating.
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