There are several criteria a good choking algorithm should meet. Network consisting entirely of themselves and in a network consisting It is very important that all new algorithms work well both in a The choking algorithm described below is the currently deployed one. Lets each peer use a tit-for-tat-ish algorithm to ensure that they get Very poorly when sending over many connections at once. Further on:Ĭhoking is done for several reasons. ![]() So, for you get data from a peer, the peer must be "interested" and you must be "not choked" - according to the protocol. When data is being transferred, downloaders should keep several piece requests queued up at once in order to get good TCP performance (this is called 'pipelining'.) On the other side, requests which can't be written out to the TCP buffer immediately should be queued up in memory rather than kept in an application-level network buffer, so they can all be thrown out when a choke happens. Implementing this properly is tricky, but makes it possible for downloaders to know which peers will start downloading immediately if unchoked.Ĭonnections start out choked and not interested. Interest state must be kept up to date at all times - whenever a downloader doesn't have something they currently would ask a peer for in unchoked, they must express lack of interest, despite being choked. The reasoning and common techniques behind choking are explained later in this document.ĭata transfer takes place whenever one side is interested and the other side is not choking. Choking is a notification that no data will be sent until unchoking happens. DHT itself depends on foreknowledge of a few well-known DHT "nodes" (unsure of the exact terminology) in order to "bootstrap" a peer who hasn't queried via DHT ever, or for a while.Ī client is free to make a connection with each peer it knows about, simultaneously, and most usually do - with the exception of considering any "connection limit" settings that the program supports.Ĭonnections contain two bits of state on either end: choked or not, and interested or not. (I believe you can specify multiple trackers in a protocol for redundancy.) With the introduction of DHT, a Bittorrent peer can use DHT to seek out other peers, in addition or instead of using a tracker. Initially, torrents could only depend on a central hub called the tracker - again, not to exchange parts of the file, but to discover who else is on the swarm. Bittorrent is not really completely "hubless" - not for the data transfer, but for peer discovery.
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