D-LAN

h1. Protocols

This page describes the protocols used by Aybabtu for network communication between cores and between core and GUI.

h2. Core <-> Core

See source:protos/network_protocol.proto for message details.

h3. Downloading threads

There is _NbDownloadThread_ threads. Each thread will choose a free chunk and download it.

There is no more than one downloading from B to A. A peer which a download is active is setted as not free.

<pre>

F : the list of all unfinished download

C : A list of chunk candidates (empty at start)

- Take the first file in F -> f.

Loop :

   If the hash chunks of f are unknown :

      - Ask the hashes to the source (see the message 'GetHashes').

   For each chunk not downloaded or not being downloaded -> c :

      If c has a free peer :

         - add c to C

   If C isn't empty :

      - Take the best chunk in C based on peer.downloadRate.

        If there is more than one best chunk then choose one randomly.

      - Grab the lock for the peer

      - Request the download   

      - Take the first file in F -> f.

   Else :

      - Take the next file in F -> f.

</pre>

h3. Updating peer to hash association thread

This thread will periodically grab the _NumberOfChunkToUpdate_ first chunks and request to all other peers what chunk they have.

If there is no chunk available the message will be send without hashes.

h3. Parameters

Most parameters will be stored as constants in their component.

|_.Name|_.Value |_.Unit|_.Explanation/Comments|

| _IMAliveFrequency_ | 0.1 | [Hz] | The message _IMAlive_ is sent each 10s. |

| _ChunkSize_ | 33554432 | [Byte] | (32 MB) |

| _LanSpeed_ | 52428800 | [Byte/s] | (50 MB/s) |

| _TimeRecheckChunkFactor_ | 4 | - | If the time to download a chunk exceeds _TimeRecheckChunkFactor_ * _ChunkSize_ / _LanSpeed_ the peers are rescanned to choose a better one (better download rate). For example : 4 * 32 / 50 = 2.6 second |

| _SwitchToAnotherPeerFactor_ | 1.5 | - | During the recheck of the peers to choose a better one the other download rate must be above the current * 1.5. |

| _DownloadRateValidTime_ | 1500 / _LanSpeed_ = 300 s | [s] | (5 min). The download rate of a peer is only valid during this time after its last update. After that its rate is set to the maximum. | 

| _TimeBetweenChunksUpdate_ | 500 / _LanSpeed_ = 10 s | [s] | Each 10 s a daemon will scan the _NumberOfChunkToUpdate_ first chunks from the first queued downloads to know which peer has which chunk. |

| _NumberOfChunkToUpdate_ | 100 * _LanSpeed_ / _ChunkSize_ = 156 | - | The first 156 hash chunks (3 kB) will by send periodically to each peer. See message _HaveChunks_ in the proto file. |

| _FindTimeout_ | 15 | [s] | A search request is abandoned after 15 seconds from the start of the request. See message _Find_. |

| _GetHashesTimeout_ | 200 | [s] | Timeout for the message _GetHashes_. |

| _GetChunkTimeout_ | 10 | [s] | Timeout for the message _GetChunk_. |

| _HaveChunksTimeout_ | _TimeBetweenChunksUpdate_ = 10 | [s] | Timeout for the message _HaveChunks_. |

| _GetEntriesTimeout_ | 10 | [s] | Timeout for the message _GetEntries_. |

| _NbDownloadThread_ | 3 | - | Number of concurrent downloading thread. |

| _BufferSize_ | 1048576 | [Byte] | (1MB). This buffer is used when reading or writing a file. |

| _TCPSocketBufferSize_ | 33554432 | [Byte] | (32Mo). Used when data are received. See _QAbstractSocket::setReadBufferSize_. |

h2. Core <-> GUI