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. A peer cannot have more than one connection per other peer. A peer which a download is active is set 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 :

      If there is already a peer asking for hashes :

         - Take the next file in F -> f.

         - continue

      Else

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

   For each chunk not downloaded and 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.

<pre>

F : the list of all unfinished download

C : list of latest chunk hashes sent

Loop :

   Time.now -> t

   Empty C

   n : number of chunk = 0

   While take the next file in F -> f

      If C.count >= 'NumberOfChunkToUpdate' :

         - Break

      If we know the hashes for f :

         For all chunks of f -> c :

            - Add c to C

      Else :

         - Break

   - Copy C to C_latest

   - Send the list of the chunk to everyone. (The received responses will be compared against C)

   - Wait 'TimeBetweenChunksUpdate' - (Time.now - t)

</pre>

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