mirror of
https://github.com/renorris/openfsd
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49 lines
2.4 KiB
Markdown
49 lines
2.4 KiB
Markdown
# About
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The FSD protocol functions primarily as a message forwarder.
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Aside from a few direct client-server interactions, its main purpose is to relay messages between flight simulator clients via a centralized server.
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This architecture is not peer-to-peer; all communication is routed through the central server.
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FSD is a plaintext protocol that can be easily intercepted and analyzed with tools such as Wireshark.
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By default, it operates on TCP port 6809, and its functionality can be tested using [telnet](https://linux.die.net/man/1/telnet):
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```
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telnet <FSD server address> 6809
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```
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Various implementations of FSD exist, each with unique protocol nuances.
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This project specifically replicates VATSIM behavior, which differs from other networks such as [IVAO](https://www.ivao.aero/).
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- FSD messages consist of plaintext MS-DOS-style lines ending with CR/LF characters.
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- The protocol is strictly limited to the [ISO/IEC 8859-1](https://en.wikipedia.org/wiki/ISO/IEC_8859-1) aka. 'Latin alphabet no. 1' character set.
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- Each message, or 'line', begins with a 1- or 3-character packet identifier, followed by colon (`:`) delimited fields.
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- All numerical values are encoded as base-10 (or occasionally base-16) ASCII strings, with no raw binary data used.
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- Clients are identified by plaintext aviation callsigns (e.g., `N7938C`).
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- Most packets include "From" and "To" fields, which serve as source and recipient identifiers, respectively.
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- Depending on the packet type, the "To" field may specify a single recipient or a group of clients.
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#### Example [Server Identification](/packets/#server-identification-di) Packet
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```text
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$DISERVER:CLIENT:VATSIM FSD V3.43:d95f57db664f\r\n
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```
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##### Hexadecimal Representation
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```text
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00000000 24 44 49 53 45 52 56 45 52 3a 43 4c 49 45 4e 54 $DISERVE R:CLIENT
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00000010 3a 56 41 54 53 49 4d 20 46 53 44 20 56 33 2e 34 :VATSIM FSD V3.4
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00000020 33 3a 64 39 35 66 35 37 64 62 36 36 34 66 0d 0a 3:d95f57 db664f..
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```
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##### Explanation
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- Packet Type Identifier: `$DI`
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- Fields are delimited by colon (`:`) characters.
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- Sender: `SERVER` (reserved callsign for the server)<br>
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- Recipient: `CLIENT` (placeholder used for an unknown client)<br>
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- Server version identifier: `VATSIM FSD V3.43`<br>
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- Random data (see [documentation](/packets/#server-identification-di)): `d95f57db664f`
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- Packet is terminated with the delimiter sequence: `\r\n` (`0x0d0a`)
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For technical documentation on packet types, see [Protocol](/protocol/).
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