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Multiplayer protocol - wiki.flightgear.org

Multiplayer protocol

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The messages

All messages are composed of XDR encoded data. (see RFC 1832 for a complete description of XDR). XDR basically means: All data is in network byte order and aligned to the nearest multiple of 4 bytes. Strings are encoded as a zero-terminated array of characters,aligned to the nearest multiple of 4 bytes. Floating point numbers (32 or 64 bit) must be encode in the IEEE standard.

The header

The header is always 32 bytes long and contains the following fields in exactly that order:

|Magic|Version|MsgId|MsgLen|ReplyAddress|ReplyPort|Callsign|Data|
Magic: 4 bytes, always 0x46474653 ("FGFS")
Version: 4 bytes, protocol version, currently 0x00010001 (1.1)
MsgId: 4 bytes, defines what data is appended to the header. Can be 0x00000001 for chat messages (deprecated) or

0x00000007 for position data
all other values are outdated and ignored

MsgLen: 4 bytes, the lenght of the data in bytes
ReplyAddress: 4 bytes, deprecated and ignored
ReplyPort: 4 bytes, deprecated and ignored
Callsign: 8 bytes, zero terminated array of characters representing

the user callsign

Data of chat messages

The data for chat messages is a zero terminated array of characters. The MsgLen field in the header represents its length. The maximum length is defined to be 256 bytes.

Data of position messages

The data of position data is more complicated and looks like this:

ModelName 96 bytes, zero terminated array of characters representing the aircraft model used by the user
time 8 bytes, representing the time when this message was generated
lag 8 bytes, time offset for network lag
PosX 8 bytes, XDR encoded double value, X-ccordinate of users

position wrt the earth centered frame

PosY 8 bytes, XDR encoded double value, Y-ccordinate of users

position wrt the earth centered frame

PosZ 8 bytes, XDR encoded double value, z-ccordinate of users

position wrt the earth centered frame

OriX 4 bytes, XDR encoded float value, X-orientation of the user wrt the earth centered frame, stored in the angle axis representation where the angle is coded into the axis length
OriY 4 bytes, XDR encoded float value, Y-orientation of the user wrt the earth centered frame, stored in the angle axis representation where the angle is coded into the axis length
OriZ 4 bytes, XDR encoded float value, Z-orientation of the user wrt the earth centered frame, stored in the angle axis representation where the angle is coded into the axis length
VelX 4 bytes, XDR encoded float value, velocity of the user in X direction wrt the earth centered frame measured in the earth centered frame
VelY 4 bytes, XDR encoded float value, velocity of the user in Y direction wrt the earth centered frame measured in the earth centered frame
VelZ 4 bytes, XDR encoded float value, velocity of the user in Z direction wrt the earth centered frame measured in the earth centered frame
AV1 4 bytes, XDR encoded float value, 1. part of the three dimensional angular velocity vector

wrt the earth centered frame measured in the earth centered frame

AV2 4 bytes, XDR encoded float value, 2. part of the three dimensional angular velocity vector

wrt the earth centered frame measured in the earth centered frame

AV3 4 bytes, XDR encoded float value, 3. part of the three dimensional angular velocity vector

wrt the earth centered frame measured in the earth centered frame

LA1 4 bytes, XDR encoded float value, 1. part of the three dimensional linear accelaration vector

wrt the earth centered frame measured in the earth centered frame

LA2 4 bytes, XDR encoded float value, 2. part of the three dimensional linear accelaration vector

wrt the earth centered frame measured in the earth centered frame

LA3 4 bytes, XDR encoded float value, 3. part of the three dimensional linear accelaration vector

wrt the earth centered frame measured in the earth centered frame

AA1 4 bytes, XDR encoded float value, 1. part of the three dimensional angular accelaration vector

wrt the earth centered frame measured in the earth centered frame

AA2 4 bytes, XDR encoded float value, 2. part of the three dimensional angular accelaration vector

wrt the earth centered frame measured in the earth centered frame

AA3 4 bytes, XDR encoded float value, 3. part of the three dimensional angular accelaration vector

wrt the earth centered frame measured in the earth centered frame

pad up to 8 bytes for padding the data to a multiple of 8 bytes

This data is followed by property-values, which are encoded in the form ID|Value

The following properties are transmitted, but not necessarily all present and not in this order:

ID Property Type(*)
100 "surface-positions/left-aileron-pos-norm" FLOAT
101 "surface-positions/right-aileron-pos-norm" FLOAT
102 "surface-positions/elevator-pos-norm" FLOAT
103 "surface-positions/rudder-pos-norm" FLOAT
104 "surface-positions/flap-pos-norm" FLOAT
105 "surface-positions/speedbrake-pos-norm" FLOAT
106 "gear/tailhook/position-norm" FLOAT
107 "gear/launchbar/position-norm" FLOAT
108 "gear/launchbar/state" STRING
109 "gear/launchbar/holdback-position-norm" FLOAT
110 "canopy/position-norm" FLOAT
111 "surface-positions/wing-pos-norm" FLOAT
112 "surface-positions/wing-fold-pos-norm" FLOAT
200 "gear/gear[0]/compression-norm" FLOAT
201 "gear/gear[0]/position-norm" FLOAT
210 "gear/gear[1]/compression-norm" FLOAT
211 "gear/gear[1]/position-norm" FLOAT
220 "gear/gear[2]/compression-norm" FLOAT
221 "gear/gear[2]/position-norm" FLOAT
230 "gear/gear[3]/compression-norm" FLOAT
231 "gear/gear[3]/position-norm" FLOAT
240 "gear/gear[4]/compression-norm" FLOAT
241 "gear/gear[4]/position-norm" FLOAT
300 "engines/engine[0]/n1" FLOAT
301 "engines/engine[0]/n2" FLOAT
302 "engines/engine[0]/rpm" FLOAT
310 "engines/engine[1]/n1" FLOAT
311 "engines/engine[1]/n2" FLOAT
312 "engines/engine[1]/rpm" FLOAT
320 "engines/engine[2]/n1" FLOAT
321 "engines/engine[2]/n2" FLOAT
322 "engines/engine[2]/rpm" FLOAT
330 "engines/engine[3]/n1" FLOAT
331 "engines/engine[3]/n2" FLOAT
332 "engines/engine[3]/rpm" FLOAT
340 "engines/engine[4]/n1" FLOAT
341 "engines/engine[4]/n2" FLOAT
342 "engines/engine[4]/rpm" FLOAT
350 "engines/engine[5]/n1" FLOAT
351 "engines/engine[5]/n2" FLOAT
352 "engines/engine[5]/rpm" FLOAT
360 "engines/engine[6]/n1" FLOAT
361 "engines/engine[6]/n2" FLOAT
362 "engines/engine[6]/rpm" FLOAT
370 "engines/engine[7]/n1" FLOAT
371 "engines/engine[7]/n2" FLOAT
372 "engines/engine[7]/rpm" FLOAT
380 "engines/engine[8]/n1" FLOAT
381 "engines/engine[8]/n2" FLOAT
382 "engines/engine[8]/rpm" FLOAT
390 "engines/engine[9]/n1" FLOAT
391 "engines/engine[9]/n2" FLOAT
392 "engines/engine[9]/rpm" FLOAT
800 "rotors/main/rpm" FLOAT
801 "rotors/tail/rpm" FLOAT
810 "rotors/main/blade[0]/position-deg" FLOAT
811 "rotors/main/blade[1]/position-deg" FLOAT
812 "rotors/main/blade[2]/position-deg" FLOAT
813 "rotors/main/blade[3]/position-deg" FLOAT
820 "rotors/main/blade[0]/flap-deg" FLOAT
821 "rotors/main/blade[1]/flap-deg" FLOAT
822 "rotors/main/blade[2]/flap-deg" FLOAT
823 "rotors/main/blade[3]/flap-deg" FLOAT
830 "rotors/tail/blade[0]/position-deg" FLOAT
831 "rotors/tail/blade[1]/position-deg" FLOAT
900 "sim/hitches/aerotow/tow/length" FLOAT
901 "sim/hitches/aerotow/tow/elastic-constant" FLOAT
902 "sim/hitches/aerotow/tow/weight-per-m-kg-m" FLOAT
903 "sim/hitches/aerotow/tow/dist" FLOAT
904 "sim/hitches/aerotow/tow/connected-to-property-node" BOOL
905 "sim/hitches/aerotow/tow/connected-to-ai-or-mp-callsign" STRING
906 "sim/hitches/aerotow/tow/brake-force" FLOAT
907 "sim/hitches/aerotow/tow/end-force-x" FLOAT
908 "sim/hitches/aerotow/tow/end-force-y" FLOAT
909 "sim/hitches/aerotow/tow/end-force-z" FLOAT
930 "sim/hitches/aerotow/is-slave" BOOL
931 "sim/hitches/aerotow/speed-in-tow-direction" FLOAT
932 "sim/hitches/aerotow/open" BOOL
933 "sim/hitches/aerotow/local-pos-x" FLOAT
934 "sim/hitches/aerotow/local-pos-y" FLOAT
935 "sim/hitches/aerotow/local-pos-z" FLOAT
1001 "controls/flight/slats" FLOAT
1002 "controls/flight/speedbrake" FLOAT
1003 "controls/flight/spoilers" FLOAT
1004 "controls/gear/gear-down" FLOAT
1005 "controls/lighting/nav-lights" FLOAT
1006 "controls/armament/station[0]/jettison-all" BOOL
1100 "sim/model/variant" INT
1101 "sim/model/livery/file" STRING
1200 "environment/wildfire/data" STRING
10001 "sim/multiplay/transmission-freq-hz" STRING
10002 "sim/multiplay/chat" STRING
10100 "sim/multiplay/generic/string[0]" STRING
10101 "sim/multiplay/generic/string[1]" STRING
10102 "sim/multiplay/generic/string[2]" STRING
10103 "sim/multiplay/generic/string[3]" STRING
10104 "sim/multiplay/generic/string[4]" STRING
10105 "sim/multiplay/generic/string[5]" STRING
10106 "sim/multiplay/generic/string[6]" STRING
10107 "sim/multiplay/generic/string[7]" STRING
10108 "sim/multiplay/generic/string[8]" STRING
10109 "sim/multiplay/generic/string[9]" STRING
10110 "sim/multiplay/generic/string[10]" STRING
10111 "sim/multiplay/generic/string[11]" STRING
10112 "sim/multiplay/generic/string[12]" STRING
10113 "sim/multiplay/generic/string[13]" STRING
10114 "sim/multiplay/generic/string[14]" STRING
10115 "sim/multiplay/generic/string[15]" STRING
10116 "sim/multiplay/generic/string[16]" STRING
10117 "sim/multiplay/generic/string[17]" STRING
10118 "sim/multiplay/generic/string[18]" STRING
10119 "sim/multiplay/generic/string[19]" STRING
10200 "sim/multiplay/generic/float[0]" FLOAT
10201 "sim/multiplay/generic/float[1]" FLOAT
10202 "sim/multiplay/generic/float[2]" FLOAT
10203 "sim/multiplay/generic/float[3]" FLOAT
10204 "sim/multiplay/generic/float[4]" FLOAT
10205 "sim/multiplay/generic/float[5]" FLOAT
10206 "sim/multiplay/generic/float[6]" FLOAT
10207 "sim/multiplay/generic/float[7]" FLOAT
10208 "sim/multiplay/generic/float[8]" FLOAT
10209 "sim/multiplay/generic/float[9]" FLOAT
10210 "sim/multiplay/generic/float[10]" FLOAT
10211 "sim/multiplay/generic/float[11]" FLOAT
10212 "sim/multiplay/generic/float[12]" FLOAT
10213 "sim/multiplay/generic/float[13]" FLOAT
10214 "sim/multiplay/generic/float[14]" FLOAT
10215 "sim/multiplay/generic/float[15]" FLOAT
10216 "sim/multiplay/generic/float[16]" FLOAT
10217 "sim/multiplay/generic/float[17]" FLOAT
10218 "sim/multiplay/generic/float[18]" FLOAT
10219 "sim/multiplay/generic/float[19]" FLOAT
10300 "sim/multiplay/generic/int[0]" INT
10301 "sim/multiplay/generic/int[1]" INT
10302 "sim/multiplay/generic/int[2]" INT
10303 "sim/multiplay/generic/int[3]" INT
10304 "sim/multiplay/generic/int[4]" INT
10305 "sim/multiplay/generic/int[5]" INT
10306 "sim/multiplay/generic/int[6]" INT
10307 "sim/multiplay/generic/int[7]" INT
10308 "sim/multiplay/generic/int[8]" INT
10309 "sim/multiplay/generic/int[9]" INT
10310 "sim/multiplay/generic/int[10]" INT
10311 "sim/multiplay/generic/int[11]" INT
10312 "sim/multiplay/generic/int[12]" INT
10313 "sim/multiplay/generic/int[13]" INT
10314 "sim/multiplay/generic/int[14]" INT
10315 "sim/multiplay/generic/int[15]" INT
10316 "sim/multiplay/generic/int[16]" INT
10317 "sim/multiplay/generic/int[17]" INT
10318 "sim/multiplay/generic/int[18]" INT
10319 "sim/multiplay/generic/int[19]" INT


(*) The types are XDR encoded as follows:

INT    4 bytes, send unconditionally
FLOAT: 4 bytes, send unconditionally
BOOL:  4 bytes, send unconditionally
STRING [LEN|STR|PAD]: send only when length > 0
LEN:    4 bytes, length of the string
STR:    n bytes, string string itself
PAD:    n bytes, padding so the overall length is a multiple of 4