LFS-Ayats

Packet Reference

Quick reference guide for InSim packets in LFS.

Full specification: https://en.lfsmanual.net/wiki/InSim.txt

Packet Structure

All InSim packets follow this basic structure:

struct PacketHeader {
    byte Size;      // Packet size in multiples of 4
    byte Type;      // Packet type (ISP_*)
    byte ReqI;      // Request ID (usually 0)
    byte SubT;      // Sub-type (depends on packet)
};

Quick Reference Table

Code	Name	Description	Direction	Priority
1	IS_ISI	InSim Init	→ LFS	Critical
2	IS_VER	Version	← LFS	High
3	IS_TINY	Tiny packet	↔ Both	Medium
5	IS_STA	State	← LFS	High
11	IS_MSO	Message Out	← LFS	Low
17	IS_RST	Race Start	← LFS	High
18	IS_NCN	New Connection	← LFS	Medium
19	IS_CNL	Connection Leave	← LFS	Medium
21	IS_NPL	New Player	← LFS	High
22	IS_PLP	Player Leave Pits	← LFS	Medium
24	IS_LAP	Lap Time	← LFS	High
25	IS_SPX	Split Time	← LFS	High
26	IS_PIT	Pit Stop	← LFS	Medium
27	IS_PSF	Pit Stop Finish	← LFS	Medium
30	IS_PEN	Penalty	← LFS	Medium
34	IS_FIN	Finished Race	← LFS	High
35	IS_RES	Result	← LFS	High
37	IS_NLP	Node and Lap	← LFS	High
38	IS_MCI	Multi Car Info	← LFS	Critical

Telemetry Packets

IS_MCI (Multi Car Info)

Most important for real-time telemetry.

Frequency: Configurable via Interval parameter (centèssimes de segon)

Contains:

Position (X, Y, Z)
Speed
Direction
Heading
Angular velocity
Node
Lap

Data conversions:

# Position in meters
x_meters = x / 65536.0
y_meters = y / 65536.0
z_meters = z / 65536.0

# Speed in m/s
speed_ms = speed / 32768.0

# Speed in km/h
speed_kmh = (speed / 32768.0) * 3.6

IS_NLP (Node and Lap)

Alternative to IS_MCI with node-based positioning.

Frequency: Configurable via Interval parameter

Contains:

Node position
Lap number
Player ID
Position in race

Lap Information Packets

IS_LAP (Lap Time)

Complete lap information.

Contains:

Lap time (ms)
Total elapsed time (ms)
Laps done
Penalty time
Number of pit stops

IS_SPX (Split Time)

Sector timing information.

Contains:

Split time (ms)
Total elapsed time (ms)
Split number (1, 2, 3)
Penalty accumulation
Number of pit stops

Race Control Packets

IS_RST (Race Start)

Race configuration and start.

Contains:

Race laps / qualifying minutes
Track name
Weather
Wind
Flags
Number of players

IS_FIN (Finished)

Player finished race.

Contains:

Player ID
Total time
Number of stops
Confirmation flags

IS_RES (Result)

Race result for a player.

Contains:

Player name
Username
Final position
Result time
Laps completed

Player Management Packets

IS_NCN (New Connection)

New player connection.

Contains:

Username
Player name
Admin status
Total connections

IS_NPL (New Player)

Player joins track.

Contains:

Player name
Plate
Car name
Skin name
Tyres
Handicaps

Control Packets

IS_TINY (Tiny)

Small control packets.

Sub-types:

TINY_VER (1): Request version
TINY_CLOSE (2): Close InSim
TINY_PING (3): Ping
TINY_REPLY (4): Ping reply
TINY_SST (7): Request state
TINY_GTH (8): Get time

IS_SMALL (Small)

Small data packets.

Usage: Various small data requests/responses

Implementation Examples

Requesting Server State

# Send TINY_SST to request IS_STA
tiny_packet = struct.pack("=4B", 1, 3, 0, 7)  # TINY_SST
client.send_packet(tiny_packet)

Enabling Telemetry

# Initialize with MCI and NLP packets
flags = 0x30  # ISF_MCI | ISF_NLP
interval = 100  # 1 second (100 centiseconds)

isi_packet = struct.pack(
    "=4BH2BH16s16s",
    44, 1, 0, 0,
    0, flags, 9, ord('!'), interval,
    b'', b'MyApp'.ljust(16, b'\x00')
)
client.send_packet(isi_packet)

Packet Priorities

Critical (Must Handle)

IS_ISI: Connection initialization
IS_MCI: Telemetry data
IS_VER: Version confirmation

High (Should Handle)

IS_STA: Server state
IS_LAP: Lap times
IS_SPX: Split times
IS_NPL: Player tracking
IS_RST: Race start
IS_FIN: Race finish
IS_RES: Results

Medium (Nice to Have)

IS_NCN: Connection tracking
IS_PLP: Pit tracking
IS_PIT: Pit stops
IS_PEN: Penalties

Low (Optional)

IS_MSO: Chat messages
Other informational packets

Error Handling

Always handle these scenarios:

Packet size mismatch: Validate size field
Unknown packet types: Log and skip
Incomplete packets: Buffer and wait
Connection loss: Reconnect logic
Invalid data: Validate ranges

Performance Considerations

High Frequency (10+ Hz)

IS_MCI: Can generate lots of data
Buffer appropriately
Consider async processing

Medium Frequency (1-5 Hz)

IS_NLP: Regular updates
Batch processing possible

Low Frequency (Event-based)

IS_LAP, IS_SPX: Per lap/split
Process immediately

References

InSim.txt: https://en.lfsmanual.net/wiki/InSim.txt
LFS Forum: https://www.lfs.net/forum
Code examples: See examples/ directory

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