Network Protocol

The protocol is based on UDP datagrams and provides means of reliable and non-reliable binary data delivery.

There are two types of datagrams:

  • package – a datagram with a header and user data payload,
  • protocol control – a datagram with a header and system data.

All integers are big-endian encoded.

The structure of each datagram is this:

  1. flags – 1 byte
  2. ID – 3 bytes
  3. payload – 504 bytes or less

Protocol control is signaled by the highest bit of the flags byte (represented by the mask 0b1000_0000).


Each user package has an ID, encoded within the last three bytes of the datagram header. These IDs increment until they reach the maximum value that can be encoded within three bytes, after which the counter resets to 0. The ID sequence for reliable and unreliable packages are independent. Each connection / client has independent reliable package numbering.

Packages can be transmitted in several reliability modes, as listed below. The second and third bits (represented by the mask 0b0110_0000) of the flags byte control the reliability.

  • Unreliable (bits 00) – these packages may be lost, delivered multiple times, or delivered out of order with respect to other packages.
  • Unordered (bits 01) – non-duplicate delivery of these packages is guaranteed. However, there are no guarantees regarding the ordering of these packages with respect to other packages.
  • Semi-ordered (bits 10) – non-duplicate delivery of these packages is guaranteed. Additionally, the packages are guaranteed to be delivered after all previously reliably sent packages, that is, all unordered and semi-ordered packages sent by the same client before a semi-ordered package are always delivered before the semi-ordered package.

Packages can be targeted to the server, as opposed to all other game participants. This is indicated by the fourth highest bit of the flags byte (represented by the mask 0b0001_0000).

Package payload comprises the user data intended for delivery.


The datagram carrying a semi-reliable package with ID 107907, targeted to the server and containing the payload bytes 0x12 0x34 0x56, would look like this: 0x50 0x01 0xA5 0x83 0x12 0x34 0x56.

  1. 0x50 (0b0101_0000) – flags: semi-reliable, server targeted
  2. 0x01 0xA5 0x83 – package ID: 107,907
  3. 0x12 0x34 0x56 – package payload

Protocol Control

Currently, the only type of control datagram is the delivery confirmation datagram. All bits in the header of these datagrams, except for the first one, are set to 0. The payload consists of IDs for all user data datagrams that have been sent reliably and delivered successfully. Each ID is encoded using 3 bytes.


A datagram confirming three packages with IDs 1238, 17, and 2443, respectively, would look like this: 0x80 0x00 0x00 0x00 0x00 0x04 0xD6 0x00 0x00 0x11 0x00 0x09 0x8B.

  1. 0x80 (0b1000_0000) – protocol control flag
  2. 0x00 0x00 0x00 – always zeros
  3. 0x00 0x04 0xD6 – first confirmed package ID equal to 1238
  4. 0x00 0x00 0x11 – second confirmed package ID equal to 17
  5. 0x00 0x09 0x8B – third confirmed package ID equal to 2443