ARINC 629 is a specification for a bus on which terminals are connected. There is no controller on the bus. Each terminal on the bus is able to identify when it is its turn to transmit. Synchronization between the terminals is ensured by three timers (the transmit interval, the synchronization gap and the terminal gap).

Up to 120 terminals can transmit on one bus. ARINC 629 messages are 31 word strings long (maximum). Word string is a 20-bit long label word followed by 0 to 256 16-bit long data words. A maximum of 31 messages can be transmitted by a terminal. Messages are transmitted at a speed of 2Mbps.

At the physical layer, it features communication of messages over bidirectional, unshielded, bipolar electrical interface. Bit-encoding is Manchester encoded doublets.