IEEE LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of the data link layer. It uses token-passing access over a bus topology and is based on the token bus LAN architecture. Each station must maintain ten different timers and more than two dozen internal state variables. The 802.4 standard is much longer than the one for 802.3. 802.4 gives the protocols as finite state machines. The actions are written in Ada.