• Token bus was standardized by IEEE standard 802.4.


  • Token bus is a LAN network protocol that implemens a Token Ring protocol over a virtual ring on a coaxial cable(ethernet).


  • The token bus is a distributed processing system. 
  • Here, each node must know the address of its neighbour in the logical ring.
  • The token bus operates on the same principle as the token ring.
  • Here,  the devices communicate via a common bus as in an Ethernet.
  • Like, the token ring network, token bus networks are also rarely used.


  • Token bus is the combination of Ethernet and token ring i.e. it combines the physical configuration feature of Ethernet (bus topology) and collision free (predictable delay) feature of token ring.
  • Token bus is a physical bus that operates as logical ring using tokens.
  • It is a linear cable onto which the stations are attached.
  • Working Mechanism :
    • In the token bus, token is passed with the help of the address of the nodes, which form a logical ring.
    • In token bus, a node currently holding the token has the ‘right to transmit’. When it has got data to send, it transmits the data and then forwards the token to the next logical node in the bus. If a node currently holding the token has no data to send, it simply forwards the token to the next node.
    • When the logical ring is initialised, the highest numbered station may send the first frame after it is done, it passes permission to its immediate neighbour by sending the neighbour a special control frame called a token. The token propagates around the logical ring with only the token holder being permitted to transmit frames. If a node doesn’t have anything to send, the token is passed on to the next node on the virtual ring.
    • The allocation of the bus is controlled by the cyclic passing of tokens in a sequential manner from lowest numbered interface unit (IU) to the next highest until all numbered IUs have been interrogated and serviced.
  • Since only one station at a time holds the token, collisions do not occur.


  • The standard is no longer being updated and not seeing wide use. This LAN protocol is restricted in use i.e. mainly in industrial manufacturing application.



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