Token Bus (IEEE 802.4)

Token Bus (IEEE 802.4) is a popular standard for the token passing LANs. In a token bus LAN, the physical media is a bus or a tree and a logical ring is created using coaxial cable. The token is passed from one user to other in a sequence (clockwise or anticlockwise). Each station knows the address of the station to its “left” and “right” as per the sequence in the logical ring. A station can only transmit data when it has the token. The working of token bus is somewhat similar to Token Ring.

The above diagram shows a logical ring formed in a bus based token passing LAN. The logical ring is shown with the arrows.

Frame Format:
The various fields of the frame format are:

  1. Preamble – It is used for bit synchronization. It is 1 byte field.
  2. Start Delimiter – These bits marks the beginning of frame. It is 1 byte field.
  3. Frame Control – This field specifies the type of frame – data frame and control frames. It is 1 byte field.
  4. Destination Address – This field contains the destination address. It is 2 to 6 bytes field.
  5. Source Address – This field contains the source address. It is 2 to 6 bytes field.
  6. Data – If 2 byte addresses are used than the field may be upto 8182 bytes and 8174 bytes in case of 6 byte addresses.
  7. Checksum – This field contains the checksum bits which is used to detect errors in the transmitted data. It is 4 bytes field.
  8. End Delimiter – This field marks the end of frame. It is 1 byte field.

Attention reader! Don’t stop learning now. Get hold of all the important CS Theory concepts for SDE interviews with the CS Theory Course at a student-friendly price and become industry ready.

My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using or mail your article to See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.