The token passing access method

'); d.write(''); d.close(); } // done hiding -->

The token passing access method

Assess the characteristics of the token passing access method.

What is token passing?

The token passing access method is a non-contention method that works very differently from the contention methods previously discussed. Token passing is a more orderly way for a network to conduct its business. A signal called a token goes from one computer to the next. In a Token Ring network, the token goes around the ring; in a token bus network, it goes down the line of the bus. If a computer has data to transmit, it must wait until the token reaches it; then that computer can capture the token and transmit data.

Token passing is the second most popular access method in use on LANs today, after CSMA/CD. The FlipBook below shows how this method differs from the contention methods you learned about in the previous lessons.

Transcript

Specifications for token passing are defined in the IEEE 802.5 standard.

There is no contention involved, and there can be no collisions on a token passing network.

There are some variations on the process above. Continue reading for more information on Token passing variations.

Different token passing architectures work differently. Token Ring networks allow only one token on the cable at a time. FDDI networks can have multiple tokens circulating simultaneously.

The token passing access method has both advantages and disadvantages.

Advantages of token passing	Disadvantages of token passing
Non-contention method; Computers do not compete for access to the cable. Each computer will get its "turn" as the token comes around the network. Effective; Collisions are prevented altogether. Reliable; The maximum amount of time before a given computer will be able to transmit can be calculated.	Slow; A large amount of network bandwidth is consumed in the process. Costly; Implementation is expensive due to the media and equipment used.

Next lesson

In the next lesson, you will learn about the demand priority access method.