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In the previous tutorials, we have studied about TDM, Polling and CSMA/CD. In this tutorial, we will study about token passing. If you wish you can skip this topic since it is no more asked in GATE but it is suggested to go through it once for a better understanding of the subject.
In CSMA/CD, efficiency decreases due to collision. To stop collision, method called token passing is used.
– Ring topology is used in token passing.
– A special packet called token revolves around the ring. If any station holds the token then only that station is supposed to transmit the data.
– Since only 1 token is present only 1 station can transmit at a time.
– The token ring operates in unidirectional way.
– Depending upon the time when token is released, there are 2 strategies of token passing:
=> Delayed token reinsertion
=> Early token reinsertion
Delayed Token Reinsertion
In this, the sender transmits the data packet and waits till the time the whole packet takes the round trip of the ring and return to it. When the whole packet is received by the sender, then it releases the token.
Early Token Reinsertion
In Early token reinsertion, sender does not wait for the data packet to complete revolution before releasing the token. Token is released as soon as the data is transmitted. Multiple packets are present in the ring. So, it is less reliable than delayed token reinsertion.
This gives an idea of the token passing method and the token ring. The topic is not covered in much detail since it is not required. In the next tutorial, we will study about Pure aloha and Slotted Aloha.