IEEE 802.5/IBM Token Ring
• The stations form a logical ring (star-wired-ring network)
– Small frame (token) circulates when idle
– Only the possession of a token allows a node to transmit
– Upon possession, a sending station changes one bit in token to
make it SOF for data frame
– Appends rest of data frame to the token
– Frame makes round trip, reaches destination and is finally
absorbed by transmitting station
• sending station can perform some checks to see if frame was
received correctly by the destination node
– Sending station then inserts new token when transmission has
finished and leading edge of returning frame arrives
– Token rings give deterministic access and delay is deterministic
• They are used in applications where predictable delay and
robustness of network is needed
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