Token-ring, developed by IBM, is embodied in the IEEE standard 802.5. The key concept in this
type of network is the idea of a token.
This is similar to a baton in a relay race when each machine must receive the token before it is
allowed to go. If a particular machine has nothing to send, it simply passes the token on to the
next machine. If it does have something to send, the message is "linked" with the token before it is
send. By seeing the token linked to the message, the other machines know that the token is in use
and pass it along to the destination. When the destination machine gets the entire bundle, it puts
the token back on the network, with a tag to indicate that it received the
packet. It is then passed to the originator as an acknowledgment. The
originator then passes the token along to the next machine.
This scheme provides guaranteed access to the network
since every machine will eventually get the token.
Even if the originator of one packet
has more to send, once it gets its acknowledgment back, it must pass the token along. If no others
want to send anything, then it can come back to the first machine. However, the others were given
the chance to send something. This method also provides reliability since the destination
machine sends the packet back with an acknowledgment.