Token Ring Network

In a token ring network, all workstations are connected in a ring or star topology and a token-passing scheme is used to prevent the collision between two workstations who want to send messages at the same time. Here, very briefly, is how it works:
  1. Empty information frames are continuously circulated on the ring.
  2. When a workstation wants to send a message, it inserts a token in an empty frame (this may consist of simply changing a 0 to a 1 in the token bit part of the frame and inserts a message and a destination identifier in the frame.
  3. The frame is then examined by each successive workstation. If the workstation sees that it is the destination for the message, it copies the message from the frame and changes the token back to 0.
  4. When the frame gets back to the originator, it sees that the token has been changed to 0 and that the message has been copied and received. It removes the message from the frame.
  5. The frame continues to circulate as an "empty" frame, ready to be taken by a workstation when it has a message to send.

The applet on this page is a simple simulation of a token ring network with four computers, one can see an animation of this network, with messages travelling between computers, and at the right of this animation is a representation of the event set. The blue line denotes the event that is taking place, the next lines denote future events that have been scheduled, the future event set. Under the animation one can see the simulation time which can be speeded up, or slowed down using the arrows at the bottom.

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