Introduction To Token Ring

IBM originally developed the first Token Ring network in the 1970’s and it now the second largest LAN technology after Ethernet.

Since it’s development the IEEE created the 802.5 specification to try and standardise the technology. It is very similar and completely compatible with IBM’s Token Ring.

Token Ring is a token passing network, there are no collisions on a this type of network, since hosts do not compete to transmit data on the network.

In Token Ring networks tokens are passed around the network, which is ring shaped, and each node passes the token to it’s neighbour.

When a node receives the token it is it’s turn to transmit data. If it has no data to transmit then it will pass the token to it’s neighbour. If on the other hand it does, then the node uses the token as a frame for the data it needs to transmit. Once it’s appended the data it passes the data to it’s neighbour, who passes it on to it’s neighbour and so on.

Each node can only hold the token for a specific amount of time, and while data is being sent around the ring no token exists on the network, and no other node can transmit.

The Token Ring star topology consists of hosts connected to Multi-Station Access Units (MSAU) via lobe cables, which are connected to the Token Ring network serially using patch cables. These Multi-Station Access Units increase the fault tolerance of the network since they can monitor and try to repair problems with the network. Using a technical process known as Beaconing, Token Ring networks can define a failure domain eliminating the portion of the network that is at fault and attempts can be made to reconfigure the network around the failed network area. Multi-Station Access Units use bypass relays in order to remove hosts from the ring.

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