Token Ring/IEEE 802.5

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Introduction of Token Ring

The concept of the Token Ring was introduced by IBM in 1984, but standardized globally in 1989 as IEEE 802.5.

Token Ring is one of the earliest local area networking technologies/protocols, used to build specific local area networks(LAN).

It uses a three-byte frame structure called a token that is passed around a logical ring network of workstations or servers.
Today, this LAN network technology is considered inactive and obsolete. In place of this network, Ethernet is used widely and commercially in most institutions and business organizations, today.
Advantages :
- In this network, Stations can be easily added and removed as needed.
- Collision-free network.
- This network has an Internal error detection and correction system.
Disadvantages :
- This network structure is comparatively slower in performance as compared to the token bus topology.
- It is a comparatively expensive structure.
- Data flow is uni-directional(mostly clockwise).
- When one workstation or node shuts down suddenly in this network, then it affects or stops or goes down the transmission in the network after that workstation.
- It is old technology now.

In this, only one token circulates around the ring network whenever all stations are idle. When a station wants to transmit a data frame, it seizes the circulating token and removes it from the ring before transmitting. Because there is only one token, only one station can transmit at a given instant, thus solving the channel access problem.
In this case, the token is passed from a node to the physically adjacent node.
In this, a node currently holding the token has the ‘right to transmit’. When it has data to send, it transmits the data and then forwards the token to the next physical node in the ring. If a node currently holding the token has no data to send, it simply forwards the token to the next node.

This protocol is used to create/prepare a specific LAN for an institution but is rarely used now.