Token Ring/IEEE 802.5

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Introduction

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

Token Ring is one of the earliest a local area networking technology/protocol, used to build a 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 are considered inactive and obsolete. In place of this network, Ethernet are used widely and commercially in most of the institutions and business organization, today.
Advantages :
- In this network, Stations can be easily added and removed as per need.
- Collision free network.
- This network has Internal error detection and correction system.
Disadvantages :
- This network structure is comparatively slower in performance as compared to the token bus topology.
- It is 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 a token ring, the only one token circulates around the ring network whenever all stations are idle. When a station wants to transmit a data frame, they seize the circulating token and remove 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 case of token ring token is passed from a node to the physically adjacent node.
In token ring, a node currently holding the token has the ‘right to transmit’. When it has got 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 rarely used now.