What Is a Token Ring?

Find out more about this LAN technology component

Token Ring is a data link technology for local area networks (LANs) in which devices are connected in a star or ring topology. IBM developed it during the 1980s as an alternative to Ethernet. It operates at layer 2 of the OSI model. Starting in the 1990s, token ring significantly decreased in popularity, and business networks gradually phased it out as Ethernet technology began to dominate LAN designs.

The standard token ring supports up to 16 Mbps. In the 1990s, an industry initiative called high-speed token ring (HSTR) developed technology that extended token ring to 100 Mbps to compete with Ethernet. The technology was abandoned because of insufficient market interest for HSTR.

Network connections lit up like stars
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How Token Ring Works

Unlike other standard forms of LAN interconnects, token ring maintains one or more common data frames that continuously circulate through the network.

All connected devices on the network share these frames as follows:

  1. A frame (packet) arrives at the next device in the ring sequence.
  2. That device checks whether the frame contains a message addressed to it. If so, the device removes the message from the frame. If not, the frame is empty (this is called a token frame).
  3. The device holding the frame decides whether to send a message. If so, it inserts message data into the token frame and issues it back to the LAN. If not, the device releases the token frame for the next device in sequence to pick up.

To minimize network congestion, only one device is active at a time. The above steps are repeated continuously for all devices in the token ring.

Tokens are three bytes that consist of a start and end delimiter that describe the beginning and end of the frame (these bytes mark the frame boundaries). Also within the token is the access control byte. The maximum length of the data portion is 4,500 bytes.

How Token Ring Compares to Ethernet

Unlike an Ethernet network, devices within a token ring network can have the same MAC address without causing issues.

Here are some more differences:

  • Cabling for token ring networks is more expensive than Ethernet CAT 3/5e cable. Token ring network cards and ports are also more expensive.
  • Administrators can configure token ring networks so that certain nodes have more priority than others. This isn't allowed with unswitched Ethernet.
  • Token ring networks use tokens to avoid collisions. Ethernet networks are more prone to collisions, especially when the system employs hubs. These systems use switches to avoid collisions.
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