What Is a Token Ring?

Find out more about this LAN technology component

Network connections lit up like stars
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Developed by IBM during the 1980s as an alternative to Ethernet, token ring is a data link technology for local area networks (LANs) in which devices are connected in a star or ring topology. It operates at layer 2 of the OSI model

Starting in the 1990s, token ring significantly decreased in popularity and was gradually phased out of business networks as Ethernet technology began to dominate LAN designs.

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

How Token Ring Works

Unlike all 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 onto the LAN. If not, the device releases the token frame for the next device in sequence to pick up.

In other words, in an effort to minimize network congestion, only one device is used 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 (i.e., they mark the frame's 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 exact same MAC address without causing issues.

Here are some more differences:

  • Cabling for token ring networks is more expensive than Ethernet's CAT 3/5e. Also more pricey are token ring network cards and ports.
  • Token ring networks can be configured so that certain nodes have more priority than others, something that isn't allowed with unswitched Ethernet.
  • As mentioned above, token ring networks use tokens to avoid collisions, whereas Ethernet networks (especially when hubs are used) are more prone to them. That's why Ethernet networks use switches.