IEEE 802.5 refers to the standard associated with Token Ring networks. Token Ring is a network protocol which resides at the data link layer (DLL) of the OSI model. It was standardized by the Institute of Electrical and Electronics Engineers (IEEE).

Here are the key points about IEEE 802.5 – Token Ring:

  1. Functionality: In a Token Ring network, a token circulates around the ring, and a device must capture this token in order to send a message. Once the data has been sent, the token is then released back onto the ring for the next device to use.
  2. Competition with Ethernet: During the 1980s and early 1990s, Token Ring was widely used in corporate networks, primarily because of its deterministic nature (predictable network performance). However, it was in competition with Ethernet, which eventually became the dominant LAN technology.
  3. Speeds: Originally, Token Ring operated at 4 Mbps. A later version provided for 16 Mbps, and there were even versions that went up to 100 Mbps. However, by the time the faster versions came out, Ethernet was already becoming more popular.
  4. Topology: While the name implies a ring topology, physically, Token Ring networks were often set up in a star topology, with all devices connecting to a multistation access unit (MSAU or MAU). Logically, the network always functioned as a ring, with the token circulating among all devices.
  5. Deterministic Nature: One of the main advantages of Token Ring was its deterministic nature, which made network performance very predictable. This was in contrast to Ethernet’s CSMA/CD (before switches were common), where collisions could introduce unpredictable delays.
  6. Decline: By the late 1990s, the cost and performance advantages of Ethernet, especially with the rise of switching and full-duplex operation, led to a rapid decline in the deployment of new Token Ring networks.
  7. MAUs: Multistation Access Units (MAUs) were the central hub-like devices in a Token Ring network. They had the intelligence to reconfigure the logical ring in the event of a device or network failure.
  8. Compatibility: The IEEE 802.5 standard was largely compatible with IBM’s Token Ring network, which helped drive the standard’s initial acceptance in corporate environments.

Despite its decline, Token Ring played a significant role in the history of local area networking. Its deterministic approach was attractive for many corporate applications, but the scalability, cost, and flexibility of Ethernet eventually overshadowed Token Ring’s benefits.