Token Ring

It uses a special three-byte frame called a token that is passed around a logical ring of workstations or servers.

Token Ring was a successful technology, particularly in corporate environments, but was gradually eclipsed by the later versions of Ethernet.

At the IBM Zurich Research Laboratory Werner Bux and Hans Müller, in particular, worked on the design and development of IBM's Token Ring technology,[2] while early work at MIT[3] led to the Proteon 10 Mbit/s ProNet-10 Token Ring network in 1981[4] – the same year that workstation vendor Apollo Computer introduced their proprietary 12 Mbit/s Apollo Token Ring (ATR) network running over 75-ohm RG-6U coaxial cabling.

[citation needed] Proteon later evolved a 16 Mbit/s version that ran on unshielded twisted pair cable.

[8][failed verification] During this time, IBM argued that Token Ring LANs were superior to Ethernet, especially under load,[9] but these claims were debated.

These differences have become immaterial, as modern Ethernet networks consist of switches and point-to-point links operating in full-duplex mode.

[18] The data transmission process goes as follows: Physically, a Token Ring network is wired as a star, with 'MAUs' in the center, 'arms' out to each station, and the loop going out-and-back through each.

Although Token Ring runs on LLC, it includes source routing to forward packets beyond the local network.

The CAUs supported features such as Dual-Ring Redundancy for alternate routing in the event of a dead port, modular concentration with LAMs, and multiple interfaces like most later MAUs.

The first function is to operate as the master clock for the ring in order to provide synchronization of the signal for stations on the wire.

A third function for the AM is to ensure that exactly one token circulates whenever there is no frame being transmitted, and to detect a broken ring.

Token Ring specifies an optional scheme of this sort, as does the CAN Bus, (widely used in automotive applications) – but Ethernet does not.

[25] In 2012, David S. Miller merged a patch to remove token ring networking support from the Linux kernel.