3.2 Layer 2 Protocol Overview - LAN Protocols
3.2.4 IEEE 802.5
IBM originally conceived Token Ring as a data-center technology for networking mainframe computers. It was first proposed to the IEEE for standardization in the 1970s for this purpose. After personal computers (PCs) were developed, it became apparent that Token Ring could serve to interconnect them as well. This was the impetus behind its inclusion in the IEEE's Project 802. IBM was a major proponent of the IEEE standardization efforts. Today, both technologies are known as Token Ring.

The IEEE designated Token Ring as its 802.5 specification. Token Ring and IEEE 802.5 networks are basically quite compatible, but the specifications do differ in relatively minor ways. IBM's Token Ring network specifies a star, with all end stations attached to a device called a multistation access unit or MSAU, whereas IEEE 802.5 does not specify a topology (although virtually all IEEE 802.5 implementations also are based on a star). Other differences exist, including media type (IEEE 802.5 does not specify a media type, whereas IBM Token Ring networks use twisted-pair wire) and Information field (or Data field) size. The figure to the left summarizes IBM Token Ring network and IEEE 802.5 specifications.