| 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.
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