The term Token Ring is generally used to refer to both IBM's Token Ring and IEEE 802.5 network implementations. IBM originally developed the Token Ring network in the 1970s, and it is still IBM's primary local-area network (LAN) technology. The related IEEE 802.5 specification is almost identical and completely compatible with IBM's Token Ring network implementations. The IEEE 802.5 specification was modeled after IBM's Token Ring specification, and the IEEE 802.5 specification continues to follow IBM's research and developmental work with Token Ring.
Although the Token Ring and IEEE 802.5 network specifications differ slightly, the network implementations are basically compatible. IBM's Token Ring network implementations specify a star topology, with all end hosts, or hosts, attached to a multistation access unit (MSAU or MAU). The IEEE 802.5 specification does not specify a topology, although practically all IEEE 802.5 implementations are based on a star topology.
Token Ring is considered a half-duplex network implementation because only one host can transmit at any given time. Token Ring's full-duplex network implementation is known as Dedicated Token Ring (DTR). Token Ring hosts connect, point-to-point, to a DTR concentrator or switch and have all available link bandwidth to use for data transmission and reception. Dedicated Token Ring will be discussed later in this chapter.
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