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Token Bus Network

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A token bus network is similar to a token ring network in that a station must have possession of a token before it can transmit on the network (see "Token and Token-Passing Access Methods"). However, the topology and token-passing method are different. The IEEE 802.4 Committee has defined token bus standards as broadband networks, as opposed to Ethernet's baseband transmission technique. The Manufacturing Automation Protocol (MAP) developed by General Motors for manufacturing floor networks uses IEEE 802.4. ARCNET (Attached Resource Computing Network) is a token bus network, although it does not conform to the IEEE 802.4 standards.

The topology of the network can include groups of workstations connected by long trunk cables. These workstations branch from hubs in a star configuration, so the network has both a bus and star topology. Token bus topology is well suited to groups of users that are separated by some distance. IEEE 802.4 token bus networks are constructed with 75-ohm coaxial cable using a bus topology. The broadband characteristics of the 802.4 standard support transmission over several different channels simultaneously.

The token and frames of data are passed from one station to another following the numeric sequence of the station addresses. Thus, the token follows a logical ring rather than a physical ring. The last station in numeric order passes the token back to the first station. The token does not follow the physical ordering of workstation attachment to the cable. Station 1 might be at one end of the cable and station 2 might be at the other, with station 3 in the middle.

While token bus is used in some manufacturing environments, Ethernet and token ring standards have become more prominent in the office environment.

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