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A multistation access unit (MAU), also called a multistation access unit or MSAU, is a Token Ring wiring concentrator: computers and other devices connect to it through separate cables, and it connects them to the network’s logical ring. The cabling forms a physical star, but that does not make the network an ordinary Ethernet hub arrangement.
What a Token Ring MAU does
A Token Ring MAU provides the connection point between multiple stations and a Token Ring network. IBM describes it as hardware used to connect a device to the ring; the U.S. Environmental Protection Agency describes it as a passive wiring concentrator for a star-wired Token Ring network.
In this context, MAU stands for multistation access unit. The same abbreviation is also used in Ethernet for media attachment unit, a different term. Cisco’s glossary notes the distinction and says Token Ring devices are usually called MSAUs to avoid confusion. When the context is unclear, write “Token Ring MAU” or “MSAU.” Cisco networking glossary
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Each station has a cable running to a central MAU, so the physical wiring resembles a star. The network connection provided by the MAU is a ring. The star describes where the cables meet; it does not mean that data travels through an Ethernet-style hub in the same way.
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The terminology also depends on which specification is being discussed. Cisco explains that IBM Token Ring specifies stations attached through an MAU in a star arrangement, while IEEE 802.5 does not specify a topology. Many IEEE 802.5 implementations use a star, but it is not accurate to say that IEEE 802.5 itself requires an MAU or a star topology. Cisco Token Ring overview
How many devices can connect to one MAU?
The answer depends on the unit. IBM’s OS/400 Token Ring manual, covering its 1997–1998 environment, describes up to eight attached devices per MAU and says multiple MAUs can be connected to provide access for more devices on the same ring. The EPA’s 1988 LAN planning guide likewise describes an IBM 8228 with eight station connections and ring-in and ring-out connections for linking additional MAUs.
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These are documented historical IBM examples, not a universal capacity limit for every MAU. The EPA guide suggested reserving a connection for expansion or in case another connection became unusable; that is historical planning advice, not a requirement for all installations. U.S. EPA, Local Area Network: Technical Guidelines, Volume I—LAN Design and Planning · IBM, OS/400 LAN, Frame-Relay and ATM Support V4R2
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Historical Token Ring speeds and cabling
IBM’s 1997–1998 manual describes adapters operating at 4 Mbps or 16 Mbps, with adapters on a given ring running at the same speed. Its example cable used a nine-pin D connector at the system end and a Token Ring modular plug at the cabling end. These are details of that historical IBM environment, not current compatibility guidance for every Token Ring device.
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- PLUG-AND-PLAY UNMANAGED NETWORK SWITCH: Simple plug-and-play setup with no software to install or configuration required.
- FLEXIBLE MOUNTING OPTIONS: Compact metal design supports desktop or wall-mount placement for versatile installation.
- SILENT & ENERGY-EFFICIENT OPERATION: Fanless design ensures silent performance, while IEEE 802.3az Energy Efficient Ethernet reduces power consumption without compromising high-speed network performance.
- REGIONAL COMPATIBILITY: Made for use in U.S. & CA only
For a legacy installation or restoration, check the documentation for the exact MAU, adapter, and cable models. Matching the connector alone does not establish that equipment is compatible; the supported speed and the rest of the ring configuration matter too. IBM, OS/400 LAN, Frame-Relay and ATM Support V4R2
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At a glance
- Purpose: Connect multiple stations to a Token Ring network.
- Physical cabling: Stations connect outward to a central concentrator in a star.
- Network arrangement: The Token Ring connection remains a logical ring.
- Abbreviation: MAU means multistation access unit in Token Ring; MSAU helps distinguish it from Ethernet’s media attachment unit.
- IEEE 802.5: The standard does not itself specify a topology, according to Cisco.
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