A multistation access unit (MAU), also called an MSAU, is a Token Ring wiring concentrator that connects multiple network stations to a ring. The stations’ cables form a physical star around the concentrator, but the network connection remains a logical ring—not an ordinary Ethernet-style hub arrangement.
What a Token Ring MAU does
A Token Ring MAU provides the physical connection between end stations—such as workstations or servers—and the Token Ring network. The U.S. Environmental Protection Agency describes it as a passive wiring concentrator for a star-wired Token Ring network, typically placed in a wiring closet or another central location. IBM likewise describes an MAU as the hardware used to connect a device to a Token Ring.
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In practical terms, each station connects to the MAU through its own cable, while the MAU provides access to the ring. It concentrates the station connections; it is not simply an Ethernet hub with a different name.
Why the cables look like a star but the network is a ring
Two topologies are involved. The physical topology describes how equipment is cabled: station cables run from individual devices to a central MAU, making a star. The logical topology describes how the network is arranged for communication: Token Ring stations participate in a ring.
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The central device can therefore make installation look like a star without changing the ring-based network arrangement. Cisco distinguishes IBM Token Ring’s specified star arrangement, with stations attached through an MAU, from IEEE 802.5: the standard itself does not specify a topology, although many implementations use a star. So it is inaccurate to say that every IEEE 802.5 network must use an MAU.
How many devices can connect to one MAU?
The number depends on the particular unit. IBM’s OS/400 Token Ring manual, copyright 1997–1998, says each MAU it describes allows up to eight attached devices to access a ring; multiple MAUs can be attached to that ring to add connections. The EPA’s 1988 LAN planning guide gives a similar historical example: the IBM 8228 has eight attaching connections, with ring-in and ring-out connections for linking additional MAUs.
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These are specifications for documented historical equipment, not a universal limit for every Token Ring concentrator. The EPA guide also recommends reserving a connection for expansion or for use if another connection becomes unusable; that is a planning suggestion in that guide, not a requirement for every network.
MAU, MSAU, and Ethernet terminology
In Token Ring, MAU means multistation access unit; MSAU is another abbreviation for the same kind of device. The abbreviation is ambiguous in networking: Cisco’s glossary also uses MAU to mean media attachment unit, an Ethernet physical-interface device. When precision matters, say “Token Ring MAU” or “MSAU.”
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- 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
Historical speeds and cabling
IBM’s 1997–1998 OS/400 manual describes Token Ring adapters operating at either 4 Mbps or 16 Mbps and says adapters on a given ring must use the same speed. It also gives a cable example with a nine-pin D connector at the system end and a Token Ring modular plug at the cabling end. These details describe the historical IBM environment, not general compatibility guidance for other equipment.
If you are restoring a legacy installation, check the documentation for the exact adapter, MAU, and cable before connecting anything. The cited manuals document older systems and do not establish current product availability or compatibility.
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Sources
- U.S. Environmental Protection Agency, Local Area Network: Technical Guidelines, Volume I—LAN Design and Planning (1988), including its LAN glossary and IBM 8228 example.
- IBM, OS/400 LAN, Frame-Relay and ATM Support V4R2 (copyright 1997–1998), Token Ring physical environment section.
- Cisco technical material on Token Ring and IEEE 802.5 topology, and Cisco’s networking glossary for MAU terminology.
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