A wiring concentrator or passive hub used in Token Ring networks. Multistation Access Units (MAUs), which are the core wiring components for building Token Ring local area networks (LANs), direct network traffic from one station to the next.
A MAU provides a physical ring topology for Token Ring traffic to follow, although the actual logical wiring topology used is a star topology with stations connected in a star pattern to a central MAU. A typical MAU might provide 8 or 16 ports for connecting stations to the ring. If a larger LAN is required, you can join MAUs to form a larger ring by connecting the ring-out connector of one MAU to the ring-in connector of another, and continue connecting until the ring-out of the last MAU in a series is connected to the ring-in of the first to complete the loop. You can connect up to 33 MAUs in this manner in a logical ring. MAUs also include circuitry that provides fault tolerance if a station fails or is disconnected from the MAU and allows Token Ring traffic to continue around the ring unaffected.
A typical MAU is a stand-alone device or a rack-mounted device that supports 8 or 16 workstations and includes one ring-out and one ring-in connector. It might support 4 Mbps or 16 Mbps or both and use either IBM data or RJ-45 lobe connectors for using IBM type 3 cabling or 100-ohm impedance shielded twisted-pair (STP) cabling. A modular MAU lets you add different connector or repeater modules for greater flexibility of network design. Stackable MAUs allow you to easily create large Token Ring LANs with up to 256 stations. Manageable MAUs include built-in Simple Network Management Protocol (SNMP) modules and might support both in-band and out-of-band management functions. Active MAUs regenerate signals at each port in order to reduce jitter and extend signaling distances beyond recommended specifications.
The acronym “MAU” also stands for Medium Access Unit (or Media Attachment Unit) and can refer to the portion of the circuitry in a hub, Ethernet switch, or network interface card (NIC) that enables the correct form of electrical or optical connection to the particular type of media being used. The MAU (also known as the transceiver) detects the carrier and signal activity on the media, notes when collisions occur, and forwards this information to the remaining circuitry. To distinguish the two different meanings of the acronym “MAU,” the acronym “MSAU” is sometimes used to refer to a Multistation Access Unit.
Graphic M-24. Connecting several MAUs.
If you need to locate your stations at distances greater than 100 meters from the MAU, you can use repeaters or a powered MAU with built-in repeaters for greater lobe distances. For larger rings, some MAUs include ring-in/out connectors for both copper cabling (RJ-45 connectors) and fiber-optic cabling (ST connectors).
A common way to bring down a Token Ring network is to connect a Token Ring station that has the wrong speed for the given network - for example, connecting a 4-Mbps station to a 16-Mbps network. This speed mismatch causes beaconing that brings down the network. A smart MAU can detect a mismatched station and lock out the station before a problem can occur.
Look for MAUs that have automatic loopback functions on their ring-in/out ports. If a break in the ring occurs between two MAUs, the break is automatically detected and traffic is routed along a preconfigured backup path.