Token Ring network adapter board
	MAU
	Network cabling

Network Adapter Board

The Token Ring network adapter board, available in 4- and 16-Mbps versions, plugs into the input/output bus on each station's motherboard. However, the two different speed boards cannot operate on the same ring. Dual-speed adapters are also available that allow the board to be switched to operate in either a 4- or 16-Mbps ring. The adapter board typically contains circuitry for implementing Medium Access Control (MAC) layer and Physical Layer protocols.

Adapter boards are available for every type of bus, and must be matched to the type of bus in the station. Connection to Token Ring cabling is made through a nine-pin DB-9 connector for connection to STP wire, or an RJ-45 connector for UTP wiring. Although the original IBM Token Ring adapters had only the DB-9 connector, many manufacturers supply adapters with both DB-9 and RJ-45 connectors. The Dual-Port Adapter Board Diagram illustrates this configuration. Token Ring wiring options and connectors are described later in this chapter.

Miniaturized Token Ring adapters are also available for laptop computers in the form of PCMCIA type-II boards which can slip into laptop stations with a compatible slot.

Multistation Access Unit

MAU is a wiring concentrator to which Token Ring stations are attached. Each station is connected to the MAU with a twisted pair adapter cable: one pair is for reception, and one pair is for transmission. At each port on the MAU, there is a relay which senses the phantom voltage coming from the adapter and opens the connection to the ring. If the adapter is powered down, the phantom voltage ceases and the relay closes, bypassing the adapter. This provides a level of fault tolerance in case of an adapter error or faulty lobe cable. A station isolated in this manner is in bypass mode, as shown on the MAU with Station Bypassed Diagram.

MAUs typically have ports for eight or more stations. More than one MAU may be linked together to expand the ring by attaching cable to the ring in (RI) and ring out (RO) ports on each MAU. The Token Ring Expanded Using Two MAUs Diagram illustrates this type of scenario.

All RI/RO interconnections in a network are referred to as the main ring path, as illustrated on the Main Ring Path Diagram.

Ring Redundancy

Most Token Ring networks are installed with redundant main rings. As illustrated on the Redundant Main Ring Configuration Diagram, each MAU is connected through both the RI and RO ports. Each main ring connection contains two pairs: one considered the primary data path and a second that serves as a backup pair. When the ring is functioning correctly, data travels only on the main pair. On the following diagram, arrows indicate data travelling on only the main pair.

In the case of a cable failure on the main ring path, some MAUs automatically cause the main ring to wrap around and use the backup pair, thereby preserving ring integrity. As illustrated on the Ring Wrap Due to Fault on Main Ring Path Diagram, only one pair is continuous, and the data path is self-looped at the RI/RO ports. Arrows indicate data travelling on both the main and backup pairs.

Active and Passive MAUs

MAUs fall into two major categories:

	Passive--Typically unpowered devices that do not regenerate or strengthen signals passing through them. Some MAUs classified as passive may have repeater circuits in only the RI/RO ports; while these devices boost signal strength, they do not improve transmission.
	Active--Powered devices that repeat and re-time network signals. This re-timing function keeps network signals synchronized, reducing the chance of signal distortion (jitter). Most active MAUs provide some level of intelligence that allows remote network management for monitoring and configuring the MAU and attached stations.

Rack Installation

MAUs are available as stand-alone devices for small workgroup. However, they are more commonly mounted in racks in a wiring closet serving a departmental area as shown on the Cabling to Rack-Mounted MAUs Diagram. MAUs in such a rack are typically interconnected through short connectorized patch cords at the RI/RO ports.

On a Token Ring network, each node or station is called a lobe. A lobe connection (the wiring between a node and the MAU) can occur through a variety of components, depending on the building's wiring system.

The Cabling to Rack-Mounted MAUs Diagram illustrates cabling connections from a Token Ring station through a rack-mounted MAU in a wiring closet. From the Token Ring adapter board in the user's computer, an adapter cable connects to a wall outlet. The building cable connects the wall outlet to a punch-down block in the wiring closet where individual wires are semipermanently interconnected. From the punch-down block, a patch cord connects the patch panel assembly. The patch panel provides fully connectorized receptacles to facilitate connections and reconfigurations at the MAU ports. Short, connectorized patch cords connect each MAU port to a receptacle on the patch panel, completing the lobe connection.

In small networks, there may not be as many connection points. For example, in very small networks, the adapter cable may attach directly to a station port on a MAU, or simply have a wall outlet as an intermediary connection point. Likewise, in the wiring closet, there may be only a punch-down block or patch panel.

The number and quality of these interconnections can have a significant effect on the maximum length of a Token Ring network, as each connection introduces signal attenuation.

Hub-Based MAUs

MAUs are also manufactured as modules that slide into the backplane of a chassis-type hub. With this implementation, the backplane of the hub can automatically provide the RI/RO connections to the main ring path, as illustrated on the MAU Modules in Chassis-Type Hub Diagram.

   Activities

See the Activities and Extended Activities section in Unit 2 Lesson 5 in your textbook Introduction to Networking to test what you have learned so far.

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