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J4167A – JetDirect 610N Token Ring LAN Interface Board


is a crossover just a Wrap Plug?





MAU Design


322 - MAU Token Ring (Multistation access unit) IBM 8228 (2), 1986


The IBM8228 is a typical passive MAU. It can operate at 4Mbps or 16Mbps and has 10 connection ports, 8 passive node ports, a ring in (RI) and a ring out (RO) connection


8228 Setup Tool

“MAUs are mechanical devices that consist of relays and connectors. Their purpose is to switch workstations in and out of the network. Each port is controlled by a relay powered by a voltage sent to the MAU from the NIC. When an 8228 is first set up, each of these relays must be initialized with a setup tool (sometimes referred to as a phaser) shipped with the unit. The setup tool is inserted into each port and held there until a light indicates that the port is properly initialized (charged).”

Im guessing that means its charging up the big capacitor


Simplified Example


Phase 0

Station Attach Signal, phantom DC current


The “phantom circuit ” is essential to ring maintenance. If a node is on a damaged section of the ring or if requested by the local-area-network management program, a node removes itself from the ring by removing its voltage from the circuit (deactivating the phantom circuit). The presence of too much or too little current in the phantom circuit indicates a wiring problem. (Figure courtesy of Texas Instruments.) If only one MAU is in the network, the MAU configures all the stations attached to it into a ring. If there is more than one MAU, each links its stations into a single ring that runs through all the MAUs. Each node attaches to the MAU via a special four-conductor connector. The connector is hermaphroditic; that is, it can mate with identical connectors. When a connector is unplugged, shorting bars inside join the send circuit to the receive circuit, allowing the attached device to perform loopback tests on itself and the cable. The connections between a node and the remainder of the Token Ring are transformer-coupled. This limits common-mode voltages and breaks ground loops that could cause harmful interference on the ring.


Early Token Release

ETR allows two frames to travel on the ring at the same time

Packet Capture

Olicom OC-3137 is the only Linux-compatible Token-Ring card that supports promiscous mode.