Token Ring Switching

Token Ring switching offers many of the same advantages as Ethernet switching. The major advantage is the speed that Token Ring switching provides. Much as Ethernet bandwidth is affected by the number of stations on a segment causing collisions, Token Ring bandwidth is affected by stations awaiting the token to transmit data. In a switched environment, ports on the same switch can belong to the same ring, but the stations on the switch ports will experience bandwidth as if they were the only stations on the ring.

Token Ring switches also offer dedicated Token Ring (DTR). With traditional 4- or 16-Mbps Token Ring, Token Ring adapters are limited to half-duplex mode. DTR defines a method that allows the switch port to emulate a concentrator port and full-duplex data-passing mode called transmit immediate (TXI), which takes advantage of the fact that there is one end station on a port, and there is no real need to pass a token. Therefore, the adapter can transmit and receive simultaneously , where the ring can now use a theoretical bandwidth of 32 Mbps.

The Token Ring switch ports operate in the following modes:

• Half-duplex concentrator port ” The port is connected to a single station in half-duplex mode. The port behaves like an active MAU port for classical Token Ring.

• Half-duplex station emulation ” The port is connected to a port on an MAU. The port behaves like a station connected to a classical Token Ring segment that contains multiple stations.

• Full-duplex concentrator port ” The port is connected to a single station in full-duplex mode.

• Full-duplex station emulation ” The port is connected to a switch or a concentrator port in full-duplex mode.

NOTE

Duplex modes are a function of the hardware built into the network interface card. Software upgrades will not allow you to run full-duplex mode. For full-duplex mode to work, the station and switch port must be capable of full-duplex mode.