2.2 IEEE 802.5 (Token-Ring)
Token Ring (IEEE 802.5) uses a ring topology. Each station on the network has two connections - one to the "downstream" station and one to the "upstream" stations. Each station receives network data from the downstream station and passes it to the upstream station. The data circulates through the network until it reaches the initiating station, which validates that it was correctly sent though the network. In practice, rather than wire directly between each station, the stations are wired into a central hub. This approach allows stations to be added by plugging them into the hub, where the plug mechanically inserts the station into the ring. Token ring operates at 4 or 16 M bits/sec using shielded twisted pair media. Fiber optic cable may be used for interconnecting hubs.
Server
PC PC
PC | PC |
PC
Figure 2 Token Ring Topology
Token Ring (802.5) uses a "token" which is passed among the stations on the network. When a station has a token, it can transmit. When it is through transmitting data, a station sends the token to the next "upstream" station.
The primary benefit of token ring is that it provides a very consistent level of network performance, since there is a maximum amount of time a token can be held. Token Ring response is sometimes referred to as deterministic, meaning that the response time can be precisely calculated. At higher levels of network loading,
On the other hand, token ring is costly (about 4 to 5 times more than Ethernet) and its technology is closely tied to proprietary IBM technology. In some situations, the ring topology of
4
CTI 2572 Technical Overview Manual
