RING TOPOLOGY
• workstations connect to the ring
• faulty workstations can be bypassed
• more cabling required than bus
• the connectors used tend to cause a lot of problems
• commonly used to implement token ring at 4 and 16mbps
• four wire, generally STP or UTP
Physical Implementation Of A Ring Network
Each workstation is connected back to a Multiple Access Unit (MAU), which supports up to eight workstations. Additional MAU are cascaded to provide greater workstation numbers.
Wiring is performed in a physical star fashion, with cables wired directly from each workstation back to the MAU.
IEEE 802.5 Token Ring
This protocol is widely used in ring networks for controlling station access to the ring. A short message (called a token) is circulated around the ring, being passed from station to station (it originates from a controller or master station which inserts it onto the ring).
A station which wants to transmit waits for the token to arrive. When the token arrives, the station changes it from a token to a connector message, and appends its message. This new message is then placed on the outgoing side of the ring.
Each station passes on received tokens if they have nothing to transmit. They monitor connector messages to see if the message is addressed to them. If connector messages are addressed to them, they copy the message, modify it to signify its receipt, then send it on around the ring. Connector messages which are not addressed to them are passed directly on to the next station in the ring.
When the connector message travels full circle and arrives at the original sending station, it checks the message to see if it's been received. It then discards the message and replaces it with a token.
Physical Ring Cable Limits
TOKEN RING NETWORK LAYOUT
Limitations
• maximum number of workstations = 96
• maximum number of 8228 MAU's = 12
• maximum patch cable distance between an 8228 MAU and a station (not including 8'adapter cable) = 150 feet (45 meters)
• maximum patch cable distance between two 8228's = 150 feet (45 meters)
• maximum patch cable connecting all 8228's = 400 feet (120 meters)
Rules
• station are connected into the jacks of the 8228 units.
• patch cables interconnect RO to RI for 8228 units.
• the last RO is connected to the first RI to form a ring.
Cabling
• patch cables generally type 6 (26) or 1 (22 awg)
• type 1 for lengths > 66 feet (20 meters)
• IBM 8310574 MIC connectors
• alternatively, UTP with RJ45 connectors
Ring Topology: Summary
Advantages Disadvantages
Cable failures affect limited users Costly Wiring
Equal access for all users Difficult Connections
Each workstation has full access speed to the rings Expensive Adaptor Cards
As workstation numbers increase performance diminishes slightly
