FDDI Topology
Star topology, each device has a dedicated point to point connection to a central 'hub'. There is no direct traffic between devices, all data travels via the central hub, which forwards it to the other connected devices. Each device in a star topology has only one I/O port and one link, making it less expensive and easier to install and maintain. There is also far less cabling to be housed, yet the links are still robust. The major draw back is the central point of failure - the hub. If this fails the whole network is out of action.
•100mbps
•normally implemented over fiber optic (fast-Ethernet, UTP)
•dual redundancy built in by use of primary and secondary ring
•automatic bypassing and isolation of faulty nodes
Fiber Distributed Data Interface
FDDI is based on two counter rotating 100-Mbit/sec token-passing rings. The rings consist of point to point wiring between nodes which repeat the data as it is received.
The primary ring is used for data transmission; the secondary is used for data transmission or to back up the primary ring in the event of a link or station failure. FDDI supports a sustained transfer rate of about 80Mbps, a maximum of 1000 connections (500 nodes) and a total distance of 200 kilometers end to end. There is a maximum distance of 2 kilometers between active nodes.
FDDI Station Types
There are two main types of stations, class A which attach directly to dual rings; or class B which attach to a station acting as a concentrator.
A concentrator is a specialized workstation that attaches to the ring and has multiple ports that allow attachment of other devices in a physical star configuration. These may be cascaded.
Logical Networks versus Physical Networks
A logical network describes how the network operates. A physical network describes how the network has been cabled. It is thus possible to have a physical star, logical bus network. In other words, the network operates as a bus network, but the cabling has been implemented using star topology.
