Fiber Distributed Data Interface (FDDI)

FDDI Facts

Fiber Distributed Data Interface (FDDI) is a fiber-optic, token-ring architecture originally standardized by the American National Standards Institute (ANSI). This standard is in many respects similar to the IEEE 802.5 standard, but is characterized by higher data transfer rates (100 to 200 Mbps).
FDDI is typically implemented in situations where high data transfer rates are needed, including:

• LAN Backbones--The FDDI network forms a high-speed backbone for the rest of the network.
• Computer-room Networks--These networks connect high-performance mainframes and other computers.
• High-speed LANs--The speed of FDDI is ideal for networks with high data traffic, powerful workstations (engineering or computer-aided design workstations), or networks requiring high transfer rates (i.e. digital video).

The following table describes various details about FDDI.

Characteristic	Description
Topology	FDDI networks are wired using a physical ring, logical ring topology or a physical star, logical ring topology. FDDI uses dual counter-rotating rings for data (two rings are used, with each sending data in the opposite direction).
Media Access Method	FDDI uses a token-passing media access method. FDDI provides a ring wrapping feature which uses both rings for sending data. If a break occurs in one ring, data can be sent on the other ring, thus isolating the break.
Transmission Media	As the name suggests, FDDI networks use fiber optic cables. Newer specifications allow the use of Cat 5 UTP (sometimes called CDDI).
Networking Devices	FDDI networks use fiber optic connectors. SC and ST are both fiber optic connectors and can be used on an FDDI network though the MIC connector is the most common. Two types of devices might be connected to an FDDI network: Dual Attachment Stations (DAS), also called Class A devices, attach to both rings (primary and secondary). Single Attachment Stations (SAS), also called Class B devices, attach to one ring (primary).
Speed	FDDI operates at 100 Mbps on a single ring. When both rings are used, data can travel at an effective rate of 200 Mbps.
Additional Specifications	FDDI can operate over distances up to 200 km (124 miles). When two rings are used, the distance is limited to 100 km (62 miles). FDDI networks can support up to 1000 devices.