|  | 7.2 | Basics of Fiber Distributed Data Interface (FDDI)
| 7.2.1 | Overview of FDDI and its variants

In the mid 1980's, high-speed engineering workstations had pushed the capabilities of existing Ethernet and Token Ring to their limits. Engineers needed a LAN that could support their workstations, and their new applications. At the same time, system managers became concerned with network reliability issues as mission-critical applications were implemented on the high-speed networks.

The ANSI X3T9.5 standards committee, to resolve these issues, produced the Fiber Distributed Data Interface (FDDI) standard. After completing the specifications, ANSI submitted FDDI to the International Organization for Standardization (ISO), who, then created an international version of the FDDI that is completely compatible with the ANSI standard version.

Although FDDI implementations are not as common today as Ethernet or Token Ring, FDDI has a substantial following, and continues to grow as its costs decrease. FDDI is frequently used as a backbone technology, and to connect high-speed computers in a LAN.

FDDI has four specifications:

1. Media Access Control (MAC) - defines how the medium is accessed, including:

- frame format
- token handling
- addressing
- algorithm for calculating a cyclic redundancy check and error recovery mechanisms

2. Physical Layer Protocol (PHY) - defines data encoding/decoding procedures, including:

- clocking requirements
- framing
- other functions

3. Physical Layer Medium (PMD) - defines the characteristics of the transmission medium, including:

- fiber optic link
- power levels
- bit error rates
- optical components
- connectors

4. Station Management (SMT) - defines the FDDI station configuration, including:

- ring configuration
- ring control features
- station insertion and removal
- initialization
- fault isolation and recovery
- scheduling
- collection of statistics