Techopedia explains
Fiber Distributed Data Interface (FDDI)
FDDI networks, which are designed for geographically large-scaled organizations that support thousands of end users, operates in the OSI model's physical and media access control (MAC layers).
The American National Standards Committee (ANSC) formally standardized FDDI as the best linking medium for local area networks (LAN), which use FDDI for long-distance communication.
FDDI also is used by single and multi-mode fiber optic, which have different communication mechanisms. Multi-mode fiber optic uses a lead generation device, whereas single-mode fiber optic uses laser for data transmission only.