The Fibre Distributed Data Interface (FDDI) is intended for use in a high performance general purpose multi-station network and is designed for efficient operation with a peak data rate of 100 Mbit/s. It uses a Token Ring Architecture with optical fibre as the transmission medium. FDDI provides for hundreds of station operating over an extent of tens of kilometres. FDDI Physical Layer Protocol (PHY) specifies the upper sublayer of the Physical Layer for the FDDI, including the data encode/decode, framing and clocking, as well as the elasticity buffer, smoothing and repeat filter functions. This Abstract Test Suite (ATS) provides a conformance test for FDDI PHY.