Like Copper Distributed Data Interface (CDDI) and Twisted Pair Distributed Data Interface
(TPDDI), Greenbook is an industry standard of a PMD variant. The Greenbook standard was written in 1991 with the collaboration of Advanced Micro Devices (AMD), Motorola, DEC and Synoptics. The Greenbook standard uses STP cables with 150 Ohmimpedance, in particular the specified IBM cables
Type 1 or Type 1A. A two-stage NRZ-I coding, Non Return to Zero Inverted (NRZ-I), is used as coding. The standarddata connector is the Sub-D connector, optionally also the RJ45 connector. The Greenbook version has restrictions regarding double ring applications.