The SDDI variant was developed by the companies IBM, Advanced Micro Devices (AMD), Madge and Chipcom and adopted as an industry standard in 1992. The cabling of SDDI is based on the token ring cabling IBM cable type 1A and type 6A. The connector system used is the Sub-D connector( DE-9). The segment length of the STP cables is fixed at 100 m, and the line impedance is 150 ohms. The SDDI coding corresponds to that of the FDDI standard: Non Return to Zero Inverted( NRZ-I) and 4B5B coding.