An international standard from the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC), specifying general-purpose telecommunications structured cabling systems. The standards include both copper wire and optical fiber inside cabling systems.The standard specifies classes of twisted pair copper performance, as follows: Class A: 100 kHz Class B: 1 MHz Class C: 16 MHz Class D: 100 MHz Class E: 250 MHz Class F: 600 MHz