The standard defines several classes of twisted-pair(双绞线) copper interconnects, which differ in the maximum frequency for which a certain channel performance is required:
Class A: up to 100 kHz using elements category 1
Class B: up to 1 MHz using elements category 2
Class C: up to 16 MHz using elements category 3
Class D: up to 100 MHz using elements category 5e
Class E: up to 250 MHz using elements category 6
Class EA: up to 500 MHz using elements category 6A (Amendment 1 and 2 to ISO/IEC 11801, 2nd Ed.)
Class F: up to 600 MHz
Class FA: up to 1000 MHz (Amendment 1 and 2 to ISO/IEC 11801, 2nd Ed.)