This is actually a somewhat complex question to answer as it involves a number of technical details. The most basic answer is that each Category of cable is supposed to meet (or exceed) a specific set of standards, the most significant of which, is the ability to pass all signals up to a particular carrier frequency (or signaling rate). Additional standards have to be met include values for attenuation, near end cross talk (NEXT), ACR, etc.

 

Cat 3	Voice	16 MHz	16 MHz	Yes
Cat 5	Voice, Data (10/100 Mbps thernet)	100 MHz	100 MHz	Yes
Cat 5e	Voice, Data (10/100 Mbps/ Gigabit Ethernet)	100 MHz	200 MHz	Yes
Cat 5 ENH1	Voice, Data (10/100 Mbps/ Gigabit Ethernet)	*	350 MHz	See note 1
Cat 6	Voice, Data (10/100 Mbps/ Gigabit Ethernet)	200 MHz	500 MHz	Yes