DATA:
Cat5:
Cables and connecting hardware with transmission characteristics up to 100 MHz
Cat 5e:
Cables and connecting hardware with transmission characteristics up to 100MHz. Differing from Category 5 by having 3 dB tighter NEXT requirements and additional requirements for PS NEXT, ELFEXT, and PS ELFEXT
CAT 6:
Cables and connecting hardware with transmission characteristics up to 200MHz.

Demands for Cat 5 Cable:
What created the demand for Category 5 cables?

• The move from application dependent cable (i.e. IBM types) to generic cabling (UTP).
• Cost advantage of UTP cabling over Coax or SRP cabling.
• The rise in personal computer (PC usage, couple with its increase in power and speed.
• The need to interconnect different systems, enabling ease of use and the need for increased cabling flexibility for moves, adds and changes.
• Demand increases placed on copper twisted pair cables for enhanced transmission characteristics. 
•  Desire for a cable plant which can keep pace with technology advances, such as 100 Mbps (TP-PMD) and Gigabit Ethernet (IEEE 802..ab).
• Development of Generic Cabling Standards, such as TIA/EIA-568-A, ICEA, NEMA and ISO/IEC 11801.

VOICE:
Cat3:
Cables and connecting hardware with transmission characteristics up to 16 MHz
Cat 5e:
Cables and connecting hardware with transmission characteristics up to 100 MHz