There are two standards of Gigabit Ethernet based on the twist copper, the 1000BASE-T and 1000BASE-TX. Please see the attachment below!
Gigabit Ethernet 1000BASE-T, the transmission speed is 1000M bps, 1G bps, based on four pairs of twist cable, and the full duplex communication of each pair which transfers signals bidirectional. It employs the complex coding technology which has higher cost, and the transmission width is 100MHz. For each of four pairs transfer signal bidirectional, there is higher NEXT, so needs higher efficiency of coding technology and higher SNR. In other words, 1000BASE-T only can operate on CAT 5E or CAT 5 system which has better performance.
1000BASE-TX, the transmission speed is 1000M bps, 1 G bps, based on four pairs of twist-pair too, but the semi-duplex communication of two pairs sending and two pairs receiving( similar to 100BASE-TX ). For each pair of transmission signal is not bidirectional, there is lower NEXT, so needs simple coding mode and simple circuit. As its transmission width exceeds 100MHz, so 1000BASE-TX can only operates on CAT 6, but not CAT 5E and CAT 5 system.
How to select the products of cabling system? We should considerate some aspects. One of the most factors is the network upgrade. Nobody can forecast the transmission speed in future 3 years, 5 years and 10 years, is the same as 5 years ago, nobody could forecast the development of network speed nowadays. So how to invest on the network system, how to leave redundancy on the network upgrade, we should considerate many circumstances.