4D-PAM5 encoding in Gigabit Ethernet

Bandwidth of twisted pair cables (Mbps) is dependent which encoding is used. Manchester encoding was used for 10 Mbps Ethernet.

Gigabit Ethernet (1000 Mbps) uses an encoding called as PAM-5 encoding, specifically 4D-PAM5. 4D-PAM5 uses five voltages. Four voltages for data transmission the fifth voltage for error correction. Since four different voltages are there, four different combinations of data can be represented on the wire instead of just one. Those are "00", "01", "10" and "11".

In Ethernet (10 Mbps) and FastEthernet (100 Mbps) different pairs of wires are used to transmit and receive data. But in Gigabit Ethernet (1000 Mbps), same pairs of wires are used to transmit and receive data. Simultaneous transmission and reception of signals on one pair of wire is possible here.

Finally, instead of using just four wires out of eight wires available in twisted pair cable, Gigabit Ethernet uses all eight wires available to achieve 1 Gbps bandwidth speed.