1000BASE-T capable PCI-X network interface card from Intel
1000BASE-T (also known as IEEE 802.3ab) is a standard for gigabit Ethernet over copper wiring.
Each 1000BASE-T network segment can be a maximum length of 100 meters (328 feet), and must utilize “Category 5″ cabling at a minimum. Category 5e cable or Category 6 cable may also be used and is often recommended.
1000BASE-T requires all four pairs to be present and is far less tolerant of poorly installed wiring than 100BASE-TX.
If two Gigabit devices are connected through a non-compliant Cat5 cable with four pairs, many FCS errors and retransmissions may occur. If two Gigabit devices are connected through a non-compliant Cat5 cable with two pairs only, negotiation takes place on two pairs only, so the devices successfully choose ‘gigabit’ as the Highest Common Denominator (HCD), but the link never goes up. Most gigabit physical devices have a specific register to diagnose this behaviour. Some drivers offer an “Ethernet@Wirespeed” option where this situation leads to a slower yet functional connection[5].
Autonegotiation is a requirement for using 1000BASE-T[6] according to the standard. At least clock source has to be negotiated, as one has to be Master and the other Slave.
Several physical layer devices and drivers will allow you to force 1000 Mbit/s full duplex to eliminate autonegotiation issues. In this non-standard use, the designer must assure only one peer is configured as the clock master. Forcing duplex settings or turning off autonegotiation can become a permanent choice in a large installation, because the forced node is now non-compliant. When deployed, this arrangement will mean that any future ethernet switch must be forced as well. A proper solution would be to realign or remove the non-compliant nodes rather than making newly-added nodes non-compliant.
