Which type of Ethernet is denoted by 802.3ab?

The designation 802.3ab refers specifically to the 1000BASE-T standard, which is part of the IEEE 802.3 family of networking standards. This standard describes a method for transmitting data at 1 Gbps over twisted-pair copper cabling, specifically using Category 5 (Cat 5) cabling or better. 1000BASE-T utilizes all four twisted pairs in the cable for data transmission, enabling full-duplex communication, and is widely used in local area networks (LANs).

To give further context, the other options represent different Ethernet standards with varying speeds and cabling requirements. 10BASE-T and 100BASE-T refer to slower standards, transmitting data at 10 Mbps and 100 Mbps respectively. 10GBASE-T, on the other hand, describes a standard that supports 10 Gbps over twisted-pair cabling but falls outside of what is covered by 802.3ab. Thus, 802.3ab is unequivocally associated with 1000BASE-T, confirming that the correct answer is indeed about Gigabit Ethernet transmission.