Media Access Layer
The 1 Gbps specification calls for the same CSMA/CD frame format and MAC protocol as used in the 10 Mbps and 100 Mbps versions of IEEE 802.3. Gigabit Ethernet is configured as a LAN switch (full-duplex operation), which provides dedicated rather than shared access to the medium. This is because data transmission and reception at a station can occur simultaneously without interference and with no contention for a shared medium.
With a switching technique, full-duplex operation is employed, and the CSMA/CD protocol is not needed. The Gigabit specification expands on the pause protocol that's defined for 100 Mbps Ethernet by allowing asymmetric flow control. Using the auto-negotiation protocol, a device may indicate that it may send pause frames to its link partner but will not respond to pause frames from its partner.