A 1998 IEEE standard for Gigabit Ethernet over optical fiber and shielded twisted pair (STP).  It provides for full-duplex transmission from switch to end station or to another switch and half-duplex over a shared channel using the CSMA/CD access method.  802.3ab is the counterpart standard for Gigabit Ethernet over Category 5 copper wiring.  See 
Gigabit Ethernet.