For gigabit ethernet over fiber, auto-negotiation negotiates full/half duplex and pause (flow control capabilities). Auto-negotiation for gigabit ethernet, unlike that for fast ethernet, does not negotiate data rate. With Gigabit_Ethernet, it is required piece of the IEEE 802.3z spec. that compliant devices support Auto-Negotiation. Basically Auto-Negotiation in Gigabit_Ethernet covers *Duplex settings: Cisco devices will only support full-duplex,the IEEE 802.3z standard does have support for half-duplex Gigabit_Ethernet. Because of this,duplex is negotiated between Gigabit_Ethernet devices.
