There are some characteristics that all of the gigabit implementations share in common:
On initialization or reset, a gigabit interface performs an Auto-Negotiation procedure with its link partner to establish the ground rules for communication.
After initialization, at the physical level, signals are transmitted concurrently in both directions on a continuous basis.
These features are described in the sections that follow.
All the gigabit technologies support the exchange of link parameters using an Auto-Negotiation Protocol. The following is true of Auto-Negotiation:
It confirms that both ends of the link can operate at 1000Mbps.
It enables each interface to announce whether it wishes to operate ...