Auto-Negotiation
When first installed, a 100BaseTX Fast Ethernet interface negotiates with
the destination device to which it is attached. The negotiation process occurs
automatically, and involves each device notifying (advertising to) the other what
connection capabilities it can support, including line speed and whether the circuit is
half- or full-duplex. The devices determine what common set of capabilities both support
and then, from that common set, select the connection that provides the greatest
throughput. The common set of capabilities is typically referred to as the "highest
common denominator." No connection is established if the two devices do not support
at least one common line speed and duplex setting combination.
For example, a Fast Ethernet interface on a VNswitch module may support
only a full-duplex circuit on either 10BaseT or 100BaseX cable. The device to which it is
connected supports a full-duplex circuit on only 100BaseX cable. The two devices
"agree" to use a full-duplex circuit at 100 Mb/s, since both support 100BaseX
cable, which provides greater bandwidth. |