The auto-negotiation function provides an information exchange method for connected devices. After auto-negotiation is enabled, devices at both ends of a physical link can exchange information and automatically choose the same working parameters. In this way, the two devices can work at the maximum rate supported by both of them. For example, a GE interface connects to an FE interface and their rate is negotiated to 100 Mbit/s, which is the maximum rate supported by both of them.