Auto-Negotiation takes place using Fast Link Pulse (FLP) signals. These signals are a modified version of the Normal Link Pulse (NLP) signals used for verifying link integrity, as defined in the original 10BASE-T specifications. The FLP signals are generated automatically at power-up, or may be selected manually through the management interface to an Auto-Negotiation device.
The Fast Link Pulse signals are designed to coexist with NLP signals, so that a 10BASE-T device that uses NLP signals will continue to detect the proper link integrity even when attached to an Auto-Negotiation hub that sends FLP signals. Like the original 10BASE-T link pulse, the FLP signals take place during idle times on the network link and do not interfere with normal traffic. Note that both Normal Link Pulses and Fast Link Pulses are specified only for twisted-pair media using eight-pin connectors, such as 100BASE-TX over unshielded twisted-pair. This means that network devices and repeater ports linked over fiber optic segments cannot participate in Auto-Negotiation.
The FLP signals are used to send information about device capabilities. The Auto-Negotiation protocol contains rules for device configuration based on this information. This is how a hub and the device attached to that hub can automatically negotiate and configure themselves to use the highest performance mode of operation.
The Auto-Negotiation feature is optional, and therefore the Auto-Negotiation protocol is designed to work with 100BASE-T interfaces that do not support Fast Link Pulses and Auto-Negotiation as well as older 10BASE-T interfaces that were built before Auto-Negotiation existed. The Auto-Negotiation system includes an optional management interface that allows you to disable Auto-Negotiation, or to manually force the negotiation process to take place. The management interface allows you to manually select a specific operational mode for a given hub port.
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