Auto Negotiation

￿Enables each two Ethernet devices to exchange information about their capabilities

￿Signal rate, CSMA/CD, half- or full-duplex

￿Using Link-Integrity-Test-Pulse-Sequence

￿Normal-Link-Pulse (NLP) technique is used in 10BaseT to check the link state (green LED)

￿10 Mbit/s LAN devices send every 16.8 ms a 100ns lasting NLP, no signal on the wire means disconnected

(C) Herbert Haas 2005/03/11

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Several Ethernet operating modes had been defined, which are incompatible to each other, including different data rates (10, 100, 1000 Mbit/s), half or full duplex operation, MAC control frames capabilities, etc.

Original Ethernet utilized so-called Normal Link Pulses (NLPs) to verify layer 2 connectivity. NLPs are single pulses which must be received periodically between regular frames. If NLPs are received, the green LED on the NIC is turned on.

Newer Ethernet cards realize auto negotiation by sending a sequence of NLPs, which is called a Fast Link Pulse (FLP) sequence.

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