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13.5 Examples of Auto-Negotiation

One End of Link Without Auto-Negotiation

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If Auto-Negotiation only exists at one end of the link, the Auto-Negotiation protocol is designed to detect that condition and respond correctly using a mechanism called Parallel Detection. For example, if a dual-speed 10/100 Ethernet interface with Auto-Negotiation is connected to a 10BASE-T hub that does not have Auto-Negotiation, the interface will generate FLPs but will only receive NLPs from the 10BASE-T hub. The Auto-Negotiation protocol in the interface will detect the presence of Normal Link Pulses and automatically place the interface in 10BASE-T mode.

Similarly, when an Auto-Negotiation hub with multiple capabilities in its ports is connected to an interface that only supports 100BASE-TX and is not equipped with Auto-Negotiation, the Auto-Negotiation protocol will set the hub port to operate in 100BASE-TX mode. Parallel Detection works for 10BASE-T as well as 100BASE-TX and 100BASE-T4 devices without Auto-Negotiation. Parallel Detection for 100BASE-TX/T4 checks the link signals being received for Link Monitor characteristics that are specific to a given mode. If Parallel Detection determines that exactly one mode of Link Monitor is satisfied by the incoming link signals, it connects to that mode.

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Quick Reference Guide to Auto-Negotiation - 25 MAY 96

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