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Quick Reference Guide to Auto-Negotiation

13.4 Auto-Negotiation Priorities


When two Auto-Negotiation devices with multiple capabilities are connected together, they find their highest performance mode of operation based on a priority table. The Auto-Negotiation protocol contains a set of priorities which result in the devices selecting their highest common set of abilities.

The priorities are listed in the table from the highest to the lowest. The full duplex mode of operation is given higher priority than the original (half duplex) Ethernet, since the full duplex system can send more data than a half duplex link operating at the same speed. Therefore if the devices at both ends of the link can support full duplex operation, and if they also both support Auto-Negotiation of this capability, then they will automatically configure themselves for the higher performance full duplex mode.

The table shows that if both devices on the link can support, for example, 10BASE-T and 100BASE-TX, then the Auto-Negotiation protocol at both ends will connect using the 100BASE-TX mode instead of 10BASE-T.


Quick Reference Guide to Auto-Negotiation - 09 SEP 95
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