Auto Negotiation

Today, Ethernet uses transmission rates of 10, 100 or 1000 Mbit/s in half duplex or in full duplex mode. However, not all devices support all possible settings. This particularly makes the optimum network configuration more difficult for networks using twisted pair cables of the same kind and components which can be used with 10 Mbit/s or 100 Mbit/s in half duplex or in full duplex mode as desired. Imperfect configurations can lead to link errors or at least to performance losses because the maximum possible transmission rate is not used.

Due to this, the auto negotiation functionality (in the past also called Nway) has been established with the introduction of Fast Ethernet. With this functionality, the stations agree on the highest possible transmission rate and, if possible, full duplex operation. Then, all subscribers on the network configure themselves optimally.

However, problems could arise if one component in one segment is configured manually, i.e. if it has been set to a fixed transmission rate and mode and the auto negotiation function has been switched off. In this case, a device operating in auto negotiation mode informs the manually configured device about its possible settings but does not receive any response.