A block diagram of the 10G/25G Ethernet Subsystem with Auto-Negotiation (AN) and Link Training (LT) is shown in the following figure.
The auto-negotiation function allows an Ethernet device to advertise the modes of operation it possesses to another device at the remote end of a backplane Ethernet link and to detect corresponding operational modes the other device might be advertising. The objective of this auto-negotiation function is to provide the means to exchange information between two devices and to automatically configure them to take maximum advantage of their abilities. It has the additional objective of supporting a digital signal detect to ensure that the device is attached to a link partner rather than detecting a signal due to crosstalk. When auto-negotiation is complete, ability is reported according to the available modes of operation.
Link Training is performed after auto-negotiation if the Link Training function is supported by both ends of the link. Link Training is typically required due to frequency-dependent losses which can occur as digital signals traverse the backplane. The primary function of the Link Training block included with this core is to provide register information and a training sequence over the backplane link which is then analyzed by a receiving circuit (part of the transceiver). The other function of the Link Training block is to communicate training feedback from the receiver to the corresponding transmitter so that its equalizer circuit (part of the transceiver) can be adjusted as required. The decision-making algorithm is not part of this core. When auto-negotiation and Link Training are complete, the datapath is switched to mission mode (the PCS), as shown in the preceding figure.