The CAUI (100 GigabitAttachment Unit Interface) is the electrical interface between the Medium Access Control (MAC) and the Physical Layer (PHY) of 100 Gigabit Ethernet, which is implemented in the transceiver modules. With the CAUI interface, the limited physical extension of the "100 Gigabit Medium Independent Interface", CGMII, can be extended to 60 cm.
Depending on the interface, the CAUI operates with ten parallel lanes and 64B66B coding. Each individual lane has an effective data rate of 10 Gbit/s and, because of the 64B66B coding, a resulting baud rate of 10.3125 GBaud. Differential signals are transmitted on the symmetrical lanes. Ten transmit lanes and ten receive lanes are available, which corresponds to 20 line pairs or 40 signals.
With 100GBase-ER4 and 100GBase-LR4 there are four lanes, each transmitting 25 Gbit/s, with 100GBase-SR10 there are ten lanes with 10 Gbit/s in each direction.