The XLAUI (40 GigabitAttachment Unit Interface) is an interface between the Medium Access Control (MAC) and the Physical Layer (PHY) of 40 Gigabit Ethernet.
With the XLAUI, the limited physical extension of the "40 Gigabit Medium Independent Interface", XLGMII, can be extended to 60 cm. The XLAUI operates with four 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 balanced lanes. Four transmit lanes and four receive lanes are available, which corresponds to 8 line pairs or sixteen signals.