HCD's XENPAK is a standardized form factor for 10 Gb/s fiber optic transponders that is used for data transfer rates from 10.3 Gb/s to 10.5 Gb/s. It is protocol-specific: Either 10G Ethernet or 10G Fibre Channel versions are available. XENPAK transponders are used in datacom optical links only (not telecom). Its electrical interface to the host board is also standardized and is called XAUI (4 x 3.125 Gb/s).