The BPL, Back PLane board, provides 8 IO slots of expansion for the IPU. Each slot supports the following interfaces; I2C ( 2 Independent buses), 10/100 Ethernet, IEEE1394A Firewire, and High-speed USB2.0. The IOP slots may also include alternative battery packs or power entry modules. The BPL utilizes a Philips PCA9548A to isolate the I2C busses for each slot, thus providing complete isolation between the slots. SMSC USB2504 4-port High Speed USB Hubs are utilized to provide 8 independent 480Mbps channels.