o be true, the optical backplane will become a real "nano-network" that is a complete high-speed network deployed on a single PCB using large scale optical integrated circuits both for transmission and detection of backplane signals on the cards and for routing and conditioning of the signal in the backplane itself. In order to acquire more specific information, the reader is encouraged to start from [49-51]. 7.5.1.4 Protocols for Very High-Speed Backplanes Protocols for slow backplanes are not suitable to work at a high transmission speed and a suitable choice has to be done, trading off simplicity with a sufficient performance. A sufficiently diffused consensus exists in avoiding the introduction of a brand new protocol for backplane application, but to rely on an existing solution [46]. Looking at the existing solutions, besides the continuous tendency to improve the per- formance of various PCI standards (see Chapter 6, the section devoted to backplane bus- ses) the XAUI, a 10 Gbit/s bus protocol stack standardized by the 10 Gbit Ethernet task Telecommunication Networks force [52] seems to have all the needed characteristics. The "AUI" portion of the name is borrowed from the Ethernet attachment unit interface. The "X" represents the roman numeral for 10 and implies 10 Gbit/s. The XAUI is designed as an interface extender, and the interface which it extends is the XGMII, the 10 Gbit media-independent interface. The XGMII is the standard interface which interfaces 10 GbE layer 2 and a physical layer device that supports PCS/PMA/PMD. PCS/PMA/PMD are three sublayers in the 10 GbE protocol stack. Physical coding sublayer (PCS): This is the GMII sublayer, which provides a uniform interface to the adaptation layer for all physical media. It uses 8B/10B coding like fiber channel. In this type of coding, groups of 8 bits are represented by 10 bit "code groups." Some code groups represent 8 bit data symbols. Others are con- trol symbols. Carrier sense and collision detect indications are generated by this sublayer. It