s differential pairs to provide dif- ferential common mode rejection. 7.5.1.1.4 Receiver The use of receiver equalization allows a channel to operate error free, with an almost closed eye, before equalization [41]. Decision feedback equalizers (DFEs) are generally used for this application (see Chapter 6 for the description of these equalizers used in optical transmission). Telecommunication Networks The performance of the DFE improves as the number of taps increases allowing designers to trade off performance with power consumption and design complexity (that frequently is proportional to cost). 7.5.1.2 Optical Backplane Since the key issue of switching network element backplanes is the transmission of high-speed signals, it is spontaneous to consider the opportunity to use optical trans- mission [41,42]. As a matter of fact, the need of using special materials with particular low losses and low parasitic capacity and the need of a more accurate process with respect to standard PCB fabrication increase the cost of very high capacity backplanes based on copper busses, creating a condition in which optical transmission can be competitive also from a price point of view. Last, but not least, optical backplanes seem to be able to concentrate more functions with respect to the electrical one, due to the smaller transmission problems. In any case, also this option presents a number of issues. The adoption of optical interconnects for use in standard systems environment would have to meet the following requirements: Optical would need to coexist with copper on a substrate in order to draw power and slow speed management interfaces [43]. Optical connectors would have to operate under current environmental condi- tions in the chassis. Optical backplane and, in particular, optical connectors would need to be resilient, being a critical part for the whole equipment availability [44]. The solution would have to be cost-effective. From the aforementioned list of qualitative requirements the two critical elements for the succ