In this book different researches on communication networks will be studied: 1.The WAN protocols with their different ring topologies. 2.The limitations of bit rate and losses in single mode fiber. 3.Ultra wideband system that improved gain-flatness of a Raman amplifier while maintaining a wide gain-bandwidth and a high gain-output power in WDM systems. 4.An 50 nm gain-flattened ultra wide band erbium-doped silica fiber amplifier for high capacity WDM optical communication systems. 5.Suitable packet switching Metropolitan Area Backbone Network to interconnect twenty-six locations. 6.MANs that support high data transmission rates and interconnectivity of devices. 7.An extremely large 3-dB gain-bandwidth of 83 nm (185.8-195.3 THz) using Raman amplifier. 8.Clutter Map-Constant False Alarm Rate is evaluated to determine the signal-to-clutter ratio required achieving a particular probability of detection in clutter environments whose amplitude statistics are modeled by the Rayleigh distribution. 9.An Improved nonlinear equalizer with Perturbation algorithm. 10.Multicarrier-Code Division Multiple Access (MC-CDMA) lying in In-Place Wavelet Transform (IP-WT) algorithm.