An efficient and intelligent resource allocation mechanism is the heart of modern control and management of engineering systems. A dynamic, distributed and online control algorithm is much in need to deal with such Achilles'' heel in today''s increasingly complex systems. To address this problem, we study the ubiquitous network systems and, in particular, WDM optical networks, in the context of coupled channel power resource management, as it represents a rich class of typical nonlinear distributed systems arising from underlying physical constraints. Based previous work on game theoretical approach and direct OSNR optimization technique, this book explores at length link level end-to-end power control models from different perspectives.