The application area that motivates this dissertation Is e cient resource allocation and control in communication networks with Quality of service (QoS) requirements.Though a natural modelling framework of packet-based networks is provided through discrete-event systems, classical queueing theory becomes impractical to deal with the huge volume of events of high-speed networks with di erent levels of service. In this dissertation, we use Stochastic Fluid Models(SFM)for control and optimization (rather than performance analysis)of communication networks nodes, focusing on problems of bu er...