The Differentiated Service Architecture (DiffServ) is currently a popular research topic as a low-cost method to provide Quality of Service to the different applications in the Internet. This paper addresses the definition and deployment of specific network services in a DiffServ environment. Each network service is appropriate for a specific type of traffic and is realized through its own network mechanisms, which are the Traffic Classes. The focus of the paper is the services appropriate for real-time delay-sensitive applications such as voice and video. Different traffic control algorithms are studied for the implementation of the proposed services. Simulation results show that the proposed traffic control mechanisms provide hard performance guarantees to different flows.