Tremendous efforts have been spent on devising mechanisms that would provide Quality of Service (QoS) needed by various applications, and network operators have spent a lot of resources trying to fit their networks with differentiated services capabilities. One of the Service Level Agreements (SLA) promising to sell these QoS services is the "triple play" SLA, bundling 3 classes of services targeting voice, data and video. In particular, circuit switched network operators envision the triple play SLA as essential to revenue maintenance, customer retention, and growth. It is their way, through the IP Multimedia Subsystem (IMS) standardization for example, to move all non-IP current and future services, such as voice, onto IP. In this thesis, we propose a "3-tier SLA with automatic class upgrades", an enhancement to the triple play SLA, in that it automatically upgrades lower classes' packets to fill gaps or unused bandwidth in the upper classes. The proposed SLA incorporates a scalable solution to the reordering problem, caused by upgrading lower class-packets to upper classes; the solution does not require per flow state information. We provide a thorough analysis of the QoS performance in terms of goodput, losses and delay of both UDP and TCP sources and show that the proposed SLA maximizes the customer's utilization of the reserved and paid-for bandwidth by maximizing the utilization of the most expensive, better service, upper QoS classes, and provides much greater throughput than the proposed "triple play" model.