Abstract
The ever increasing importance of IP networks to home and business users, the steadily growing number of devices and services that run on them and the evolution of Internet towards the global multiservice network of the future make the efficient utilization of resources an issue of great importance and the capability to provide Quality of Service (QoS) an important challenge. It is widely accepted that the current Internet, using the simple best effort service model, is not able to support in a satisfactory fashion emerging services and market demands, such as Voice over IP (VoIP), Videoconferencing and real-time traffic in general. The latter has QoS requirements that the current best effort Internet cannot provide in a resource and, consequently, cost efficient manner, e.g. without massive overprovisioning. Differentiated Services (DiffServ) are seen as the emerging technology to support QoS in IP networks without the inherent scalability problems of Integrated services (IntServ). This is achieved by grouping traffic with similar QoS requirements into a finite number of traffic classes, allocating bandwidth to these classes, and differentiating their forwarding treatment in the network. However, by simply providing forwarding differentiation, DiffServ does not fundamentally solve the problem of controlling congestion. If the amount of traffic injected in a given class is not controlled through admission control, overload situations will occur and all traffic flows in that class will suffer a potentially harsh QoS degradation. The main objectives of this thesis are to investigate issues related to bandwidth allocation for provisioning real-time traffic classes and to propose admission control functions that can prevent overload situations so that the designated QoS guarantees are provided, while at the same time improving the allocated resources utilization under any offered traffic load conditions. We begin by investigating certain bandwidth management related issues with respect to bandwidth allocation and admission control schemes for the support of real-time traffic in DiffServ networks, related to the performance of the schemes as a function of topological placement and assumed multiplexing gains. We validate our study using simulations with the publicly available ns-2 simulator. Taking into account the implications of our bandwidth management study we then proceed to present our approach towards admission control for real-time traffic in DiffServ network domains, covering both the case where the traffic originates and terminates within the same domain (intradomain traffic) as well as the case where the traffic has to traverse a sequence of domains before reaching its destination (inter-domain traffic). By means of simulations we show that our proposed schemes perform very well and that they compare favourably against other schemes found in the literature. Key words; Admission Control, Bandwidth Management, Differentiated Services (DiffServ), Quality of Service (QoS).