Abstract
Owing to the different traffic characteristics associated with real-time (RT) and non-real-time (NRT) traffic, ATM networks should provide them with differentiated quality of service (QoS) requirements. RT services such as constant bit rate (CBR) and real-time variable bit rate services (rt-VBR) have become increasingly important owing to the rapid proliferation of multimedia applications. A cell scheduling method capable of handling RT traffic should satisfy QoS requirements including cell transfer delay (CTD), cell delay variation (CDV) and cell loss ratio (CLR). Moreover, NRT services such as non-real-time variable bit rate (nrt-VBR), available bit rate (ABR) and unspecified bit rate (UBR) services are intended for data applications. Although NRT services do not have stringent QoS requirements with respect to CTD and CDV, ATM networks should provide NRT services while considering other criteria to ensure an excellent performance such as CLR, buffer size requirement and service fairness. Therefore, this dissertation presents two novel cell schedulers to provide related QoS requirements for RT and NRT traffic in ATM networks. First, we propose a method, called longest delay beyond expectation (LDBE), to schedule RT and NRT traffic simultaneously. For RT connections, LDBE scheme can minimize CDV, and reduce CLR and CTD, particularly when different CDV tolerance (CDVT) values are applied at each ATM node along the path of a connection. Simulation results demonstrate that the proposed LDBE performs better than other cell scheduling methods regarding these CLR, CDV and CTD criteria for real-time traffic. Furthermore, the LDBE is also suitable for scheduling NRT traffic by providing a low CLR for nrt-VBR and minimizing the CTD for UBR traffic. Second, to provide as much as good performance as possible for NRT traffic, we present another scheduling scheme, called buffer minimized and service fairness (BMSF), to schedule NRT services in ATM networks. Using probability constraints and selecting a connection with the longest buffer size to transmit first allow BMSF to attain satisfactory performance with respect to maximum buffer size requirement, CLR, and service fairness in terms of the maximum buffer size and cell waiting delay. Simulation results demonstrate that BMSF performs better than conventional schemes in terms of these criteria, particularly when NRT services have diverse arrival rates. Thus, the BMSF scheme proposed herein can feasibly schedule NRT services in ATM networks.