||With the development of multimedia applications, e.g., IP phone, Video Conferencing, through the Internet, the ability to provide Quality of Services (QoS) is becoming a crucial consideration in high speed packet switch design. There are two ways of providing QoS in a high-speed packet switch: Integrated Services and Differentiated Services. Differentiated Services are proven to be more practical and scalable. In this thesis, we propose using a virtual output queued crossbar switch with iSLIP scheduling algorithm, together with distributed, independent QoS schedulers in each virtual output queue to enforce differentiated services. In the study we propose 2 such QoS schedulers, the first one is Enhanced Wait Time Priority (NWTP) that enforces proportional average delay for non real time traffic, the second one named Weighted Earliest Due Date First with Tail Extrapolation DVR Estimation (WEDF-TEE) that enforces proportional deadline violation rate (DVR) for real time traffic. It is possible to incorporate both kinds of schedulers into the same switch. NWTP is a modified version of Wait time priority (WTP) scheduler that adjusts the scheduling parameter with measured load. We also modify the WEDF with non-window based DVR estimator into WEDF-TEE that uses window based DVR estimator to adapt to abrupt change of traffic load, and uses tail extrapolation to shorten the monitor period in DVR estimation. From simulations studies on the ability to provide various QoS, the performance of QoS in NWTP is slightly better than WTP, and WEDF-TEE processes the improvements described above.