How Many Traffic Classes Do We Need In WiMAX?

This paper addresses the issue of multiservice support in IEEE 802.16 or WiMAX networks. The capacity for supporting multiple service classes is indeed important for any access technology where bandwidth is limited, which is the case for IEEE 802.16. The standard currently proposes four traffic classes, and specifies that for uplink traffic, the first one (UGS) receives periodic grants whereas the other three are served via polling. Supporting two different scheduling mechanisms may have a significant impact on the complexity of network interface cards, and therefore on the CAPEX for WiMAX networks. Based on this analysis, the present work investigates whether a 802.16 network that only supports the 3 polling based classes is still capable of providing the QoS levels expected for all types of applications. Both the transfer plane QoS, in terms of latency and jitter, and the command plane QoS, in terms of blocking probability are assessed. In particular, a simple, multiservice call admission control (CAC) mechanism is proposed that significantly improves on a previously proposed CAC mechanism by favouring real time traffic over non real time traffic. The outcome of this study shows that it is indeed possible to support stringent QoS with only polling based traffic classes, and fairly simple traffic engineering mechanisms fully described in the paper.