On the Impact of IEEE 802.16 Bandwidth Request-Grant Mechanisms on TCP

In IEEE 802.16 networks, bandwidth allocation is centralized at the base station (BS). For the uplink traffic, data transmission is scheduled after the BS processes bandwidth requests (BW-REQs) sent by mobile stations (MSs). In this paper we focus on the multicast/broadcast polling method, where MSs send their BW-REQs during contention periods. Contention-based polling is deemed suitable for Best-Effort TCP flows, since the latter have less stringent needs, in terms of delay and throughput, than traffic carried by other classes of service. We propose a novel analytical model for Best-Effort TCP performance over 802.16 networks. This model explicitly considers the impact of the uplink request/grant mechanism, including the influence of bandwidth-perception mismatch at the BS. The effect of MAC-layer parameters, such as the MAC queue length, is also studied. The accuracy of the model is verified by means of ns-2 simulations.