Cross-layer approach for supporting QoS in IEEE802.11 DCF wireless LANs

Abstract

We propose a cross-layer approach for supporting the quality of service (QoS) of bidirectional real-time applications in IEEE802.11 DCF WLANs. In the proposal, the class-based queueing with the priority queue (PQ) scheduler is exploited in network layer at the access point (AP), and real-time applications are given the highest priority. In order to regulate the best effort traffic sent from wireless stations, we apply the MAC-frame Receive Opportunity Control (ROC), in which the AP intentionally does not return the ACK frame with a given probability when receiving a data frame of best effort traffic from a wireless station. By the intentional failure in acknowledging the receipt of frames, the ROC can control the packet sending rate on a per-station basis. The class-based queueing in network layer and the ROC in MAC layer are jointly utilized with the TCP window control in transport layer to provide the QoS guarantee for bidirectional real-time applications. The proposed cross-layer approach requires only the upgrade of the hardware (or software) of the AP, which is an important advantage over existing proposals on the QoS support in WLANs. The extensive simulation experiments reveal that, when best-effort TCP flows compete with voice conversations (VCs) in a WLAN, the proposed cross-layer approach provides better QoS to VCs than IEEE802.11e and, when best-effort UDP flows compete with VCs, the proposed approach and IEEE802.11e provides the same level of QoS to VCs.