Feedback-based bandwidth allocation with call admission control for providing delay guarantees in IEEE 802.11e networks

The 802.11e working group has recently proposed innovative functionalities in or- der to support delay-sensitive multimedia applications, such as real-time voice and video, in Wireless Local Area Networks (WLANs). In particular, the 802.11e pro- posal introduces: (1) the Hybrid Coordination Function (HCF), which is an im- proved channel access method aimed at allocating the ¯rst-hop WLAN bandwidth to delay-insensitive and delay-sensitive °ows; (2) a Call Admission Control (CAC) algorithm for preventing network overloads, which would drastically degrade the service o®ered by the network; (3) and a Signalling scheme for service request and QoS service level negotiation. This paper proposes a dynamic bandwidth allocation algorithm along with a mea- surement based CAC algorithm for providing delay guarantees to real-time media °ows in IEEE 802.11e networks. The dynamic bandwidth allocation algorithm has been designed using classic feedback control; whereas the CAC scheme is an ex- tension of the one proposed by the 802.11e working group because it takes into account the actually used resources rather than the average rates declared by data sources. Both of the schemes exploit the HCF Controlled Channel Access (HCCA) centralized access method. The proposed algorithms have been implemented in the ns-2 simulator and ex- tensive computer simulations have been carried out to assess their validity. Simu- lation results have shown that proposed algorithms protect the WLAN from heavy overloads and guarantees bounded delays for multimedia °ows, whereas, analogous algorithms proposed by the 802.11e working group fail when in the presence of high network loads.