Experimental Validation of Middleware-based QoS Control in 802.11 Wireless Networks (Invited paper) Wenbo He * wenbohegcs.uiuc.edu Hoang Nguyen t hnguyen5guiuc.edu Klara Nahrstedt klaragcs.uiuc.edu Department of Computer Science University of Illinois at Urbana-Champaign Champaign, IL, 61801, United States Abstract Due to the shared medium nature of wireless networks, the uncertainties caused by collisions and interferences make the Quality of Service (QoS) issue harder than its wired counterpart. Many publications have been focused on network and MAC layer design to address the QoS issue in wireless networks. However, the middleware design has been overlooked For QoS support, we need to map the QoS requirement of applications to performance metrics. Mid- dleware is the place we do such mapping. In this paper, we use packet level priority to bridge the QoS requirements andperformance. Through middleware priority adaptation, we aim to make the premium traffic meet the QoS require- ment. we study the impact of middleware priority adap- tation on QoS performance, including bandwidth and end- to-end delay, via experiments with multimedia flows over IEEE 802.11 environment. Our evaluation is based on ex- periments in both WLAN and ad hoc network environment. Our investigation shows that middleware adaptation is effi- cient in assisting to achieve QoS in many scenarios. 1. Introduction Multimedia services over wireless ad hoc networks or multihop WLAN are becoming pervasive in applications such as music sharing, voice telephony and others. The scenarios where multimedia applications and ordinary data traffic co-exist on wireless ad hoc networks or multihop wireless LAN, include, but are not limited to: * In a neighborhood community, people play games, share music or movies in a wireless mesh network, while other services such as email, ftp, and www are being used simultaneously. * In a university auditorium, the audio or video record- ing the speakers' speech or activities are sent to the storage through multihop wireless links. Meanwhile, the audience is sending or receiving email, browsing websites using the same multihop WLAN resources. As the demand of multimedia services over 802.11 wire- less networks increases, we are facing the challenge of of- fering premium applications with Quality of Service (QoS) requirements over wireless networks, since the bandwidth of a wireless link is limited, unpredictable, and the channel capacities and error rates are time-varying in comparison to wired networks. The existing protocols follow several di- rections to achieve the goal of QoS in wireless networks: The first type of QoS protocols on wireless networks is based on admission control and conflict resolution. [1] provides an admission control scheme according to the re- source prediction by probing method. The uncertainties of wireless network may cause false admissions, since admit- ting new traffic increases contention in the shared channel due to the admission control. [2] proposes an admission control and dynamic bandwidth management scheme that provides fairness and a soft rate guarantee without using distributed MAC-layer weighted fair scheduling. [3] ad- dresses the contention-aware admission control so that the admitted flows in the network do not exceed network capac- ity. [4] addresses the QoS in wireless networks by utility- based resource allocation. The second type of QoS protocols for wireless net- works is based on MAC layer scheduling, including TDMA scheduling protocols [5] [6] and IEEE802.11 based proto- cols [7]. QoS over TDMA based protocols is obtained by assigning different time slots to different nodes within the same contention range. TDMA based MAC protocols re- 1-4244-0425-8/06/$20.00 ©2006 IEEE