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American Journal of Operations Research, 2012, 2, 382-390 doi:10.4236/ajor.2012.23046 Published Online September 2012 (http://www.SciRP.org/journal/ajor)

Admission and Traffic Control Schemes Suitable for QoS Applications in WLAN Systems
Takefumi Hiraguri1, Takayuki Kimura1, Toshiyuki Ogawa2, Hiroshi Takase1, Akira Kishida3, Kentaro Nishimori4
2 1 Nippon Institute of Technology, Saitama,Japan Doctoral Program in Graduate School of Electrical Engineering, Nippon Institute of Technology, Saitama, Japan 3 NTT Access Network Service Systems Laboratories, Yokosuka, Japan 4 Graduate School of Science & Technology, Niigata University, Niigata, Japan Email: hira@nit.ac.jp

Received July 23, 2012; revised August 27, 2012; accepted September 7, 2012

ABSTRACT
This paper proposes the useof admission and traffic control schemes for real-time applications. The admission control scheme determines the admission of high-priority real-time applications such as voice and video streams in terms of their bandwidth utilization time (medium time), whereas the traffic control scheme maintains the communication quality of applications permitted admission by restricting other traffic. Owing tothe use of contention-based access, a conventional scheme without admission control will degrade the communication quality when the number of terminals using high-priority applications increases. Moreover, only the capabilities (i.e., frame and sequence procedures) of admission control are defined in the IEEE 802.11e standard; the detailed usage in terms of the application characteristics is notspecified, and it may be difficult to achieve a sufficient level of quality of service (QoS). The proposed schemes achieve the optimum QoS for actual services. The software used in the proposed schemes was implemented into hardware at the access point, and was evaluated experimentally. Based on the evaluation results, excellent performances with high QoS applications were obtained. Keywords: QoS;IEEE 802.11; Admission Control; Traffic Control; EDCA

1. Introduction
Wireless local area network (WLAN) services providing Internet access have recently become ubiquitously available, such as in the home or office, on moving trains, and at transportation platforms and airports. In these types of environments, a variety of applications demanding realtime communication capability, such as voiceand video streaming, have emerged for WLANs, in addition to traditional best-effort applications such as Web access and email, as shown in Figure 1. Therefore, WLAN services need to support both real-time and best-effort traffic with limited wireless bandwidth. For such a wide variety of applications, a wireless access control called an Enhanced Distributed Channel Access (EDCA) mechanism, asspecified in the IEEE 802.11e standard [1], can prioritize and differentiate the quality of service (QoS) between real-time and best-effort traffic. For real-time traffic, it is desirable to ensure a stable QoS during the entire communication process. However, the quality of realtime traffic when using EDCA may be not ensured when the number of high-priority flows increases, as EDCA is
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based on contention access [2]. Therefore, even when using EDCA, when the bandwidth utilization is saturated, the quality of the communication will degrade if new flows start making connections. Hence, an admission control function is provided in the IEEE 802.11e standard. This admission control function decides whether to accept or reject a connection. If the QoS of a previouslyFigure 1. WLAN network scenarios. AJOR

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established flow is degraded, it is reasonable to deny the flow and avoid further deterioration. Accordingly, an admission control that can determine whether the QoS of a flow is adequate before communication begins will be an effective means of guaranteeing the QoS for real-time traffic in EDCA. As another method for...