Prioritized support of different traffic classes in IEEE 802.11e wireless LANs Nikos Passas * , Dimitris Skyrianoglou, Panagiotis Mouziouras Department of Informatics and Telecommunications, University of Athens, Greece Available online 6 April 2006 Abstract IEEE 802.11e is an amendment to the popular 802.11 standard that defines quality of service mechanisms to support sensitive appli- cations, such as voice and video. An important component of these mechanisms is the traffic scheduler, an entity that decides on the channel allocation among different stations. This paper proposes a scheduling algorithm for IEEE 802.11e, referred to as P-ARROW (Prioritized and Adaptive Resource Reservation over Wireless), that effectively handles multimedia traffic by utilizing the formal spec- ification of each traffic stream. Using a single ‘‘priority factor’’ parameter, the scheduling can vary between strict prioritization and pure- ly deadline-driven allocation. Performance evaluation results extracted from an advanced simulation model, show that P-ARROW is very efficient in supporting the desired level of service differentiation and prioritization among different traffic classes. Ó 2006 Elsevier B.V. All rights reserved. Keywords: IEEE 802.11e; Medium access control; HCCA; Traffic scheduling 1. Introduction The IEEE 802.11 standard is considered today the dom- inant technology for wireless local area networks (WLANs). Its legacy version [1] provides transmission speeds up to 2 Mbps, while recent improvements in the physical layer, such as 802.11g [2], increase this figure to several tens of Mbps, facilitating the use of broadband applications. A number of amendments to the standard, such as 802.11i [3] and 802.11f [4], provide increased func- tionality in areas not covered by the first standard, namely security and fast handover. 802.11d [5] addresses the restrictions of different regulatory domains to eliminate the need for country-specific products. Concerning Quality of Service (QoS) provision, the major improvement comes from amendment 802.11e, which targets one of the main weaknesses of the 802.11 Medium Access Control (MAC) protocol, i.e., the inability to provide differentiated treat- ment to different traffic classes. The mandatory access mode in 802.11, referred to as Distributed Coordination Function (DCF), provides con- tention-based access to the wireless medium, while the optional Point Coordination Function (PCF) allows con- tention-free access, but has no means to control the time allocated to each mobile station (STA). In IEEE 802.11e [6], the QoS mechanism is supervised by the Hybrid Coor- dinator (HC), an entity that implements the Hybrid Coor- dination Function (HCF). The HC is typically located at the Access Point (AP), and utilizes a combination of a pri- oritized contention-based scheme, referred to as Enhanced Distributed Coordination Access (EDCA), and a polling- based scheme, referred to as HCF Controlled Channel Access (HCCA), to provide QoS-enhanced access to the wireless medium. The main feature of HCCA is that it can provide parameterized QoS services to different traffic streams, based on their traffic specifications and QoS requirements. To perform this operation, the Hybrid Coor- dinator incorporates a scheduling algorithm that decides on how to allocate the available radio resources to the 0140-3664/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.comcom.2006.03.010 * Corresponding author. Tel.: +30 210 7275651; fax: +30 210 7275601. E-mail address: passas@di.uoa.gr (N. Passas). www.elsevier.com/locate/comcom Computer Communications 29 (2006) 2867–2880