A survey of MAC based QoS implementations for WiMAX A survey of MAC based QoS implementations for WiMAX

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  • Computer Networks xxx (2009) xxx–xxx


    Contents lists available at ScienceDirect

    Computer Networks

    journal homepage: www.elsevier .com/ locate/comnet

    A survey of MAC based QoS implementations for WiMAX networks

    Y. Ahmet S�ekercioğlu a,*, Milosh Ivanovich a, Alper Yeğin b

    a Department of Electrical and Computer Systems Engineering, Monash University, Australia b Standards and Industry Initiatives Group, Samsung Electronics, Korea

    a r t i c l e i n f o a b s t r a c t

    Article history: Received 9 September 2008 Received in revised form 20 April 2009 Accepted 10 May 2009 Available online xxxx

    Responsible Editor: L. Jiang Xie

    Keywords: Wireless networks WiMAX Quality of Service QoS MAC Media Access Control

    1389-1286/$ - see front matter � 2009 Elsevier B.V doi:10.1016/j.comnet.2009.05.001

    * Corresponding author. Tel.: +61 3 99053503; fa E-mail address: Asekerci@ieee.org (Y. A. S�ekercio URL: http://titania.ctie.monash.edu.au (Y. A. S�eke

    Please cite this article in press as: Y. A. S�ekercio (2009), doi:10.1016/j.comnet.2009.05.001

    We present a comprehensive survey of proposed Quality of Service (QoS) mechanisms in the Media Access Control (MAC) sublayer of WiMAX based wireless networks. QoS support in WiMAX is a fundamental design requirement, and is considerably more difficult than in wired networks, mainly because of the variable and unpredictable characteristics of wire- less links.

    We discuss various QoS architectures, signaling mechanisms and admission control tech- niques proposed in the WiMAX research literature, summarizing the operation of each, and providing comparative evaluations that include advantages and limitations.

    � 2009 Elsevier B.V. All rights reserved.

    1. Introduction

    IEEE 802.16 Wireless Metropolitan Area Network Air Interface Standard [17,19] provides the details of physical layer and Media Access Control (MAC) sublayer of an ad- vanced wireless communication system which aims to build a cost effective, multi-service network with WiMAX (Worldwide Interoperability for Microwave Access) tech- nology. The standard published in 2004 [17] describes the physical and MAC sublayer specifications for fixed wireless access systems supporting multiple services. It consolidates the IEEE Standards 802.16, 802.16a, and 802.16c. The WiMAX Forum describes WiMAX as ‘‘a stan- dards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL (Digital Subscriber Line)”. The newer version of the standard, IEEE 802.16e-2005 [19], published in 2005 con- tains numerous revisions, adds higher layer handovers be-

    . All rights reserved.

    x: +61 3 99053454. ğlu). rcioğlu).

    ğlu et al., A survey of MAC

    tween base stations, as well as support for mobile terminals at vehicular speeds.

    This standard is the outcome of a convergence of the market need and current wireless technological achieve- ments, and is considered a benchmark solution for wireless metropolitan area networks (WMANs), as opposed to Wi-Fi wireless local area networks (WLANs). High data rates, large area of coverage, ease and cost effectiveness of deployments makes WiMAX suitable for a number of applications. This includes connecting multiple Wi-Fi hot- spots, backhaul services and high speed mobile data communication.

    When the aim is to provide a multi-service wireless net- work, a key challenge is the optimal allocation and utiliza- tion of the available raw data transmission capacity of shared wireless links among users and services. In this sur- vey, we use the term ‘bandwidth’ to refer to the data trans- mission capacity of the links. Bandwidth utilization is considered optimum when there is no over- or under-allo- cation of capacity for a particular service type. Data trans- mission requirements depend on the type of services requested by a subscriber, and suboptimal distribution of

    based QoS implementations for WiMAX networks, Comput. Netw.

    mailto:Asekerci@iee.orgAsekerci@ieee.org mailto:Asekerci@iee.orgAsekerci@ieee.org http://titania.ctie.monash.edu.au http://www.sciencedirect.com/science/journal/13891286 http://www.elsevier.com/locate/comnet

  • Table 1 Network performance parameters and their characteristics maintained by QoS.

    Network performance parameter


    Latency Delivery delay of a packet from source to destination

    Jitter Variation in latency

    Reliability The percentage of traffic that should be successfully delivered from source to destination to maintain the service quality

    Data transmission rate

    The amount of data that should be carried from source to destination in a given period of time to maintain the service quality

    2 Y. A. S�ekercioğlu et al. / Computer Networks xxx (2009) xxx–xxx


    available transmission capacity inevitably affects the ser- vice quality. Another factor is latency. Some services have greater tolerance for latency (e.g., FTP or e-mail), while others (like VoIP or video-conferencing) have strict delay bounds. Taking such QoS requirements into account, pack- et flows need to be prioritized via appropriate QoS man- agement and scheduling methods. In broad terms, these always seek to achieve the optimal trade-off between the conflicting goals of maximized user performance and max- imized system utilization.

    WiMAX has a built-in QoS framework for real-time applications as well as data, which can take advantage of its polling architecture, and dynamically adaptable modu- lation in the physical layer. It should be noted that, while the standardized WiMAX QoS framework provides the de- tails about the types of service flows that are supported, it does not explicitly define the actual packet mechanisms for achieving QoS differentiation in the MAC sublayer. As in other standards of this kind, such mechanisms are left open for vendor implementation, as long as they conform to the stated WiMAX QoS framework.

    In Section 2, we provide an overview of this WiMAX- specific QoS framework, and separately consider point- to-multipoint and Mesh Network variants. Our work examines QoS implementation in WiMAX by subdividing the relevant issues into three distinct categories: packet scheduling and admission control (Section 3.1), signalling and internetworking (Section 3.2) and Mesh Network (Sec- tion 4). In each of these three sections we summarize the state of the art research activity along with results, possi- ble implementation, drawbacks and scope for further development. In Section 6, an overall analysis is provided along with our concluding remarks.

    2. QoS and the MAC sublayer of WiMAX networks

    2.1. Definitions of Quality of Service

    There are two broad definitions of Quality of Service (QoS):

    User-Centric QoS is ‘‘the collective effect of service per- formances which determine the degree of satisfaction of a user of the service” [22]. Network-Centric QoS comprises ‘‘the mechanisms that give network managers the ability to control the mix of bandwidth, delay, variances in delay (jitter), and packet loss in the network in order to deliver a network service (e.g., voice over IP)” [9].

    Our paper is primarily concerned with the second defi- nition of QoS, and in the rest of this work, the term QoS shall be taken to mean ‘‘Network-Centric QoS”.

    Network engineers can use the existing resources effi- ciently by implementing a QoS mechanism. Early packet networks typically catered for one service type and all packets were treated equally. There was no QoS differenti- ation or guarantee of reliability, minimum latency, jitter or other performance characteristics (Table 1) for any set of packets. As a result of such a regime, a single bandwidth

    Please cite this article in press as: Y. A. S�ekercioğlu et al., A survey of MAC (2009), doi:10.1016/j.comnet.2009.05.001

    intensive application may cause the performance of other applications to degrade significantly. In a multi-service network, the QoS mechanism has to ensure that it can pro- vide preferential delivery service to packets according to their performance requirements and QoS priority level, while maintaining a high network utilization. QoS differen- tiation can be implemented on either a per-application or per-user basis. With this in mind, QoS mechanisms can broadly be grouped under the following two categories:

    Admission Control determines how and when the traf- fic generated by a given application or user can have access to the network resources. Typically operates at a session or flow timescale (i.e. decisions relate to admission of user sessions or flows). Traffic Control determines how packet marking, sched- uling and shaping (flow rate control) is performed for packet traffic generated by a given application or user. Typically operates at packet timescales (i.e. decisions relate to which packet from which flow is to be trans- mitted next).

    By implementing a well functioning QoS mechanism (or a combination thereof), network engineers can control available network resources to suit a particular require- ment model, and to ensure that critical services are not af- fected by services of lower-priority. The end result is improved user experience, and reduced system cost due to more efficient and targeted use of available resources

    2.2. QoS architecture of WiMAX

    In wireless networks, including WiMAX, QoS support usually resides in the MAC sublayer because of the need to interact with radio resource management and physical layer dynamics. Fig. 1 shows the WiMAX QoS architecture as defined by the standard [19]. The base