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  • 400 J. OPT. COMMUN. NETW./VOL. 2, NO. 7 /JULY 2010 Dhaini et al.

    This article has been accepted for inclusion in a future issue of this journal. Content is final as presented.

    WiMAX-VPON: A Framework ofLayer-2 VPNs for

    Next-Generation Access NetworksAhmad R. Dhaini, Pin-Han Ho, and Xiaohong Jiang

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    AbstractThis paper proposes WiMAX-VPON, anovel framework for establishing layer-2 virtual pri-vate networks (VPNs) over the integration of WiMAXand Ethernet passive optical networks, which haslately been considered as a promising candidate fornext-generation fiber-wireless backhaul-access net-works. With WiMAX-VPON, layer-2 VPNs support abundle of service requirements to the respective reg-istered wirelesswired users. These requirements arestipulated in the service level agreement and shouldbe fulfilled by a suite of effective bandwidth manage-ment solutions. To achieve this, we propose a novelVPN-based admission control and bandwidth alloca-tion scheme that provides per-stream quality-of-service protection and bandwidth guarantee for real-time flows. The bandwidth allocation is performedvia a common medium access control protocol work-ing in both the optical and wireless domains. Anevent-driven simulation model is implemented tostudy the effectiveness of the proposed framework.

    Index TermsEthernet PON (EPON); IEEE 802.16(WiMAX); QoS; Virtual private network (VPN).

    I. INTRODUCTION

    T he massive increase of broadband access applica-tions with varying QoS requirements, such as In-ternet Protocol television (IPTV) and video on demand(VoD), has significantly contributed to the evolution ofnext-generation wired and wireless networks.

    Lately, the integration of Ethernet passive opticalnetworks (EPONs) and WiMAX has been presented asan attractive broadband access network (BAN) solu-tion [13]. The complementary features of these net-works has motivated interest in using EPON as a

    Manuscript received January 19, 2010; revised May 10, 2010; ac-cepted May 18, 2010; published June 9, 2010 Doc. ID 122862.

    A. R. Dhaini (e-mail: [email protected]) and P.-H. Ho (e-mail:[email protected]) are with the Department of Electricaland Computer Engineering, University of Waterloo, Canada.

    X. Jiang (e-mail: [email protected]) is with the School of SystemsInformation Science, Future University-Hakodate, Japan.

    Digital Object Identifier 10.1364/JOCN.2.000400

    1943-0620/10/070400-15/$15.00

    Authorized licensed use limited to: University of Waterloo. Downloaded on

    ackhaul to connect multiple dispersed WiMAX basetations (BSs) [1,4]. More specifically, EPON andiMAX perfectly match in terms of capacity hierar-

    hies. EPON, for instance, supports a total of 1 Gbpsandwidth in both downstream and upstream direc-ions, shared by typically N32 remote optical net-ork units (ONUs) [5]. On average, each ONU ac-

    esses 70 Mbps bandwidth, which matches the totalapacity offered by a WiMAX BS over a 20 MHz chan-el as well [6]. The integration can take advantage ofhe bandwidth benefit of fiber communications andhe non-line-of-sight (NLOS) features of wireless com-unications. In addition, it enables integrated re-

    ource allocation and packet scheduling paradigmshat help better support the emerging quality-of-ervice (QoS) services, as well as to improve the over-ll network throughput. Finally, the integration canelp realize fixed-mobile convergence (FMC) by sup-orting mobility in the broadband access, thereby sig-ificantly reducing network operational costs [1].

    The EPON-WiMAX integration has been well re-orted in the past few years [1,2]. Nonetheless, build-ng up virtual private networks (VPNs) directly on thentegration has never been investigated in the litera-ure to our knowledge. In addition, the already pre-ented upstream bandwidth allocation schemes areoo trivial [2,79] and are neither able to provide per-ow QoS protection nor able to offer end-to-end [fromhe subscriber station (SS) to the optical line terminalOLT)] bandwidth guarantee, features that are essen-ial for establishing VPN tunnels over EPON-WiMAX.

    . Supporting VPNs Over EPON-WiMAX

    VPNs have been known as a superb technology thatre provisioned over a public or third-party networknfrastructure and are positioned to provide dedicatedonnectivity to a closed group of users with a stronger-flow QoS guarantee [10].

    VPNs over EPON-WiMAX could be deployed to sup-ort mission-critical (police, health care, fire-fighting)overnmental or corporate systems in order to achieve

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    Dhaini et al. VOL. 2, NO. 7 /JULY 2010/J. OPT. COMMUN. NETW. 401

    This article has been accepted for inclusion in a future issue of this journal. Content is final as presented.

    a secure high-speed and efficient wireless connectivityamong registered users in rural and urban areas.

    Building up layer-2 VPNs is most suitable when anEPON-WiMAX integrated network is installed. This isdue to their support for premium services withcustom-designed control, diverse QoS requirements,and security assurance, features that can be intrinsi-cally provided by the layer-2 medium access control(MAC) protocols [11]. Such VPNs are referred to aslayer-2 VPNs in the sense that they are built upon thelayer-2 protocols. Compared with layer-3 [12], layer-2VPNs can do a better job in resolving the complica-tions due to network dynamics, communication mediaheterogeneity, and fast-changing channel status. Thiscan be at the expense of a more complicated designthat considers any possible layer-2 issue. In otherwords, when a layer-3 VPN is installed, a specializedsoftware that forms a control plane [e.g., multiprotocollabel switching (MPLS)] has to be in place instead ofsimply deploying standard IP protocol stacks on top oflayer-2. Alternatively, deploying layer-1 VPNs overthe integration cannot be achieved due the physicalmedia heterogeneity of both networks and because itrequires complex hardware-dependant VPN solutionsthat can operate over both networks simultaneously[13].

    For these reasons in this paper, we investigate therealization of layer-2 VPNs over the EPON-WiMAXintegration. To achieve the latter, we propose a novelframework for establishing IEEE 802.16 virtual pri-vate passive optical networks, namely, WiMAX-VPON.

    To the best of our knowledge, this is the first workthat considers the support of layer-2 VPNs over EPONor WiMAX networks or over their integration as well.

    B. Contributions of This Work

    Supporting layer-2 VPNs gives rise to the followingmain resource management challenges that will bethe focus of our study:

    Meeting the QoS requirements of the supportedVPN services.

    Providing guaranteed resources for each service.To resolve these issues, we propose a new VPN-basedadmission control (AC) and upstream/uplink dynamicbandwidth allocation (DBA) paradigm that will pro-vide guaranteed bandwidth for each VPN service.This paradigm will ensure and protect end-to-end per-flow QoS (in both the wireless and optical planes) fornew and existing traffic, respectively, while maintain-ing their expected performance as defined in the ser-vice level agreement (SLA).

    More specifically, the contributions of this paper canbe summarized as follows:

    1) This paper proposes, to the best of our knowl-

    Authorized licensed use limited to: University of Waterloo. Downloaded on

    edge, the first framework for supporting layer-2VPNs over the EPON-WiMAX integration.Layer-2 VPNs act as a cost-effective, secure, andflexible link between the underlying fiberwireless infrastructure and higher-level mission-and business-critical services.

    2) This paper presents a new VPN-based QoS pro-visioning framework that enables a robust band-width and QoS assurance for each wireless reg-istered VPN user in the uplink/upstream sharedmedia. From a user perspective, once a VPN tun-nel is established, it is definite that the properresources are reserved for this tunnel and thatits bandwidth is allocated by means of the DBA.

    3) Our work differs from previous related work[2,79] in that we offer a novel joint VPN-basedAC and DBA scheme that enables an end-to-end(from SS to OLT) QoS guarantee while takinginto consideration the different wireless channelconditions. In other words, our scheme offers arobust bandwidth allocation with a MAC-PHYcross-layer consideration so that the physicallayer (PHY) burst profile is taken into accountrather than relying solely on MAC requests [14].

    4) The proposed AC scheme is implemented on athree-stage system, which is involved in the col-laboration among the SS, ONU-BS, and OLT.Such a decentralized AC design reduces the com-plexity and decision time of the AC scheme, asopposed to installing it at one end (e.g., theOLT).

    5) WiMAX-VPON provides a per-flow QoS protec-tion and bandwidth guarantee for admitted traf-fic. Our simulation results show that in the casewhere no AC is applied, a drastic performancedegradation is witnessed for already admittedand newly admitted VPN services.

    he rest of the paper is organized as follows. In Sec-ion II, the different EPON-WiMAX architectures thatay be used for supporting our framework are sum-arized, and the research challenges related to QoS

    nd resource management are highlighted. WiMAX-PON is presented in Section III, and its potential ad-antages and the related design issues are demon-trated. The proposed three-stage admission controlechanism is described in Section IV, and the VPN-

    ased bandwidth allocation scheme is presented inection V. Section VI presents the performance evalu-tion, and Section VII concludes the paper.

    II. EPON-WiMAX-RELA

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