QoS Mesh Routing Protocol for IEEE 802.16 based

Wireless Mesh NetworksMin Kim', Ilkyeun Ra2, Jisang Yoo3, Dongwook Kim4 and Hwasung Kim5"Dept. ofElectronics and Communications Eng, 3Dept. ofElectronics Eng,4Dept ofElectronic Materials Eng, Kwangwoon University, Seoul, Korea

('beyond, jsyoo, 4dwkim, 5hwkim}@kw.ac.kr2Dept. ofCSE, University ofColorado at Denver and Health Sciences Center, USA

2ikragcarbon. cudenver. edu

Abstract- This paper proposes QoS Mesh routing protocol forIEEE 802.16 based wireless mesh networks. QoS Mesh RoutingProtocol proposed in this paper is a proactive hop-by-hop QoSrouting protocol. The goal of our protocol is not only to findroutes from a source to a destination node, but also optimalroutes that satisfies QoS requirements, given in terms ofbandwidth and delay as default QoS parameters. In this paper,we first analyze possible types of routing protocols that havebeen studied for MANET and show proactive hop-by-hoprouting protocols are the most appropriate for wireless meshnetworks. Then, we present a network model for IEEE 802.16based wireless mesh networks and propose a proactivehop-by-hop QoS routing protocol. Through our simulation, werepresent that our routing protocol outperforms QOLSRprotocol in terms of end-to-end delay, packet delivery ratio androuting overhead.

Keywords - Wireless Mesh Networks, IEEE 802.16, Proactive,Hop-by-Hop, QoS Routing.

1. Introduction

In recent years, wireless mesh networks (WMNs) haveactively been studied as the main technology for the nextgeneration wireless networks. In comparison with an existingwired infrastructure, WMNs form a wireless backbonenetworks at low cost and enable a flexible scalability. WMNsconsist of mesh routers and mesh clients. Mesh routers act asbrides which can connect to different networks and gatewayswhich can connect to the Internet, and provide mesh clientswith a wireless backbone. Mesh clients are the end-userwireless devices serviced by mesh routes [1].WMNs are analogous to Ad-Hoc networks in terms of

wireless multi-hop communication, but WMNs have differentcharacteristics in that mesh routers have minimal mobility andno energy constraint, and form a wireless backbone for meshclients. Therefore, to consider the special characteristics ofWMNs, it is necessary to design a new routing protocol amongmesh routers.

There have been many works related to WMNs, which aremostly based on IEEE 802.11 NIAC protocol. IEEE 802.11based WMNs are technologies extending the coverage at lowcost by changing existing AP (Access Point) to wireless AP

and communicating with each other. By the way, IEEE 802.11based WMNs have a small capacity, compared to that ofwirednetworks. Besides, an available capacity per node decreasesfurther, since several nodes share the small capacity again bywide interference range. This small capacity is inappropriatefor backhaul networking in WMNs that processsimultaneously both data among mesh routers and data ofmesh clients which belong to mesh routers. Also, IEEE 802.11MIAC protocol, CSMA/CA does not suit MAC protocol formesh connectivity among mesh routers because it is originallydesigned for single-hop WLAN environment, not formulti-hop wireless networks [2]. Hence, in this paper, wenotice WMNs using IEEE 802.16 Mesh Mode as the physicaland MIAC layers. As IEEE 802.16 based WMNs cover a widerservice range and provide a higher bandwidth than IEEE802.11 based WMNs, they are adequate for not only wirelessInternet access but also multimedia applications such asvideoconferencing.

The remainder ofthe paper is organized as follows. Section2 provides a brief overview of the related works. Section 3presents a network model and the most appropriate type ofrouting protocol for IEEE 802.16 based WMNs. In section 4,we introduce in detail our proposed routing protocol. Section 5compares the performance ofrouting protocols via simulations.In section 6, we conclude our work.

2. Related Works

2.1 Overview ofWMNs

WMNs are multi-hop wireless networks which are similarto Ad-Hoc networks and comprised of two types of nodes:mesh routers and mesh clients. As shown in Fig. 1 [1], wheredashed and solid lines indicate wireless and wired linksrespectively, mesh routers serve as brides which connect to notonly the same networks but also different networks such ascellular, IEEE 802.11, IEEE 802.15, IEEE 802.16 andwireless sensor networks and gateways which connect toInternet. Mesh routers also establish a wireless backbonenetwork automatically, maintain the mesh connectivity andprovide mesh clients with wireless access to WMNs. Meshrouters have minimal mobility and no power restriction.

This research was supported by the Basic Research Program (GrantRO1-2006-000-10199-0) of the Korea Science & Engineering Foundation

Feb. 17-20, 2008 ICACT 2008ISBN 978-89-5519-136-3 -812-

Oni the other hand, mesh clients can be stationary or moffbile heders.g Intermediate nofdes only needd to relay pacdkets basedndes as the ed-userid Wireless de-vices serviced by mesdh on the addresses int the packet headers. But, as menitioned In

routers. ~~~~~~~~~~~~~~[5],considering that the packet size int WMNsN is usuailly -verysmall to cope With the high bit error rate of Wireless chhannlsand a smaill capacity comnpared to Wired netwrs, puittinig the

.Wireless ireles Mesh Bacdkbone entire AMAdRese in the pacdket hededrs imiposes very expensiveroufitin overhUEad Furthermore, if sourc ruinffifg uses WHOees

mokEr link quality as routfintg meitrics to cadlculat an opthimal rouffitin~~~~ path, there is a serious probiflemt that Wiireless linik quality as the

N ~~~~~source nofde clulates; an opitimadl rouityingpt for traffic isM~. diffrent fro that as the trafHUficctaly passe the calculated

hop-bffLty-hopi rouiting, every node madintains a rouitinigMMIviMAX W sh table tha indicates the nexkt hopsi for routes to all other Hnode inNetworks Clients -Sbb bW)k dHWEtilk sourced i ntermeiidiidiate nodes

Figure 1. Wireless Mesh Networks forward the packet along its path based oni their frouting tables.Due to its simlefil forwarding schemei and low message

2.2 Routinig Protocols1 for WM\Ns o-verhead, hop-bty-hopf routinig is the most preferable forWMNs. Ho-wever, hop-fby-hopl rouinffg needs to avoid rouitinig

To Support effecti-ve rouiting int WI\NsN, it is necessaryto loops As it can incur loopsg in designing routfing metrics.first understand what roufitin protocols best fit WMNsN fromdmany stuiOgdieso rouiniig prodtocols for Ad-Hoc nedtworks.ig 2.3 QOILSR (QoS for Ad hoc Opitimized Linik Staite RoutingAccording to wvhen routes are computefi d,the rotinig protocols0 ProtocolH)can be di-vided intotwoJN caitegories: on-Edemanfd (reacti-ve)rouinifg and table-dri-ven (proacditive) routfing. Based on how QOLSR [6] is a QodS routing exteniondi to OLSR [7]pakets are routed along the patfhs, the rouinffg protocols can proposeid for Ad-Hoc networks. it is based oni the use of aals be di-vided intof two categories: sourced routing and heuisticfi for MPR selecitAionad a moffdificaftioni of TC4ho-y-hopl rouiting. messages to spread QodS information fiithroughout the nUetwrkFirst of all, on-Edemanfd rouitinig protocols6 detect a route MPR selecftioni in QOLSR is snimilar to that in OLSR, buit to

betwee a pair of sourc and destinationi nofdes by flooig considerf QoS requirements,i it is to select NMPRs tha maximizecnrlmessages in networksl when the source node actuailly the bandwidth and minimizei the delay towargd the 2-hopf

need to send packets to the desitinaition, and consequently, thedy neighbors. To select MtPRs, each nofde needsd QoS informationfifcan significanitly rekduc rouiting o-verhed.d For Ad-Hoci abouft the 2-ihop nighborhood. HELLO messages arenetworks, there are fRequeNt link breaks due to the mobility of modified to suppoirt the excihang ofQoS hfinforaionfif betweennode. However, WMNs have Vfew topology changes because &1-hopneighbors. Each nofde periodically announces theof the static niatur of nofdes. Using on--demanfd roufting bandidth and the deay for each of its 1-hop nebighbors.tprotocolsU int WMANs, since the frequency of link breaks is Having recei-ved such HEILLO messages, no6des can choosemuch lowerd tha the frequency of flow detection, on--demand their NMPR usingy the heuristic of MPR se66lecion.routing protocols9 issu both redudandt and very exNpensive In QOLSR, TC messages are similarto thsoiAf OLSR, buftcontroldf messages [5]. Moreover it is difficuilt to apply the they additionallty carry QoS ififnformation associated -with lNks.on-demandd roufting protocol to QoS routing protocols TC messages inclded the baddwidth and the delay of link addproposefid in this paper, because on-Edemangd ruinffifg protocols propagate throuighouit thed &netok by NMPRs. Each nodeintrokkduc a high latency when the source nodes first search the obtains QoS hfinfformation fromn TFC messages anid computes anroute TFherefore, on-demanid ruinffifg protocols aRe generadlly opitimail routing route usging the route com(putationfi algorigthm.not scalable or appopiateflU for WI\NsN. QOLSR specdifies Mthat rouefompufiftatio algorithmt is to find a

Int poacditive rouiting protocols,d each node maintains the path With maimumiiifn baddwidth,i and when there is more thanlatest rouiting tAbles incldiniffg routing information to every one widest path, it choose thec one With shortest deliayotheri nofde int networksf by broadcastingfl controfl messageswhen thec neltwork topology changes or periodiCally. Tfhere Is 3IEE821bae WM snolatency wheni the traffic occurs, since all nofdes alwaysupdat theiri tables to maidintain a consgistent and up-to-date 3.1 Networ6k Modelviwf the netWork buft there is a disadvantage thadt rouffitinoverhed to mainiitain routinig taibles is too mucflh. AccodMingly, Fig. 2 shows a network moffdel ofIEEE 802.~16 based WMNspraciv ruting protcol are -moe utal forWMAFTs thn poosdi hs ae.Te ewr odliiilrth

Oned is IEEE 802.16 Mesh Modeb uSed as a Wiireless backhauil respectively, sinced tha is ineffecti-ve in termsi of complexfiityprotoco to conifigure WMANs and the other is IEEE 802. 16e to and resource. To reduced the comeityfNii of a routing pathfprvide SSs withi NNEtwr access services Ifwireless BS is a comutatfionfifi and be an effecti-verouting protocol, ouR roUtingateay wich can connect to lInternet, it addditionallty nUEed protoco consgiders banidwidth and delay as defalt routinigth rlated infterface. meitrics and compuftes QoS rouitinig pathsNObase o intem,SSs are mesh clientsi using IEEE 80216e and the MSam because they are commnon QoS parameters used in the five

wireles mobiidile devices in traditional IEEE 802.i16 Networks. scheduinig services. Besides, our routing protocol simpflycomnpue several rouitinig paths by chaniging thresholdsfi of theQoS parameters.

Wirees nere 4. QMRP: QoS Mesh RouINg~ProtocoldIthisfi chapfter, we propose a QoS roUtin protocol for

IEEE 802.16 based WMNs. As dBiscssd int chapfter 2 and 3,/BS /BS

X SQMRP is based oni proacdtive hofip-by-ho routiing proltocol/ / SsW Which is the most appropiategfb routinig protoco for WMNs and

X~~~ ~ ~ ~~~~aQoS routing oprtocol that sBatife the QoS rqidreMens

~BS 41 Basc Ide

2.ffOIHEEE 802.16 based Wireless Mesh Networks if QoS rouitinig protocol is based oni praciveifU hop-by-hopFigure ~~~~~~~~~~routinigprotocol, iallno descMpute an opitimail path tha

32Routing Protocols for IEEE 802.16 based NVMNhT satifies QoS requitrements in ad-vance. Wheni QoS trafficoccurs, all nodes use the computed rouitinig paths. HThisrotinig

in this section, We Will dScuss a routinifg proEtocol for IEEE protocol has no latency and no additionalt cost for path802.6 bsed MNs Sine a wel asothe IEE stndads, computaRtion, buit there is a problem- that an available link

IEEE 802.16 Mesh Mode defines the physical layer and the resourcchnefrqntyFoexml,asigtatehMAC, layer, it is necessary to gstdyh undefined upperi layers router A MameasuresQo information (Qi) at the time (Tu) thesuch as a roUtin protocol. Morideovr stadarfdizationi mesh rounte broaidcasts Qi to the neighborhood.Rl Qi isac,tivfities of IREEE 802.16 Mesh NMod were compleitRed wvhile deli-vered to other mesdh router at the timei (T2) and otheri mesdhIEEE 802.11 based NVMNs are still stadarddizing in thed IEEE ruters would computei routinig paths by Qi recei-ved at T2.i By802.1 is9 [8]. Since Both support mesdh neftworkiing, one would th way, QoS iibnformtioni Which mesh route A meiasures at TiaOSsm that the many research output fromi IEEE 802.11 is different Qi.based NWMNs are appflicableto IEEE 802.i16 based WMNs as QOLSR is a QoS routing extensiona to OLSR poposed forwell. However, these are not directly appicaleasthetd M tWo Ad-Hoc, networks. Sinced QOLSR is a proacdtive hop-by-hopMAC, protocols are very diffeirent.t routiing proltocol like QMRP, it cani be assumefid that QOLSR is

Also, mesdh clientsg use IEEE 802. 16e as Wireless access USed for WIVMNs But QOLSR hSe a numberlg of drawbacks.technlofbgy to access the mesh network One of the ky First SomilEdlink' QoS informailtiohnmight not be broadcast duefuncitions o theM IEEE 802.16 MAC layer is toensfiure thadt QoS to the obligaftioni to select MIPR and QMPR. Second,g QOLSRrequiremenfts of different data services are met as reliably as considdQErSKonlyband idth ]anddla6a bIAsic mefitric.Tirdpossible gi-venhe loa1dinig coniditionsg of thed system. IEEEFic,OS saQSruig rtclfrA-o ewrs802.16 layer deflines fived scheduling services to deliver and it is niot suiitable for WMNs.0handle SDUs and MAC, PDUs§ With differenit QoS 42 Controld Message Mfaenageentsrequirements: UGS (Unso6licited Gran Services),rtPS(real-time Pollinig Services) non--real-timed pollinfgservices (nrtPS), best-effort service (BE) anid extededd Int thi section, we propose managing conitrol messages.real-timei pollting service (ertPS).g In IEEE 802.16 based Since Qos informaftionff is nodt up-to-date if mucdh timei hasWMNs, the mesgh clientsg excmehange the Qo; traffic wvithi mesh passed sicemeh rounter received it, We propose thadt therouites,1 and the mes§h rountersmut forward thed QoS traffi to numberof mesh routers fowardinig QoS ififnndforaion ofthe gaiteway or other meshgi rounter int the same network. cbontro miessages is restricted withini 2-hop. But the hop--countlLikewise, the gateway musdt fowaArd the QoS traffic which is of controld mfessages broaidcasts throughout the network as thecomei finto the network to accurate mesah Nroutrs QoS hop count does not change frequentfily dudeto6lw moifidfty of

guarntein he ontet o rouingprotcol is to compute a Mesh routers. Wheiinmesh roufter accepts controld messagesruouting ipthiwh nichmets QoSINrequrmntoffvsceuig fo alnegbrrur,ifhyaecnrlmsaesrm

routers, the mesh router updates and broadcasts onlyhop-count.

4.3 QoS Information Measurements

In this paper, Using IEEE 802.16 Mesh Mode as lowerlayers, we propose measuring an available bandwidth and anaverage delay. IEEE 802.16 Mesh Mode uses OFDM asphysical layer and TDMA as MIAC layer. As data channelconsists of several time slots, mesh routers measure thebandwidth by calculating the number of time slots withoutdifficulty. In other words, the available bandwidth is measuredby the number of free slots. With the available bandwidth,mesh routers inform other mesh routers of link's delay. Thescheme that mesh routers measure delay is to utilize controlmessages. To measure delay by control messages, meshrouters broadcasts control messages included in time stamp.Mesh routers measure the average delay periodically andbroadcast it attaching control messages.

4.4 Routing Table Calculation

In general, QoS routing protocols consider QoS parameterssuch as bandwidth, delay, delay jitter, logarithm of successfultransmission, packet delivery ratio, and cost to calculaterouting paths. The computation complexity is primarilydetermined by the composition rules of the parameters. Thethree basic composition rules are: additive (such as delay,delay jitter, logarithm of successful transmission, hop-countand cost), multiplicative (like 1-loss probability = probabilityof successful transmission) and concave/minmax (e.g.,bandwidth). To treat each parameter individually is notfeasible due to the algorithm complexity. The problem offinding a path with n additive and m multiplicative parametersis NP-complete if n + m >2 [9]. A path with both maximumbandwidth and minimum delay may not necessarily exist.Thus, we must decide the precedence among the metrics inorder to define the best path. We define the precedence asbandwidth and then the propagation delay.

To ensure loop-free routing and reflect changeable QoSinformation and characteristics ofWMNs for routing metrics,we use hop-count and QoS information as routing metricstogether. Mesh routers obtain QoS information and hop-countthrough a periodic broadcasting of control messages. WhileQoS information is delivered to only 2-hop neighbor routers,hop-count is broadcasted throughout the network.

Figure 3 shows an example of routing table calculationproposed in this paper. Let us suppose that mesh router 2calculates a routing path destined for gateway in networktopology of figure 3. Each mesh router accepts hop-count fromall neighbor routers of the network and QoS information from2-hop neighbor routers. First, to calculate QoS optimal path,mesh router 2 selects 2-hop paths. 2-hop paths for mesh router2 are 2->3->6, 2->5->6, 2->5-*8, 2->5->4, 2->1->4 paths.From here, let us suppose that figure 4 shows QoS informationthat mesh router 2 receives from 2-hop neighbor routers. Tocompute a routing path, mesh router 2 search a 2-hop path thatsatisfies QoS requirements among 2-hop paths. For example,if QoS requirements are above 2Mbps and below 3ms, meshrouter 2 selects 2->3->6 path and 2->1->4 path. Asmentioned earlier, to consider QoS information and hop-countas routing metrics together, we propose a formula for proposedrouting metrics.

RoutingMelics =

2-hop

HopCount* (1-_w) + E (LinkDelay* w)source

(1)

Where, Hop Count is hop-count of a route from a source to adestination and Link Delay is an average delay to 2-hop routers.W is a tunable parameter subject to 0 < w < 1. We conductedseparate simulations on w and found a 0.4 value to be best.

For an example discussed earlier, 2-*3->6 path'shop-count is 3 and, 2-*1->4 path's hop-count is 5. Ifhop-count and QoS information are substituted for proposedrouting metrics formula, 2- >1-4 path's routing metric is 3.4and 2->3->6 path's routing metric is 3.0. Therefore, a pathsatisfying the minimum hop-count and QoS requirements is2->1->4 path.

4

2

5

3

6

BWi 4MbPs fDelayt 3rns 65)

Figure 4. QoS Information for 2-hop path calculation

5. Simulation3

5 6

8GW

Figure 3. Example of Routing Table Calculation

Table 1. Simulation ParametersParameter Value

Simulation topology 5x5 Grid TopologySimulation time 400 Seconds

The number of nodes 25Distance between nodes 100 m

Transmission range 100 mPHY, MAC protocols Mesh Mode

Traffic Voice trafficPacket size 1000 bytesPacket rate 0.51.5 packetss

Feb. 17-20, 2008 ICACT 2008ISBN 978-89-5519-136-3 -815-