Hybrid Landmark Routing in Ad Hoc Networks with Heterogeneous Group Mobility

Transcription

1 Hybrd Ladmark Routg Ad Hoc Networks wth Heterogeeous Group Moblty Yeg-Zhog Lee, Kax Xu 2, Xaoya Hog 3, Maro Gerla Computer Scece Departmet, Uversty of Calfora, Los Ageles, CA, {yeglee, 2 Scalable Network Techologes, Ic, Los Ageles, CA, 3 Departmet of Computer Scece, Uversty of Alabama, AL, Abstract Scalablty s a mportat cosderato the desg of ay large etwork. I ad hoc etworks, scalablty s partcularly crtcal as ode moblty mposes addtoal challeges to growth. For example, frequet updates requred by moblty make the covetoal proactve routg protocols uable to work large scale moble ad hoc etworks. Tradtoally, ode moblty a wreless ad hoc etwork s vewed as the superposto of dvdual, depedet radom moves of each ode. I realty, moble users ted to exhbt some kds of collectve group moblty patters especally whe the etwork sze grows large. I fact, group moblty has bee exploted to mprove the scalablty of etwork protocols such as routg. For example, routg uses moble groups as the bass of herarchcal etwork archtecture. However, the orgal routg assumes that ALL odes move groups (e.g. homogeeous group moblty), whch s qute urealstc. I geeral, movg teams do coexst wth dvdual roamg odes creatg what may be called heterogeeous group moblty scearos. I ths paper, we propose a hybrd ladmark routg (Hybrd ) scheme whch takes advatages of group moblty to mprove etwork scalablty, whle at the same tme supportg dvdual moblty effcetly. Moble groups are explored followg a way smlar to routg ad dvdually movg odes are hadled a o-demad fasho. I ths way, we gracefully tegrate advatages of both proactve ad o-demad routg. Smulato results show that hybrd ca greatly mprove etwork scalablty heterogeeous moto scearos. Idex Terms MANET, routg, moblty, scalablty I. INTRODUCTION THE ad hoc wreless etworkg techology has bee gag creasg vsblty ad mportace dstrbuted applcatos that caot rely o a fxed frastructure but requre stat deploymet ad easy recofgurato. Some of these applcatos volve several thousads of odes. Scalablty becomes the a crtcal desg ssue, especally f the odes are moble. Oe of the most challegg research areas that have recetly emerged the desg of MANETs (Moble Ad Hoc Networks) s fact scalablty, partcular, scalablty of the routg protocols. Covetoal proactve routg protocols, such as DSDV[2] ad Fsheye[], rely o perodc exchages of routg formato of the etre etwork. They do ot scale well because they propagate routg formato of all odes perodcally throughout the whole etwork. Wth moblty preset, more frequet updates are requred to keep the formato up to date, thus producg a large amout of cotrol overhead. I a large scale moble evromet, the o-demad routg protocols such as [3] ad DSR[6] etc., whch geerate routg overhead oly whe there s data Ths work was supported part by the ONR MINUTEMAN proect uder cotract N4--C_6, ad part by NSF WHYNET proect uder cotract CNS traffc to sed, ad thus have bee tradtoally cosdered more sutable for ad hoc wreless etworks, also ted to cause heavy overhead due to the large-scale flood search. Recetly some efforts have bee made to mprove the scalablty of ad hoc routg protocols. Oe techque s to explore the moblty patters such as the group moblty. For example, the routg scheme[4] uses oe ladmark ode to represet a whole group of moble odes. Aother techque s to utlze geographcal formato such as LAR[9] ad GPSR[8], whch try to use the geographc formato (typcally from GPS) to acheve scalablty. All of these schemes provde promsg ways to mprove the etwork scalablty. I ths paper, we take the same desg phlosophy that spred routg (amely group moblty), ad exted t to acheve eve greater scalablty ad robustess to moblty. Group moblty s actually a qute commo moblty patter the real world, especally mltary scearos ad dsaster recovery evromets. For example, battlefeld, mssos are usually group based (e.g., tak battalos, UAV (Umaed Ar Vehcles) swarms etc). Durg rescue operatos, teams of fre-fghters ad medcal assstats are movg as groups followg dfferet patters. Eve cvla scearos, group moblty s qute prevalet. Examples clude a team of travelers movg groups, studets movg to oe class to aother, cars platoog alog the hghway. Explotg such group moblty patters could greatly smplfy routg. I routg, a ladmark ode s elected from each group. Nodes the etwork, but outsde a group, do ot eed to track routes to all odes that group. Oly oe route toward the ladmark s eeded. Such kd of summarzed routg wll ot affect the routg accuracy sce the odes a group are movg together. However, the overhead reducto s sgfcat. For example, f the average group sze s g, the routg table sze mght be reduced to /g. The routg cotrol overhead s tur reduced as the routg packet sze s sgfcatly shorteed. Explorg group moblty s deftely a good way to mprove etwork scalablty ad performace. However, realstc models are dffcult to come by. It s urealstc for example to assume that all odes the etwork are orgazed groups. It s stll qute commo that some odes may move radomly ad dvdually. Prevous work such as routg smply assumes homogeeous group moblty. Thus, f a fracto of the odes move radomly, caot support them effcetly. Of course, a dvdually movg ode ca be treated as a group of sze oe. But f the fracto s o eglgble, ths turs out to be a tradtoal dstace vector routg whch has bee prove to be ot scalable the moble evromet. I ths paper, we target the large scale mltary ad hoc etwork scearos where group moblty s commo. However, we do't assume homogeeous group moblty. Istead, we assume that groups of movg odes, dvdually movg odes as well as statc

2 odes all coexst the same etwork. Ths we defe as heterogeeous group moblty. Our goal s the to develop a effcet ad scalable routg scheme uder such evromet. We propose a hybrd ladmark routg (Hybrd ) scheme that ca explore the advatages of a group moblty patters, ad at the same tme support dvdually movg odes effcetly. For trackg group movg odes, we use of course the Ladmark cocept. If the group sze s o-trval (e.g. beyod a certa threshold) ad traffc targetg to or tatg from the group s o-trval, the group leader wll start broadcastg ts exstece usg the Dstace Vector (DV) routg scheme. All other odes outsde of ths group wll lear routes to t va a DV lke route dssemato (as ). O-demad routg, o the other head, s utlzed to support dvdually radom movg odes ad odes of groups wth small sze. Both proactve routg ad odemad routg techques are well tegrated wth each other. The maor ovelty of our work s mproved scalablty ad flexblty. Scalablty s mproved by usg oly the group leader to represet a whole group. Flexblty s guarateed by usg odemad routg to dvdually movg odes or very small groups wth very lght traffc. Thus, flexbly comes from the combato of proactve routg ad o-demad routg. Moreover, MANETs are hghly dyamc wth odes og ad leavg; etwork groups splttg ad mergg, dyamc address allocato accordg to movemet behavor or accordg to host s logcal afflato. These dyamcs lead to potetal frequet chages of a ode s IP address. Applcato programs are more lkely to use well kow doma ames that are uque, easy to remember ad/or that bear logcal sematcs of the groups, to ga odes ewly assged etwork address va Iteret Doma Name Systems quckly. Those updated etwork addresses ca be used to dstgush dvdually movg odes ad group members. The rest of the paper s orgazed the followg way. We brefly revew some related work secto II. Secto III troduces the heterogeeous group moblty scearos targeted to be explored. I secto IV, we preset the proposed hybrd routg scheme detal. Itesve performace evaluatos are preseted secto V ad we coclude the paper secto VI. II. RELATED WORK A cosderable body of lterature has addressed research o ad hoc routg protocols [7][2][3]. Most of these protocols work well small or medum sze ad hoc etworks. However, much larger ad hoc etworks emerge several applcato scearos, such as mltary or dsaster recovery stuatos. Scalablty becomes a mportat ssue such stuatos. To mprove routg scalablty, several techques have bee proposed such as [4][][][4][6]. For example, Fsheye [] propagates lk state packets wth dfferet frequeces to odes sde vs. outsde ts Fsheye scope respectvely. OLSR [4] reduces the cotrol packets by selectg oly part of the eghbor odes for packet forwardg. TBRBF [] reduces the update overhead a Lk State routg scheme by matag ad sharg a tree for update broadcast. [4] uses a ladmark ode to represet a group of moble odes. ZRP [6] combes both proactve routg ( local zoe) ad o-demad routg (to remote odes). R- DSDV [2] troduces cogesto cotrol to the orgal DSDV [2] routg for lmtg cotrol overhead. The cotrol overhead of o-demad routg protocols ca also be reduced by reparg a broke route locally at the ode, whch expereces the lk breakage as s doe WAR[5]. Geographcal formato asssted routg such as LAR [9] ad GPSR [8] try to use the geographc formato (typcally from GPS) to acheve scalablty. All these schemes attack the scalablty problem varous aspects. Amog them, the routg scheme ad ZRP routg scheme share varous smlarty wth our scheme. We use the same mechacs as the routg to explore the group moblty patter. However, orgal routg ca ot support dvdually radom movg odes effcetly, whch s supported va o-demad fasho our routg scheme. Hybrd also shares smlarty wth the ZRP routg protocol. Both of them use proactve routg wth the local scope or zoe ad o-demad routg to remote odes. However, gve the small sze of the local zoe, ZRP s mostly same as the covetoal odemad routg the large-scale ad hoc etwork evromet; thus, ZRP shares the same scalablty lmtatos. I hybrd, we oly use o-demad routg to track dvdually movg odes or very small groups. Group moblty s explored to reduce the overhead ad mprove the scalablty. III. TARGETED SCENARIO Moble ad hoc etworks have foud may applcatos tactcal commucatos ad cvla forums. I the realty, oe may otce that moble odes are ofte orgazed groups (e.g., tak battalo, fatry compay, UAV swarm, etc.) wth dfferet tasks ad, correspodgly, dfferet fuctoal ad operatoal characterstcs, e.g., orgazed groups of small umaed groud, sea ad arbore vehcles to lauch complex mssos that comprse several such groups. More possble applcatos clude: coordated aeral sweep of vast urba/suburba areas to track suspects, search ad rescue operatos areas ufredly to humas (e.g., chemcal splls, terrorst attacks, etc), explorato of remote plaets, recoassace of eemy feld the Battle Theater, etc. The successful, dstrbuted maagemet of the msso wll requre effcet, relable, low latecy commucatos wth members of each group, across groups ad to a maed commad post. I the cvla evromet, group moblty s also domat. A group of travelers headg for the same place may form a ad hoc etwork va ther hadheld. The collaborato amog members of the same team makes t possble to partto the etwork to several groups, each wth ts ow moblty behavor. However, the moblty behavors exhbted realty s always complcated. Dfferet moblty patters are usually coexstg oe etwork. Oe commo scearo s that some wreless odes form several teams ad move groups. Whle some other odes may move depedetly ad radomly. I ths paper, we target such scearos where group movg odes ad dvdually movg odes co-exst. The term "heterogeeous group moblty" refers to the mx of group movg odes ad dvdually radom movg odes. Gve the commoess of such moblty scearos, t would make sese to explore the advatages of the group moblty behavors whle supportg the dvdually movg odes effcetly at the same tme. IV. HYBRID LANDMARK ROUTING SCHEME I ths secto, we preset our hybrd routg detal to explot advatages of group moblty the heterogeeous group moblty realstc scearos where both group movg odes ad dvdually movg odes co-exst. The basc dea of the hybrd s to combe both the proactve routg ad o-demad routg schemes together. Movg teams are tracked va proactve Dstace Vectors routg. Idvdually movg odes are hadled va the o-demad routg scheme. By ths way, we take the advatages of group moblty to mprove the etwork scalablty. The hybrd cludes three sub-schemes; the local scope lmted proactve routg, proactve routg for trackg groups ad

3 o-demad routg for trackg dvdual moble odes. I ths secto, we descrbe them detal. A. Proactve Local Scope Lmted Routg Proactve routg schemes provde good route qualty ad stat route avalablty. However, t trggers bg routg overhead whe beg appled to moble etworks wth medum ad large sze. But f we lmt the propagato scope of routg packets of proactve routg schemes, t wll provde good routg accuracy to earby odes wthout causg too much overhead. Thus, hybrd, we propose to use proactve routg schemes oly wth a lmted scope. I our mplemetato, the Fsheye routg s selected as the local scoped routg protocol. Fsheye routg s bascally a Lk State (LS) routg. It has dfferet propagato frequeces of LSs to odes dfferet hops away. Sce the local routg s ru wth a few hops (scope lmted), oly oe frequecy s used Fsheye routg. That s each odes broadcast ts topology formato at most K hops away. Here, K s the scope lmt of the local routg. Now, wth the proactve routg wth the local scopes, each ode wll have accurate routg formato to all odes at most K hops away from t. B. Trackg Moble Groups The local scope lmted routg protocol oly provdes routes to earby odes. A ode stll has o routg formato to remote odes outsde of ts local scope. I ths subsecto we descrbe how we track remote odes movg groups. The basc dea s same as routg. Each moble group wll elect a ladmark ode (e.g. the group leader). A ode tracks oe moble group by matag oly oe route to ts ladmark ode. I the orgal routg, the ladmark ode s dyamcally elected to acheve relablty case of ode falures. The electo algorthm bascally ca be ay type of clusterg algorthm. Here we adopt the ladmark ode electo algorthm of orgal routg. Its basc dea s to elect the odes wth the most umber of eghbors wth ts local scope as the ladmark of that group. After oe ode s elected as the ladmark ode, t wll start broadcastg Dstace Vectors (DV) to form the etre etwork of ts exstece. All odes the etwork mata a ladmark dstace vector routg table wth matag routg formato to ladmark odes t has heard so far. Membershp Cache Host ID IP Address <GID, Host ID> dest Local Routg Table Fgure. Illustrato of group membershp cache ad rougg tables of the hybrd routg protocol C. Trackg Idvdually Movg Nodes The prevous subsecto has explaed how remote group movg odes are tracked usg the proactve dstace vector routg scheme. However, there are stll two problems left usolved. Frst, as we have metoed, there are some odes whch are ot ay group. They move radomly ad dst Ladmark Routg Table GID dst O-Demad Routg Table dest dst dvdually. We must support such odes effcetly. Secodly, whe oe ode eeds to sed a packet to a remote ode outsde of ts local scope, t must have a certa way to fd out whch group the destato ode s. It s urealstc to assume that a ode has pre-cofgured kowledge regardg the group membershp of ay other ode except tself. For the frst problem, supportg dvdually movg odes, oe smply way s to treat each such ode as a group cotag oly tself. Ths s equvalet to rug a covetoal dstace vector routg o top of such odes. Gve the scalablty problem of proactve routg schemes, ths method wll trgger a lot of overhead whe the umber of dvdually movg odes s ot small. To support the dvdually movg ode wthout troducg sgfcat overhead, we propose to apply the o-demad routg techque to track such odes. I the orgal routg, sce the group afflato s statc ad pre-kow, the ode IP address s pre-cofgured as <Group IP, Host ID>. Such a method may ot be practcal our scheme sce our targeted scearos are dyamc wth odes og ad leavg; etwork groups splttg ad mergg, dyamc address allocato accordg to movemet behavor. These dyamcs lead to potetal frequet chages of a ode s IP address. Therefore, to smplfy dscoverg the group membershp, our desg, we propose to reserve the frst half of the IP address, say 6 bts IPv4, to store the group ID, ad the secod half of the IP address for Host ID, smlar to the orgal. Both Group ID (GID) feld ad Host ID feld have same sze bts that allows us smply to use ladmark Host IDs (that are uque ad fxed) as Group IDs. The GID feld should be kept as f the ode does ot belog to ay group, ad whe the ode s partcpatg a group the GID feld should be flled wth the group ladmark Host ID. I ths paper, we reserve GID felds for exclusve access by, ad use Host IDs as doma ames. Applcato programs ca use the well kow doma ames, to ga odes ewly assged etwork address va dstrbuted Iteret Doma Name Systems (DNS) quckly [7]. Those updated etwork IP addresses ca be used to dstgush dvdually movg odes ad group members, thus the secod problem metoed above ca be solved easly Outgog Data Packet Cosultg Local Routg Table Put packet a temporary Cache Ga a update IP Address va DNS Cosultg O-Demad Routg Table Not Foud No Fd Route? Member of a group? Cosultg Ladmark Routg Table Route Packet to Next Hop Fgure 2. Illustrato of the procedure for routg a data packet D. Packet Forwardg Procedure I ths subsecto, we descrbe detal the routg tables ad the group membershp cache mataed at each ode ad the procedure of data packet forwardg. After the hybrd routg s performed, each ode wll ow have oe group membershp cache ad three routg tables. The group membershp cache keeps the group membershp formato of destato odes dscovered va dstrbuted DNS. Ths cache s refreshed ad ts etres are expred No Cosultg Membershp Cache Foud Yes Yes

4 after a certa tme. The refresh tme of these etres are hghly related to the stablty of the groups. If the group members seldom chage ther group afflato, log refresh tme ca be used. If, o the coutry, the moble groups are very dyamc wth frequet group splt or mergece, the group membershp cache should be refreshed frequetly. The three routg tables are ) Local proactve routg table, 2) Ladmark Dstace Vector routg table, ad 3) O-demad routg table. They provde completed routg formato to all destato odes. The local routg table s bult va the local scoped proactve routg protocol (e.g. Fsheye our mplemetato). It provdes the exact routg formato to ay odes wth the local scope of curret ode. The ladmark dstace vector routg table cotas routg formato to ladmark odes of all groups leared through propagated ladmark dstace vectors. The o-demad routg table matas the route formato to dvdually movg odes dscovered va ther checkg GID felds. The group membershp cache ad three routg tables are llustrated Fgure. Whe a data packet eeds to be routed, the ode wll frst cosult the local routg table as t provdes the accurate ad up to date routg formato to earby odes. If a route s foud by examg oly Host ID, the packet s routed drectly. If, ufortuately, the destato ode s a remote ode ot the local routg table, the ode the checks the group membershp cache to see f the destato ode s a member of ay group. If t s a member of a group, the the packet s routed towards the ladmark ode of that group va the ladmark routg table. Oce the packet reaches the remote group, t wll the be forwarded va the local routg table. If the ode s a dvdually movg ode, the the o-demad routg table s used for forwardg the packet. It s also possble that the destato ode s ether the routg tables or the group membershp cache, e.g. f a remote destato ode s requested the frst tme. I such stuatos, gag a update IP address va dstrbuted DNS s performed. The packet s the temporarly cached utl the group membershp of the destato ode s dscovered. Ths routg procedure s llustrated Fgure 2. V. PERFORMANCE EVALUATION We use the QualNet [] smulator, a packet level smulator to evaluate the proposed hybrd routg scheme. The ma purpose s to verfy ts scalablty varous scearos ad ts flexblty to hadle both dvdual movg odes ad groups. I our smulatos, stadard IEEE 82. rados are adopted wth chael rate as 2M bps ad trasmsso rage as 367 meters. Radomly geerated UDP based Costat Bt Rate (CBR) traffc s used for evaluato. CBR traffc pars are radomly selected amog all etwork odes. The umber of pars rages from to 6 pars; ths causes a gradual chage of the traffc load ected to the etwork. Idvdual odes move followg the radom waypot moblty model. The group movg odes adopt the group moblty model preseted [4] Metrcs selected clude ) Data packet delvery rato: the rato betwee the umber of data packets receved ad those orgated by the sources; 2) Average ed-to-ed packet delay: the average tme from whe the sources geerate the data packets to whe they reach the destato odes; 3) Normalzed routg overhead: the total umber of routg cotrol packets dvded by the total umber of successfully delvered data packet; 4)Aggregated Throughput: the aggregate of the throughput of all coectos, computed at each destato ode. The orgal has two choces to hadle the dvdually movg odes. Oe way s to treat each such ode as oe group. Aother way s to vew all the dvdually movg odes as a bg group. The former method ca provde accurate routg formato to each dvdual ode. However, t has to mata a bg ladmark routg table, thus bg overhead. The latter method does ot troduce ay addtoal overhead. However, sce the dvdual odes move depedetly, perhaps they are ot physcally close to each other. Thus, remote odes may ot be able to route packet to such dvdual odes uless they are the local scope of the sources ( such stuatos, routg s doe va the local scoped routg). I our expermets, we take the secod way sce the frst method shows very poor performace ad ay way worse tha the secod method. A. Performace uder Dfferet Load I the set of prelmary expermets, we vestgate the scalablty of the proposed hybrd routg. 225 moble odes are deployed a 3mX3m feld. 2% of these odes (e.g. 45 out of 225) are assged as dvdually movg odes. These 45 odes are tally radomly deployed the whole feld. The rest 8 odes are the dvded to 9 groups (2 odes per group). These groups are uformly assged to the feld where each group occupes a mxm square. Nodes wth each group are also uformly dstrbuted wth ther group area. Moblty speed s fxed as 6 meters per secod. We vary the traffc load (e.g. umber of CBR pars) to vestgate the performace of the proposed hybrd routg as well as orgal routg ad routg. From Fgure 3, we observe that whe the etwork load s lght, routg shows better packet delvery rato. However, whe the traffc s creased, ts packet delvery rato drops rapdly. The routg ad the hybrd routg schemes outperform as etwork load creases. Moreover, the hybrd routg costatly shows better data packet delvery rato tha the orgal. Ths because that there are 2% moble odes that are dvdually movg, whch the orgal caot support well. The aggregated throughput of the CBR applcatos uder the three routg protocols Fgure 4 shows smlar behavor. Fgure 5 shows the average ed-to-ed data packet delay uder the 3 dfferet routg protocols. The packet delay of creases very quckly whe the etwork load s creased. It also cosstetly shows loger packet delay tha routg ad the hybrd routg. Ths ca be explaed by ts odemad ature. Whe there s o path avalable or the path the broke, data packets are queued utl the route dscovery procedure fds a path. The same reaso explas why the hybrd routg shows slghtly loger packet delay tha the orgal. Uder the hybrd routg, packets targetg the dvdually movg odes are routed smlar to the o-demad routg. Smlar results are also observed Fgure 6, where the ormalzed routg overhead of the three routg protocols s preseted. The reaso that the routg overhead of creases dramatcally alog wth the crease of traffc s because lk breaks wll happe more frequetly whe the etwork load s creased. geerates a lot of addtoal overhead to recover the paths whe lk breaks happe. B. Performace uder Dfferet Fracto of Idvdually Movg Nodes I ths set of expermets, we demostrate the flexblty of the proposed hybrd routg scheme hadlg the coexstece of groups of movg odes ad dvdually movg odes. The scearo s mostly the same as the prevous expermet. However, ow the umber of CBR pars s fxed to 4 pars. We stead vary the fracto of dvdually movg odes from % to % to compare the hybrd routg scheme wth the orgal routg. The results are gve Fgure 7 ad Fgure 8.

5 Data Packet Delvery Rato Aggregated Throughput (kbps) Hybrd Fgure 3. Delvery rato vs. dfferet traffc load 5 45 Hybrd Fgure 4. Aggregated throufhput vs. dfferet traffc load Avg. Data Packet Delay (s) Normalzed Routg Overhead.9 Hybrd Fgure 5. Average data packet delay vs. dfferet traffc load Hybrd Fgure 6. Normalzed routg overhead vs. dfferet traffc load Data Packet Delvery Rato Normalzed Routg Overhead Hybrd.4.2 Fracto of Idvdually Movg Nodes Fgure 7. Delvery rato vs. dfferet fracto Hybrd Fracto of Idvdually Movg Nodes Fgure 8. Normalzed routg overhead vs. dfferet fracto I Fgure 7, we observe that, whe a lot of odes are dvdually movg, the hybrd shows much better delvery rato tha the orgal due to the capablty of the orgal to hadle the dvdually movg odes. Whe the fracto of group movg odes s creased, the performace of hybrd s more ad more close to the performace of the orgal. Whe all odes are movg groups (e.g. fracto of dvdually movg odes s %), the two protocols show detcal data packet delvery rato. The reaso that the delvery rato of the orgal s above zero eve there s o group moblty s because of the local scope routg of. Eve perhaps o ay ladmark s elected as all odes are movg depedetly ad dvdually, the local scope routg ca stll route some packets f ther destato odes happe to be the local scope of the source odes. Fgure 8 shows the ormalzed routg overhead of the hybrd ad orgal uder dfferet fractos of dvdually movg odes. The hybrd routg geerates more overhead tha the orgal whe the fracto of dvdually movg odes s large. Ths s because hybrd trggers more route request ad reply packets to search the paths to dvdually movg odes. Whe most odes are movg groups, the ladmark dstace vector routg takes care of most of the data packets. The the two protocols have mostly same routg overhead. VI. CONCLUSION I ths paper, we proposed a ufed routg scheme called hybrd, whch explores the advatages of moblty patters the heterogeeous group moblty scearo where both group movg odes ad dvdually movg odes co-exst. The maor cotrbutos are the scalablty ad flexblty of the proposed routg scheme. Good scalablty s realzed by explorg ad explotg the group moblty patter. Flexblty comes from the fact that the hybrd gracefully combes the proactve routg ad o-demad routg together. Thus the resultg scheme takes advatage of both kds of routg schemes to support varous etwork evromets. The smulato results prove that our scheme ca work well varous scearos (e.g. flexblty) ad acheves good scalablty. REFERENCES [] Qualet smulator. Avalable at [2] A. Boukerche, S. K. Das, ad A. Fabbr. Aalyss of radomzed cogesto cotrol wth dsdv routg ad hoc wreless etworks. Joural of Parallel ad Dstrbuted Computg (JPDC), 6, 2. [3] S. R. Das, C. E. Perks, ad E. M. Royer. Performace comparso of two o-demad routg protocols. Proceedgs of IEEE INFOCOM, Mar. 2. [4] M. Gerla, X. Hog, ad G. Pe. Ladmark routg for large ad hoc wreless etworks. Proceedg of IEEE GLOBECOM 2, Nov. 2. [5] X. Hog ad M. Gerla. Dyamc group dscovery ad routg ad hoc etworks. Proceedgs of the Frst Aual Medterraea Ad Hoc Networkg Workshop (Med-hoc-Net 22), Sept. 22. [6] A. Iwata, C.-C. Chag, G. Pe, M. Gerla, ad T.-W. Che. Scalable routg strateges for ad-hoc wreless etworks. IEEE Joural o Selected Areas Commucatos (JSAC), 7(8), Aug [7] D. B. Johso ad D. A. Maltz. Dyamc source routg ad hoc wreless etworks. Moble Computg, Chapter 5, 996. [8] B. Karp ad H. T. Kug. GPSR: Greedy permeter stateless routg for wreless etworks. Proceedgs of ACM MobCom, Aug. 2. [9] Y. B. Ko ad N. H. Vadya. Locato-aded routg (LAR) moble ad hoc etworks. Proceedgs of ACM/IEEE MOBICOM98, Oct [] R. Oger, F. Templ, ad M. Lews. Topology dssemato based o reverse-path forwardg (TBRPF). IETF Draft, Oct. 23. [] G. Pe, M. Gerla, ad T. W. Che. Fsheye state routg moble ad hoc etworks. Proceedg of ICDCS 2 workshops, Apr. 2. [2] C. Perks ad P. Bhagwat. Hghly dyamc destato sequeced dstace-vector routg (DSDV) for moble computers. Proceedg of the ACM SIGCOMM 94, Sep [3] C. E. Perks ad E. M. Royer. Ad-hoc o-demad dstace vector routg. Proceedgs of IEEE WMCSA 99, Feb [4] T. Clause ad P. Jacquet. Optmzed lk state routg protocol (OLSR). RFC 3626, Oct 23 [5] I.D, Aro ad S.K.S. Gupta. A wtess aded routg protocol for moble ad hoc etworks wth udrectoal lks. Proceedgs of the st Iteratoal Coferece o Moble Data Access 99, Dec [6] Z. Hass ad M. Pearlma, The zoe routg protocol (ZRP) for ad hoc etworks, Iteret IETF Draft, Jue 999. [7] Xaoya Hog, Ju Lu, Rady Smth, ad Yeg-Zhog Lee, Dstrbuted Namg System for Moble Ad-Hoc Networks, Proceedg of the ICWN 5, Jue 27-3, 25.