Adaptive Resource Discovery for Ubiquitous Computing

Transcription

1 Aptive Resoure Disovery for Uiquitous Computing Re Hrir Dept. of Computer Siene University College Lonon Gower Street, Lonon WC1E 6BT, Unite Kingom Stephen Hiles Dept. of Computer Siene University College Lonon Gower Street, Lonon WC1E 6BT, Unite Kingom Ceili Msolo Dept. of Computer Siene University College Lonon Gower Street, Lonon WC1E 6BT, Unite ABSTRACT The terms pervsive n uiquitous omputing re use to esrie smrt spe populte y hunres of intelligent evies tht re emee in their surrounings. Chrteristilly, uiquitous omputing evies must len into the kgroun, unotrusively ollorting to provie vluee servies for users. Servies re thus essentil to the suess of this tehnology n, s result, oth servie isovery n servie mngement will ply vitl role in generting the revenue strem tht is prerequisite for sustinle uiquitous eployment. On the one hn, the servies provie shoul e evient y their rihness n vriety n on the other, the omplexity inherent in the environment must e hien from users. In this pper, we esrie RUBI, resoure isovery frmework for uiquitous omputing. RUBI represents novel pproh to resoure isovery, euse the primy of the nee for ptive utonomi ehviour is estlishe within its esign. Ctegories n Sujet Desriptors C.2.4 [Computer-Communition Networks]: Distriute Systems Distriute Applitions; C.2.2 [Computer- Communition Networks]: Network Protools Applitions Generl Terms DESIGN, ALGORITHMS Keywors Resoure isovery, uiquitous omputing, moile ho networks, utonomous, ptive 1. INTRODUCTION This work ws supporte y BT Ls, Mrtleshm, s prt of the UCL@Astrl Prk, MARS projet. Permission to mke igitl or hr opies of ll or prt of this work for personl or lssroom use is grnte without fee provie tht opies re not me or istriute for profit or ommeril vntge n tht opies er this notie n the full ittion on the first pge. To opy otherwise, to repulish, to post on servers or to reistriute to lists, requires prior speifi permission n/or fee. 2n Workshop on Milewre for Pervsive n A-Ho Computing Toronto, Cn Copyright 2004 ACM $5.00. The pervsive omputing vision is one in whih the everyy environment eomes populte with emee miroproessors, n where tht omputing is invisile to users. It omes s surprise to most people (n testment to the invisiility of these evies) tht the verge househol in the evelope worl lrey possesses in the orer of proessors some rs lone possess in exess of 60 seprte proessors. Over 250 million 8 it proessors re sol every month, wrfing the sles of nything proue for onventionl omputers: less thn 2% of miroproessors re estine for PCs, n tht proportion is flling. Few of these emee miroproessors re urrently networke; however, the eresing ost of wireless networking n the eveloping rnge of ifferent wireless tehnologies mens tht this is out to hnge. Given the sle of eployment this, in turn, opens huge potentil mrket, in whih return on investment will e riven y the provision of novel joineup servies tht enhne the pilities of these evies 1. Consequently, servie (or, more generlly, resoure) isovery n mngement re neessrily vitl omponents in the relistion of the uiquitous omputing vision, n key enler for the genertion of revenue strems. Resoure isovery is, oneptully, reltively simple. A servie vertises its ttriutes n lotion in some form of istriute iretory; lient queries the sme istriute iretory, speifying the ttriutes tht it esires. Implementing this simple ilogue is, however, omplex. Amongst mny other things, there is nee to eie: how the ttriutes shoul e expresse, [2]; wht shoul e the form of the istriute iretory use; where to ple informtion out servies n how tht informtion shoul e move roun the system, [3]; n how to seure ess to tht informtion. More generlly, uiquitous omputing systems operte in omin of unertinty; huge heterogeneity, huge sle, n gret ynmiity re expete. Mny evies re likely to e very resoure poor n yet will e omplex to minister, sine the numer, types, n preise ttriutes of the servies in use will hnge frequently, s evies hnge ontext of opertion. As result, utonomi mehnisms for resoure isovery n onfigurtion re importnt in reuing the ognitive lo on nive humn users who woul otherwise e expete to selet from wie n ever-hnging rnge of servies n then mnge ynmi ess. Autonomy is essentil to fulfill the requirement of unotrusive opertion. 1 Given the urrent stte of oth rio n ron tehnology, we o not expet lrge returns from simply proviing onnetivity.

2 The effets on resoure isovery re severlfol: An uiquitous omputing resoure isovery protool must e istriute, ville t mny points in the network, n highly slle, in orer to ope with the potentil numer of resoures ville. Users n e expete to possess vriety of evies tht rnge from very resoure poor to resoure rih. They will expet lrgely evie inepenent intertion using ommon interfes in whih humn intervention must e miniml to reue onfusion. Clerly, pilities suh s memory, proessor spee n nwith shoul e exploite where these exist. The ommunition moel will influene the esign of the resoure isovery protool. There is no single ommunition prigm for uiquitous omputing n the ommunition moel in opertion epens upon severl ftors: the network tehnology use, the reltive moility of the noes n the vilility of fixe infrstruture. In sitution where noes hve low reltive moility n there is se sttion in the viinity then the most ovious onfigurtion is tht of wireless Lol Are Network (LAN). Moile A ho Networks (MANETs) o not require the presene of se sttion n, in some irumstnes, it is fesile to form MANET even if noes hve reltively high moility, or re filure-prone, provie tht there is oopertion (whih n e negotite on-the-fly). In relity, n prtiulrly in less well evelope res, the network is unlikely to onform to one moel or the other: the ommunition moel might e mixe, with res of the network tht hve firly goo stility n rehle infrstruture, n other res in whih there re neither. Following from the requirements outline ove, resoure isovery protool must e ptive, proviing up-tote resoure informtion over rnge of network topologies, espite the frequent filure or unvilility of evies, servies n the links etween them. It must ommote n exploit the heterogeneity of prtiipnts, whilst still serving informtion out lrge numer of fst-hnging resoures. In the reminer of this pper, setion 2 ontins n nlysis of urrent pprohes to resoure isovery. Following this isussion, setion 3 ontins esription of RUBI, our resoure isovery protool, whih hs een esigne to ress the requirements ientifie ove. Setion 4 ontins ritil nlysis of RUBI ompre with the servie isovery protools reviewe in setion 2. Setion 5 onlues the pper with n outline of propose future work. 2. PREVIOUS WORK Existing resoure isovery protools n e tegorise oring to whether glol inex of resoures is mintine entrlly, istriute inex is mintine, or resoures re isovere s they re neee. The min purpose of mintining entrl iretory is to provie effiient mngement of lrge numer of resoures. Jini [16] onforms to this rhiteture, ssuming stle, fully route, unerlying network n the presene of relile noe to t s the iretory. These ssumptions re vli for Jini s it ws evelope for use in fixe networks ut it my not fit n uiquitous omputing environment where the topology of the network is voltile n the iretory my not e rehle t ll times. Resoure lotion mehnisms evelope for peer-to-peer networks provie interesting exmples of istriute inexes. A series of istriute filesystems se on hsh tles, known s Distriute Hsh Tles (DHTs), hs een inepenently evelope, for exmple, [12]. INS/Twine, [1] is resoure lotion servie se on DHT with noes in the DHT responsile for mintining prt of the hsh rnge whih represents n inex to ville resoures. The priniple vntges of DHTs re their slility n effiieny. A reltively smll mount of stte is mintine per noe in orer to route queries; query resolution pth lengths re short, only inresing logrithmilly with the numer of noes in the network. However, it is unlikely tht the integrity of DHT n e mintine esily where there is high noe or link filure rte without signifint messge trnsmission overhe. This issue is resse in the serh protool use in JXTA [15] whih is se on DHT ut iffers in tht it is loosely-onsistent. A ertin mount of inonsisteny is tolerte euse hsh tle inexes re replite t neighours n, if noe fils, request resolver n inspet the inexes losest in rnge to the trget. Although this lgorithm n tolerte ertin level of noe filure, the messge overhe inreses s the istriute inex eomes inresingly inonsistent. The DHT my eome unusle in onitions of high reltive noe moility tht hrterises some uiquitous omputing opertions. In [8] the resoure isovery protool mintins istriute inex of resoure informtion ut glol resoure informtion is replite in eh iretory. The protool is esigne for use in MANET n is integrte with the unerlying, protive routing protool. Noes with the gretest trnsmission rnge re use s oth iretory gents n routers. The routing lgorithm my not e suitle where noes hve high link filure rte s the overhe of eleting n mintining the iretories will e too gret. Konrk [6], UPnP [9] n SLP [4] llow isovery of resoures on emn. They re ll ptive in the sense tht they n mke use of pre-onfigure, entrlly lote server, lthough they o not rely on the presene of suh n entity; ny noe my hoose to t s iretory n pulish requests. The resoure isovery lgorithms re simple ut gin, they rely on fully route network infrstruture whih my not e ville in pervsive omputing environment. 3. RUBI RUBI, our resoure isovery frmework for uiquitous omputing, represents novel pproh. This is primrily euse it enpsultes n overrhing ptive proess, ontrolling the wy tht informtion is isseminte n retrieve, se on lol views of the struture of the network. The esign of RUBI is foune on the hypothesis tht there re signifint similrities etween resoure isovery in network n the opertion of routing lgorithm, sine oth re funmentlly onerne with the issemintion of informtion out the vilility n effiieny of ess to resoures. It is, therefore, our ontention tht the lessons lerne in this omin n e pplie more generlly n, inee, tht the regulr exhnge of routing informtion n form the sis for the exhnge of more generl informtion

3 out servies. Within the fiel of moile ho networking, there re, roly, two ifferent pprohes to the issemintion of routing informtion. The first is protive, in whih tles of forwring pths re perioilly exhnge, s in fixe network routing lgorithms suh s OSPF, [10]; the seon is retive, in whih informtion out routes is etermine on n s-neee sis suh s in DSR n AODV, [7, 11]. These ifferent pprohes re useful in ifferent irumstnes. Thus, for exmple, in res of high reltive moility, routing informtion eomes outte rpily, so retive isovery is more likely thn protive to give goo nswer. In res of low reltive moility, protive issemintion of informtion is more effiient, sine little hnges. Unsurprisingly, rnge of hyri pprohes to issemintion hve lso een evelope; ZRP, [5] is n exmple. The sme istintion etween high n low reltive moility is importnt in more generl servie isovery: the former mens tht effiient plement of servie informtion is iffiult n expensive, the ltter tht it is resonle to expen yles in orer to ensure effiient lookup. In line with this, in res of low reltive moility, RUBI uses isovery mehnism se on protive routing lgorithm n resoures re vertise throughout the network. In regions of high reltive moility, where it is possile to gurntee neither the vilility of noe tht will t s iretory nor the ury of resoure informtion, RUBI initites ynmi resoure isovery using retive protool n isovers resoures s they re neee. It is importnt to note tht RUBI llows noes to mke lol eisions out whih of these pprohes it will opt t ny given point: in other wors, within lrge onnete network, there re expete to e ynmilly efine n ynmilly hnging res of protivity n of retivity tht must interwork to llow semless servie isovery for lients. This pproh is refletive of the ft tht it is unresonle to expet networking environments to e either entirely stti or entirely free moving. The ility to pt lso mens tht RUBI is resilient to filure over the wie rnge of network onitions tht my e foun in n uiquitous omputing environment n n operte in oth infrstruture-se n moile ho network types, migrting semlessly etween oth. RUBI hs een esigne to operte t either the network lyer of the OSI moel or ove the trnsport lyer. It relies on the servies provie y link lyer protool suh s ut oes not require routing protool or relile trnsport servie: s RUBI is se on routing protools, it n provie this funtionlity if neee. In the following setion, we exmine the etile opertion of RUBI. For the ske of lrity we rek this own into four key spets: the protive n retive isovery mehnisms themselves; the lol eision proeure tht etermines whih type of servie vertisement n isovery to use; the issues in ensuring interopertion etween the ifferent isovery mehnisms; n the issue of filure. 3.1 Disovery opertion The two ho network routing lgorithms selete s sis for RUBI re OLSR [14], whih is protive lgorithm suite to firly stle, ensely populte networks, n AODV, retive protool suite to networks of up to thousns of noes in size, where the popultion of noes my hve reltively high moility rte. These lgorithms hve een hosen euse they integrte well in situtions where oth re running in lose proximity: oth lgorithms llow noes to he resoure informtion n requests n e nswere y n intermeiry tht is not the resoure provier yet hs up-to-te he informtion. There re four messge types use in RUBI n these re resoure vertisements, resoure nelltions, resoure requests n replies. The two resoure isovery lgorithms proess these messges ifferently. The protive resoure isovery lgorithm uses informtion from the neighour estlishment proess esrie in setion 3.2 n eh noe elets suset of its neighours s relys. Relys re highly-onnete noes responsile for propgting resoure informtion further through the network using other rely noes in turn. In this wy, the use of relys enles optimise flooing of messges, reuing the trnsmission osts of istriuting resoure informtion s ompre with lssi flooing. E E E F () F () F () g g g h I h I h I k k k j j j Key: Noe ting s rely Noe Figure 1: Protive Resoure Avertisement Figure 1, shows protive resoure vertisement s series of steps with the rrows representing messge trnsmission. In Figure 1(), noe rosts resoure vertisement whih will e reeive y rely E. The rely my not forwr the vertisement immeitely ut will perioilly onstrut n forwr omposite vertisements tht ontin etils out ll the resoures ville t those noes

4 iretly onnete to it. Figure 1() shows the resoure vertisement eing forwre in turn y rely E to its own rely set. Finlly, in Figure 1(), n vertisement is forwre to ll the neighours of rely F n rely I. At this point noes in the network will know out every resoure ville through rely E. Although resoure vertisements re istriute perioilly, the perio my vry in length epening on whether there hve een ny hnges in either the neighour memership or the resoures ville. If hnges re etete y rely then the resoure vertisements will e more frequent. The overhe of hing resoure informtion is only inurre y relys, lthough ny noe my store the resoure etils it reeives. In the se where noe hs hosen not to he resoure informtion then it will sen resoure request messge to its relys s neee n the rely noes will respon with reply messge if the resoure exists. A resoure nelltion messge reeive from resoure owner will e trete in the sme mnner s n vertisement. The rely reeiving the messge will upte its he, this time eleting the resoure etils, n susequent resoure vertisements will reflet the hnge. Protive isovery is goo strtegy for regions where noes hve low moility. The primry reson for this is tht urrent informtion out resoures is mintine t mny points: in this se, wherever there exists rely. Retive resoure isovery is hieve y mintining resoure informtion in the network for reently querie resoures only. Unlike protive isovery, ll noes re responsile for mintining their own hes of resoure informtion. A lient neeing to lote resoure initites request tht is flooe through the network. The sope of the request, in terms of the numer of hops it trverses, is ontrolle y time-to-live (TTL) vlue n noes n perform n Expning Ring Serh (ERS) y repeting the request with higher TTL if there is no response initilly. In this wy, the overhe of fining resoure in terms of the totl numer of messges generte is reue in irumstnes in whih resoure is ville nery. Any noe tht reeives request n owns, or hs lernt out, mthing resoure my reply to request; this reply is then unist k to the lient with informtion out the istne of the resoure holer in hops from the responer. Any noe operting the retive isovery lgorithm will ignore resoure vertisement n resoure nelltion messges, only proessing requests n replies. Retive isovery is goo strtegy for res where noes re firly moile n the overhe of mintining urte resoure informtion throughout the region woul rry high messge trnsmission overhe. For oth lgorithms, routes to noes serving resoures oul e onstrute if neessry just s they woul e in the norml opertion of the routing lgorithms use s sis for RUBI. In the se of the protive lgorithm, routes woul e lulte s resoure vertisements trvel through the network; wheres for the retive lgorithm, routes woul e lulte t the sme time s request messges re forwre. 3.2 Neighour estlishment n lgorithm seletion Hving seen tht RUBI n operte in iniviul res of protivity or retivity, we nee to onsier how noe etermines to whih suh re it elongs. Eh noe must e ple of mking this eision in n utonomous fshion, se on the informtion it is le to glen from its immeite lolity. A noe will only use protive resoure isovery lgorithm if the links with its neighours re suffiiently stle, tht is to sy, they hve remine neighours for t lest the urtion of given threshol vlue. For RUBI, the optimum rnge for this threshol will e etermine through simultion. Although neighour estlishment represents n overhe in terms of the resoure isovery proess, in tht it oes not iretly ontriute to it, it serves n importnt purpose. The ojetive of neighour estlishment is twofol. Firstly, s with OLSR, it enles noes to sertin the most effiient metho of isseminting the protool, (resoure isovery) messges through the network. Essentilly, this is hieve y eleting noes with the gretest trnsmission pility n the highest numer of links in the lolity to t s relys thus ensuring tht messges re propgte through the network with the minimum numer of retrnsmissions, n importnt onsiertion for power-onstrine noes. Seonly, in RUBI, neighour estlishment llows eh noe to monitor the longevity of links in its immeite lolity n, se on the pereive stility, to utonomously selet the most effiient resoure isovery lgorithm to use. In RUBI, the neighour estlishment proess use is extly the sme s tht use in the OLSR routing lgorithm. A RUBI noe rosts HELLO eons perioilly n the reeiving noes use these s wy of uiling up piture of the lol topology to 2-hop istne. Eh HELLO messge ontins willingness vlue n list of the noe s neighours. Willingness is expresse s numeri vlue etween 0 n 7 representing the menility of the sener to fulfill the role of rely y forwring messges, hing resoure lotion informtion n responing to resoure isovery requests. A limite mount of informtion out neighours is lso psse on with their ientity n neighours re tegorise oring to whether the sener hs selete the neighour s rely. In this wy, eh noe n uil up piture of oth its immeite neighours, n those neighours 2 hops wy (tht is to sy, its neighours neighours). It will lso lern whether it hs een selete s rely y the origintor of the HELLO messge n shoul fulfill the rely funtion for tht neighour. Informtion out oth immeite n 2-hop neighours is store y noes in neighour tle n 2-hop neighour tle n these tles re upte with every HELLO messge reeive. Entries re ssoite with n expiry time n will e remove from the tle if no upte rrives. The heuristi use y eh noe to selet the suset of its neighours to use s relys n e summrise in 3 steps. Firstly, ll neighours vertising the mximum willingness vlue re utomtilly selete s relys. Seonly, neighour noes tht re the only noes through whih 2-hop neighour is (or neighours re) rehle re e to the set. Finlly, neighours through whih the remining noes in the 2-hop group n e rehe re inlue in the rely set. If there is more thn one neighour noe tht fulfills this onition then the one with the gretest numer of links is hosen. Rely seletion is illustrte in Figure 2 n in this exmple, the seletion proess for noe Z is esrie. It is ssume tht neighouring noes hve i-iretionl ommunition. The trnsmission overge for noe Z is shown

5 s irle with soli irumferene n noe Z s neighours re w, x n A. The irle with otte irumferene represents the trnsmission overge for noe A. Noe A is se sttion n hs muh greter trnsmission pilities thn the other noes surrouning it. noe A s neighours re,,,e,f,w n Z. Assuming tht noe A sens noe Z HELLO eon ontining the mximum willingness vlue it will e selete y Z s rely. Using the neighour informtion ontine in the HELLO eon from noe A, noe Z n tell tht it n reh ll of its 2 hop neighours prt from noe Y, through A. Assuming tht noe Y n only e rehe through noe x, noe x will e e y Z to its rely set. At this point, lultion of the rely set is omplete s ll neighours n 2-hop neighours n e rehe. When noe Z onstruts its own HELLO eon it will set flg initing tht it hs hosen noe A n noe x to t s relys on its ehlf. request oring to the rules of the retive lgorithm. This is hieve y setting flg in the resoure request messge to inite tht it shoul e elt with in the sme wy s the retive protool n the request is rost onwrs. At noe q, the request is stisfie, n reply is onstrute n returne long the route of the request. B Protive Region C D p Key: Noe ting s rely Noe r Retive Region q Key: e f A The trnsmission rnge of noe A The trnsmission rnge of noe Z The trnsmission rnge of noe Y Z w x Noe Y Bse Sttion Figure 2: Neighour Estlishment for Noe Z 3.3 Coexistene of protive n retive protools In orer for glol system to operte, the res in whih the ifferent pprohes to servie isovery re eploye must interwork. Sine, y efinition, suh res will orer one nother, there must e jent hosts tht onsier themselves prt of ifferent types of re n n t s gtewys etween the res. In most ses, opertion etween the protive n retive regions t gtewy noes is semless, ut there is one senrio in whih the protive protool must e moifie. A simple ltertion is propose in the first instne. In Figure 3, there is user t noe in the region where the protive resoure isovery protool is use tht wishes to know out printing servie. Thus, s noe is lrey wre of ll the resoures ville in the re, (or n fin this out from rely D), it is wre tht tht there is no suh resoure ville. In this se, it is neessry to forwr the query into the retive region n noe ttempts to serh eyon the oun of the immeite re y forwring the Figure 3: Integrte Disovery Protools 3.4 Reovery from filure Filures n e tegorise s those in whih resoure eses to e ville, n those where noe, n therefore ll the resoures it offers, is no longer ville for some reson. The freshness of resoure informtion in RUBI is mintine in the sme wy s in Jini. Tht is to sy, ny resoure informtion he is ssoite with n expirtion perio, fter whih it is elete. If resoure eomes unville efore the expirtion perio hs elpse then the informtion serve will e inorret. Where retive lgorithm is in opertion, there is no simple wy to etet whether the resoure remins ville throughout the expirtion perio. This is euse resoure request my e nswere y noes tht hve reently he informtion, rther thn y the resoure owner. If protive lgorithm is use, resoure filure etetion my e more urte s it is possile for resoure owner to istriute resoure nelltion messge. As result, rely n elete resoure informtion n will not istriute it with the next vertisement. RUBI hs no speil reovery proeure for resoures tht go offline n return short while lter n in this se, resoure owners will register resoures with relys in the usul wy if protive lgorithm is in use. A noe tht noties hnge in its lol topology, suh s the ispperne of link to its neighour, will permnently elete the neighour from its tse long with ny resoures hoste on it. Inorret informtion regring the vilility of the file noe n its resoures will remin in the network until either, resoure vertisement is propgte tht reflets the hnge or, informtion out the noe n its resoures expires. In terms of resoure informtion vilility, the protive lgorithm is resilient in the fe of rely filure n if one or more of lient s relys fils, lient n still hve its queries nswere y ny remining relys in its set. In the

6 sitution in whih rely omes k online fter short ispperne, there re severl possile reovery mehnisms. A rely tht temporrily loses onnetivity oul request resoure informtion from one of its own rely set when it omes k online n if the RUBI noe is lso proviing route informtion for the resoures it hs then this n lso e requeste. 4. DISCUSSION In this setion, RUBI is ompre with the other resoure isovery protools esrie previously in setion 2 n the vntges n isvntges of the RUBI frmework re evlute. Unlike the other resoure isovery protools reviewe, RUBI hs een esigne with n uiquitous omputing environment in min. The novel esign of RUBI reflets treoff etween the ility to pt ynmilly se on knowlege of lol onitions n the effiienies gine y ssuming firly stle environment. Aptility omes t ost n RUBI must perioilly monitor the urtion of neighour links to ssess the stility of its lolity. This represents n overhe in terms of nwith onsumption tht the resoure isovery protools reviewe o not inur s they ssume fully route infrstruture. Furthermore, RUBI will not hieve the effiieny of those servie isovery protools tht he informtion entrlly (Jini) in terms of the numer of messges trnsmitte in orer to mintin n up-to-te view of resoures. Neither will it ttin the slility of those protools tht mintin istriute inex suh s INS/Twine. In RUBI, informtion is he t mny more ples in the network, inurring itionl resoure overhe to upte the informtion in eh he. 5. CONCLUSIONS AND FURTHER WORK Resoure isovery will e key ftor in enling the uiquitous omputing vision where the evies emee in our surrounings utonomously ooperte to isover n provie servies with miniml humn intervention. By ientifying the fetures tht typify opertion in suh n environment, it hs een possile to esign resoure isovery frmework tht is well-suite to it, nmely RUBI. Primrily, the ppliility of resoure isovery lgorithm epens on the fetures of the network in whih it is operting. For uiquitous omputing, the network is hrterise y regions tht re firly stle possily oexisting with regions where noes re highly moile n filure-prone. RUBI represents novel pproh euse it is se on routing lgorithms, thus ensuring the effiient issemintion of resoure informtion. Furthermore, RUBI is ptive n, y monitoring the network in the lolity, noes utonomously selet the most suitle routing lgorithm to use. In the future, the performne of RUBI will e evlute through simultion uner ifferent network onitions, vrying the network size, noe egree n noe moility level n the numer of resoures n requests. Furthermore, series of esign improvements will e ssesse. As strting point, the protool integrtion in RUBI is too simplisti with relys flooing requests through the protive region if they nnot e resolve. It woul e more effiient to unist requests to gtewy noe tht orers the protive region n mens of hieving this will e explore. Finlly, the seurity of the RUBI protool will e resse y integrting it with it with ADAM [13], milewre rhiteture for istriute ess-ontrol. 6. REFERENCES [1] M. Blzinsk, H. Blkrishnn, n D. Krgr. INS/Twine: A slle peer-to-peer rhiteture for intentionl resoure isovery. In Pro. of the Interntionl Conferene on Pervsive Computing (PERCOM 2002). Springer-Verlg, [2] D. Chlmers, M. Slomn, n N. Duly. Mp pttion for users of moile systems. In WWW10, pges , [3] K. Cheverst, N. Dvies, K. Mithell, n A. Friy. Experienes of eveloping n eploying ontext-wre tourist guie: the GUIDE projet. In Moile Computing n Networking, pges 20 31, [4] E. Guttmn. Venor Extensions for Servie Lotion Protool, Version 2, Network Working Group, Request for Comments: [5] Z. Hs. A new routing protool for the reonfigurle wireless networks. In Pro. of the IEEE Int. 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