Explicit Proactive Handoff with Motion Prediction for Mobile IP

Transcription

1 Explicit Practiv Handff with Mtin Prdictin fr Mbil IP Fang Fng, and Duglas S. Rvs Dpartmnts f Elctrical and Cmputr Enginring and Cmputr Scinc Nrth Carlina Stat Univrsity Raligh, NC Tl: (919) , {ffng, rvs}@s.ncsu.du Abstract Mbil IP has bn widly accptd, but lacks a fast handff mchanism. In this papr, w intrduc an xplicit practiv handff schm with mtin prdictin. Sinc ach usr has pattrns f mvmnt, a mbil nd prdicts its futur mtin and xplicitly ntifis its ld frign agnt which subnt it is likly t handff t. During a handff, th ld frign agnt duplicats and frwards packts t th prdictd subnts. With ur schm, ntwrk-layr handff latncy can b rducd t th lvl f link-layr handff latncy, and th numbr f packts lst during handffs is als minimizd. With a ral ntwrk activity trac, w dmnstrat that this schm is abl t prdict mtin accuratly, with nly a small vrhad in bandwidth cnsumptin and cmputatin. I. INTRODUCTION Wirlss lcal ara ntwrks (WLANs) hav bcm xtrmly ppular in ths yars. Link-layr mchanisms prvid supprt fr link-layr handff, which is usd t switch a mbil nd (MN) frm th radi link f n accss pint (AP) t that f anthr accss pint. Fr WLANs cnnctd by an IP backbn, Mbil IP [1] is th prtcl fr lcatin managmnt and ntwrk-layr handff. This updats th ruting infrmatin fr th MN, t rflct mvmnt frm n subnt t anthr subnt. Mbil IP, hwvr, still has prblms. First, it uss IP packts t transfr mbility managmnt infrmatin. Th latncy f ntwrk-layr handff is in th rdr f 0.1 t 1 scnd, 10 tims largr than link-layr handff latncy. This cannt mt th rquirmnt f dlay-snsitiv r ral-tim traffic. Th scnd prblm is handff disruptin. Mbil IP dsn t buffr packts snt t an MN during handffs. Thrfr, ths packts may b lst and nd t b rtransmittd. Th third prblm is that th tw typs f handffs ar cupld. Bcaus f th latncy gap btwn thm, packt lss will ccur vn aftr th cmpltin f link-layr handff. In mst circumstancs, an MN is carrid by an individual. As a rsult, it will b mvd accrding t hurly, daily r wkly pattrns crrspnding t a prsn s rgular activitis. Packt arrival pattrns als dpnd n th srvics and applicatins th prsn uss. Significant changs t ths pattrns ar likly t b infrqunt. Studis f wirlss ntwrks by Tang [2] [3] and Ktz [4] cnfirm this bsrvatin. An MN s pattrns can b utilizd t prdict its futur bhavir and assist handff. With prdictin, it is pssibl t prpar ntwrklayr handff bfr link-layr handff t rduc latncy and packt lss. Th MN s ptimal handff stratgy shuld als b adjustd dynamically accrding t th prdictin t minimiz handff cst. Handff dcisins basd n mvmnt prdictin liminats th nd t wait fr bacn signals frm thr subnts, and assists th discvry f handff targt in an nvirnmnt f vrlapping cvrag aras and changing wirlss channl cnditins. Basd n ths bsrvatins, w prps an xplicit practiv handff schm with mtin prdictin fr Mbil IPv4. It adpts a practiv apprach t prpar ntwrk-layr handff bfr link-layr handff. Each MN rcrds its mvmnt pattrns and prdicts its futur subnts. Bfr link-layr handff, th MN xplicitly ntifis its currnt frign agnt (FA) f th prdictd subnts. Th currnt FA thn duplicats packts snt t this MN, and frwards thm t ths prdictd subnts. Ntwrk-layr handff latncy is cls t that f link-layr handff, and packt lss is rducd by buffring frwardd packts at FAs. This schm is fully distributd bcaus th ntwrk-layr handff is cntrlld by th MN, and FAs ar ntifid nly if th MN rcmmnds packt frwarding. Th xtra bandwidth cnsumptin intrducd is much lss than that f thr practiv handff schms. Th rst f this papr is rganizd as fllws. W first rviw sm f th rlatd wrk in Sctin II. In Sctin III, th prpsd schm is dscribd. W valuat its prfrmanc with simulatin rsults in Sctin IV, and Sctin V is th cnclusin and futur wrk. II. RELATED WORK A numbr f schms hav bn prpsd t slv th prblms f Mbil IP mntind abv. Hr w fcus n ddicatd fast handff schms, which can b catgrizd as ractiv, practiv, r a cmbinatin f th tw accrding t whthr th packts snt t th MN start t arriv at th nw subnt aftr r bfr th link-layr handff. A. Ractiv Handff In simultanus and MIPv4 handff [5], whn an MN assciats with a nw AP, it snds MIPv4 rgistratin infrmatin t th nw FA. This infrmatin is cntaind within frams, and initiats MIPv4 lcatin rgistratin prcss. This schm rducs handff latncy, but dsn t

2 slv th prblms causd by th latncy gap btwn linklayr handff and ntwrk-layr handff. [6] utilizs a filtring databas and a MAC bridg cnncting WLANs. Whn an MN assciats with a nw WLAN, its MAC addrss is bradcast lcally by th nw AP. It is rcivd by th MAC bridg and strd in th filtring databas, alng with th crrspnding prt. Bfr th MN cmplts ntwrk-layr handff, th MAC bridg rlays MAC frams fr th MN frm th ld WLAN t th nw WLAN. Scalability and rliability may b prblms fr this schm, du t its dpndnc n a cntralizd bridg mchanism. B. Practiv Handff Th Dadalus prjct [7] uss IP multicast and buffring t rduc packt lss. Each bas statin and its nighbring bas statins frm a multicast grup. Whn an MN cnncts t a bas statin, it rgistrs a crrspnding multicast addrss at th hm agnt (HA). Using this addrss, packts ar multicast t and buffrd at th bas statins f this multicast grup. If an MN switchs t a nighbring bas statin, it can rciv packts bfr prfrming a ntwrk-layr handff t rgistr a nw multicast addrss. E. Shim t al. usd nighbrcasting [8] t achiv lw latncy handff. An MN can transfr its ld FA infrmatin t th nw FA, which thn cnstructs a nighbr tabl. Bfr link-layr handff, th MN ntifis th ld FA t frward duplicatd packts t all nighbring FAs. Ntwrk-layr handff latncy can b rducd significantly in this schm. R. Hsih t al. prpsd a samlss handff architctur fr Mbil IP [9]. A dcisin ngin is addd t th architctur f hirarchical Mbil IPv6. A handff is initiatd by an MN whn it rcivs bacn signals frm nighbring accss rutrs (ARs). And th dcisin ngin uss lcatin tracking infrmatin f th MN and lad infrmatin f ths ARs t dtrmin handff tim and targt. Packts snt t th MN ar initially frwardd t th nw AR by th ld AR, and simulcastd t bth ARs aftr th ld AR rqusts simulcast. This schm succssfully rducs ntwrk-layr handff latncy and packt lss, but it is cntralizd, rquirs xtra signaling and impss a bund n th spd f MNs. C. Cmbind Handff Lw latncy handff [10] [11] utilizs th L2 triggr mchanism (dscribd in sctin III-B). In pr-rgistratin handff, an MN prfrms ntwrk-layr handff bfr th link-layr handff, basd n infrmatin frm th L2 triggr. In pstrgistratin handff, an MN first cmplts link-layr handff. It cntinus using th ld FA and car-f addrss (CA) thrugh a bi-dirctinal tunnl btwn th ld FA and th nw FA. Th cmbind handff mthd first tris a pr-rgistratin handff. If it fails, pst-rgistratin handff is usd. Simultanus Binding [1] [13] aims at dcupling ntwrklayr handff frm link-layr handff, by nabling an MN t bind t multipl subnts simultanusly. An MN can rtriv th FA/CA infrmatin frm th bacn signals f APs, and rgistr multipl CAs with th HA bfr r aftr th linklayr handff. Th HA r crrspndnt nd (CN) frwards duplicatd packts t ths CAs simultanusly until th MN cmplts ntwrk-layr handff. Y. Gwn t al. intrducd Mbil Initiatd Tunnling Handff [14]. Bfr discnncting frm th ld AP, an MN can initiat a handff by snding th ld FA a handff rqust cntaining th nw FA s infrmatin gt frm th mbil prtriggr. Or it can initiat th handff prcss aftr cnncting t th nw AP and rciving a link-up triggr, and snd th nw FA a handff rqust cntaining th ld FA s infrmatin. A bi-dirctinal tunnl is st up btwn ths tw FAs fr th MN until it cmplts Mbil IP rgistratin. This schm achivd lw latncy and lw lss handffs with lss rquirmnts n L2 triggrs and accss ntwrks than thr fast handff schms. Gnrally th practiv apprach prvids bttr prfrmanc, sinc packts ar frwardd t th nw subnt in advanc. But ths practiv schms can caus unncssary handff prparatins and frward t many duplicatd packts. Nighbrcasting frwards duplicatd packts t all nighbr FAs withut cnsidring th MN s mving dirctin. With simultanus binding, an MN binds t any subnt frm which it can rciv a bacn signal, althugh in fact it may nt dirctly mv t all ths subnts. As argud in th shadw clustr cncpt [12], a MN has influnc nar its currnt lcatin and alng its anticipatd path, and rsurc rsrvatin shuld b mad fr th MN basd n th prdictd dmands. This ida can b applid t imprv th prfrmanc f practiv handff, and is n f th majr mtivatins f ur prpsal. III. PROACTIVE HANDOFF WITH MOTION PREDICTION A. Mtivatins W wish t minimiz th ffrt and ptimiz th prfrmanc f ntwrk-layr handff whn an MN is mving amng WLANs cnnctd by an IP backbn. Each MN prdicts its futur mvmnt basd n th rcrdd mvmnt pattrns, and us this t prpar ntwrk-layr handff t rduc handff latncy and packt lss. Handff dcisin basd n mvmnt pattrns liminats th nd fr th MN t wait fr bacn signals frm nighbring subnts, which typically taks hundrds f milliscnds. Handff targt discvry nly basd n rcivd signal strngth can b a prblm whn th MN is in th vrlapping cvrag aras f multipl subnts and wirlss channl cnditins hav grat fluctuatin. Mvmnt pattrns can prvid anthr critrin t find th mst pssibl handff targt in such a cas. Mvmnt pattrn and mtin prdictin ar nly cncrnd with ntwrk-layr mvmnt, i.., th lgical mvmnt btwn subnts. Physical r ggraphic lcatin is f n imprtanc t ur schm. W spculat that ntwrk-layr mvmnt is simplr and mr prdictabl than ggraphic mvmnt, and is mr maningful fr ur purpss. Fr xampl, sinc subnts ar f diffrnt shaps and sizs, an MN s ggraphic mvmnt paramtrs may nt dirctly

3 crrspnd t its rgular activitis, which n th thr hand can b infrrd by its ntwrk-layr mvmnt. It is als dsirabl t imps as fw mdificatins t Mbil IPv4 as pssibl, and t rquir th minimum amunt f additinal capabilitis frm th link layr. Aftr dscribing th mthd, w will rturn t ths statd mtivatins. B. Systm Ovrviw Th systm is assumd t hav multipl WLANs cnnctd by a wird IP backbn. Mbil IPv4 is usd fr lcatin managmnt amng subnts. Th prpsd practiv handff schm is usd t rduc th latncy and packt lss f ntwrk-layr handff. Authnticatin and authrizatin f usrs ar issus that must b handld by sparat prtcls. Th prpsd schm utilizs th L2 (layr 2) triggr mchanism 1. Th Mbil Triggr ntifis th MN abut an impnding link-layr handff, and th Link-Up Triggr infrms th FA that an MN has cnnctd t th radi link f its subnt. Bacn signals (link-layr frams) pridically transmittd by ach AP cntain infrmatin fr bth link-layr and ntwrk-layr handffs, such as th ID f th AP, th AP s frquncy hpping r dirct squnc paramtrs, th subnt ID and th IP addrss f th FA in that subnt, tc. Thrfr an MN ds nt nd t wait fr an FA advrtismnt t initiat lcatin rgistratin whn it cnncts t th radi link f an AP in anthr subnt. Tw nw mssags ar ndd at th ntwrk layr. Th first, th Frwarding Rqust mssag, is snt frm an MN t th FA f its currnt subnt nc th mvmnt is prdictd and th MN dcids t handff. This mssag cntains th ID(s) and FA IP addrss(s) f th subnt(s) t which duplicatd packts shuld b frwardd. Th scnd, th Stp Frwarding mssag, is snt by th MN s HA t its prvius FA nc th MN cmplts lcatin rgistratin. This infrms th prvius FA t stp frwarding duplicatd packts. Th MN is rspnsibl fr rcrding ntwrk-layr mvmnts. Frm this mvmnt histry, th MN will prdict its futur mtin using th path prdictin algrithm. Each MN maintains a FIFO mvmnt histry cach. An ntry in th mvmnt histry cach rcrds th ID f a subnt t which th MN was prviusly attachd, th start tim f this attachmnt, and th IP addrss f th FA in that subnt. Aftr th MN cnncts t th radi link f a nw subnt, it crats a mvmnt histry cach ntry f this cnnctin, accrding t th bacn signal. It als has a pattrn databas t str mvmnt pattrns, which ar squncs f mvmnt histry cach ntris. C. Handff Prcss Figur 1 shws th mssag diagram f a handff. Th handff prcss is dscribd as th fllwing: 1) Th MN mvs t a subnt bundary. Th Mbil Triggr infrms th MN abut an impnding link-layr 1 As spcifid in th Intrnt Draft Supprting Optimizd Handvr fr IP Mbility - Rquirmnts fr Undrlying Systms d r i P g a rdin rw F l ta T MN r a l g rv t rig T In il b a n c Md v Old FA Frw arding R qust Packts Old AP A Disassciatin Rqust Disassciatin Rply a y r f Ḻ Assciatin k a n d n c y Rqust a t in H L Assciatin Rply L c y n IP a t L b il n ti M g istra R Fig. 1. Actual Actual Prdictd Nw AP Nw FA Nw FA(s) Mbil Triggr Fird Frward Duplicatd Packts Link-Up Triggr Fird Dlivr Frwardd Packts Lcatin Rgistratin Rqust Lcatin Rgistratin Rply Stp Frwarding Mssag Diagram during a Handff Lcatin R gistratin Rqust Lcatin Rgistratin Rply handff whn th rcivd signal strngth frm th currnt AP falls blw th thrshld lvl. 2) Th MN, with th infrmatin in its mvmnt histry cach and pattrn databas, uss th path prdictin algrithm t prdict th subnt r subnts t which it is likly t mv. (If th histry data is nt sufficint t mak a prdictin, th MN will randmly chs n f th nighbring subnts as th prdictd subnt. If it is first tim that th MN assciats with th currnt subnt, it will nt d any practiv handff, and th standard Mbil IPv4 mchanism will b usd.) Th numbr f prdictd subnts can b pr-dfind. 3) If thr is a prdictd subnt r subnts, th MN snds th ID(s) and FA IP addrss(s) f th prdictd subnt(s) t th currnt FA. Thy ar snt in a Frwarding Rqust mssag. 4) Data packts snt t th MN during th handff ar first tunnld t th currnt FA by th HA, r dirctly by th CN with rut ptimizatin. Th currnt FA first dcapsulats ths packts, and thn duplicats and frwards thm t th FA(s) f th prdictd subnt(s) using IP-within-IP ncapsulatin. Th prdictd FA(s) dcapsulats and buffrs ths data packts in anticipatin f th arrival f th MN. 5) If th MN cntinus mving, it vntually prfrms a link-layr handff t cnnct t th radi link f an AP in th nw subnt. A nw ntry fr this mvmnt is cratd in th mvmnt histry cach. Th MN thn cmpars th ID(s) f th prdictd subnt(s) with th HA

4 ID frm th bacn signal f th nw AP. 6) If th prdictin was nt crrct, th duplicatd packts snt t th prdictd FA will nt rach th MN. Ths packts will vntually hav t b rtransmittd, as is nrmally th cas withut practiv handff. Thrfr th schm falls back t th standard Mbil IPv4. 7) If th prdictin was crrct, th Link-up Triggr infrms th FA f th nw subnt t dlivr its buffrd data packts t th MN. 8) Th MN rgistrs its nw car-f-addrss with th HA using Mbil IPv4 mchanisms. 9) Th HA snds a Stp Frwarding mssag t th ld FA t finish th handff prcss. Our schm can als wrk in cnjunctin with thr schms t dtrmin th handff targt. A sparat mchanism can initially chs a crtain subnt as th handff targt accrding t a varity f critria such as th functinality f this subnt. Thn ur schm will captur such a rgular bhavir and us it t prdict th futur ntwrk-layr mvmnt f this MN. Th xtra vrhad f ur schm includs th cst t rcrd mvmnt histry and d prdictin, th transmissin and prcssing cst f Frwarding Rqust and Stp Frwarding mssags, and th cst t duplicat and frward data packts. D. Path Prdictin Algrithm Thr hav bn a numbr f mbility mdls, such as th fluid flw mdl and th randm walk mdl. Ths mdls dscrib th aggrgat bhavir f th MNs, and ach MN s mvmnt is indpndnt and randm frm th systm s viw. Ths mdls als dscrib mvmnt in trms f th chang in th physical lcatin f th trminals, rathr than in trms f th chang in th subnts thy attach t. Thrfr, w adptd an imprvd vrsin f th mtin prdictin algrithm prpsd by Liu and Maguir [15]. This mthd is dsignd fr tracking individual MNs using histrical mvmnt pattrns, and is basd n lgical mvmnts rathr than ggraphical mvmnts. In this mdl, an MN ntrs a nw stat whn it cnncts t th radi link f a subnt. If it stays cnnctd t this subnt fr mr than a spcifid prid f tim, this stat is a statinary stat. Othrwis it is a transitinal stat. A mvmnt track (MT) mdls th mvmnt f a MN n a rgular rut, starting frm and nding at diffrnt statinary stats. A mvmnt circl (MC) mdls th MN s lngtrm rgular bhavir, and starts frm and nds at th sam statinary stat. Fr prdictin purpss, th algrithm attmpts t crrlat currnt mvmnt (i.., a squnc f subnts that has just bn visitd) with past mvmnt (i.., a squnc f subnts that was visitd at sm prvius tim and strd in th pattrn databas). Thr ar thr typs f matching fr crrlatin analysis. Th first typ is stat-matching, which indicats th fractin f stats in cmmn btwn th currnt squnc and a past squnc. In Equatin 1, m s is th numbr f idntical stats and N s is th ttal numbr f stats. µ = m s (1) N s Th scnd typ f matching is vlcity-matching. This indicats th similarity btwn th mvmnt vlcitis f th currnt squnc and a past squnc. In Equatin 2, (t i+1 t i ) j is th intrval btwn stat i and stat i +1 f squnc j. Ns 1 i=1 (t i+1 t i ) currnt (t i+1 t i ) past η = (2) N s 1 W prps a third typ f matching, calld ccurrncmatching. Lt T currnt b th starting tim f th currnt squnc, T past,l b th tim f th last ccurrnc f sm past squnc, and τ past,k b th kth intrval btwn tw cnscutiv ccurrncs f this past squnc. Equatin 3 cmputs hw cls th intrval btwn th currnt squnc and th last ccurrnc f a past squnc matchs th intrval btwn any tw cnscutiv ccurrncs f th past squnc. (T currnt T past,l ) τ past,k Φ=min (3) k τ past,k Whn an MN cnncts t th radi link f a nw subnt, it ntrs a nw transitinal stat. If it stays attachd lng nugh, this stat bcms statinary, and th MN starts pattrn dtctin. It uss stat-matching t crrlat th currnt squnc in th mvmnt histry cach with ach MT and MC strd in th pattrn databas. If thr is n match, th currnt squnc is addd t th pattrn databas, thrwis th infrmatin f this MC/MT in th pattrn databas is updatd. Thn th currnt squnc is rmvd frm th mvmnt histry cach if ncssary. Whn a Mbil Triggr firs, th MN initiats th handff prcss and starts mtin prdictin. It crrlats th currnt squnc in th mvmnt histry cach t th strd MCs and MTs, using (in rdr) stat-matching, thn vlcity-matching, and aftr that ccurrnc-matching, until n f th MC/MT matchs th currnt squnc. Th subnt at th crrspnding psitin f th final matchd MC/MT is th prdictd subnt. Th numbr f prdictd subnts can b adjustd as rquird by th MN. Th MN can als ptinally maintain a transitin prbability matrix amng th subnts, fr us in cas th currnt mvmnt ds nt match any prviusly-strd pattrn. IV. PERFORMANCE EVALUATION Thr ar svral ways t valuat th prfrmanc f th prpsd practiv handff schm. T valuat its ffctivnss, w us handff latncy and prdictin miss rat. T valuat its fficincy, w us th fractin f duplicatd packts in all packts, which indicats hw many xtra data packts ar gnratd by ur schm. A. Simulatin Scnari Fr purpss f valuatin, w simulatd handff bhavir f a st f mbil nds. This simulatin is basd n an actual trac takn frm th campus-wid wirlss ntwrk f

5 Dartmuth Cllg [4]. It rcrdd th activitis f almst 2000 MNs fr an acadmic trm in an IEEE b ntwrk which cvrs 161 buildings and cntains 81 subnts. Th trac includs charactristics f bth rsidntial and wrk-rlatd mvmnts, sinc it rcrdd th ntwrk activity in bth drms and acadmic buildings. Th trac cntains tim-stamps and infrmatin n MNs assciatin and rassciatin activitis with accss pints, but lacks dtails abut th ntwrk tplgy, r rliabl disassciatin signaling. It als ds nt distinguish a dirct handff with th cas that an MN was turnd ff, mvd t anthr subnt and turn back n. Du t th limitatin f th trac, w mad th fllwing assumptins in ur simulatin: 1) Each subnt has n and nly n AP. 2) Each transitin frm a subnt t anthr subnt is a dirct handff. 3) Each MN stays at a subnt until it assciats with anthr subnt. 4) Tw subnts ar nighbrs if and nly if thr is at last n transitin btwn thm. 5) Rassciatin t th sam subnt is nt a handff. Thr is n training prid in ur simulatin. Fr purpss f cmputing packt lss and duplicatin rats, w usd a simulatd CBR traffic, with a packt intrarrival tim f 3.75ms fr asir cmparisn with thr prpsd schms. Sinc ur schm is fr highly mbil usrs, w nly shw th simulatin rsult fr th mbil nds with at last an avrag f 6 handffs daily; thr wr 585 such MNs. Fr prfrmanc cmparisn purpss, w assum link-layr handff latncy is 50ms, and Mbil IP rgistratin latncy is unifrmly distributd btwn 200ms and 700ms. W simulatd th prfrmanc f ur schm fr th cas f n prdictd subnt, and tw prdictd subnts. B. Handff Latncy Figur 2 shws th distributin f th avrag ntwrk-layr handff latncy f ach MN, using ur schm with prdictin f n r tw subnts. It can b sn that th latncy f ur schm is much lss than that f Mbil IP, and quit cls t link-layr handff latncy. With prdictin f tw subnts, th latncy f ur schm is lss than 160ms fr abut 80% f th MNs. This is 3X fastr than nrmal Mbil IP handff latncy. Th avrag tim t cmput a prdictin was lss than 0.15 ms pr handff n a Pntium IV 1.7GHz PC with 256MB mmry. Thrfr w spculat that th algrithm is mr than fast nugh t supprt practiv handff, vn n a PDAtyp dvic. C. Prdictin Miss Rat In Figur 3, w shw th distributin f prdictin miss rat f ach MN, using ur schm with prdictin f n r tw subnts. With prdictin f tw subnts, abut 80% f th MNs hav a prdictin miss rat lss than 0.3. With prdictin f n subnt, abut 80% f th MNs hav a prdictin miss rat f lss than Cmpard with th miss Fractin f MNs Fractin f MNs Empirical CDF L2 handff 2 prdictin 1 prdictin Mbil IP Avrag Latncy (sc) Fig. 2. CDF Plt f Avrag Handff Latncy Empirical CDF nighbrcast 2 prdictin 1 prdictin 2 randm 1 randm Miss Rat Fig. 3. CDF Plt f Prdictin Miss Rat rat f randmly slcting n r tw nighbring subnts, ur prpsd schm has a much lwr miss rat. Only abut 8% f th MNs hav a miss rat lss than 0.3 whn randmly slcting 2 nighbr subnts. Nighbrcasting snds packts t all nighbring subnts, and s shuld rprsnt th lwr limit f th prdictin miss rat. Its miss rat is shwn by th lftmst lin in th figur, and is gratr than zr bcaus a miss is incurrd whn a mvmnt frm n spcific subnt t anthr ccurs fr th first tim. Our rsult using prdictin f tw subnts is quit cls t this limit. This cnfirms th valu f prdicting MN mvmnt basd n past histry. W bliv that prdictin using mr cmplt tracs, with infrmatin abut ntwrk tplgy and MN pwr-dwn vnts, shuld d vn bttr. Using ur schm with prdictin f tw subnts, th avrag numbr f packt lsss pr handff du t prdictin misss is abut 19, cmpard with 133 fr Mbil IP and 5 fr nighbrcasting.

6 Fractin f MNs Empirical CDF 1 prdictin 2 prdictin nighbrcast Fractin f Duplicatd Packts Fig. 4. CDF Plt f Fractin f Duplicatd Packts D. Extra Handff Ovrhad Sctin III discussd th xtra vrhad f th prpsd schm. Sinc ur schm is fully distributd, mvmnt rcrding and prdictin dn t incur any cst t th ntwrk. Th numbr f Frwarding Rqust and Stp Frwarding mssags is trivial cmpard with th ptntial numbr f duplicatd data packts, s w fcus n masuring ths duplicatd data packts. Figur 4 shws th distributin f th fractin f duplicatd packts in th 585 MNs, basd n CBR traffic surcs. With prdictin f tw subnts, th fractin f duplicatd packt is lss than fr abut 90% f th MNs, and lss than fr 80% f th MNs. This is much bttr than nighbrcasting. Fr instanc, nly abut 45% f th MNs hav a fractin f duplicatd packts lss than with nighbrcasting. Our schm is vn mr fficint whn thr ar multipl MNs laving th sam subnt at th sam tim and a burst f duplicatd data packt ccurs. V. CONCLUSION AND FUTURE WORK In this papr w prpsd an xplicit practiv handff schm basd n th mvmnt pattrns f mbil nds. An MN can anticipat a handff frm th L2 triggr, and us lcally strd mvmnt pattrns t dynamically prdict th nxt subnt. As a rsult, handff latncy and packt lss rat is dramatically rducd, with a cst f a small numbr f duplicatd packts. This schm wrks in a fully distributd fashin and intrducs much lss duplicatd packts than anthr practiv handff schm, nighbrcasting. It als liminats th nd t wait fr bacn signals, and slvs th prblm f handff targt discvry whn th cvrag aras f multipl subnts vrlap with ach thr. It ds nt rquir spcific radi tchnlgy, r spcial ruting tchniqus such as multicast. It kps th currnt Mbil IP infrastructur and augmnts it t imprv prfrmanc. Our futur wrk includs using a bttr trac, if availabl, t furthr dmnstrat th bnfits f th prpsd schm. W plan t xtnd this apprach t th cas f multi-tir wirlss ntwrks as th MN can practivly switch t subnts n diffrnt tirs accrding t its wn pattrn. W als plan t us it t nfrc QS in handffs sinc an MN can ngtiat handff paramtrs with FAs accrding t its QS rquirmnts. Adptin f this schm in Mbil IPv6 and implmntatin ar als undr cnsidratin. REFERENCES [1] C. Prkins, Ed., IP Mbility Supprt fr IPv4, IETF RFC3344, August [2] D. Tang and M. Bakr, Analysis f a Lcal-Ara Wirlss Ntwrk, in Prc. MOBICOM 2000, August [3] D. Tang and M. Bakr, Analysis f a Mtrplitan-Ara Wirlss Ntwrks, Kluwr Wirlss Ntwrks, 8(2-3), pp , March-May [4] D. Ktz and K. Essin, Analysis f a Campus-Wid Wirlss Ntwrk, in Prc. MOBICOM 2002, Sptmbr [5] S. Gswami, Simultanus Handff f Mbil-IPv4 and , Intrnt Draft, IETF, draft-gswami-mbilip-simultanus-handff-v4-02.txt, Fbruary [6] H. Ykta t al., Link Layr Assistd Mbil IP Fast Handff Mthd vr Wirlss LAN Ntwrks, in Prc. MOBICOM 2002, Sptmbr [7] S. Sshan t al., Handffs in Cllular Wirlss Ntwrks: Th Dadalus Implmntatin and Exprinc, Kluwr J. Wirlss Prsnal Cmmun., vl. 4, n. 2, pp , March [8] E. Shim t al., Lw Latncy Handff fr Wirlss IP QS with Nighbrcasting, in Prc. ICC 2002, April [9] R. Hsih t al.. S-MIP: A Samlss Handff Architctur fr Mbil IP, in Prc. INFOCOM 2003, March [10] K. Malki t al., Lw Latncy Handffs in Mbil IPv4, Intrnt Draft, IETF, draft-itf-mbilip-lwlatncy-handffs-v4-04.txt, Jun [11] R. Kdli, Ed., Fast Handvrs fr Mbil IPv6, Intrnt Draft, IETF, draft-itf-mbilip-fast-mipv6-7.txt, Sptmbr [12] D. Lvin, I. F. Akyildiz and M. Naghshinh, A Rsurc Estimatin and Call Admissin Algrithm fr Wirlss Multimdia Ntwrks Using th Shadw Clustr Cncpt, IEEE/ACM Trans. Ntwrking, vl. 5, n. 1, pp. 1-12, Fbruary [13] K. Malki and H. Sliman, Simultanus Binding fr Mbil IPv6 Fast Handffs, Intrnt Draft, IETF, draft-lmalki-mbilip-bicastingv6-02.txt, Jun [14] Y. Gwn t al., Fast Handffs in Wirlss LAN Ntwrks Using Mbil Initiatd Tunnling Handff Prtcl fr IPv4 (MITHv4), in Prc. WCNC 2003, March [15] G. Liu and G. Maguir, A Class f Mbil Mtin Prdictin Algrithms fr Wirlss Mbil Cmputing and Cmmunicatin, Mbil Ntwrks and Applicatins, vl. 1, n. 2, pp , Octbr 1996.