A Smart Decision Model for Vertical Handoff

Transcription

1 A mart Dcson Modl for Vrtcal Handoff Lng-Jyh Chn *, Tony un *, Bnny Chn *, Vnkatsh Rajndran, Maro Grla * * Dpartmnt of Computr cnc, Unvrsty of Calforna at Los Angls, Los Angls, CA 90095, UA Dpartmnt of Computr Engnrng, Unvrsty of Calforna at anta Cruz, anta Cruz, CA 95064, UA {cclljj, tonysun, cudokdo, grla}@cs.ucla.du, vnkat@so.ucsc.du Abstract As mobl computng ncrass n prvalnc and popularty, t s bcomng ncrasngly mportant to hav a vrtcal handoff soluton, whch can prform a vrtcal handoff samlssly and smartly. In ths papr, w propos a mart Dcson Modl to dcd th bst ntwork ntrfac and bst tm momnt to handoff. A scor functon s utlzd n th modl to mak th smart dcson basd on varous factors, such as th proprts of avalabl ntwork ntrfacs, th systm nformaton, and th usr prfrncs. A UHA basd tstbd s cratd to valuat ths modl n varous scnaros, and th rsults show that our modl s fasbl and hlpful n mobl computng scnaros. Addtonally, ths modl s smpl and also applcabl to othr vrtcal handoff approachs. Ky-Words samlss handoff, vrtcal handoff, smart dcson, polcy-basd handoff, mobl computng Introducton As mobl computng ncrass n prvalnc and popularty, mor and mor mobl hosts nowadays ar quppd wth multpl ntwork ntrfacs whch ar capabl of connctng to th Intrnt. As a rsult, an ntrstng problm surfacd on how to dcd th bst ntwork ntrfac to us any gvn momnt. It s apparnt to us that th dcson should b basd on varous consdratons such as th capacty of ach ntwork lnk, IP charg of ach ntwork conncton, powr consumpton of ach ntwork ntrfac, and battry status of th mobl dvc. A smlar polcy-basd handoff schm has bn proposd n [8], whr th authors dsgnd a cost functon to dcd th bst momnt and ntrfac for vrtcal handoff. Howvr, th cost functon prsntd n ths papr s vry prlmnary and not abl to handl mor sophstcatd confguratons. Th logarthmc functon usd n th cost functon wll also hav dffculty n rprsntng th cost valu whl th valu of th constrant factor s zro (.g. th conncton s fr of charg). Anothr schm proposd n [] modls th handoff wth HTTP traffc, but t may hav problms wth othr typs of traffc, such as vdo and audo stramng, whr th bandwdth dmand s much hghr than HTTP traffc. In ths study, w propos a mart Dcson Modl to smartly prform vrtcal handoff among avalabl ntwork ntrfacs. Usng a wll-dfnd scor functon, th proposd modl can proprly handoff to th bst ntwork ntrfac at th bst momnt accordng to th proprts of avalabl ntwork ntrfacs, systm confguratons/nformaton, and usr prfrncs. A mart Dcson Modl mplmntaton s mployd on th top of th Unvrsal amlss Handoff Archtctur (UHA), whch s a smpl and practcal samlss handoff soluton [2], and a st of xprmnts ar prformd to valuat th fasblts of th modl. Th rsults show that th proposd smart dcson modl can adquatly prform vrtcal handoff to th bst ntrfac at th bst momnt. Th rst of th papr s organzd as follows: cton 2 dscrbs th handoff ovrvw and a smpl samlss handoff approach, UHA. cton 3 prsnts our proposd mart Dcson Modl. cton 4 dmonstrats th modl usng a dtald xampl. Fnally, scton 5 concluds th work. 2 Background In ths scton, w prsnt th background of ths study. cton 2. clarfs th dffrnc of vrtcal and horzontal handoff, and dfns th samlss handoff. In scton 2.2, w dscrb a smpl and practcal handoff approach: UHA, whch wll b usd n th followng dscussons and tstbd xprmnts. 2. Handoff Handoff occurs whn th usr swtchs btwn dffrnt ntwork accss ponts. Handoff tchnqus hav bn wll studd and dployd n th doman of cllular systm and ar ganng a grat dal of momntum n th wrlss computr ntworks, as IP-basd wrlss ntworkng ncrass n popularty. Dffrng n th numbr of ntwork ntrfacs nvolvd durng th procss, handoff can b charactrzd nto thr vrtcal or horzontal [6], as dpctd n Fgur. A vrtcal handoff nvolvs two dffrnt ntwork ntrfacs, whch usually rprsnt dffrnt tchnologs. For xampl, whn a mobl dvc movs out of an 802.b ntwork and nto a xrtt ntwork, th handoff vnt <Papr No.>/

2 would b consdrd as vrtcal. A horzontal handoff occurs btwn two ntwork accss ponts that us th sam tchnology and ntrfac. For xampl, whn a mobl dvc movs btwn 802.b ntwork domans, th handoff vnt would b consdrd as horzontal snc th conncton s dsruptd solly by th chang of 802.b doman but not of th wrlss tchnology. provdrs and ar stll rarly dployd n ralty. Wth th prolfraton of mobl applcatons and mobl usrs, a smpl and practcal samlss handoff soluton wth mnmal changs to th currnt Intrnt nfrastructur rmans ncssary. In th nxt subscton, w prsnt a smpl and practcal handoff soluton, UHA, whch s abl to provd both vrtcal and horzontal handoff samlssly. 2.2 Unvrsal amlss Handoff Archtctur Fgur : Horzontal and Vrtcal Handoff A samlss handoff s dfnd as a handoff schm that mantans th connctvty of all applcatons on th mobl dvc whn th handoff occurs. amlss handoffs am to provd contnuous nd-to-nd data srvc n th fac of any lnk outags or handoff vnts. Achvng low latncy and mnmal packt loss durng a handoff ar th two crtcal dsgn goals of our handoff archtctur. To achv low latncy path swtchng should b compltd almost nstantanously and srvc ntrruptons should b mnmzd. In cas of an actual conncton falur, th archtctur should attmpt to r-connct as soon as th srvc bcoms avalabl; packt losss durng th swtchng should also b mnmzd. A Unvrsal amlss Handoff Archtctur (UHA) was proposd n [2] to dal wth both horzontal and vrtcal handoff scnaros wth mnmal changs n nfrastructur (.., UHA only rqurs dploymnt of handoff srvrs on th Intrnt.) UHA s an uppr layr soluton; howvr, nstad of ntroducng a nw ssson layr or a nw transport protocol, t achvs samlss handoff by followng th mddlwar dsgn phlosophy [5], ntgratng th mddlwar wth xstng Intrnt srvcs and applcatons. UHA s basd on th fundamntal assumpton that handoff, thr vrtcal or horzontal, only occurs on ovrlad ntworks wth multpl Intrnt accss mthods (.. soft handoff), whch translats to zro watng tm n brngng up th targt ntwork ntrfac whn th handoff vnt occurs. If covrag from dffrnt accss mthods fals to ovrlap (.. hard handoff), t s possbl for UHA to los connctvty to th uppr layr applcatons. Varous samlss handoff tchnqus [4] [7] [8] [0] hav bn proposd. Ths proposals can b classfd nto two catgors: ntwork layr approachs and uppr layr approachs. Ntwork layr approachs ar typcally basd on IPv6 [3] or Mobl IPv4 [3] standards, rqurng th dploymnt of svral agnts on th Intrnt for rlayng and/or rdrctng th data to th movng host (MH). Most uppr layr approachs mplmnt a ssson layr abov th transport layr to mak conncton changs at undrlyng layrs transparnt to th applcaton layr [6] [] [4] [5]. Othr uppr layr approachs suggst nw transport layr protocols such as CTP [7] and TCP-MH [2] to provd th ncssary handoff support. Prvous samlss handoff solutons, whthr ntwork layr or uppr layr approachs, ar oftn complx to mplmnt and oprat. For th ntwork layr solutons, dploymnt mans upgradng vry xstng routr wthout mobl IP capablts. Th cost mposd by ths solutons hndrs thr chancs of dploymnt. For th uppr layr solutons, a nw ssson layr or transport protocol rqurs an updat to all xstng applcatons and srvrs not supportng t, th potntal cost s also dscouragng. Consquntly, vn though many handoff solutons hav managd to mnmz both latncy and packt loss, thy ar oftn dmd mpractcal by th majorty of srvc Fgur 2: Unvrsal amlss Handoff Archtctur In Fgur 2, a handoff srvr (H) and svral mobl hosts (MHs) ar shown. UHA s mplmntd usng IP tunnlng tchnqus (IP ncapsulaton), wth th handoff srvr functonng as on nd of th tunnl and th mobl host as th othr. An IP tunnl s mantand btwn vry MH and th H such that all applcaton layr communcatons ar bound to th tunnl ntrfac nstad of any actual physcal ntrfacs. All data packts communcatd through ths IP tunnl ar ncapsulatd and transmttd usng th connctonlss UDP protocol. <Papr No.>/2

3 Th IP tunnl abov utlzs two pars of vrtual/fxd IP addrsss, on on H and on on MH. Th fxd IP addrsss ar ncssary for an MH to stablsh a physcal conncton to th H. Whn th handoff vnt occurs and th physcal conncton from MH to H changs, th MH s rsponsbl for automatcally swtchng th undrlyng physcal conncton of th vrtual tunnl to th nw ntrfac, as wll as notfyng th H of ts chang n physcal conncton. Upon handoff notfcaton, th H mmdatly updats ts IP tunnl sttngs so that any subsqunt data packts wll b dlvrd to MH s nw physcal lnk. nc all data packts ar ncapsulatd and transmttd usng UDP, thr s no nd to rst th tunnl aftr th handoff. Thrfor, nd-to-nd applcaton sssons (.g. TCP) that ar bound to th IP tunnl ar kpt ntact. Ths provds handoff transparncy to uppr layr applcatons. On th othr hand, though UHA provds a smpl and practcal samlss handoff soluton, t stll has dffculty n prformng handoff smartly,.. th handoff cannot b trggrd automatcally so far. It turns out that a manual handoff soluton s stll far from bcomng practcal, snc an apprcabl soluton should kp moblty transparnt to th mobl usrs,.. th samlss handoff soluton should b smart nough so that t s abl to prform a handoff proprly at th propr momnt. A mart Dcson Modl s proposd n ths study. In th proposd modl, a handoff dcson s mad basd on th ntwork proprts, systm nformaton, and usr prfrncs. Addtonally, t s abl to prform a handoff automatcally to th most approprat ntwork ntrfac at th most approprat momnt. Th proposd modl s dsgnd for UHA and s also applcabl to othr handoff approachs. Th dtals of th proposd mart Dcson Modl ar prsntd n scton 3, and a ral tstbd mplmntaton and xprmnt rsults wll b prsntd n scton 4. 3 mart Dcson Modl In ths scton, w prsnt th proposd mart Dcson Modl to support flxbl confguraton n xcutng vrtcal handoffs. Fgur 3 dpcts th proposd mart Dcson Modl. In ths fgur, a Handoff Control Cntr (HCC) provds th conncton btwn th ntwork ntrfacs and th uppr layr applcatons. HCC s composd of four componnts: Dvc Montor (DM), ystm Montor (M), mart Dcson (D), and Handoff Excutor (HE). DM s rsponsbl for montorng and rportng th status of ach ntwork ntrfac (.. th sgnal strngth, lnk capacty and powr consumpton of ach ntrfac). M montors and rports systm nformaton (.g. currnt rmanng battry). D ntgrats usr prfrncs (obtand from usr st dfault valus) and all othr avalabl nformaton provdd by DM, M to achv a mart Dcson, to dntfy th bst ntwork ntrfac to us at that momnt. HE thn prforms th dvc handoff f th currnt ntwork ntrfac s dffrnt from th bst ntwork ntrfac. Fgur 3: mart Dcson Modl A Handoff Control Cntr (HCC) n accordanc to abov has bn mplmntd on our vrtcal handoff tstbd to prform automatc handoffs to th bst ntwork ntrfac. In our dsgn, thr ar two phass n D: th prorty phas and th normal phas. Th D algorthm s dscrbd n Fgur 4. mart Dcson Procss Prorty Phas:. Add all avalabl ntrfacs nto canddat lst. 2. Rmov usr spcfd dvcs from th canddat lst. 3. If canddat lst s mpty, add back rmovd dvcs from stp 4. Contnu wth Normal Phas. Normal Phas:. Collct nformaton on vry wrlss ntrfac n th canddat lst from th DM componnt. 2. Collct currnt systm status from M componnt. 3. Us th scor functon to obtan th scor of vry wrlss ntrfac n th canddat lst. 4. Handoff all currnt transmssons to th ntrfac wth th hghst scor f dffrnt from currnt dvc. Fgur 4: Algorthm for makng mart Dcsons on HCC Prorty and normal phass ar ncssary n D to accommodat usr-spcfc prfrncs rgardng th usag of ntwork ntrfacs. For nstanc a usr may dcd not us a dvc whn th dvc may caus undsrabl ntrfrncs to othr dvcs (.g. 802.b and 2.4GHz cordlss phons). Wth prorty and normal phass n plac, th D modul provds flxblty n controllng th dsrd ntwork ntrfac to th usr. Addtonally, D dploys a scor functon to calculat a scor for vry wrlss ntrfac; th handoff targt dvc s th ntwork ntrfac wth th hghst scor. Mor spcfcally, suppos thr ar k factors to consdr n calculatng th scor, th fnal scor of ntrfac wll b a <Papr No.>/3

4 sum of k wghtd functons. Th scor functon usd s th followng: k = w f 0 < <, j j, j= k wj = () In th quaton, w j stands for th wght of factor k, and f j, rprsnts th normalzd scor of ntrfac of factor j. Th bst targt conncton ntrfac at any gvn momnt s thn drvd as th on whch achvs th hghst scor among all canddat ntrfacs. W furthr brak down th scor functon to thr componnts whr ach accounts for usag xpns (E), lnk capacty (C), and powr consumpton (P), rspctvly. Thrfor Eq. bcoms: w f, + wc fc, + wp f p, j= = (2) Addtonally, thr s a corrspondng functon for ach trm f,, f c,, and f p,, and th rangs of th functons ar boundd from 0 to. Th functons ar llustratd blow: β f, = f c, = f p, = α M γ (3) whr α 0, M β 0, and γ 0 Th coffcnts α, β, γ can b obtand va a lookup tabl or a wll-tund functon. In Eq. 3, w usd th nvrsd xponntal quaton for f, and f p, to bound th rsult to btwn zro and on (.. ths functons ar normalzd), and proprly modl usrs prfrncs. For f c,, a nw trm M s ntroducd as th dnomnator to normalz th functon, whr M s th maxmum bandwdth rqurmnt dmandd by th usr. Wthout spcfd by th usr, th dfault valu of M s dfnd as th maxmum lnk capacty among all avalabl ntrfacs. Not that, th proprts of bandwdth and usag cost/powr consumpton ar oppost (.. th mor bandwdth th bttr, whras lowr cost/powr consumpton s prfrrd). 4 Tstbd Exprmnts A mart Dcson Modl mplmntaton s mployd on th top of UHA vrtcal handoff tstbd, and a st of xprmnts has bn prformd to valuat ths modl. Our mart Dcson Modl mplmntaton workd wll n all th tstng scnaros. To clarly dmonstrat how ths modl works, w show a dtald xampl n th followngs. An xampl of how ths coffcnts n mart Dcson Modl work wth usr dfnd functons s llustratd n Fgur 5, whr x s th usag cost (IP charg), y s th masurd lnk capacty, and z s th powr consumpton of th -th wrlss ntrfac. In a sns, ths functons ar smply transformaton from a spcfc doman (.g. /mn, kbps, and hours) to a unvrsal unt doman, and th rturn valus ar normalzd as a postv ral numbr btwn 0 and. On top of that, th usr can also dcd what sh valus th most by gvng wght w j to j-th functon. α = x / 20 β = Mn(y, M)/M γ = 2 / z ; x : /mn ; M = 2Mbps ; z : hours Fgur 5: An coffcnt functon xampl Th followng llustrats an xampl of how mart Dcson s achvd. uppos a mobl usr who s currntly usng th xrtt dvc ntrs a café. Th HCC mmdatly dscovrs an 802.b accss pont nsd th café and dos th followng comparsons: Th xrtt cost s lss than /mn bcaus th usr has alrady subscrbd to th srvc usng monthly unlmtd plan ($80 / month), whl 802.b nsd th café costs 0 /mn. Th lnk capacty nformaton s gathrd from CapProb [9], a nwly nvntd capacty stmaton tool, whch rports that xrtt has a capacty of 00Kbps and th 802.b wrlss LAN has a capacty around 5Mbps. Wth th currnt battry status, th usr can thr contnu hs xrtt conncton for 4 hours or 2 hours wth 802.b conncton. At ths tm, th mobl usr dcds that h wll stay n th café for a whl, so h gvs mor wght to powr consumpton (w p =0.4), and qual wght to usag cost and bandwdth rqurmnt (w = 0.3, w c = 0.3). Th HCC thn computs th scor accordng to Eq. 2 and Eq. 3 usng coffcnt functons llustratd n Fgur 5. Fgur 6 dsplays th scor rsults of both xrtt and 802.b ntrfacs, whr xrtt = 0.83 and 802.b = nc xrtt > 802.b, th HCC thrfor dcds to contnu usng xrtt ntrfac nstad of swtchng to th fastr 802.b ntrfac. xrtt 802.b α γ kbps / 2Mbps 2 / α β γ 0 / 20 Mn(2,5) Mbps 0.44 β / 2Mbps / Fgur 6: An HCC calculaton xampl for both xrtt and 802.b ntrfacs Not that, though th xampl shown n ths scton uss th coffcnt functons dfnd n Fgur 5, ths coffcnts ar changabl upon usrs nds and prfrncs. Ths coffcnts can b obtand va a lookup tabl or a wll-tund functon; howvr, thy nd to b normalzd so that th scor functon (Eq. ) can rasonably dcd th scor for ach ntwork ntrfac from dffrnt factors. 2 <Papr No.>/4

5 5 Concluson In ths papr, w prsnt a mart Dcson Modl to smartly prform handoff to th bst ntwork ntrfac at th bst momnt. Th proposd modl s abl to mak th smart dcson basd on th proprts of avalabl ntwork ntrfacs (.g. lnk capacty, powr consumpton, and lnk cost), systm nformaton (.g. rmanng battry), and usr prfrncs. Usng UHA tstbd xprmnts, w prsntd a dtald xampl to show how ths modl works wth gvn a st of coffcnt functons. Th mart Dcson Modl s smpl and applcabl not only for UHA, but also for othr vrtcal handoff approachs. 6 Rfrncs [] M. Angrmann and J. Kammann, Cost Mtrcs For Dcson Problm In Wrlss Ad Hoc Ntworkng, IEEE CA Workshop on Wrlss Communcatons and Ntworkng, [2] L.-J. Chn, T. un, B. Chung, D. Nguyn, and M. Grla. Unvrsal amlss Handoff Archtctur n Wrlss Ovrlay Ntworks, Tchncal Rport TR04002, UCLA CD, [3]. Drng, and R. Hndn, Intrnt Protocol, Vrson 6 (IPv6) pcfcaton, RFC 2460, Dc [4] G. Dommty t al, Fast Handovrs for Mobl IPv6, draft-tf-moblp-fast-mpv6-04.txt, IETF Intrnt draft, Mar [5] A. Fox,. Grbbl, Y. Chawath, E. Brwr, and P. Gauthr, Clustr-basd calabl Ntwork rvcs, OP'97, 997. [6] V. Ghn, G. Pau, P. alomon, M. Rocctt, and M. Grla, mart Download on th Go: A Wrlss Intrnt Applcaton for Musc Dstrbuton ovr Htrognous Ntworks, n Procdngs of ICC, [7] R. Hsh, Zh Guang Zhou, and A. nvratn, -MIP: a samlss handoff archtctur for mobl IP, In Procdngs of IEEE INFOCOM [8] D. B. Johnson, C. Prkns, and J. Arkko, Moblty upport n IPv6, draft-tf-moblp-pv6-7.txt, IETF Intrnt draft, May [9] R. Kapoor, L.-J. Chn, M. Y. anadd, M. Grla, CapProb: A mpl and Accurat Tchnqu to Masur Path Capacty, Tchncal Rport TR04000, UCLA CD, [0] K. El Malk t al, Low Latncy Handoffs n Mobl IPv4, draft-tf-monlp-lowlatncy-handoffs-v4-03. txt, IETF Intrnt draft, Nov [] D. Maltz, and P. Bhagwat, MOCK: An archtctur for transport layr moblty, In Proc. of IEEE Infocom, p.p , March 998. [2] A. Matsumoto, M. Kozuka, K. Fujkawa, and Y. Okab, TCP Mult-Hom Optons, draft-arfum-tcp-mh-00.txt, IETF Intrnt draft, Oct [3] C. Prkns, Ed. IP Moblty upport for IPv4, RFC 3344, Aug [4] M. chlagr, B. Rathk,. Bodnstn, and A. Wolsz, Advocatng a Rmot ockt Archtctur for Intrnt Accss usng Wrlss LANs, Mobl Ntworks & Applcatons, vol. 6, no., pp , January 200. [5] A. C. nnorn, A sson-basd Approach to Intrnt Moblty, PhD Thss, Massachustts Insttut of Tchnology, Dcmbr [6] Mark tmm, and Randy H. Katz. Vrtcal Handoffs n Wrlss Ovrlay Ntworks, ACM MONET, 998. [7] R. twart t al. tram Control Transmsson Protocol, RFC 2960, Oct [8] H.J. Wang, R. H. Katz, and J. Gs, Polcy-Enabld Handoffs across Htrognous Wrlss Ntworks, Proc. of ACM WMCA, 999. <Papr No.>/5