QoS-Assured Service Composition in Managed Service Overlay Networks

Transcription

1 QoS-Assued Sevie Compositio i Maaged Sevie Ovelay Netwoks Xiaoui Gu, Klaa Nastedt epatmet of Compute Siee Uivesity of Illiois at Ubaa-Campaig xgu, s.uiu.edu Rog N. Cag, Cistope Wad Netwok Hosted Appliatio Sevies IBM T.J. Watso Resea Cete og, us.ibm.om Abstat May value-added ad otet delivey sevies ae beig offeed via sevie level ageemets (SLAs. Tese sevies a be iteoeted to fom a sevie ovelay etwok ( ove te Iteet. Sevie ompositio i as emeged as a ost-effetive appoa to quikly eatig ew sevies. Pevious esea as addessed te eliability, adaptability, ad ompatibility issues fo omposed sevies. Howeve, little as bee doe to maage geei quality-of-sevie (QoS povisioig fo omposed sevies, based o te SLA otats of idividual sevies. I tis pape, we peset QUEST, a QoS assued omposeable Sevie ifastutue, to addess te poblem. QUEST famewok povides: (1 iitial sevie ompositio, wi a ompose a qualified sevie pat ude multiple QoS ostaits (e.g., espose time, availability. If multiple qualified sevie pats exist, QUEST ooses te best oe aodig to te load balaig meti; ad (2 dyami sevie ompositio, wi a dyamially eompose te sevie pat to quikly eove fom sevie outages ad QoS violatios. iffeet fom te pevious wok, QUEST a simultaeously aieve QoS assuaes ad good load balaig i. 1 Itodutio Te Iteet as evolved to beome a ommeial ifastutue of sevie delivey istead of meely povidig ost oetivity. iffeet foms of ovelay etwoks ave bee developed to povide attative sevie povisioig solutios, wi ae diffiult to be implemeted ad deployed i te IP-laye, su as otet delivey ovelays [1] Tis wok was suppoted i pat by te NASA gat ude otat umbe NASA NAG , Natioal Siee Foudatio ude otat umbe , , ad EIA EQ. Ay opiios, fidigs, ad olusios o eommedatios expessed i tis mateial ae tose of te autos ad do ot eessaily eflet te views of te Natioal Siee Foudatio (NSF, NASA o U.S. Govemet. Aess omai Potal Potal Aess omai Sevie Ovelay Netwok ( Potal Sevie Povide: XXX.om sevie istae X sevie istae Y Aess omai sevie istae Z Figue 1. Illustatio of te Sevie Ovelay Netwok Model. ad pee-to-pee file saig ovelays [2]. Beyod tis, we evisio te emegee of sevie ovelay etwoks (, illustated by Figue 1. Ea ode povides ot oly appliatio-level data outig but also a set of value-added sevies (e.g., media tasodig, data eyptio. Ea sevie ompoet is offeed via a sevie level ageemet (SLA otat [15]. Sevie ompositio i as beome eessay i ode to ost-effetively eate ew Iteet sevies [8]. Tus, a allegig poblem is to povide a sevie ifastutue to eable effiiet sevie ompositio wit quality-of-sevie (QoS assuaes. Mu esea wok as addessed te sevie ompositio poblem. Te SAHARA poet [8] addessed te fault-esiliee poblem i wide-aea sevie ompositio. Te CANS poet [9] addessed te adaptability poblem i sevie ompositio. Te SPY-Net [17, 18] famewok addessed te poblem of esoue otetio wile fidig a multimedia sevie pat. I te Gaia poet [11], we addessed te QoS osistey ad load patitio issues fo omposig sevie pat i ubiquitous omputig eviomets. Howeve, little as bee doe to suppot geei 1

2 QoS povisioig fo omposed sevies, based o te SLA otats of idividual sevie ompoets. I tis pape, we peset QUEST, a QoS assued omposeable Sevie ifastutue, wi a povide bot QoS assuaes ude multiple QoS ostaits, ad load balaig i. Sevie ompositio is pefomed by te sevie ompose (SC usig a omposed sevie povisioig potool. Te potool is desiged based o a etwok-eti liet-service model [4]. Istead of otatig sevie povides dietly, te liet otats SC toug a well-kow addess ad speifies its desied sevies ad QoS equiemets. Te, SC, as a itemediate aget, omposes ad istatiates a qualified sevie pat i. Te key algoitms used by SC ilude: (1 iitial sevie ompositio, ad (2 dyami sevie ompositio. Te iitial sevie ompositio algoitm popely ooses ad omposes te sevie istaes, based o tei SLA otats ad uet pefomaes i ode to best mat te QoS ostaits of te use. QUEST aieves ot oly QoS assuaes but also load balaig i by ompeesively osideig bot QoS ad esoues of diffeet sevie istaes. Moeove, QUEST povides dyami sevie ompositio, wi is used duig utime we sevie outages o QoS violatios ou. Te algoitm fids a alteative sevie pat i, wi a quikly eove te failed omposed sevie delivey. Extesive simulatio esults sow tat QUEST a povide mu bette QoS assuaes ad load balaig fo omposed sevies i ta ote ommo euistis. Te est of te pape is ogaized as follows. Setio 2 itodues te oveall system desig. Setio 3 desibes te desig details ad te key sevie ompositio algoitms. Setio 4 pesets te pefomae evaluatios. Setio 5 disusses elated wok. Fially, te pape oludes i Setio 6. 2 System Oveview I QUEST, osists of vaious sevie ompoets 1, alled odes. Ea ode epesets a sevie ompoet, wi is maaged by idividual ompoet sevie povide (CSP. Te oetios betwee odes ae alled liks, wi ae appliatio-level vitual liks. We assume tat ea CSP a maage ad otol te quality levels of its ow sevies i aodae to te SLA otat wit te sevie povide (PSP. O te ote ad, te PSP as a SLA otat wit te use fo ea omposed sevie. I ode to allow PSP to moito ad maage te quality levels of te omposed sevie, we itodue s tat seve as te etae/ poits of te. I QUEST, s 1 seveal sevie istaes a o-loated o te same pysial ost. Figue 2. Illustatio of te QUEST s sevie ompositio model. defie te maagemet bouday of QoS povisioig fo omposed appliatios. We all su a wit s a maaged. Te QUEST sevie ompositio model iludes two mappig steps, illustated by Figue 2 (a. Fo ea use equest, te sevie ompose (SC fist maps it to a omposite sevie template, ad te maps te template to a istatiated sevie pat. Te mappig fom te use equest to diffeet omposite sevie templates (mappig- 1 is ostaied by te use s appliatio-speifi quality equiemets ad diffeet pevasive liet devies, su as PAs ad ell-poes. Mappig-1 as bee addessed by seveal esea wok [11, 9]. It a be pefomed based o te appliatio-speifi QoS speifiatios [12] o usig automati ompositio pla tools [13]. Te mappig fom te omposite sevie template to a istatiated sevie pat (mappig-2 is ostaied by distibuted pefomae (e.g., espose time ad esoue availability oditios. Little esea as addessed te mappig-2 tat is te fous of tis pape. I QUEST, te omposed sevie delivey, witi, stats fom te etae, taveses toug te ose sevie istaes, eds at te, illustated by Figue 2 (b. We assume tat ea sevie istae (o ovelay lik is assoiated wit a SLA otat speifyig its QoS assuaes su as espose time 2

3 Y e E Q i f i f N Y Y \ (o delay ad availability (o. Te availability is alulated by "!#%$ &'(*+ &,-&/.01 '(('( 2'435 2" 687:9*+;2(<*= <!#. Te oetio betwee two sevie istaes is alled te sevie lik, wi is mapped to a ovelay outig pat?>a@cb FE GHGIGJE K. Te availability MLON of te sevie lik (HP is alulated as <R/S ; ad te delay L N of te sevie lik ( P is deived usig T R/S. Ea CSP povides a SLA otat to te PSP ad is esposible fo maagig its ow sevie ompoets o ovelay liks. Te omposed sevie U is also assoiated wit a SLA otat speifyig te QoS assuae tat te PSP pomises to te use. 3 Iitial Sevie Compositio I tis setio, we peset te iitial sevie ompositio solutio, wi ae used duig te setup pase of te omposed sevie delivey. Suppose ea sevie istae (o sevie lik P is offeed to te PSP via a SLA otat speifyig its povisioig QoS: availability (o VLWN ad espose time (o delay XLON. Te QoS assuaes (availability: Y ad espose time: Y of te omposed appliatio U :Z GIGHG[E \/] a be deived as follows 2, fg; ^I_a` i bd e ^H_C` b-m o ^H_q` kl p b- kl fg; sdt i sdt m kl p kl8u vdwyx{zx} l-~ x _4 z _8 x (ƒz ^ fg; ~ x{ y yƒz ^ (1 N (2 Suppose also tat te PSP as a SLA otat wit te use to speify its povisioig QoS fo te omposed sevie X (availability ˆ2 {ŠŒ <ˆ 0 ad espose time Y ˆ2 {ŠŽ <ˆ. I ode to guaatee a suessful sevie delivey, te esoue equiemets of te istatiated sevie pat ave to be satisfied. Fo simpliity, we oly oside te CPU esoue fo ed osts ad badwidt fo ovelay liks. We defie te tem pu atio fo te sevie istae as > ;Š: Œ Š5 9, { IL L. Te ;Š5 Š: epesets te equied CPU esoue fo uig a ew poess. Te { IL L epesets te available CPU esoue i te pysial ostig eviomet of. If 1, te te sevie equest a be admitted. Otewise, te sevie equest will be deied. Te smalle te, te moe advatageous we oose te sevie istae i tems of CPU load balaig beause we stat te ew 2 I ode to make te meti availability beomes additive ad miimum-optimal, we apply te logitm ad ivese opeatios o te meti availability. We assume tat š m ad œ N ae measued fo a appliatio data uit (e.g., a video fame. sevie poess o a ligtly loaded ost. Similaly, we defie te tem badwidt atio fo te sevie lik P as ž L NV>Ÿ3{'(1 V Œ LŠ5 N Š: 9 3{'(1 M<Œ { LON IL L. Wit te above otatios, we a fomulate te QoS-assued sevie ompositio poblem as follows, EFINITION 1. QoS-assued Sevie Compositio (QSC Poblem Suppose we ae give a dieted gap epesetig a sevie ovelay etwok ( topology, G = (V, E, wee V ad E ae te sets of N odes ad M liks, espetively. Suppose also ea ode is aateized by oegative values of 2 additive QoS attibutes (21 0,, i = 1...N. Ea lik is also aateized by oegative values of 2 additive QoS attibutes ( 1 ;,, i = 1...M. Give te template fo a omposed 0 sevie X ad use QoS equiemets 1 ª «ad ˆ2 {ŠŽ <ˆ, te poblem of QoS-assued sevie ompositio is to ompose a sevie pat p E GIGHḠ E fom Z (etae to \/] (, su tat 1 ª «2 1 0 (equ.(1 ad ˆ2 {ŠŽ <ˆ 0 Y (equ. (2, ad also J ž 1, i = , ad L N 1, = 0... We ow pove tat te QSC poblem is NP-omplete. Teoem 1 QSC poblem is NP-omplete. Poof: We pove tis by sowig tat te Multiple Costaied Pat seletio (MCP poblem, wi is kow to be NP-omplete [] maps dietly to a speial ase of te QSC poblem. Te detailed poof is omitted due to te page limitatio. Besides its NP-ompleteess, te above QSC poblem defiitio also eglets seveal impotat patial issues. Fist, i te eal wold SLA otat, te QoS attibutes ae ofte speified usig aveage values measued ove a log time peiod su as a mot o a yea [15]. Howeve, te omposed sevie sessio a last fo oly seveal miutes o ous. Hee, we eed to oside ot oly SLA otat values but also eet pefomae oditios of sevie istaes/liks. Seod, te PSP a ouetly seve tousads of use equests by omposig available sevie istaes. To aieve best aggegate QoS assuaes fo all uses, we also eed to oside te load balaig poblem. Tid, beause is igly dyami, QoS violatios a appe sometimes. Commeial SLA otats usually make te PSP lose moey we QoS violatio appes [15]. Hee, te goal of ou QSC algoitms is to ompose a sevie pat tat a best avoid QoS violatios o miimize te QoS violatio degee if a violatio ous. We ow povide a polyomial euisti algoitm, alled QSC-basi, fo te QSC poblem. Te basi idea is to use a modified iksta algoitm by ompeesively osideig multiple ostaits (e.g., SLA otats, eet pefomae, system load. Te QSC-basi pimaily ivolves two steps: (1 Geeate te weigted adidate 3

4 e u u u N ' ' T B f 5. m N ' N M. S M M M e Z Z S0 (S0, etae (S0, (, S12 (, (a (, (,S4 (,S4 (S0, S4 S0 etae (S0, (, S12 (, (b (, (,S4 (,S4 Figue 3. Illustatio of te QSC-basi algoitm. S4 gap. Istead of seaig te sevie pat i te etie, we fist geeate a adidate gap, illustated by Figue 3 (a, to miimize te seaig age. Te "Œ olum i te adidate gap iludes all te sevie istae adidates povidig te <Œ sevie futio i te appliatio template. Te ost value o te edge 0> P 7 P is defied usig te followig itegated meti: ^H_ ^ ^H_C ^H_ N ^H_ sdt m s t f* f+-, f.!. m ^H_ f*.! "#%$! &'( ( / ( ^I_ f*. N ^H_ 01 ^H_ ( f. sdt f*. u sdt f. f* ( $! &' ( 2 s m 2 s 4Ms 4Ms 3 f m '(5 Ituitively, te atio (9 epesets ay of te above paametes epesets te omalized ost of seletig a potio of te sevie pat i tems of oe speifi fato (e.g., QoS assuaes o load balaig; ad (2 Ru te iksta algoitm to fid te sotest pat, wi is etued as te esult of te QoS-assued sevie ompositio, illustated by Figue 3 (b. Howeve, te above QSC-basi algoitm does ot oside ea idividual QoS ostait wile omposig a sevie pat. We ow peset a eaed algoitm, alled QSC-eaed. Afte geeatig te adidate gap, we assoiate ea edge > P*7: ; P< = wit a ost value, wi modifies te equatio (3 by multiplyig a o-egative value?> >FE7 wit Ã@ C Z ea atio 6. Te weigt epesets te sigifiae of te "HIŒ fato 6G7 wile seletig te sevie istae duig ea EXTRACT Mi step i te iksta algoitm. Te ige te value, te moe impotat te (HIŒ fato. iffeet fom te QSC-basi, te QSC-eaed algoitm dyamially ages te impotae of diffeet fatos by adustig aodigly. Te adustmet of is based (3 o te pessue of diffeet QoS ostaits. Ituitively, if te uet aumulated value of a QoS attibute (e.g., espose time appoaes its ostait, we iease its weigt i ope tat its aumulatio will at up i te late stage of te sevie pat ompositio. Suppose is te uet ose ode by Extat Mi, wose fial sotest pat fom te soue Z is ust detemied. We defie te espose time pessue IKJ/L, availability pessue I { WL, ad te weigt adustmet futios as follows, MON%P s t m!q1rm ^I_ Q1T e sdt. ^H_ "# ª «v l e v e vvu e vxw e ` Y[Z `V\ vv] \ vv^ vx_ e vv` e vva e vxb e ` Y[Z (4 M N%P (5 M N%P `V\ vv] \ vv^ M N%P (6 Bot QSC-basi ad QSC-eaed algoitms ave te same omputatioal omply ed 7, wee d is te umbe of odes i te adidate gap. 4 yami Sevie Compositio is a igly dyami system ompaed to te IP etwok ifastutue. Fist, ulike outes, osts a dyamially oi o leave ove log time sales. Seod, osts o udelyig IP etwok pat a expeiee pefomae failues, outages, o degadatios ove sot time sales [3]. Hee, duig utime, a establised sevie pat a beome boke o violate QoS ostaits, patiulaly fo te log-lived appliatio sessio su as multimedia steamig. We te sevie istae (o lik expeiees outage o sigifiat quality degadatios, te SC is otified. It eoves all te affeted sessios usig te dyami sevie ompositio algoitms. We ave desiged two dyami sevie ompositio algoitms: (1 QSC-omplete, wi ompletely e-omposes te sevie pat witout osideig te oigial sevie pat, to eove fom failues; ad (2 QSC-patial, wi patially e-omposes te sevie pat based o te oigial sevie pat. Figue 4 illustates te omplete sevie e-ompositio algoitm QSC-omplete. Figue 4 (a sows te adidate gap ad te oigial sevie pat, o wi te sevie istae is failed ad te sevie lik betwee adf is boke. Te QSC-omplete algoitm fist modifies te adidate gap by emovig tose failed o pooly-pefomig sevie istaes, ad also eplaig te boke sevie liks wit alteate outig pats we it is possible, illustated by Figue 4 (b. I tis example, is emoved fom te seod olum of te adidate gap. Te failue sevie lik betwee ad f is eplaed wit a alteative pat. Te eoveed sevie lik is illustated as a dotted lie i Figue 4 (b. Te, we use 4

5 E f E etae etae S12 etae etae (a (b ( Figue 4. Illustatio of te omplete sevie e-ompositio algoitm QSC-omplete. S12 etae (a (b ( Figue 5. Illustatio of te patial sevie eompositio algoitm QSC-patial. etae Reoveed Sevie Lik Reoveed Sevie Lik quikly e-ompose a ew sevie pat to eove fom failues o QoS violatios. Howeve, ea of tem as bot advatages ad disadvatages. Te advatage of te QSComplete algoitm is tat it a e-ompose a bette sevie pat i tems of QoS assuaes ta te QSC-patial algoitm, sie it as moe oies of sevie istaes. Te disadvatage of te QSC-omplete algoitm is tat te sevie e-ompositio takes loge time sie it eomposes te etie sevie pat. O te ote ad, te advatage of te QSC-patial algoitm is tat it is quike ad easie to implemet sie it oly ages pat of te sevie pat. Howeve, its disadvatage is tat te ew omposed sevie pat may ot be optimal. We will fute ompae tese two diffeet dyami sevie ompositio appoaes i te ext setio. 5 Pefomae Evaluatio 5.1 Evaluatio metodology te QSC-eaed algoitm, desibed i Setio 3.1, to ompose a ew qualified sevie pat. Tus, te sevie sessio a quikly eove fom failues o QoS violatios by switig fom te old sevie pat to te ew oe 3. Cotastig wit te QSC-omplete algoitm, QSCpatial algoitm patially e-omposes te sevie pat based o te oigial sevie pat. Figue 5 (a sows te same sevie pat example as Figue 4 (a. I te oigial de E sevie pat etae, sevie istae is failed ad sevie lik betwee ad f is boke. I Figue 5 (b, oweve, we modify te adidate gap by ot oly emovig te pooly-pefomig o failed sevie istaes (e.g., ad eoveig te boke sevie liks (e.g., te sevie lik betwee ad f, but also emovig, i te olum wee te old sevie istae is good, te ote adidate sevie istaes. I tis example, adf still pefom well. Tus, we emove Ž ad f i te tid olum of te adidate gap, ad f adf1f i te fout olum. Te, we use te QSC-eaed algoitm to ompose a ew sevie pat o te modified adidate gap, illustated by Figue 5 (. Te pupose of su a appoa is to keep tose oigial well-pefomig sevie istaes i te ew sevie pat. Hee, we a edue te migatio oveead fo switig fom te old sevie pat to te ew oe. Te omputatioal omply of QSComplete ad QSC-patial is still ed 7, wee d is te umbe of odes i te adidate gap. Bot QSC-omplete ad QSC-patial algoitms a 3 We assume tat te states of all te sevie istaes a be eoveed by softwae. We evaluate te pefomae of te iitial ad dyami QoS-assued sevie ompositio algoitms usig extesive simulatios. We fist use te degee-based Iteet topology geeato Iet 3.0 [16] to geeate a powe-law adom gap topology wit 3200 odes to epeset te Iteet topology. We te adomly selet 500 odes as te odes ad 40 ote odes as te s. We assume a equal-degee adom gap topology fo te. Ea ode is adomly assiged 5 ote odes as its eigbos. Hee, te pobig oveead of ea ode is witi 9 >8>J> E. Te iitial esoue availability of ea IP lik ad sevie istae is uifomly distibuted i a etai age. Te SLA values of ea IP lik o sevie istae ae also uifomly distibuted witi etai age. iffeet values eflet te eteogeeity ad divesified quality guaatees i. Moeove, to simulate te pefomae vaiatio i te eal wold, te QoS attibutes of ea IP lik ad sevie istae ae set by uifom distibutio futios, wit SLA values as te mea values. We assume te iksta sotest pat algoitm fo bot te IP laye ad ovelay laye outig, usig te istataeous value of delay as te outig meti. Te badwidt of a ovelay lik is te bottleek badwidt alog te IP etwok pat. Te delay of a ovelay lik is te additio of te delays alog te IP etwok pat. uig ea miute, etai umbe of use equests ae geeated. Te use equest is epeseted by ay of 40 omposite sevie templates tat ompise 2 to 6 sevies. Ea use sessio lasts fom 15 to 60 miutes. Te metis we use fo evaluatig te QoS assuaes ilude QoS violatio ate ad QoS violatio degee. Te QoS violatio ate is measued by te atio of te sessios duig 5

6 wi QoS violatio appes ove te total sessios. Fo ea sessio, te QoS violatio is said to appe if te measued aveage QoS attibute values (i.e., availability, espose time is wose ta tat speified i te SLA otat. Te QoS violatio degee measues tat if a QoS violatio ous, ow sevee te QoS violatio is. It is measued by te atio of diffeee betwee te measued QoS attibute value ad its taget value, ove te taget value. Tose two metis ae ofte assoiated wit te fiaial efud/pealty poliies speified i te eal wold SLA otats. Te miimizatio of tose two metis meas to edue te fiaial loss of te sevie povide. Te meti we use fo evaluatig te load balaig is te povisioig suess ate. A omposed sevie povisioig is said to be suessful if ad oly if duig its etie sessio, all te sevie istaes ad liks esoue equiemets o te sevie pat ae always satisfied. Te omposed sevie povisioig suess ate is defied as te umbe of suessful equests ove te total umbe of all equests. Give te total amout of esoue i, ige povisioig suess ate epesets bette load balaig i. Fo ompaiso, we also implemet two ommo euisti algoitms fo omposig sevie pat: fixed ad adom algoitms.te fixed algoitm always ooses te same sevie istaes fo a omposed appliatio. Te adom algoitm adomly ooses sevie istaes to ompose te sevie pat. Availability Violatio Rate [%] QSC-Basi QSC-Eaed QSC-Patial QSC-Complete Load: Sessio Request Rate [sessios/mi] Figue 6. Aveage availability QoS violatio ate ude diffeet system load. 5.2 Results ad aalysis Figue 6 ad Figue 7 sow te simulatio esults about te violatio ates of two QoS attibutes: availability ad espose time, espetively. I Figue 6, te X axis epesets diffeet sessio equest ate, alulated by te umbe of omposed sevie sessio equests pe miute. Te age of sessio equest ate is seleted to eflet Respose Time Violatio Rate [%] QSC-Basi QSC-Eaed QSC-Patial QSC-Complete Load: Sessio Request Rate [sessios/mi] Figue 7. Aveage espose time QoS violatio ate ude diffeet system load. diffeet system wokload put o te. Te Y axis sows te aveage QoS violatio ate fo te availability attibute, aieved by te fixed, adom ad ou fou QSC (QoS-assued sevie ompositio algoitms. QSC- Basi ad QSC-Eaed epeset te two iitial sevie ompositio algoitms. Bot of tem do ot ilude ay dyami sevie e-ompositio meaisms. Bot QSC- Complete ad QSC-Patial use te QSC-Eaed fo te iitial sevie ompositio ad also dyamially eoves fom te sevie outage/quality degadatios by ompletely o patially e-omposig te sevie pat. Ea aveage availability QoS violatio ate ( value is alulated ad aveaged ove a peiod of 200 miutes fo all suessfully omposed sessios. Te esults sow tat all te fou QSC algoitms aieve mu lowe ta te fixed ad adom algoitms. Te QSC-Eaed as as mu as 20% impovemets ta te QSC-Basi. Bot QSC- Complete ad QSC-Patial fute edue ( to almost 0% lowe. Te easo is tat te appliatio-level sevie outage eovey a quikly fiis i a few seods wile te IP-laye Iteet pat eovey may take seveal miutes o eve ous [3]. Howeve, te pefomae diffeee betwee QSC-Complete ad QSC-Patial is vey small. Similaly, Figue 7 sows te esults of te QoS violatio ate fo te espose time (. Agai, te QSC algoitms aieve mu lowe ta fixed ad adom. Te pefomae ode of diffeet QSC algoitms is QSC-Basi (wose ta QSC-Eaed QSC- Patial QSC-Complete. Te easo wy te QSC algoitms ae bette ta te QSC-Eaed is tat sevie e-ompositio always uses te most eet pefomae ad load ifomatio, wi allows it to make bette sevie istae oies i tems of espose time. Figue 8 ad Figue 9 sow te esults about te QoS violatio degee. Figue 8 sows te availability QoS violatio degee ( f. Oe agai, te QSC algoitms osistetly aieve bette pefomae ta fixed ad adom. Figue 6

7 Aveage Violatio egee [%] QSC-Basi QSC-Eaed QSC-Patial QSC-Complete Load: Sessio Request Rate [sessios/mi] Figue 8. Aveage availability QoS violatio degee ude diffeet system load. Suess Rate [%] QSC-Basi QSC-Eaed QSC-Patial QSC-Complete Load: Sessio Request Rate [sessiois/mi] Figue. Aveage povisioig suess ate ude diffeet system load (load balaig. Aveage Respose Time Violatio egee [%] QSC-Basi QSC-Eaed QSC-Patial QSC-Complete Load: Sessio Request Rate [sessios/mi] Figue 9. Aveage espose time QoS violatio degee ude diffeet system load. 9 sows simila esults fo te espose time QoS violatio degee. Hee, te simulatio esults fute validate ou algoitms by sowig tat QSC algoitms a ot oly geatly edue te violatio ate but also aieve lowe violatio degee we QoS violatios ou. Figue sows te esults about te omposed sevie povisioig suess ate. Simila to te above expeimets, ea povisioig suess ate value is alulated ad aveaged ove a peiod of 200 miutes. Te esults sow tat all fou QSC algoitms a similaly aieve mu ige povisioig suess ate, amely bette load balaig, ta te fixed ad adom. I all of te above expeimets, we obseve tat te pefomae gais of te QSC-Complete ae vey small ompaed to te QSC-Patial. Te easo is tat te iitial sevie ompositio algoitm QSC-Eaed is aleady vey good. Hee, te seleted sevie istaes i te old sevie pat ae still, by lage pobability, te best oes we we e-ompose te sevie pat. Hee, it is a ea optimal solutio tat we keep te old good sevie istaes i te ew sevie pat, wi is exatly te QSC-Patial algoitm. 6 Related Wok Besides to te elated wok metioed i te Itodutio, mu ote esea wok as also addessed te sevie ompositio poblem. Te SWOR poet at Stafod [13] povided a develope toolkit fo te web sevie ompositio. It a automatially geeate a futioal ompositio pla give te futioal equiemets fo te omposed appliatio. Howeve, SWOR oly addessed te mappig-1 poblem defied i ou famewok. Te eflow poet at HP labs [7] povided a adaptive ad dyami sevie ompositio meaism fo te ommeial e-busiess poess maagemet. It did ot addess te edto-ed QoS assuaes fo te omposed sevie. Ou wok is also diffeet fom te taditioal IP-laye QoS outig poblem [5] beause: (1 Te goal of IP-laye QoS outig is to fid a etwok outig pat satisfyig QoS ostaits wile QUEST addesses two mappig poblems to aieve ot oly QoS assuaes but also load balaig ad faulttoleae; ad (2 IP-laye QoS outig oly osides te etwok esoue wile QUEST osides ot oly etwok esoues but also ed-system esoues (e.g., CPU. Ote losely elated wok iludes vaious ovelay etwoks. Adeso et al. poposed a esiliet ovelay etwok (RON aitetue [3] to allow distibuted appliatios to quikly detet ad eove fom te Iteet pat failue. RON a eove fom etwok pat outage witi seveal seods usig te appliatio-level outig. RON is useful ad beefiial to QUEST altoug it oly solved a subset of te dyami sevie ompositio poblems. I [6], ua et. al. also poposed te oept of, wi a povide value-added sevies wit QoS assuaes to te use via SLA otats. Howeve, tey oly addessed te badwidt povisioig poblem fo, wile QUEST osides ot oly esoue povisioig (e.g., badwidt ad CPU, but also vaious sevie QoS (e.g., espose time ad availability. Te OveQoS [14] poposed a aite- 7

8 tue to povide Iteet QoS (e.g., statistial badwidt ad loss ate assuaes usig ovelay etwoks. QUEST is diffeet fom OveQoS by povidig QoS assuaes fo omposed sevies, based o SLA otats of idividual sevie ompoets. 7 Colusio We ave peseted a QoS-assued omposed sevie delivey famewok, alled QUEST, fo a maaged sevie ovelay etwok (. Te mao otibutios of tis pape ilude: (1 fomally defie te QoS-assued sevie ompositio poblem ad pove tat it is NP-omplete. We te desig effiiet appoximate optimal algoitms to ompose sevie pats ude multiple QoS ostaits. Moeove, QUEST a aieve soud load balaig i to povide best possible QoS fo all uses; (2 povide bot patial ad omplete dyami sevie eompositio algoitms, wi a quikly eove te sevie pat fom failues o QoS violatios. We ave implemeted a lage-sale simulatio test-bed ad ou extesive simulatio esults sow tat QUEST a povide bot QoS assuaes ad load balaig fo omposed sevies i. Te simulatio esults also idiate tat ou patial dyami sevie e-ompositio algoitm a aieve almost te same level of QoS assuae as te omplete e-ompositio algoitm, but wit mu lowe oveead. 8 Akowledgmet We would like to tak. Ei Wu at IBM T.J. Watso esea ete fo is elpful iput to ou wok. We wis to tak aoymous eviewes fo tei elpful suggestios. Refeees [1] Akamai I. ttp:// [2] Gutella. ttp://gutella.wego.om/. [3]. Adese, H. Balakisa, F. Kaasoek, ad R. Mois. Resiliet Ovelay Netwoks. Po. of 18t ACM SOSP 2001, Baff, Caada, Otobe [4] R. Cag ad C. Ravisaka. A Sevie Aquisitio Meamism fo Seve-Based Heteogeeous istibuted Systems. IEEE Tasatios o Paallel ad istibuted Systems, 5(2, Febuay [5] S. Ce ad K. Nastedt. A Oveview of Quality-of- Sevie Routig fo te Next Geeatio Hig-Speed Netwoks: Poblems ad Solutios. IEEE Netwok Magazie, Speial Issue o Tasmissio ad istibutio of igital Video, 12(6, pp , [6] Z. ua, Z.-L. Zag, ad T. Hou. Sevie Ovelay etwoks : SLAs, QoS ad Badwidt Povisioig. Po. of t IEEE Iteatioal Cofeee o Netwok Potools(ICNP2002, Pais, Fae, Novembe [7] B. Rama et. al. Te SAHARA Model fo Sevie Compositio Aoss Multiple Povides. Po. of Iteatioal Cofeee o Pevasive Computig (Pevasive 2002, Aug [8] F. Casati et. al. Adaptive ad yami Sevie Compositio i eflow. HP teial Repot HPL , Ma [9] X. Fu, W. Si, A. Akkema, ad V. Kaameti. CANS: Composable, Adaptive Netwok Sevies Ifastutue. Po. of 3d USENIX Symposium o Iteet Teologies ad Systems, Ma [] M. R. Gaey ad. S. Joso. Computes ad Itatability. A Guide to te Teoy of NP-Completeess, Feema, Sa Faiso, [11] X. Gu ad K. Nastedt. yami QoS-Awae Multimedia Sevie Cofiguatio i Ubiquitous Computig Eviomets. Po. of IEEE 22d Iteatioal Cofeee o istibuted Computig Systems (ICCS 2002, July [12] X. Gu, K. Nastedt, W. Yua,. Wiadakul, ad. Xu. A XML-based Quality of Sevie Eablig Laguage fo te Web. Joual of Visual Laguage ad Computig, Speial Issue o Multimedia Laguage fo te Web, 13(1, pp , Febuay [13] S.R. Poekati ad A. Fox. SWOR: A evelope Toolkit fo Buildig Composite Web Sevies. Po. of te Elevet Wold Wide Web Cofeee (Web Egieeig Tak, Hoolulu, Hawaii, May [14] L. Subamaia, I. Stoia, H. Balakisa, ad R. H. Katz. OveQoS: Offeig QoS usig Ovelays. Po. of Fist Woksop o Hop Topis i Netwoks (HotNets-I, Pieto, New Jesey, Otobe [15] C. Wad, M. Buo, R. Cag, ad L. Lua. A Geei SLA Semati Model fo te Exeutio Maagemet of e- Bussiess Outsouig Cotats. Po. of 3d Iteatioal Cofeee o e-commee ad Web Teologies (EC-Web 2002, Septembe [16] J. Wiik ad S. Jami. Iet3.0: Iteet Topology Geeato. Te Repot UM-CSE-TR (ttp://il.ees.umi.edu/ami/, [17]. Xu ad K. Nastedt. Fidig Sevie Pats i a Media Sevie Poxy Netwok. Po. of SPIE/ACM Multimedia Computig ad Netwokig Cofeee, Sa Jose, CA, Jauay [18]. Xu, K. Nastedt, ad. Wiadakul. QoS ad Cotetio Awae Multi-Resoue Resevatio. Cluste Computig, te Joual of Netwoks, Softwae Tools ad Appliatios, 4(2, Kluwe Aademi Publises,