Supporting a seamless map in peer-to-peer system for massively multiplayer online role playing games

Transcription

1 Univeriy of Wollongong Reearch Online Faculy of Informaic - Paper (Archive) Faculy of Engineering and Informaion Science 008 Supporing a eamle map in peer-o-peer yem for maively muliplayer online role playing game Xinbo Jiang Univeriy of Wollongong, j9@uowmail.edu.au Farzad Safaei Univeriy of Wollongong, farzad@uow.edu.au Publicaion Deail Thi conference paper wa originally publihed a Jiang, X and Safaei, F, Supporing a eamle map in peer-o-peer yem for maively muliplayer online role playing game, 33rd IEEE Conference on Local Compuer Nework, LCN 008, Monreal, Canada, -7 Ocober 008. Copyrigh Iniue of Elecrical and Elecronic Engineer 008. Original conference paper available here Reearch Online i he open acce iniuional repoiory for he Univeriy of Wollongong. For furher informaion conac he UOW Library: reearch-pub@uow.edu.au

2 Supporing a eamle map in peer-o-peer yem for maively muliplayer online role playing game Abrac Maively Muliplayer Online Role Playing Game feaure huge map ha can be pariioned ino maller componen called zone o achieve calabiliy. In peer-o-peer (PP) yem, hoe zone can be aigned o peer who are willing o ake up he role of zone erver. A eamle map require iner-zone communicaion o allow ineracion beween player acro zone boundarie. In aigning zone o peer, i i criical o eek approache o reduce he iner-zone communicaion co in PP yem. In hi paper, we formulae he zone aignmen problem for PP yem and demonrae ha he problem i NP-hard. We hence propoe a lowco heuriic ha pariion he phyical nework ino bin, a well a, aggregaing he pariion of he virual world by cluering neighboring zone in a game map. We hen demonrae ha by aigning cluered neighboring zone in he virual map ino peer in common phyical nework bin, we are able o achieve imilar iner-zone communicaion co for he zone aignmen problem a ha can be achieved by he opimizaion model we formulaed, while avoiding he prohibiively high compuaion co required by he laer. Dicipline Phyical Science and Mahemaic Publicaion Deail Thi conference paper wa originally publihed a Jiang, X and Safaei, F, Supporing a eamle map in peer-opeer yem for maively muliplayer online role playing game, 33rd IEEE Conference on Local Compuer Nework, LCN 008, Monreal, Canada, -7 Ocober 008. Copyrigh Iniue of Elecrical and Elecronic Engineer 008. Original conference paper available here Thi conference paper i available a Reearch Online: hp://ro.uow.edu.au/infopaper/683

3 Supporing a Seamle Map in Peer-o-Peer Syem for Maively Muliplayer Online Role Playing Game Xinbo Jiang, Farzad Safaei TITR, Univeriy of Wollongong, Auralia Abrac Maively Muliplayer Online Role Playing Game feaure huge map ha can be pariioned ino maller componen called zone o achieve calabiliy. In peer-o-peer (PP) yem, hoe zone can be aigned o peer who are willing o ake up he role of zone erver. A eamle map require iner-zone communicaion o allow ineracion beween player acro zone boundarie. In aigning zone o peer, i i criical o eek approache o reduce he iner-zone communicaion co in PP yem. In hi paper, we formulae he zone aignmen problem for PP yem and demonrae ha he problem i NP-hard. We hence propoe a low-co heuriic ha pariion he phyical nework ino bin, a well a, aggregaing he pariion of he virual world by cluering neighboring zone in a game map. We hen demonrae ha by aigning cluered neighboring zone in he virual map ino peer in common phyical nework bin, we are able o achieve imilar iner-zone communicaion co for he zone aignmen problem a ha can be achieved by he opimizaion model we formulaed, while avoiding he prohibiively high compuaion co required by he laer. I. Inroducion The developmen and growh of online game have been phenomenal in recen year. Online game uch a Lineage [], World of WarCraf [] and EverQue [3] have araced million of player on a global cale and achieved huge commercial ucce. Among genre of online game, calabiliy i a paricularly criical iue for Maively Muliplayer Online Role Playing Game (MMORPG), in which houand of player need o be uppored concurrenly in a large virual world. In hi repec, calabiliy refer o he number and geographic pan of player ha can be uppored. Currenly, online MMORPG are predominanly deployed uing a clien erver model, in which a cenral erver ha he auhoriy o eecue he majoriy of he game logic and hen end a li of objec o he clien for rendering (ae updae). Clien erver model achieve calabiliy by employing erver cluer. While having advanage uch a he eae of cenral managemen and applicaion of ecuriy meaure, hi model i ubjec o poenial ingle poin of failure and he reource have o be over-proviioned o handle peak load. I hould alo be noed ha in a co-locaed erver cluer, while he compuaion aociaed wih he imulaion of a virual world can be diribued among he erver in he cluer, he poible bandwidh congeion a he erver ide canno be removed. There i a ignifican body of work relaed o a cla of calable deign o uppor MMORPG. A deailed urvey regarding hee deign i conduced in [] and reference herein. While differing in many apec, he fundamenal idea of hoe deign i o advocae he ue of he reource of clien compuer (peer) including CPU cycle, bandwidh and orage. Ideally, a peer-o-peer (PP) yem can dynamically cale up and down wih he number of player, and hence addre he inheren calabiliy iue of he clien erver model. Regardle of he upporing model, he general approach for game o achieve calabiliy i o pariion he virual world ino maller componen called zone. In a cenral erver model, he imulaion of hoe zone can be diribued among he erver in a erver cluer, wherea in a PP cenario, hee zone can be aigned o he peer who are willing o ake up he role of zone erver. If he zone of a game virual map are egregaed from each oher, hen here would be no communicaion beween zone erver. In hi cae, cerain echnique are required o give he player he impreion ha he virual world i coniguou. For inance, when a player move from one zone o anoher, he or he ha o walk hrough a pah or flying acro a valley o be diconneced from one zone erver and conneced o anoher. While hee echnique can obviouly eae he managemen of iner-erver communicaion, hey alo impoe conrain on game deign, paricularly on he calabiliy of he zone. For inance, a recen udy of he player populaion in a game virual world [5] ha found ha a mall number of zone could have a high player populaion of up o 00 player. Thee are mainly place in he virual world, uch a marke place, ha encourage player congregaion. Given he approach of uing egregaed zone for he game world, he ae of each zone are uually managed by a ingle erver. Hence, he calabiliy of he zone i largely conrained by he capaciy of he erver. A a reul, when a zone i highly populaed, furher connecion reque may be rejeced, which would negaively affec player eperience. On he oher hand, o creae a eamle map wih ranparen boundary beween zone, erver of neighbouring zone need o echange ae informaion of player o enable he cro-boundary ineracion beween player. We enviage ha a map of eamle deign would have ignifican poenial o enhance game feaure for beer playabiliy. For inance, a widepread balefield ha engage a large number of player or a ocial congregaion of hundred of paricipan, could adop a eamle map ha give he player he impreion of a coniguou virual pace wihou boundary limiaion. I hould be noed while he calabiliy of a zone can be enhanced by joining neighbouring zone ino a eamle map, he co i iner-zone communicaion beween neighbouring zone erver, which i he focu of hi paper. While he co of iner-zone communicaion migh be of le concern for erver in a cenral erver cluer ince he raffic i mainly carried by he Local Area Nework (LAN), in /08/$ IEEE 3 Auhorized licened ue limied o: Univeriy of Wollongong. Downloaded on November, 008 a : from IEEE Xplore. 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4 a PP cenario, he communicaion co could be prohibiively high in upporing a eamle map if neighbouring zone in he game world are aigned o peer wih limied bandwidh and far apar from each oher in erm of laency. Hence, i i of paramoun imporance o find an effecive approach o aign zone o peer o reduce he iner-zone communicaion co. Hereafer we refer o he problem of finding uch an approach a he zone aignmen problem. Our previou work have been mainly on he deign of PP yem o uppor MMORPG. To ha end, in [6] we have developed a game uppor cenario aking ino conideraion he raffic race of a MMORPG. We propoed he ue of applicaion-level mulica ree o carry he raffic from zone erver o player, he former would be he roo of he mulica ree and he laer he leave or relay poin. We demonraed ha, hrough he diribuion of bandwidh of he mulica ree buil on op of a rucured PP overlay (e.g., Pary), a peer wih a ypical bandwidh capaciy (e.g., ADSL) could poenially uppor even a crowded zone, while a unica model would lead o eceive capaciy requiremen for a ypical peer. However, he mulica ree may creae era laency beween he zone erver and he player leading o degraded performance for ineracion beween player. A a reul, we propoed in [7] o ue a wo-level hierarchical overlay: he higher level among node locaed cloe o nework acce poin, he lower level among node in a local domain. We demonraed ha, hrough fairly low-co echnique we developed, while bandwidh incurred by he game raffic can be diribued by he mulica ree buil on he overlay, he laency performance ha improved ignificanly o allow real-ime ineracion beween player. In boh [6] and [7], we have aumed a game world pariioned ino egregaed zone. In hi paper, we focu on he uppor of a eamle map and conider iner-zone communicaion co ha lead o he zone aignmen problem. I i a coninued effor in building a framework for PP yem o uppor MMORPG. To ha end, we propoe a heuriic o pariion boh he phyical nework and he virual world (game map) in conrolling he communicaion co in PP yem for upporing MMORPG. In pariioning he phyical nework, we are acually rying o group peer ha are opologically cloe o each oher and elec hem o be poenial zone erver. We hen demonrae ha he zone aignmen problem i NP-hard and incur a high compuaional co even rericing he aignmen of zone o a mall e of peer eleced hrough he phyical nework pariion. A a reul, he propoed heuriic aggregae he zone in a virual map ino larger pariion. In pariioning boh he phyical nework and virual game map, we are able o aign a group of neighbouring zone o a group of opologically cloe peer. Through he heuriic, we demonrae ha we are able o achieve a near opimal iner-zone communicaion co when deploying a eamle map in a PP yem. The re of he paper i organized a follow. In ecion II, we fir dicu he raionale and approach for phyical nework pariion. Then hrough formulaion, we demonrae he NP-hardne of he zone aignmen problem. We hence propoe o furher pariion he virual world. We finally preen he dual-pariion heuriic. In ecion III, we preen imulaion procedure and reul. We finally dicu relaed work in ecion IV and conclude in ecion V. II. Dual-pariion Heuriic In hi paper, we propoe a dual-pariion heuriic ha pariion boh he phyical nework and he virual map for upporing a eamle map in PP yem. In pariioning he phyical world, we are acually eploring he phyical nework proimiy in order o elec poenial peer a candidae zone erver wih coare granulariy. In pariioning he virual world, we aim o opimize he iner-zone communicaion co by eploring proimiy of virual zone in a eamle map. A. Phyical Nework Pariion Cluering echnique i a widely ued echnique in he reearch lieraure [8-0]. The fundamenal idea i o find node ha are cloe o each oher, and provide hi localiy informaion o applicaion o achieve beer performance. For inance, Ranaamy e al. [0] propoed o ue he landmark cheme o have node cluered ino bin. In hi cheme, he landmark are a number of well known node in he Inerne. A peer in he overlay can ping hoe landmark o obain i opological coordinae. Peer wih he ame coordinae are hen cluered ino he ame bin. Simulaion hrough a Trani-Sub [] opology ha hown ha he RTT beween node wihin he ame bin i on average.06 ime horer han he RTT beween node acro bin. In hi paper, we rely on available echnique for cluering node ino bin. However, we noe ha game diribued deign migh have pecific need for cluering echnique. For inance, while he landmark binning cheme [0] can effecively group node ha are cloe o each oher, he number of bin can no be eaily conrolled. A a reul, when he number of landmark increae, cluering heuriic may generae oo many bin wih each bin having only a few node in i. We will leave i o fuure work o inveigae game pecific need for cluering heuriic. Afer cluering node ino bin, inead of aigning game zone o acual ho, we aign zone o bin. In a large-cale PP yem, he number of available peer who are willing o ake he role of zone erver could be high. A demonraed in laer ecion, he zone aignmen problem incur high compuaion co. By aigning zone o bin inead of acual ho, we are able o ignificanly reduce he earch pace. For inance, inead of rying o find an opimal aignmen cheme among hundred of available peer, we cluer hoe peer ino a mall number of bin. Effecive cluering enure ha aigning zone o differen ho in a common bin would incur imilar iner-zone communicaion co. Furhermore, he iue of churn [] i a criical concern for any PP yem deign. Churn refer o he phenomena ha in a PP yem, peer or clien compuer come online and go offline unpredicably. Hence, any opimizaion cheme or heuriic for zone aignmen problem ha eek reduced iner-zone communicaion co by finding he opimal aignmen of game zone o peer would be impracical. Thi i paricularly rue for MMORPG given he high churn rae of peer [3] in online game. However, by aigning zone o bin inead of paricular ho, if churn occur, for Auhorized licened ue limied o: Univeriy of Wollongong. Downloaded on November, 008 a : from IEEE Xplore. Rericion apply.

5 inance, a zone erver goe offline, anoher backup peer in he ame bin can ake up he role of he zone erver wihou affecing much he iner-zone communicaion co ha migh have impac on he game qualiy for cro-boundary ineracion beween player. B. Formulaion Afer cluering node ino bin, we formulae he zone aignmen problem a follow. The general known variable are: d : The delay beween bin and bin. m : The number of avaar in he boundary of zone i and zone j. c :The delay co of ae informaion echange beween zone i and zone j if aigning zone i and zone j o bin and bin repecively. c = m d () N:The number of zone in a eamle map. M:The number of phyical bin. b : The number of peer who are willing o ake he role of zone erver in bin, M. The deciion variable i i = The objecive funcion i Minimize c ubjec o N i, j, i j i j (3) = i: i N () i = M i i= b : M (5) To ranform (3) ino a linear programming problem, we inroduce a binary variable y uch ha y = if = i j = (6) 0 oherwie The objecive funcion (3) hen become Minimize ( c y ) i j (7) ubjec o N i = M i i= y if zone i i aigned o bin 0 oherwie i, j, = i: i N (8) () b : M (9) i (0) y + i j () + j y () The conrain in (8) enure ha each zone in he map can only be aigned o one bin. The conrain in equaion (9) enure ha he number of zone aigned o a bin i le han or equal o he number of peer in ha bin who are willing o ake up he role of he erver for he zone. The conrain in (0) () and () are o make ure ha equaion (6) i aified. C. NP-Hardne of he Zone Aignmen Problem Given he objecive funcion in (3), we aume i a conan T. We furher aume = T j j =. In oher word, for each pair of neighboring zone, one ha o be aigned o a paricular bin T. An eample i given in Figure o demonrae he feaibiliy of uch an aignmen cheme. Then (3) become Minimize T c i (3) i, j ubjec o () and (5). Thi model ha been proved in [] o be equivalen o he well-known Bin Packing Problem[], which i NP-hard. Hence, he Zone Aignmen Problem i NP-hard. N T N T T N T N N T N T T N T N Figure : T zone aigned o bin T, N- zone aigned o any bin bu T. 5 Auhorized licened ue limied o: Univeriy of Wollongong. Downloaded on November, 008 a : from IEEE Xplore. Rericion apply.

6 D. Virual World Pariion Pariion one Pariion wo Pariion hree Figure : Pariioned Map The compuaional co could be prohibiively high for zone aignmen problem, even if we chooe o aign zone o a limied number of bin uing he model formulaed above. For an equally divided quare map a hown in Figure, each zone ha a lea wo neighboring zone. Le he number of zone be N, here are a lea N pair of neighboring zone. Le M be he number of nework bin pariioned, here will be M(M-) poibiliie o aign each pair of neighboring zone o he bin. Hence, he number of y deciion variable i a lea NM(M-) or O ( NM ). The number of conrain i N + M + NM(M-) or O ( NM ). Given he compleiy of he model, a demonraed in ecion IV, he formulaion can only olve he zone aignmen problem in real ime for a eamle map having a limied number of zone. A a reul, in addiion o phyical nework pariion a dicued previouly, we propoe o judiciouly aggregae he zone in a virual world map ino large pariion o reduce he co of he zone aignmen problem. While a eamle map ha muliple zone, neighboring zone can be grouped ogeher and regarded a a ingle pariion o be aigned o a bin. For inance, if a eamle map ha ieen zone a demonraed in Figure, neighboring zone 6 could be grouped ogeher o form a pariion and aigned o peer in a common bin. The zone grouping policy i a deign iue ha hould conider performance requiremen of a eamle map. Zone grouped in one pariion, when aigned o peer in a common bin, would have beer capaciy for cro-boundary ineracion beween player ince he iner-zone communicaion co incurred beween peer in a common bin would be low. In oher word, a an eample in Figure, he map deign for zone in pariion one could allow more cro boundary ineracion. However, ince zone in pariion wo are aigned o anoher bin, ineracion acro zone 3 and 7, for inance, hould be kep low ince he iner-zone communicaion co could be high. A an eample, he map for pariion one could be deigned o handle crowded pace like ciie, balefield and marke. On he oher hand, for boundary area beween zone in differen pariion, uch a zone 3 and 7, he map hould be deigned a wall or pah o avoid eceive iner-zone communicaion co. E. Selecion of Bin In elecing candidae bin for aigning he zone, we conider he delay co incurred by he laency beween player ho o he zone erver. To ha end, we or bin baed on he um of delay co S. Le P be he number of peer in bin and d be he delay beween bin and. S i defined a S = P d () Hence, S repreen he um of delay co incurred by he laency from player ho o zone erver if all zone are aigned o bin. Baed on dicuion o far, we preen he dual-pariion heuriic in Figure 3. In he following ecion, we will compare he reul obained from running he opimizaion model and he heuriic. When preening he reul of he heuriic, we will dicu he heuriic in more deail.. Pariion he phyical nework ino M bin.. Sor he phyical nework bin baed on uch ha < < < M 3. Le b i be he number of available zone erver in bin i.. Le N be he number of zone in a map. 5. Selec he fir n bin uch ha n i= b i N n n 6. If b i > N, reduce bn uch ha bi = N i= i= 7. Sor he eleced bin uch ha b b b n 8. for i = o n 9. if feaible 0. group b i neighboring zone along he edge of he map. ele. group b i neighboring zone 3. end A. Topology Seup Figure 3: Dual-pariion Heuriic III. Simulaion Procedure and Reul We ued Georgia Tech. GT-ITM o generae a rani-ub (TS) opology for eperimenal purpoe. The opology have node grouped ino eiher rani or ub domain. In our opology, here are hree rani domain wih on average eigh node (rani node) in each domain. Each rani node i conneced o hree lower level ub domain on average. There are on average eigh node (ub node) in each ub domain. TS opology emphaize he localiy feaure of he Inerne. To 6 Auhorized licened ue limied o: Univeriy of Wollongong. Downloaded on November, 008 a : from IEEE Xplore. Rericion apply.

7 hi end, link weigh i aigned uch ha raffic pah beween wo node in he ame domain will remain wihin ha domain []. In [5], a imilar opology i ued o model he Inerne. We hen have 5 ho on average conneced o each node in he opology o model an overlay nework of 0000 ho. We ue he opology aigned link weigh a RTT for he link. The link beween an end-ho and a opology node i aigned a random RTT value beween 3 0 m. We hen ake advanage of he localiy properie of he TS opology by cluering node baed on he domain hey belong o. Thu, we are able o have cluer of node becaue here are ub domain in our opology model. We conider each cluered ub domain a a candidae bin for he zone aignmen problem. Given our opology, we have on average 0 end-ho (peer) in each bin. B. Reul of Solving he Opimizaion Model To inaniae he opimizaion model preened in ecion II.B, we randomly elec a mall number of peer who are willing o ake up he role of zone erver. In able, we li he number of available zone erver in he fir five bin ored baed on (). Bin Inde 3 5 Number of available zone erver Table: Available zone erver in bin Noe ha in able, he bin are ored baed on he value of S a defined () uch ha, for inance, he model hould ry o aign zone o bin one fir, ince he um of delay co incurred by aigning zone o bin one would be minimal. 3 3 (a) zone (c) 0 zone (b) 6 zone We chooe Cple opimizaion ofware o opimize he model in ecion B, III on a Penium IV Ghz Linu erver wih GB of RAM. We eperimened wih a quare map and gradually increaed he number of zone from o 5. The reul are preened in Figure. The ime aken in olving he (d) 5 zone Figure : Reul of Opimizaion Model opimizaion model increae a he number of zone increae, and i lied in able. Number of zone Time aken o run he opimizaion model (econd) Table : Time aken o run he opimizaion model In Figure, each pariioned quare repreen a zone in he map. The number in he quare repreen he bin number ha a correponding zone i aigned o. For inance, in () of Figure, hree zone are aigned o bin one, even zone are aigned o bin wo and he remaining wo zone are aigned o bin hree. From Figure, i can be fir oberved ha, zone are aigned o bin in a ored order a epeced. For inance, here are hree peer available o be zone erver in bin one, and hoe peer are populaed fir before bin, 3, and 5 are coninually o be populaed. Thi i becaue when we inaniae he opimizaion model, we aign bin in a ored order a dicued in ecion II.E. In doing o, i i enured ha he um of delay co beween player and zone erver i minimal. Secondly, he heuriic group neighboring zone in he virual map and aign hem o he common bin o achieve minimal iner-zone communicaion co. I can be oberved in he figure ha, zone aigned o a common bin are placed ogeher, wih be effor, in a coninued fahion wihou being eparaed by oher zone. Thi i becaue he iner-zone communicaion co i incurred by ineracion acro hared boundarie of neighboring zone. Grouping neighboring zone ogeher and aigning hem o he common bin would be beneficial in reducing he iner-zone communicaion co ince he iner-zone raffic i conrained wihin he peer in a common bin, in which peer are cloe o each oher in erm of laency. Finally, he opimizaion model i no calable in erm of compuaion co. For inance, a hown in able, when he number of bin i above 6, he compuaion co will become prohibiively high in olving he model in real ime. C. Reul of running he heuriic Enlighened by he reul in Figure, our general inuiion for he heuriic i ha if we pariion he virual map and cluer he neighboring zone, and hen aign he enire pariion o a common bin, he iner-zone communicaion co hould be comparable o he reul achieved by he Figure 5: 5-zone aggregaed map 7 Auhorized licened ue limied o: Univeriy of Wollongong. Downloaded on November, 008 a : from IEEE Xplore. Rericion apply.

8 opimizaion model. We eperimened wih a 5 zone map. A hown in Figure 5, we applied he heuriic in Firugre 3 o pariion he map by cluering neighboring zone baed on available zone erver in each bin (able ). Sum of he iner-zone communicaion co Boundary Figure 6: Boundary Comparion Figure.d Figure 5 Random Zone Aignmen Figure 7: Comparion of he Iner-zone Communicaion Co For inance, in bin one, here are hree available peer who are willing o ake up he role a zone erver, we hence cluer hree zone o be aigned o bin one a a ingle pariion. When we cluer zone in he virual map, we ry o place he big pariion, for inance, pariion, along he edge of he map o reduce he number of hared boundarie beween differen pariion (ep 6-3 of he heuriic). An eample i given in Figure 6. If we have pariion wo (all zone in pariion wo are aigned o peer in bin wo) placed along he edge of he map, we will have i boundarie hared wih oher pariion a hown on he lef par of Figure 6. However, if we have he pariion placed in he middle of he map, we would have eleven boundarie a demonraed in he righ par of he figure. Since iner-zone communicaion i incurred by cro-boundary raffic, we would epec le communicaion co if we had le hared boundarie when we aign he pariion along he edge of he map. To compare he performance in erm of iner-zone communicaion co beween Figure.d, which i he reul of olving he opimizaion model, and Figure 5, which i achieved by running he heuriic, we aign zone of he map o randomly eleced peer in he correponding bin. For inance, baed on Figure 5, we aign he four zone on he op lef corner of he map o four eleced peer in bin hree, wherea baed on Figure.d, we aign he four zone on he down righ corner o four eleced peer in bin hree. I hould be noed ha when aigning zone o peer in he ame bin, we do no furher eek opimizaion goal beuae of he iue of churn in PP yem a we dicued in ecion II.A. m = To normalize he imulaion reul, we e (ecion II.B). Again, we ue he nework opology a dicued in ecion III.A. We run he imulaion for 0000 ime and he reul are demonraed in Figure 7. Bo plo in Figure 7 how ha he um of he iner-zone communicaion co baed on Figure 5 i only lighly higher han ha of Figure.d, which i obained by olving he opimizaion model. The mean of he um of he communicaion co of he opimized model (Figure.d) i 87, wherea he mean of he um of he communicaion co of he pariioned map (Figure 5) i 95 and only 5 percen higher han ha of he opimized model. m = (one player a Given our paricular opology, each boundary of each zone) and a 5 zone map ha 5 hared boundarie alogeher, he player a he boundary of a zone would be ubjec o an era m delay co on average due he requiremen of he iner-zone communicaion for he opimized model (87/5 = ), wherea for he pariioned map, he player would be ubjec o.6 m delay co (95/5 =.6). The minor difference of.6 m in delay co i negligible a far a he game qualiy of MMORPG i concerned. For comparion purpoe, we finally aign zone of a 5 zone map o peer in he opology randomly and calculae he um of he iner-zone communicaion co. A hown in Figure 7, boh he opimized model and he pariioned map can ave he communicaion co by a facor of hree in comparion wih a map for which zone are randomly aigned o peer. To conclude for hi ecion, he compuaion co for zone aignmen problem i prohibiively high (able ) when olving he opimizaion model. We are able o achieve nearly he ame level of opimizaion goal in reducing he iner-zone communicaion co by pariioning he zone in he virual map and aigning he pariion o phyical nework bin. D. Map wih Hopo In he previou imulaion, we have e m = acro all boundarie. In oher word, player are uniformly diribued acro he boundarie of he map. However, in MMORGP, player flocking may occur due o he feaure of he game deign. For inance, an inereing occurrence of an even may arac more player o come o a cerain par of he game world and creae a hopo in he map. To eperimen wih a map wih hopo a he boundarie, we eleced a number of boundarie of a 0-zone map and e m = a hoe boundarie o imulae hopo a which he ineracion beween player are wice a much a ha of a normal boundary. In Figure 8.a, hoe hopo are marked wih croe. We hen run he opimizaion model for he zone aignmen problem and he reul are preened in Figure 8.b. I can be oberved from he figure ha, in addiion o wha we 8 Auhorized licened ue limied o: Univeriy of Wollongong. Downloaded on November, 008 a : from IEEE Xplore. Rericion apply.

9 have dicued in ecion III.B, he opimizaion model reric he hopo wihin common phyical nework bin. In oher word, he opimizaion model aign he wo neighboring zone connecing a hopo o a common bin. In doing o, he communicaion co incurred by he hopo would be kep low ince he wo neighboring zone are aigned o peer in a common bin, and hence are cloe o each oher in erm of laency. hopo Sum of Iner-zone Communicaion Co (a) Map wih hopo 00 Opimizaion Model Pariioned Map (b) Reul of Opimizaion Model (c) Pariioned Map Figure 8: A map wih hopo a boundarie Enlighened by he reul we dicued above, we again apply he virual map pariion following he heuriic in Figure 3. In addiion, while aigning he big pariion along he edge of he map, we reric he neighboring zone connecing a hopo o be aigned o peer wihin a common phyical nework bin. The pariioned map i preened in Figure 8.c. The oal communicaion co of boh Figure 8.b and Figure 8.c i compared in Figure 9, a he reul of imilar procedure o he previou ecion. In Figure 9, he mean of he um of he communicaion co of he opimizaion model (Figure 8.b) i 699, wherea he mean of he um of he communicaion co a a reul of running he heuriic (Figure 8.c) i 739, le han 3 percen higher han ha of he opimized model. Given ha a 0-zone map ha 8 hared boundarie in oal, he player a he boundary of a zone would be ubjec o an era 60.7m delay co on average due he requiremen of he iner-zone communicaion for he opimized model (699/8 = 60.7), wherea for he pariioned map, he player would be ubjec o 6. m delay co (739/8 = 6.). The minor difference of. m in delay co i negligible a far a he game qualiy of MMORPG i concerned. To conclude hi ecion, if game feaure hopo a cerain area of he map ha could lead o increaed iner-zone communicaion co a he boundarie, he map ha i pariioned baed on he locaion of he hopo could achieve nearly he ame level of communicaion co a ha can be achieved by he opimizaion model. We again demonraed he effecivene of pariioning boh he phyical nework and virual map in reducing iner-zone communicaion co, while avoiding he high compuaion co required by he opimizaion model. Figure 9: Comparion of he Communicaion Co IV. Relaed Work To our be knowledge, here i no eiing work ha direcly addree eamle map deign in PP yem. Diribued erver archiecure i uually conidered a an alernaive o cenral erver model in addreing he calabiliy and performance boleneck of he laer. In [] and [6], heuriic are developed for diribued erver yem o improve performance. The main focu of hoe heuriic i o aign player o erver o ha he communicaion co beween he player and he erver (e.g., laency) i low, wherea our focu i o aign zone o erver o ha he communicaion co beween erver i low. In [6], iner-erver communicaion co i addreed a par of a deign of pariioning cheme for diribued erver yem. However, he heuriic developed i ubjec only o a mall number of erver (e.g. 8 erver). Given he pariioning of phyical nework and virual map, our approach i no limied by he number of erver. Thi i imporan ince in PP yem, a virual map migh need o be pariioned ino much maller componen o be aigned o peer wih maller capaciy comparing o erver in a diribued erver yem. A a reul, more peer are required for he zone aignmen problem. I hould alo be noed ha diribued erver yem i relaively aic, wherea PP yem feaure dynamic of peer paricipaion or churn. A a reul, we chooe o aign zone o bin inead of o paricular ho. V. Concluion Maively Muliplayer Online Role Playing Game uually feaure a huge virual world for player o eplore. To achieve deploymen calabiliy, he game world can be pariioned ino maller componen called zone. In a peer-o-peer yem, hoe zone can be aigned o peer who are willing o ake up he role of zone erver o achieve calabiliy. A eamle map require iner-zone communicaion o allow ineracion acro zone boundarie beween player. A eamle map improve game playabiliy by making he boundarie of zone ranparen o player. To enable a eamle map in PP yem, i i criical o find effecive approache uch ha when aigning zone o peer, he iner-zone communicaion co can be kep minimum. In 9 Auhorized licened ue limied o: Univeriy of Wollongong. Downloaded on November, 008 a : from IEEE Xplore. Rericion apply.

10 hi paper, we formulaed an opimizaion model for he zone aignmen problem and demonraed he NP-hardne of he problem. We hen propoed a low-co heuriic o pariion he phyical nework ino bin uch ha peer in a common bin are opologically cloe o each oher. Furhermore, enlighened by he reul of he opimizaion model, he heuriic pariion he virual world map uch ha neighboring zone in he map are cluered ogeher and aigned o a bin a a ingle pariion. In doing o, we demonrae ha we are able o achieve he ame level of iner-zone communicaion co a hoe can be achieved by he opimizaion model we formulaed, while avoiding he prohibiively high compuaion co required by he laer. Acknowledgemen Thi work i uppored by he Co-operaive Reearch Cenre for Smar Inerne CRC (SITCRC) and he Univeriy of Wollongong (UOW), Auralia. [5] C. D. Nguyen, F. Safaei, and P. Bouead, "A diribued erver archiecure for providing immerive audio communicaion o maively muli-player online game," preened a IEEE Inernaional Conference on Nework (ICON 00), Singapore, 00. [6] J. C. S. Lui and M. F. Chan, "An Efficien Pariioning Algorihm for Diribued Virual Environmen Syem," IEEE Tranacion on Parallel and Diribued Syem, vol. 3, pp. 93-, 00. Reference [] Blizzard. [] Couner-Srike. [3] Everque. hp://everque.aion.ony.com. [] X. Jiang, F. Safaei, and P. Bouead, "Laency and Scalabiliy: A Survey of Iue and Technique for Supporing Neworked Game," preened a Inernaional Conference on Nework (ICON 005), Kuala Lumpur, Malayia, 005. [5] D. Piman and C. GauhierDickey, "A meauremen udy of virual populaion in maively muliplayer online game," preened a he 6h ACM SIGCOMM workhop on Nework and yem uppor for game, Melbourne, Auralia, 007. [6] X. Jiang, F. Safaei, and P. Bouead, "An approach o achieve calabiliy hrough peer-o-peer nework for maively muliplayer role playing game," ELSEVIER Journal on Compuer Communicaion, vol. 30, pp , 007. [7] X. Jiang, F. Safaei, and P. Bouead, "Enhancing he mulica performance of rucured PP overlay in upporing Maively Muliplayer Online Game," preened a IEEE Inernaional Conference on Nework 007 (ICON 007), Adelaide, Auralia, 007. [8] X. Y. Zhang, Q. Zhang, Z. Zhang, G. Song, and W. Zhu, "A Conrucion of Localiy-Aware Overlay Nework: moverlay and I Performance," IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, vol., pp. 8-8, 00. [9] R. A. Ferreira, S. Jagannahan, and A. Grama, "Enhancing Localiy in Srucured Peer-o-Peer Nework," preened a Tenh Inernaional Conference on Parallel and Diribued Syem (ICPADS?), 00. [0] S. Ranaamy, M. Handley, R. Karp, and S. Shenker, "Topologically-Aware overlay conrucion and erver elecion," preened a INFOCOM, 00. [] E. Zegura, K. Calver, and S. Bhaacharjee., "How o Model an Inerne," preened a IEEE INFOCOM, 996. [], D. Suzbach, and R. Rejaie, "Underanding churn in peer-o-peer nework," preened a Proceeding of he 6h ACM SIGCOMM conference on Inerne meauremen, Rio de Janeriro, Brazil, 006. [3] J. Kim, D. Chang, and T. Kwon, "Traffic Characeriic of a Maively Muli-player Online Role Playing Game," preened a Negame'05, New York, USA, 005. [] D. N. B. Ta and S. Zhou, "A wo-phae approach o ineraciviy enhancemen for large-cale diribued virual environmen," Compuer Nework, vol. 5, pp. 3-5, Auhorized licened ue limied o: Univeriy of Wollongong. Downloaded on November, 008 a : from IEEE Xplore. Rericion apply.