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1 2612 JOURNAL OF SOFTWARE, VOL 8, NO 1, OCTOBER 213 C-Cell: A Efficiet ad Scalable Network Structure for Data Ceters Hui Cai Logistical Egieerig Uiversity of PLA, Chogqig, Chia Eail: caihui_cool@126co ShegLi Li Logistical Egieerig Uiversity of PLA, Chogqig, Chia Eail: @qqco Wei Wei Logistical Egieerig Uiversity of PLA, Chogqig, Chia Eail: viviaww@yeahet Abstract Data ceters play a crucial role i curret Iteret architecture supportig cotet-cetric etworkig How to efficietly itercoect a expoetially icreasig uber of servers is a fudaetal challege i data ceters etworkig This paper presets C-Cell, a ew etwork architecture which is desiged o the basis of recursive structure A high-level C-Cell is costructed by low-level C-Cell Ad this structure ot oly has a low-ratio i switch/server, but also provides ultiple parallel short paths betwee ay pair of servers O the preise of low proportio of switches ad servers, C-Cell ca efficietly achieve routig echaiss i shorter ea path legths with less etwork cost Idex Ters Data ceter, etwork, routig, protocol I INTRODUCTION I recet years, data ceter etworkig (DCN) has bee attractig uch attetio of researchers, which desigs both the etwork structure ad associated protocols that itercoect thousads of servers at a data ceter But the developet of DCN ot oly leads to great challeges to the high ad balaced etwork capacity, ad robustess to lik/server faults, but also results i high hardware ifrastructure cost ad power cost Therefore, fault-tolerace, scalability, ad power cosuptio of the distributed storage for a data ceter becoe key parts i order to esure the data availability ad reliability I this paper, the authors focus o a siple techical proble Ca we build a fault-tolerace, scalability ad low-cost etworkig ifrastructure for data ceters, usig oly coodity server with 3 ports ad coodity switch? There are ay potetial beefits to solve this proble Firstly, we do ot use the high-ed ad expesive switch which is widely used today Ad coodity server ca also be available Secodly, the wirig becoes easier if oly 3 ports server is used for itercoectio There is o eed to add additioal hardware or wire o a server Thirdly, ore acadeic research ito data ceters ca be spawed New probles i data ceter etworkig ca be foud ad assessed through soe easy-build tests i istitutio But recet proposals ad curret practice caot solve those probles The tree-based structure eeds expesive ad high-ed switch as the core switch at the top level of the tree Ad the core switch failure ay tear dow thousads of servers The Fat-Tree solutio eeds ore switches, ad the uber of ports at a switch liits the scale of the Fat-Tree[1] DCell[2] ad BCube[3] also require ore ports i a server (typically four), to establish a large server populatio The fudaetal proble is that, we eed to desig a ew data ceter etworkig structure that works for servers with ode degree of oly 3 i order to scale We propose C-Cell, a Efficiet ad Scalable etwork structure for a data ceter C-Cell defies a recursive structure to itercoect servers A high-level C-Cell is costructed by low-level C-Cell Ad this structure ot oly has a low-ratio i switch/server, but also provides ultiple parallel short paths betwee ay pair of servers Therefore, C-Cell has fault tolerace ad load balace The rest of the paper is orgaized as follow Sectio 2 discusses the backgroud Sectio 3 describes the C-Cell structure ad its properties Sectio 4 presets the C-Cell routig ad sectio 5 discusses the solutio to icreetal expasio Sectio 6 uses both siulatios ad experiets to evaluate the C-Cell Sectio 7 cocludes the paper II BACKGROUND I this sectio, we firstly explai the traditioal hierarchy data ceter, ad the discuss the isufficiecy Secodly, we itroduce the curret data ceter ad aalyze their features Traditioal data ceter uses the hierarchy structure As show i Fig 1, a layer of servers at the botto is coected to a Top of Rack (ToR) switch ToR is 213 ACADEMY PUBLISHER doi:1434/jsw

2 JOURNAL OF SOFTWARE, VOL 8, NO 1, OCTOBER coected to two L2 switches for redudacy L2 switches further coect to L3 routers At the top of this structure, core routers are very iportat because they aage the traffic ito ad out of the data ceter ad carry all traffic betwee L3 routers But there are soe fudaetal liitatios to this covetioal desig[4-6] INTERNET Data Ceter Layer 3 Layer 2 TOR SERVERS CR CR AR AR AR AR AS AS S S S S TOR TOR SERVERS SERVERS TOR SERVERS Key CR=L3 Core Router AR=L3 Access Router AS=L2 Aggr Switch S=L2 Switch TOR=Top-of-Rack Switch Figure 1 A etwork architecture for traditio data ceters Liited scale: Servers which are coected i the sae access router costitute a sigle layer-2 Because of the covetioal desig, the scale of a sigle layer-2 oly has 4 thousad servers It eas that traditioal data ceter caot afford a scale of illios of servers Liited server-to-server: If we go up the hierarchy, the traffic ovig up the differet layer-2 eeds to go through layer-3 Ad the lik betwee layer-2 to layer-3 is oversubscriptio So, the badwidth i layer-2 is liited by the oversubscriptio ratio For exaple, the upliks fro layer-2 are 1:2 oversubscribed, ad paths through layer-3 ca be 1:24 oversubscribed This large oversubscriptio factor fragets the server pool by prevetig idle servers fro beig assiged to overloaded services, ad it severely liits the etire data ceter s perforace Fragetatio of resources: As the cost ad perforace of couicatio depeds o distace i the hierarchy, the covetioal desig ecourages service plaers to cluster servers earby the hierarchy Moreover, spreadig a service outside a sigle layer-2 doai frequetly requires the oerous task of recofigurig IP addresses ad VLAN truks, sice the IP addresses used by servers are topologically deteried by the access routers above the Collectively, this cotributes to the squaderig of coputig resources across the data ceter The cosequeces are egregious Eve if there is pletiful spare capacity throughout the data ceter, it is ofte effectively reserved by a sigle service (ad ot shared), so that this service ca scale out to earby servers to respod rapidly to dead spikes or to failures I fact, the growig resource eed oe service to have forced data ceter operatios so as to evict other services i the sae layer-2 doai, icurrig sigificat cost ad disruptio Poor reliability ad utilizatio: Above the ToR, the basic resiliece odel is 1:1 For exaple, if a aggregatio switch or access router fails, there ust be sufficiet reaiig idle capacity o the couterpart device to carry the load This forces each device ad lik to ru up to at ost 5% of its axiu utilizatio Iside a layer-2 doai, the use of the Spaig Tree Protocol eas that eve whe ultiple paths betwee switches exist, oly a sigle oe is used I the layer-3 portio, Equal Cost Multipath (ECMP) is typically used: whe ultiple paths of the sae legth are available to a destiatio, each router uses a hash fuctio to spread flows evely across the ext available hops However, the covetioal topology offers at ost two paths High cost of hardware: core-switches ad core-routers which are used i traditioal data ceter etwork are expesive Ad the load balacer i layer-2 ust be used i pairs There are soe requireets ad features i the ew data ceter[7-8]: The data ceter ifrastructure ust be scalable to a large uber of servers ad allow for icreetal expasio The data ceter ust be fault tolerat agaist various types of server failures, lik outages, or server-rack failures The data ceter ust be able to provide high etwork capacity to better support badwidthhugry services The data ceter ust support virtualizatio which is the biggest differece betwee traditioal data ceter ad ew data ceter Curretly, data ceters use coodity-class coputers ad switches istead of specially desiged high-ed servers ad itercoect for better price-perforace ratio There are soe represetative data ceters likig Fat-tree[1,12], DCell[2], BCube[3] ad VL2[11] The Fat-tree is a layered etwork topology with equal lik capacity at every tier ad is cooly ipleeted by buildig a tree with ultiple roots The structure of Fat-tree has k pods, ad each pod has k/2 switches which have k ports The k/2 ports coect k/2 servers, ad aother k/2 ports coect core-switches The core layer has k core-switches which have k ports The Fat-tree has several parallel paths betwee odes, ad reoves the costraits about upper lik throughput But the Scalability of Fat-tree is liited by the uber of port of core-switch, ad Fat-tree is very sesitive to the fault of low-layer switch DCell uses a recursively-defied structure to itercoect servers Each server coects differet levels of DCells via ultiple liks We build high-level DCells recursively fro ay low-level oes, i a way that the low-level DCells for a fully-coected graph Usually, the uber of servers i DCell is 3 to 8 Whe a DCell has 6 servers, the uber of servers i a DCell 3 is 326- illio But there are soe defects i DCell The fullycoected graph used i DCell is too coplex to aage ad aitai Ad the flow of DCell at differet level is ueve BCube is the odular versio of DCell A BCube is siply servers coectig to a -port switch A BCube 1 is costructed fro BCube s ad -port 213 ACADEMY PUBLISHER

3 2614 JOURNAL OF SOFTWARE, VOL 8, NO 1, OCTOBER 213 switches Geerically, a BCube k (k 1) is costructed fro BCube k-1 s ad k -port switches Each server i a BCube k has k+1 ports, which are ubered fro level- to level-k BCube ca sigificatly accelerate oe-to-x traffic patters ad provides high etwork capacity for all-to-all traffic The BCube Source Routig (BSR) further eables graceful perforace degradatio But the weakess of BCube is a relatively poor scalability Whe k=3ad =8 (k is the degree of BCube, is the uber of servers i a BCube ), BCube 3 oly has 496 servers VL2 is a scalable ad flexible data ceter etwork VL2 uses flat addressig to allow service istaces to be placed aywhere i the etwork, Valiat Load Balacig to spread traffic uiforly across etwork paths, ad ed syste-based address resolutio to scale to large server pools without itroducig coplexity to the etwork cotrol plae Figure 2 (a) A Cell of C-Cell with k=3 (b) A C-Cell with k=3 III THE C-CELL NETWORK STRUCTURE I this sectio, we firstly preset the C-Cell structure ad the aalyze its efficiecy ad soe properties Sectios 3-5 describe these copoets i detail A C-Cell Physical Structure ad the Way to Build C- Cell There are two types of devices i C-Cell: Servers with ultiple ports, ad switches that coect a costat uber of servers We kow that DCell ad BCube are a recursively defied structure I C-Cell, we also use a recursive way to defie its structure The C-Cell is costructed by a C-Cell -1 ad several C-Cell s This structure has soe advatages Firstly, the odularized ad recursive structure is good for coectio Secodly, it is easy to expad C-Cell +1 whe C-Cell is icoplete A C-Cell which is the buildig block to costruct larger C-Cell is siply k servers coectig to a -port ( > k) switch The followig exaple i Fig 2(a) illustrates a C-Cell (k=3) 3 servers are coected to a switch We the equally adjust each server to the circle which has the switch as the ceter, ad a arc of the circle betwee every two servers bridges the coectio of two servers, as illustrated i Fig 2(b) I order to distiguish the differece betwee Fig 2(a) ad Fig 2(b), the structure of Fig 1(b) we called C-Cell (k=3), ad the structure of Fig 1(a) we called Cell O the basis, a C- Cell 1 is structured fro a C-Cell ad k Cells The ethod is to break k arcs which coect two adjacet servers ad addig a Cell A C-Cell 1 (k=3) is illustrated i Fig 3(a) More geerically, a C-Cell ( 1) is costructed fro a C-Cell -1 ad k +1 Cell I our desig, each server i a C-Cell has 3 ports ad the uber of ax-port i each switch is k+2 Fig 3(b) illustrated a C- Cell 2 (k=3) The costructio of a C-Cell is as follows Firstly, we break k -1 arcs which coect adjacet two servers o the circle -1 Secodly, we add a Cell i each broke arc This eas that the two adjacet servers of C-Cell -1 o the circle -1 are coected by a Cell Thirdly, we equally adjust each ewly-joied server to the circle ad coect the ewly-joied servers which are adjacet o the circle Figure 3 (a) A C-Cell 1 with k=3 (b) A C-Cell 2 with k=3 The recursive C-Cell costructio procedure BulidC- Cells: /* stads for the level of C-Cell k is the uber of servers i a C-Cell */ 1 BuildC-Cells (k,) 2 if (= =) /* build C-Cell */ 3 for (it ; i<k; i++) 4 {coect i-th server to switch; 5 if (i+1<k) 6 coect ith server to i+1-th sever; 7 else 8 coect th server to i-th sever; 9 put each pair of servers i a queue; 1 } 11 record the legth of queue (queue_le); /* queue_le is the uber of Cell to add i the ext C-Cell k+1 */ 12 retur; 13 else while (!=) 14 {it = =; 15 while (queue_le!=) 16 {take a pair of servers fro queue, break they coectio ad add a Cell; 17 =+3; /* record the ew-servers */ 18 queue_le--; 19 } 213 ACADEMY PUBLISHER

4 JOURNAL OF SOFTWARE, VOL 8, NO 1, OCTOBER for (it ; i<; i++) 21 {if (i+1<) 22 coect i-th ew-server to i+1-th ew-server; 23 else 24 coect -th ew-server to i-th ew-sever; 25 put each pair of ew-servers i a queue; 26 } 27 record the legth of queue (queue_ew_le); 28 queue_le=queue_ew_le; 29 --; /* whe =, fiish */ 3 } Figure 4 The procedure to build a C-Cell etwork B Properties of the C-Cell The followig theore describes ad bouds the properties of C-Cell The uber of the servers i a C-Cell is V ad the uber of the switches i a C-Cell is S Theore 1 V = S k (1) = (2) V k + for, where k is the uber of servers i C-Cell ad Cell Proof of Theore 1 A C-Cell is structured by addig Cells i a C-Cell -1 So, the first equatio ca directly derive fro the defiitios The, we use atheatical iductio to prove Theore 1 (2) Whe =, V =k, k + =k, V = k + Whe =1, V =k+k k, k + =k1 +k 2, V = k + If =, V = k + Whe =+1, V +1 = V +k (the uber of servers i circle ) The uber of servers i circle = V V 1 1 i + 1 i + 1 = k k =k+1 So V +1 = V +k k +1 = k + +k+2 = k + The coclusio V = k Theore 1 shows that, the uber of servers i a C- Cell rapidly scales as the circle degree icreases A larger etwork size ca be lead by a sall circle degree For exaple, whe k=6 ad =4, a C-Cell ca have as ay as 933 servers, ad oly 1555 switches A ratio of switch/server is 167 Copare with BCube, the uber of servers is 7776 whe k=6 ad =4, ad the uber of switches is 285 A ratio of switch/server is 367 Through above copariso, we ca draw a coclusio that the C-Cell has ore servers ad lower ratio of switch/server tha the BCube i the sae scale Whe k=3 ad =4, the ratio of switch/server i a BCube is 1667 This coditio is disadvatageous because the cost of refrigeratio facilities ad switches is expesive i a large data ceter But whe k=3( ), the ratio of switch/server i a C-Cell is also 333 C Bottleeck lik of the C-Cell The bottleeck lik of C-Cell ca be divided ito 2 aspects, ode-bottleeck ad path-bottleeck The ode-bottleeck eas that a ode ca t afford whe its data flow is too large I a C-Cell, the lower circle a ode (server/switch) is o, the ore probability it becoes the ode-bottleeck So we use high-ed switch istead of the ode (server/switch) o low circle This way ca reduce data trasissio pressure I sectio 5, this questio will be discuss i detail There is oly oe path to coect A subet ad B subet Whe this path is broke, the coectio betwee A ad B is lost This path ca be called path-bottleeck But i a C-Cell, we cosider that two arbitrary servers have several parallel paths (this ca be proof i theore 5) So, a coclusio ca be draw that C-Cell does ot have path-bottleeck i theory IV ROUTING IN A C-CELL Our goal is to itercoect up to illios of servers i a C-Cell Whe k=8 ad =6, 2 illios of servers are coected i a C-Cell 6 The routig i a C-Cell should be able to fully utilize the high capacity ad autoatically load-balace the traffic i our desig So, existig routig protocol such as OSPF is ot suitable sice it eeds a backboe area to itercoect all the other areas Badwidth bottleeck ad sigle poit failure are OSPF s biggest defect I this sectio, we firstly itroduce the routig without failure i C-Cell Secodly, we propose the routig protocol of C-Cell called C-CellRoutig Fially,a exaple is used to illustrate C-CellRoutig A Routig without Failure We assue two servers src ad des Theore 2 The haig distace of two rado servers i a C- Cell is oe I a C-Cell, each server is coected to the sae switch i Fig 1(b) So theore 2 is easy to be proved Theore 3 Whe k=3, the shortest distace of two rado servers i a C-Cell 1 is at ost 2 Ad whe k>3, the shortest distace of two rado servers i a C-Cell 1 is at ost 3 Proof of Theore 3 Whe k=3, there are 5 cases i a C-Cell 1 ( Fig 2(a)) 1 {server i C-Cell, server i C-Cell 1 }, ACADEMY PUBLISHER

5 2616 JOURNAL OF SOFTWARE, VOL 8, NO 1, OCTOBER {server i C-Cell 1, server i C-Cell }, 1 3 {server i C-Cell, server i C-Cell }, {server i C- Cell, server i C-Cell 1 }, 2 4 {server i C-Cell 1, server i C-Cell }, {server i C- Cell, server i C-Cell 1 }, 2 5 {server i C-Cell 1, server i C-Cell }, {server i C- Cell, server i C-Cell }, 2 The haig distace of two rado servers i a C- Cell is oe (show i theore 2) So, whe k>3, there is aother case i a C-Cell 1 {server i C-Cell 1, server i C-Cell }, {server i C- Cell, server i C-Cell }, {server i C-Cell, server i C- Cell 1 }, 3 Therefore, theore 3 is proved Theore 4 I a C-Cell, the logest shortest distace of two rado servers is at ost 2+1 Proof of Theore 4 If src is a server o circly i (i ) i a C-Cell, des is a server o circly j (j ) i a C-Cell Accordig to theore 2 ad 3, we kow that there are i steps whe src jup to a server o circly (o circly i-1, circly i-2, circly ) I the sae way, there are j steps whe des jup to a server o circly Ad the distace of two rado servers i a C-Cell is oe (theore 2) So, the logest shortest distace fro src to des is i+j+1 (i, j ) Whe j=, the logest shortest distace fro src to des is 2+1 Therefore, we ca draw the coclusio that the logest shortest distace of two rado servers is at ost 2+1 i a C-Cell Theore 5 The parallel paths of two rado servers i a C-Cell are at least 3, ad at ost 3 2 Proof of theore 5 Fro the Physical Structure of C-Cell i sectio 31, it ca be see that each server is coected by 3 odes (server/switch) So, it is easy to prove that the parallel paths of two rado servers i a C-Cell are at least 3 Ad i theore 4, we kow that there are i steps whe src jup to a server o circly It eas that there are at ost 3 i parallel paths fro src to a server o circly Therefore, there are at ost 3 i+j parallel paths fro src to des (i, j ) Whe j=, there are at ost 3 2 parallel paths fro src to des Cosequetly, the parallel paths of two rado servers i a C-Cell are at least 3, ad at ost 3 2 B Protocol Naig rule I a C-Cell (k is the uber of servers i a Cell), we deote a server usig the 3-tuples which is [i, j, p] (circle, uber, agle) i eas that a server is i circle i ( i ) j eas that a server is the j-th server i circle i ( j k i+1-1) p eas the agle of a server i circle i ( p 36 )This aig rule ot oly uique idetify a server, but also ark the positio of a server by usig agle Likewise, we deote a switch usig the for [ i, j, p, S ] The letter S eas the ode is a switch, ot a server There is a special switch which is located i the ceter of a C-Cell We deote it usig [, S] A C-Cell whe k=3 is structured i sectio 31 (Fig 2(b)) Now, we use the aig rule to deote each server ad switch i Fig 5(a) We rule the ode O[,S] ad A[,,] Accordig to clockwise directio, we ode the server-b[,1,12] ad server-c[,2,24] Fig 5(b) illustrated the aig rule i a C-Cell 1 (k=3) Figure 5 (a) The aig rule i a C-Cell with k=3 (b) The aig rule i a C-Cell 1 with k=3 C-CellRoutig C-CellRoutig uses a efficiet ad siple sigle-path routig algorith for uicast by exploitig the recursive structure of C-Cell, is show i Fig 5 We follow a (recursive ethod) divide ad coquer approach to desig the C-CellRoutig We assue two servers src[s i, s j, s p ] ad des[d i, d j, d p ] that are i differet circle (I s I d ) Whe coputig the path fro src to des i a C-Cell, we first calculate the server id k [ i, j, p ] which ust satisfy the followig coditios: 1 i = d i -1 2 p <d p < p,( id [ i, j +1, p ]) The coditios ea that id ad des are coected by the sae switch Routig is the chage how to coputig the path fro src to id Followig the recursive ethod, we ca calculate the id o circle after d i steps The fial path of C- CellRoutig is the cobiatio of path(src, id )+path(id, id 1 )+ path(id 1, id 2 )+ + path(id k- 1, id k )+path(id k, des) /* src=[s i, s j, s p ] des=[d i, d j, d p ]*/ 1 C-CellRoutig (src, des ) 2 for (it k= d i ; k ; k--) 3 {calculate a server id k /* id k ad des are coected i the sae switch*/ 4 record the path(id k, des) 5 des= id k 6 if (k= =) 7 record the path(src, id k ) 8 } 9 retur path= path(src, id )+path(id, id 1 ) + + path(id k-1, id k )+path(id k, des) Figure 6 Pseudocode for routig i a C-Cell 213 ACADEMY PUBLISHER

6 JOURNAL OF SOFTWARE, VOL 8, NO 1, OCTOBER Traffic Distributio i C-CellRoutig I this sectio, we discuss the oe-to-ay ad all-toall couicatio odel i C-CellRoutig Uder the couicatio odels, high badwidth ca be achieved So C-Cell ca provide the high badwidth for servers such as GFS ad MapReduce Oe-to-ay eas oe server trasfer the sae data to several servers It is useful for servers such as GFS Ad the beefit of this is to iprove reliability of the syste Whe a ew data is writte i the syste, it eeds to be siultaeously replicated to the several servers (typically three) We kow that each server has 3 ports i a C-Cell So, a C-Cell server ca utilize its ultiple liks to achieve high throughput All-to-all eas every server trasits data to all the other servers MapReduce is the represetative exaple of all-to-all traffic I all-to-all couicatio odel, every server establishes a flow with all other servers We assue that there is oe flow betwee ay two servers So, the total uber of flows are t (t +1), t is the uber of servers i C-Cell Fro the structure of C-Cell (Fig 2), lik at differet circle carry a differet uber of flows Lik at circle carry ore uber of flows tha lik at other circle We ca draw the coclusio that the bottleeck lik is at the lowest-circle liks rather tha at the highest-circle liks V INCREMENTAL EXPANSION With the expasio of the scale, a C-Cell has ore ad ore servers ad lik o circle ust carry ore ad ore uber of flows So, there are two questios we should discuss Firstly, we deote a server usig the 3-tuples which is [i, j, p] (circle, uber, agle) i sectio 421 But whe servers becoe huge i a C-Cell, the servers o the highest-circle are too ay to ark these agles Therefore, if several servers o the highest-circle are coected i the sae switch, we ark the agle of these servers to use the agle of the switch Fig 7 shows the iproved aig rule i a C-Cell 2 with k=3 Thirdly, we kow the C-Cell is costructed by a C- Cell -1 ad several C-Cell s i sectio 3 If the switch of ewly added C-Cell is broke, the servers which are coected by this switch caot work So, to avoid this situatio, we rule the ew addig servers sed a essage to the switch every 3s Whe the servers caot coect, it eas that the switch does t work properly We ust check the switch Figure 8 The iproved C-Cell VI SIMULATION AND IMPLEMENTATION I this sectio, we use siulatios to evaluate the perforace of C-Cell by java laguage ad NetBeas developet tools A Node without Failure I table 1, we ca see the average shortest distace whe there is ot ode failure (k=3) Because of ode without failure, the iaccessible ode is Ad whe =4, the average shortest distace is i 3 steps The coclusio is cosistet with the theore 4 TABLE 1 THE AVERAGE SHORTEST DISTANCE WHEN THERE IS NOT NODE FAILURE B Node Failure I our siulatio, ode failure eas server failure Firstly, we set the ode failure ratio Ad with the ode failure ratio icrease, we test the average path legth chages i C-Cell 4 (k=3) I Fig 9, whe the ode failure ratio is fro 6 to 16, the fluctuatio of average path legth is sall, ad i 27~28 Figure 7 The iproved aig rule i a C-Cell 1 with k=3 Secodly, we kow that lik at circle carry ore uber of flows tha lik at other circle i sectio 432 If the scale of C-Cell is too large, the lik at circle ay becoe bottleeck lik So, we odify the structure of C- Cell by usig switches istead of the servers which are o circle Fig 8 shows the iproved C-Cell structure 213 ACADEMY PUBLISHER

7 2618 JOURNAL OF SOFTWARE, VOL 8, NO 1, OCTOBER 213 k=3 Ad we copare the test results with DCell 4 (k=3) I fig 12, the path failure ratio of C-Cell 4 is ore stable tha the path failure ratio of DCell 4 ad also i 1~5 Figure 9 The fluctuatio of average path legth whe the ode failure ratio icreases The we study the path failure ratio for the foud path with the ode failure I this sectio, we vary the ode failure ratio fro 2%~2% ad the etworks are a C- Cell4 with k=3 Fially, we copare the test results with DCell4 (k=3) Fig 1 shows the path failure ratio of both C-Cell4 ad DCell4 versus the path failure ratio uder ode failures icreasig We observe that, the path failure ratio of C-Cell fluctuates with DCell chages,ad C- Cell results are very close to DCell results Figure 1 The path failure ratio of DCell ad C-Cell whe the ode failure ratio icreases Figure 12 The fluctuatio of average path legth whe the lik failure ratio icreases D Fault-tolerace The experiet is coposed by a C-Cell 1 with over 12 server odes Each C-Cell has 3 servers (see Fig 5(b) for the topology) Each server is a desktop with Iter 33GHz dual-core CPU, 4GB DRAM, ad 5GB hard disk The Etheret switches used to for the C-Cell s are D-Lik 8- port Gigabit switches DGS-18A I this experiet, we set up a TCP coectio betwee servers [1,,2] ad [1,5,22] The path betwee the two servers is [1,,2], [,,], [,1,12], [1,5,22] To study the perforace uder lik failure, we aually uplugged the lik ([,,], [,1,12]) at tie 3s ad replugged it at tie 4s The, we shutdow the server [,1,12] at tie 7s to estiate the ipact of ode failure After the failures, the ew path is chaged to [1,,2], [,,], [,2,24], [1,5,22] After re-pluggig, the path returs to the origial oe C Lik Failure Lik failure eas the path break betwee server ad switch or switch failure So, we have studied the effect of lik failure Fig 11 shows that, the average path legth is i 26~29 whe the lik failure ratio is lower tha 2 Figure 13 TCP throughput with lik ad ode failure Figure 11 The fluctuatio of average path legth whe the lik failure ratio icreases Therefore, ext we study the path failure ratio for the foud path with the lik failure We vary the lik failure ratio fro 2%~2% ad the etworks are a C-Cell 4 with There are two coclusios fro the experiet i Fig 13 Firstly, the TCP throughput of C-Cell is quickly recovered to its best value fro both failures after a few secods Secodly, the resiliece speed of lik failure is faster tha ode failure The lik failure occurs, the TCP throughput takes oly 1-secod to recover, while the ode failure occurs, the TCP throughput takes 4-secod to recover 213 ACADEMY PUBLISHER

8 JOURNAL OF SOFTWARE, VOL 8, NO 1, OCTOBER E Network Capacity I this experiet, we copare the total throughput of C-Cell ad the tree structure Each server established a TCP coectio to all other 11 servers Each server seds 1GB data ad therefore each TCP coectio seds 833MB This is to eulate the reduce-phase operatios i MapReduce I the reduce phase, each Reduce worker fetches data fro all other workers, resultig i a all-toall traffic patter Figure 14 Total throughput uder C-Cell ad Tree Fig 14 plots both the total throughput of C-Cell ad the tree structure The data trasfer copletes at ties 167 ad 337 secods for C-Cell ad the tree structure, respectively C-Cell is about 2 ties faster tha the tree structure The per-server throughput i C-Cell is 517Mb/s, but it was oly 256Mb/s The iitial throughput of the tree is due to the TCP coectios aog the servers coectig to the sae switches After the coectio teriate, all the coectios have to go through the root switch So, the total throughput decreases But there are o such bottleeck liks i C-Cell VII CONCLUSION I this paper, we firstly aalyze the isufficiecy of traditioal hierarchy data ceter, ad propose soe features of ew data ceter Secodly, we preset the desig, aalysis ad ipleetatio of C-Cell which is a ew data ceter etwork Fially, through the siulatio test, o the preise of low proportio of switches ad servers, C-Cell ca efficietly achieve routig echaiss i shorter ea path legths with less etwork cost ACKNOWLEDGMENT Fud project: the ary logistics key scietific research progra fuded projects of PLA (BS211R99) REFERENCES [1] Leiserso C E Fat-trees: Uiversal etworks for hardware-efficiet supercoputig IEEE Trasactios o Coputers 1985 C34(1): [2] Chuaxiog Guo DCell: A scalable ad fault-tolerat etwork structure for data ceters//proceedigs of the SIG-COMM 28 Seattle WA, USA 28: [3] Chuaxiog Guo BCube: A high perforace, servercetric etwork architecture for odular data ceter//proceedigs of the SIGCOMM 29 Barceloa Spai, 29: [4] Da Li ESM: Efficiet ad Scalable Data Ceter Multicast Routig IEEE/ACM Trasactios o Networkig, Vol 2, No 3, Jue 212: [5] A Shieh, S Kadula, A Greeberg, ad C Ki Seawall: Perforace Isolatio for Cloud Dataceter Networks I HotCloud, 21 [6] Greeberg A, Hailto J, Mahz D A, Patel P Cost of cloud ACM SIGCOMM Coputer Couicatio Review, 29 39(1) [7] D Li, J Yu, J Yu, ad J Wu, Explorig efficiet ad scalable ulticast routig i future data ceter etworks, i Proc IEEE INFOCOM, Apr 211, pp [8] Kai Che DAC: Geeric ad Autoatic Address Cofiguratio for Data Ceter Networks IEEE/ACM Trasactios o Networkig, Vol 2, No 1, FEBRUARY 212:84-99 [9] Xidog You ARAS-M: Autoatic Resource Allocatio Strategy based o Market Mechais i Cloud Coputig Joural of Coputers, Vol 6, No 7, 211: [1] Tog Yag Mass Data Aalysis ad Forecastig Based o Cloud Coputig Joural of Software, Vol 7, No 1, 212: [11] Albert Greeberg VL2: A scalable ad flexible data ceter etwork//proceedigs of the SIGCOMM 28 Seattle, WA USA 28: [12] B Bogdaski sftree: A Fully Coected ad Deadlock- Free Switch-to-Switch Routig Algorith for Fat-Trees ACM Trasactios o Architecture ad Code Optiizatio, Vol 8, No 4, Article 55, Jauary 212 CAI Hui, bor 983, PhD His research orietatios are cloud ad P2P coputig LI Sheli, bor 964, professor, PhD His research iterests iclude Logistic Iforatioizatio ad cloud coputig WEI Wei, bor 977, PhD Her research directio icludes cloud ad grid coputig 213 ACADEMY PUBLISHER