A KIND OF ROUTING MODEL IN PEER-TO-PEER NETWORK BASED ON SUCCESSFUL ACCESSING RATE

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1 A KIND OF ROUTING MODEL IN PEER-TO-PEER NETWORK BASED ON SUCCESSFUL ACCESSING RATE 1 TAO LIU, 2 JI-JUN XU 1 College of Informaton Scence and Technology, Zhengzhou Normal Unversty, Chna 2 School of Mathematcs and Statstcs, Zhengzhou Normal Unversty E-mal: 1 lutao770910@126.com ABSTRACT The peer-to-peer network s based on locaton mechansm of dstrbuted obects, whch s conducve to sharng of resources among users. The commonly usng overlay network topology method based on nterestng group n the exstng peer-to-peer network should be accomplshed collaboratvely by users, whch ncreases system traffc and occupes large bandwdth. The paper brought out a knd of routng model n peer-to-peer network based on Successful Accessng Rate (SAR). The model organzes user group based on SAR and conductng resource searchng n the hgh-low order of SAR. In the model, each node runs ndependently, whch decrease system mantenance cost and provdes new dea to solve free-rder problem. Smulaton results show that the model effectvely mprove recall rate of system and also solve farness problem. Keywords: Peer-To-Peer Network, Routng; Successful Accessng Rate 1. INTRODUCTION The emergency of peer-to-peer (P2P) network comes from requrements of users on sharng and adequately usage of Internet resources. The most promnent character of P2P network s that users share resources drectly, the core of whch s postonng mechansm of dstrbuted obects. There are several routng methods currently as followng. The frst s centralzed ndexng manner as Napster system [1]. It has problems of sngle pont falure as well as performance bottlenecks, so t cannot be appled n large-scale network. The second s structural P2P system based on dstrbuted Hash table DHT, such as Chord and CAN systems [2, 3]. It can acheves hgh effcency searchng but only support searchng based on accurate obect key value and lack of fuzzy searchng ablty. It also does not support complex ndexng based on semantc. On the contrary, unstructured P2P network as Gnutella [4-7] can better support varous forms of nformaton ndexng. However, the searchng strategy based on floodng or random roar ncrease messages on P2P network, whch restrcts scalablty of P2P network. In order to mprove routng performance of unstructured P2P network, the method to construct overlay topology based on nterest group s manly used now [8-10]. Its man bass s that nodes wth same nterest has common request on resources and storage. The users wth same nterests are lnked together by overlay network. In the searchng, t s easer to fnd resources meet requrements n local nterest group so as to mprove successful rate for resource postonng. The constructon of overlay network based on nterest group needs users publsh own nterest or more specfc fle character n the network, and then establsh nterest group by ndexng or self-organzaton. We can see that the method can only be accomplshed by cooperaton among users, whch ncreases system communcaton amount and occupes large bandwdth. The successful accessng rate-based (SARB) peer-to-peer network routng model n ths paper organzes based on node SAR. It looks for resource n the hgh-low order of successful accessng rate. Nodes n the model operate ndependently, whch decreases system mantan cost and provde new dea to solve free-rder problem. Smulaton results show that the model can effectvely mprove system recall and better solve system far problem at the same tme. The paper s organzed as follows: secton 2 descrbes SARB model; secton 3 gves specfc SARB algorthm; secton 4 conduct performance analyss and smulaton on SARB; secton 5 concludes our work. 275

2 2. SARB MODEL DESCRIPTION The startng pont of SARB s that more tmes of node storage resources been successfully accessed, the node has hgher SAR. Other nodes have hgher probablty to fnd needed resources on ths node. Therefore, organze nodes wth smlar successful accessng rate n the system together. In case of searchng, frstly access to node wth larger SAR so that the resource recall ncreases. Assume there are N nodes n the system marked as P1, P2,, PN. Use D to represent successful accessng rate of node P, the ntal value of D s 0. In the system operaton process, other nodes P (0 N, ) successfully access resources from node P, then D ncreases correspondngly. Dvde node successful accessng rate nto K levels 0,1,, K 1 based on value. The boundary value 0 1 K 1 s D, D,, D m m 1. If D D < D +, d s the m- th level and d = dd ( ) = m. Usng T as tme nterval, compute current successful accessng rate D of current node P and determne ts level. To facltate descrpton, the cyclc structure s used as basc structure of SARB. After node enters nto system, assgn a node sgn for each one to dentfy t unquely. Takng node as example, when the node enters nto system, t uses the manner of normal cyclc structure. At ntervals of tme T, compute successful accessng rate D of node at current tme and dvde ts level. Here we assure level d s m. Fnd nodes n the system. If there s other nodes whose successful accessng rate level s m, the node also enter nto cyclc structure of ths level. In ths way, each node actually has two logc postons n the system. It also has two routng selecton nformaton. The fnal structural dagram s shown n Fg. 1. 1' 0,d 0=1 4,d 4=3 6,d 6=4 7,d 7=4 1,d 1=1 2,d 2=3 3' 4' 3,d 3 =3 0,d 0 =1 1,d 1 =1 d=0 2,d 2 =3 6,d 6=4 7' 5,d 4=2 5,d 5 =2 3,d 3=3 7,d 7=4 4,d 4=3 Fgure 1: SARB logcal structure wth cyclc structure As shown n Fg. 1 n the system wth 8 nodes, the successful accessng rate level where node 5 locates only has the node tself, whle node (0, 1), (2, 3, 4) and (6, 7) respectvely belong to same successful accessng rate. 1, 2,3,7 respectvely represent another logcal poston of node 1,2,3 and node SARB ROUTING ALGORITHM 3.1 Routng Table Structure Each node n the SARB model keeps two sets of routng nformaton. One s routng nformaton of node n the whole system, whch s called system routng table. Another s routng nformaton of successful accessng rate level where the node locates, whch s called level routng table. The system routng table should add an tem to represent successful accessng rate level of the tem successor. In addton, the successor n system routng table tem s not the frst exstng node of ths area, but the node most closely to node sgn wth maxmum successful accessng rate level and the node dentfer closest node. The routng table structure of node 0 n Fg. 1 s shown n Table

3 nt. [1, 2) [2, 4) [4, 0) Table 1: Routng table structure of node 0 n Fg. 1 System routng table (fnger table) succ Level routng table (fnger table) d=1 [1, 0) 1 d d 1 =1 d 2 =3 d 6 =4 3.2 Node Status Changes The node poston n system of SARB model s determned commonly by node dentfer and node successful accessng rate level. The node dentfer wll no longer change after node enters system, whle node successful accessng rate dynamcally change accordng to response of node on other nodes and then perodcally conduct level transton. Therefore, the node status change n system manly ncludes three knds of on, leave as well as successful accessng level transton. Here these three statuses are descrbed as followng Identfcaton of subsectons Step1: Determne own node dentfer that assumed to be p. Step2: contact wth another member node p n the system. The node wll act as bootstrap node of new oned node p. Step3: The node p ntates lookng for node p and fnd the node whose dentfer only below than p as ts prevous node. Step4: Intate system routng table of p. The node successful accessng rate level d p =0. Step5: Update system routng table of related nodes needed for modfcaton because of on of p. Under crcumstance of system node number N, the node number should be updated s O(log N ). Step6: Based on own system routng table, the node p fnd nodes wth same successful accessng rate level and on level cyclc structure to construct level routng table Process of node leaves system Assumed node dentfer p, and the level of successful accessng rate d p =m. Step1: Conduct leavng operaton accordng to level routng table n the cyclc structure whose successful accessng rate level s m. Update level routng tables of other related nodes correspondngly. Step2: Complete leavng operaton accordng to system routng table n the system and update system routng tables of related nodes correspondngly Process of node level transton Assume p s the current node and successful accessng level d p =m. The level to be transted s d = n. ' p Step1: Conduct leavng operaton accordng to level routng table n the cyclc structure whose successful accessng rate level s m. Update level routng tables of other related nodes correspondngly. Step2: Modfy successful accessng rate level of node p to n. Step3: Update system routng tables of related nodes correspondngly. In the Fg. 1, assume node successful accessng rate level of node 7 transts from level 4 to level 5, then routng table update of node 0 updates as Table 2 shows. Step4: The node p fnds nodes whose successful accessng rate level s n accordng to own system routng table. Jon ths level cyclc structure and buld level routng table. 3.3 Routng Algorthm The basc dea of SARB routng algorthm s as followng. Source node send query message wth ntal TTL value to network. Frstly send message to node wth hghest successful accessng rate level accordng to system routng table. Then search n the same level based on level routng table, and 277

4 return query result to source node after found correspondng target. nt. [1, 2) [2, 4) [4, 0) Table 2: Routng table of node 0 after node 7 transt level System routng table (fnger table) succ Level routng table (fnger table) d=1 [1, 0) 1 d d 1 =1 d 2 =3 d 6 =5 As the node system routng table stores nodes wth hghest successful accessng rate level n the whole system area, the system routng table of node sendng request can fnd the node wth hghest Algorthm 1 successful accessng rate level n the system. Therefore, t only needs one step from source node to node cluster wth hghest successful accessng rate level. The algorthm s shown n Fg. 2. Assume P s current node. Input s query message Q=query(message, Src, TTL). Where, message s query semantc descrpton; Src s query message ntate node; TTL s maxmum lfetme of ths query message. The output s target result R to Src. f (P==Src) Look for node wth maxmum level successful accessng rate n local system routng table and forward query message; else Set Q.TTL=Q.TTL-1; Execute local query, return query result to Src; f (Q.TTL>0) Send query to other nodes n same successful sccessng rate elvel wth P accordng to level routng table; end f end f From the algorthm 1 we can see that the nodes wth hghest successful accessng rate level are accessed n each tme of query, whch wll ncrease overhead of these nodes. However, the nodes wth lower level only have fewer tmes been accessed, whch also not conductve for ncrease of node level. Therefore, the paper brought out SARB routng algorthm 2. In the query process of algorthm 2, source node adds successful accessng rate level of t n the query packet. The query was carred out on same success rate level wth source node except for hghest level. The contrbuton level of routng s equal to or lower than node request from query Fgure 2: Specfc steps of algorthm 1 node. On the contrary, t can refuse the request wth certan probablty. The algorthm 2 s shown n Fg. 3. The node accepts resource request from node wth probablty pd ( ) and the probablty 1 pd ( ) to refuse the request. The computaton of probablty pd ( ) s as followng: 1 d d pd ( ) 1 = d < d λ d (1) 278

5 Assume P s current node and d p s successful accessng rate level of node P. Input s query message Q=query(message, Src, TTL, d src ). Where, message s query senmatc descrpton; Src s query message ntate node; TTL s maxmum lfetme of query message; d src s successful accessng rate level of source node. Output target result s R to Src. f (P==Src) Forward query message accordng to local level routng table; Look for node wth maxmum level successful accessng rate n local system routng table and forward query message; else set Q.TTL=Q.TTL-1; Execute local query wth probablty p(d p -d src ) and return query result to Src; f (Q.TTL>0) Send query to other nodes n same successful sccessng rate elvel wth P accordng to level routng table; end f end f Where, λ s constant coeffcent factor and ts value s n the nterval of (1, 2]. Therefore, f the successful accessng rate level d of node s small, the node wth hgher level than node lkely refuse request from node. We can see that the above two algorthms use abler way. In the algorthm 2, hgher level node can refuse response to query request for decreasng overhead. Meanwhle, t also needs to constantly mprove own level by respondng to query requests. The node wth lower level can only access to opportunty to response request of nodes n same level by sendng request, so as to ncrease successful accessng rate level. Therefore, algorthm 2 s a knd of routng algorthm wth reward mechansm. In addton, the above two knds of routng algorthms may not fnd necessary resources, whch s determned by query on resources by resource node accordng to unstructured P2P network floodng or random walk way. 3.4 Supervse Mechansm Nodes n the SARB routng algorthm automatcally compute ts own successful accessng rate and perform level transton accordng to value of success rate. When the node n algorthm 2 receves query request, t determnes whether to answer ths request from dfference between successful accessng rates from send and receve node. It may have forge behavor for node ntated query to obtan hgher response rate. In vew of ths stuaton, the successful accessng rate Algorthm 2 Fgure 3: Specfc steps of algorthm neghborhood montorng mechansm (NMM) was proposed. The man dea of NMM s to constran node behavor relayng on montorng mechansm from neghbors. The specfc descrpton s as followng. Each node keeps all neghbor statuses. The neghbor status s determned by answer stuaton of neghbor on query request, whch can be dvded nto two knds of met or un-met. The node dynamcally mantans neghbor based on recorded neghbor status. If a neghbor s n met status, normally routes t. Otherwse, unlnk connecton to ths neghbor. If all adacent nodes unlnk connectons wth ths node, t s n solated status n system. So t cannot perform queryng or routng, so as to avod forgery behavors. The method does not need large amount of nformaton nteracton among nodes n EgenTrust algorthm. Furthermore, dynamc changng feature of node successful accessng rate level enable neghbor nodes not easly form colluson. It s smple for mplementaton and has good scalablty [11-13]. 4. PERFORMANCE ANALYSIS 4.1 Evaluaton Indexes The paper uses followng two ndexes to evaluate ts semantc query performance, namely recall T(Q) and average message number generated n queryng. Recall s the proporton of searched documents number met condtons n all related documents, the formula of whch s as follows:

6 Dgetcorrect TQ ( ) = (2) D Where, D total s set of all related documents dstrbuted on P2P network amng at some query; D getcorrect s the actually obtaned document set. The quered average message number M means average generated message number n the propagaton process on P2P network. Its sze determnes network overhead change caused by query operaton, whch s mportant ndex to measure network structure. 4.2 Algorthm Analyss Assume there are N nodes n the system that marked as P1, P2,, PN. The node successful accessng rate level can be dvded nto K levels (0,1,, K 1) accordng to value. The successful accessng rate level of node P d =m. The node number n ths level s num(m). The hghest level of node successful accessng rate level n current system s n. Node number n ths level s num(n). When the node P ntate query Q, the average message number generated by queres by algorthm 1 s M = 1 + log(num( n)). In the algorthm 2, the average message number generated by queres s M = 1 + log(num( n)) + log(num( m)). We can see that the average query message number s larger than that of algorthm 1. total Clearly, the routng algorthm under SARB structure s sgnfcantly lower than floodng mechansm n Gnutella n the aspect of query average message number. 4.3 Performance Smulaton In the smulaton experment, GT-ITM topology generator was used to generate random network topology. The transt-stub (TS) model that s more representatve of Internet structure was also used. Network node sze s Dstrbute documents for each node accordng to Zpf dstrbuton wth parameter α =1.2. The requred resources n query also ntates accordng to Zpf dstrbuton wth parameter α =1.2. Assume each node has at most 100 documents n the test. All the results are average value under tmes of queres. The comparson of recall between two algorthms and Gnutella wth dfferent TTL s shown n Fg. 4. From the fgure we can see that the recall of algorthm s bgger than that of algorthm 1 n lower TTL value as t use the strategy that synchronous query of own level wth hghest level. However, wth ncrease of TTL value, as algorthm 2 has stuaton that hgh level refuse to access lower level servce, the recall s lower than that of algorthm 1. Under crcumstance of TTL<6, the routng algorthm based on SARB structure proposed n the paper s sgnfcantly hgher than Gnutella, whch shows ts superorty. 5. CONCLUSION Fgure 4: Comparson of recall n algorthms under dfferent TTL condtons In order to mprove routng performance of unstructured P2P network, the method to construct overlay topology based on nterest group s manly used now. The method can only be accomplshed 280 by cooperaton among users, whch ncreases system communcaton amount and occupes large bandwdth. The peer-to-peer network routng model SARB based on successful accessng rate ust organze nodes wth smlar successful accessng rate together. It s frstly conducted n nodes wth larger successful accessng rate so that the resource

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