A Scalable and Reliable Mobile Agent Computation Model

Transcription

1 A Sclble nd Relible Mobile Agent Computtion Model Yong Liu, Congfu Xu, Zhohui Wu, nd Yunhe Pn College of Computer Science, Zhejing University Hngzhou , Chin Abstrct. This pper presents high performnce service bsed mobile gent computtion model. The sclbility nd relibility of this model is secured through the service clone policy nd ccess privilege policy. With the introduction of service density of group, we cn further decrese resource witing nd blnce the service occupncy for the whole network. 1 Introduction Mobile Agents re progrms tht cn be migrted nd executed between different network hosts. There re tow types of mobile gents clssified by the migrtion bility of the gents. They re strong migrtion mobile gents nd wek migrtion mobile gents. When using the strong migrtion policy, the mobile gent system needs to record ll the sttes nd relted dt in ech position of the gent, which will spend huge mount of time nd spce for the trnsport, nd will led to low efficiency. When using wek migrtion policy, the trnsporttion of dt will decrese gretly, however, the bilities of dpting the complicted network topology will decrese too. Therefore, how to design relible nd high-efficiency work pttern for the mobile gent is one of the most importnt problems. In fct, the Grid[3] technology hs provided powerful pltform for the mobile gent. The WSDL[4] provides web service description lnguge for service disposing. How dose the service be composed together cn be described by the WSFL[6]. And the UDDI (Universl Description, Discovery nd Integrtion)[5] is used to enble online registry nd the publishing nd dynmic discovery of Web services offered by businesses. The RDF[7], which is recommended by W3C nd cn support domin-independent metdt description, is used to describe the resources. The mobile gent computtion model tht is built upon these bove techniques is convergence nd hrd to sclbility. In order to solve this problem, sclble nd relible service bsed mobile gent computtion model is proposed bsed on decentrlized virtul orgniztion rchitecture. J. Zhng, J.-H. He, nd Y. Fu (Eds.): CIS 2004, LNCS 3314, pp , c Springer-Verlg Berlin Heidelberg 2004

2 A Sclble nd Relible Mobile Agent Computtion Model Overview of MACM nd Fbric Architecture Our computtion model is estblished upon the virtul orgniztion rchitecture, nmely virtul orgniztion (VO or group), which cn gretly reduce the mobile gent size during migrtion, nd this rchitecture cn provide more intelligent support for mobile gent. The bsic elements of virtul orgniztion re nodes, which cn be PC, PDA, lptop, nd other devices connected by network. The nodes re grouped in virtul, nd they cn join nd leve the group dynmiclly. The groups re virtully hierrchicl, which mens tht the groups cn be clssified into root-lyer, middle-lyers nd lef virtul lyers. The virtul group bsed fbric rchitecture is the pltform of the mobile gent migrtion. By this wy, the mobile gent cn discovery nd move more effective nd it cn lso gretly decrese the mobile gent size during migrtion. 2.1 Forml Definition of Infrstructure The VO bsed rchitecture mentioned in this pper is structure similr to the fbric lyer in [1]. Some definitions re given s the following: Definition 1. Node, the minimized devices tht cn lod nd execute the mobile gents in network re denoted s R i. Ech node in VO cn be service provider or service consumer. Definition 2. Key Node is kind of nodes tht dels with the remote communictions, denoted s Ri 0. Ech group must contin key node. And the key nodes re lwys positioned in two or more thn tow groups. Normlly the contiguity key nodes form kernel group. Definition 3. Group, the set includes one node or severl nodes, denoted s G i = {R,R 0,R 1, 2..., R}, n where is the nme of the group. Ech group hs lyer identifier i, which mens tht the group is the ith lyer in VO. The node cn join in more thn one group in VO, which mens tht ech node including key node cn belong to two or more thn two groups. Rj i mens tht node belongs to group G j. Group is comprtively stble orgniztion; the nodes belonging to certin group cn leve this group nd join in nother group dynmiclly. The login nd logout of nodes dopt the GGMP (Grid Group Mngement Protocol)[1], which is similr to the IGMP. Definition 4. Service, in VO rchitecture, service is kind of deling process tht provided by certin nodes in VO. It cn be formlly defined s four-tuple: S(GUIDS, P rivilege, Content, Opertion), where GUIDS is the globl unique ID of the service. And privilege is the privilege defined by the service provider, which include public nd privte privileges. Content is the process of service. Opertion is kind of specil opertions ssocited with service, which includes clone, serve, migrtion etc.

3 348 Y. Liu et l. Definition 5. Service Mngement Node, is kind of nodes tht contins the services informtion of current group, denoted s R s. Normlly, ll these contiguity service mngement nodes form service mngement group utomticlly. Definition 6. Virtul Orgniztion, VO is fbric structure tht composed of nodes nd is estblished by seril of protocols. It is hierrchicl tree structure constituted by virtul groups. There exist root group (denoted s RG, nd it is the first lyer) nd other middle lyer groups, denoted s G i j, i mens tht the group is the ith lyer in the virtul orgniztion. L is the lef group, which is positioned t the bottom of the virtul tree, shown s figure 1. Normlly, the group contins resembling nd djcent nodes. There is key node Ri 0 in ech group G i. The functions of the key node in group re similr to the gtewy in LAN, which communictes with other nodes outside the group. A protocol clled GGMP (Grid Group Mngement Protocol)[2] hs been used to determine the key node. Among ll the nodes nd groups, the key nodes constitute virtul group clled kernel group, G k. It is the most importnt portion tht serves for other nodes. It dels with communiction nd seeking etc. Among ll of the nodes in virtul orgniztion topology, the root (first lyer) group in the tree structure of virtul orgniztion is lwys chosen from one of the kernel groups. 2.2 Sfe Service Mngement Protocol Service is disposed upon the virtul orgniztion. Compred with the UDDI[5], the virtul orgniztion bsed service is more dispersed. It is not necessry to Root lyer (First) RG G 1 2 G 2 2 Middle lyer G 1 i G 2 i G n i Lef lyer L 1 L i L j L k L p L q Fig. 1. Tree-Structure of the Virtul Orgniztion

4 A Sclble nd Relible Mobile Agent Computtion Model 349 estblish universl service informtion server in virtul orgnize, on the contrry, the service informtion is distributed in norml group, there is service mngement node in ech group. The vilble service informtion is stored in these service mngement nodes. For sfe service mngement protocol, once the service hs been relesed by the originl node, it cn be replicted to the sme group nodes nd others, nd this opertion is clled clone. However, there my exist some services tht would not shre them with ll the other nodes in VO. So the service disposed in the virtul orgniztion hs privilege ttribute. For the virtul tree is orgnized in hierrchy, the privilege of ech lyer is different, nd in generl the higher privilege is ssigned to the higher lyer group in VO. Tble 1. Privileges defined by the SSMP Privilege Types Privte privileges Public privileges Privilege Sub-types Self privte Notes The node, which releses the service, engrosses the service. Group privte The service is privtely belonged to the relesed node nd its group. Below ccess Sme level ccess Full tree ccess Specil ccess level The service is public to the groups, which re the children of the originl service relesed group. The service is public to the sme lyer group nodes in VO, which mens the service relesed by the ith lyer group node, nd it cn be cloned to the sme ith lyer group nodes. The service is public to ll the tree nodes. The service cn specify the public lyer from ith lyer to jth lyer, i<j. Tble 1 lists the privileges tht re defined by the SSMP. The privilege cn be clssified into two ctegories: privte service nd public service. This ctegory division is bsed on the concept of the group, tht is to sy, whether the service is privte or public to other groups. A frther ctegory in privte privilege cn be clssified into self-privte nd group-privte, the difference between these two ctegories is whether the service cn be cloned mong the originl group. There re four kinds of frther public privilege ctegories, they re below ccess, sme level ccess, full tree ccess, nd specil level ccess respectively. This kind of public privilege ctegory mens tht the services cn be cloned out of their relesed groups, nd the ccess degree out of the originl groups is controlled by this privilege ctegory.

5 350 Y. Liu et l. 2.3 Service Density Before the service dispose protocol is presented, tolernce nmed Service Density should be introduced firstly. It is one of the most importnt fctors in our mobile gent computtion model. Definition 7. Service Density of Group, is function,f s (A G i,n G i ), which symbolizes certin vilble service in groups. Where s is the service nme. A G i is the number of nodes in group G i, which contins vilble service of s. N G i is the node number in group G i. In our mobile gent computtion model, the service density of group (SDG) is defined s formultion (1). In SSMP, the service density of current group is stored in this service mngement node. Other groups cn request for service density by sending messge to this mngement node. η S G i = A G i N G i 100% (1) 3 Service Bsed Mobile Agent Computtion Model Definition 8. Service bsed mobile gent computtion model, is sixtuple MACM =(R, S, M, φ, v, E), Where, R is the node set, S is the finite stte set of the mobile gent. S does not include the stte of the gent migrtion Λ nd the null stte ε. Here, migrtion stte Λ mens tht the mobile gent strts to move to nother node to execute new stte; null stte mens tht the mobile gent does not perform ny ction (execution nd migrtion). M S is the set of ll the messge opertion sttes for mobile gent. M = {M s,m }, M s is the stte of sending messge, nd M is the stte of receiving messge. v R is the initil node tht the mobile gent hs been produced, mobile gent s service firstly comes from the node v, nd then cycles re driven by the finite sttes. E R is the set of finl node for the mobile gent, only in the finl node the mobile gent cn be destroyed nd the service ends. φ, the trnsition reltion, is finite subset of (R (S {Λ, ε})) R: φ :(R (S {Λ, ε})) R, Where (1)To ll the R i,r j R, ifφ(r i,ε)=r j, then R i = R j, (2)To ll the R i,r j R, ifφ(r i,λ)=r j, then R i R j, (3)To ll the R i,r j R, S k S, ifφ(r i,s k )=R j, then R i = R j, (4)To ll the R i R, ifφ(r i,m ) = R i, then the next trnsition stte reltion is φ(r i,m s )=R i, (5)To VO = {G n m,n =1, 2, 3,..., m =1, 2, 3,...}, η Sr G is the service S n r s m density of group G n m. When mobile gent begins to switch to S r service, there will be: φ Sr (R i,λ)=r j

6 A Sclble nd Relible Mobile Agent Computtion Model 351 Here R i is the current position node of the mobile gent. To the trget node R j,wehve: (R j SN Sr ) (SN G q Sr G q k G q k ) (G q k G n m ) (η Sr =mx(η k G q Sr G,n,m=1, 2, 3,...)) n k m where SN Sr is the vilble service node in G q G q k of service S r. k (6)After the migrtion in (5) hs finished, the service S r s density of G q k chnge to: will A Sr 1 η Sr G q = k 100% (2) G q k N Sr G q k In this computtion model, the migrtion stte Λ is estblished by the communiction of the nodes in VO. By dopting the service fbric communiction protocol, mobile gent cn move from the originl node to the destintion node efficiently. The stte trnsition nd messge communiction re ll implemented by this protocol. The service density hs been treted s n importnt tolernce to disptch the mobile gent s migrtion. 4 Conclusions In this pper, sfe service bsed mobile gent computtion model is introduced. With the policy of service clone in tree structure hierrchy group nd the policy of flexible service ccess, the model is more effective nd relible compred with trditionl methods. Furthermore, gent cn use group service density to monitor the whole network service occupncy in groups. It cn blnce the service s serving time nd decrese the witing list of service. Acknowledgements. This pper ws sponsored by Chin Defense Ministry, nd ws prtilly supported by the Aerospce Reserch Foundtion (No HT- ZJDX-13). Thnks for Dr. Zhng Qiong s dvice to this pper. References 1. Hung, L.C., Wu, Z.H., nd Pn, Y.H.: Virtul nd Dynmic Hierrchicl Architecture for E-Science Grid. Interntionl Journl of High Performnce Computing Applictions, 17 (2003) Hung, L.C., Wu, Z.H., nd Pn, Y.H.: A Sclble nd Effective Architecture for Grid services Discovery. First Workshop on Semntics in Peer-to-Peer nd Grid Computing. Budpest, Hungry, 20 My 2003: Foster, I., Kesselmn, C., nd Tuecke, S.: The Antomy of the Grid: Enbling Sclble Virtul Orgniztions. Interntionl J. Supercomputer Applictions, 15(3), 2001

7 352 Y. Liu et l. 4. Christensen, E., Curber, F., Meredith, G. nd Weerwrn., S.: Web Services Description Lnguge (WSDL) 1.1. W3C, Note 15, 2001, w3. org /TR/wsdl 5. UDDI 6. Web Services Flow Lnguge (WSFL) Version 1.0, softwre/ solutions/ Webservices/pdf/WSFL.pdf 7. Brickley, D., nd Guh,R. V.: Resource Description Frmework (RDF) Schem Specifiction 1.0, W3C Cndidte Recommendtion 27 Mrch 2000.