Bootstrapping Chord over MANETs - All Roads Lead to Rome

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1 Bootstrapping Chor over MANETs - All Roas Lea to Rome Wei Ding, Member, IEEE, S. S. Iyengar, Fellow, IEEE Abstract This paper presents a novel approach on bootstrapping Chor over mobile a hoc networs (MANETs). The approach uses only neighborhoo information to buil a ring topology in noe ID space of structure peer-to-peer (PP) networs, upon which entire Chor protocol coul be put into normal operation without lengthy stabilization. RAN protocol suite is propose. It inclues three patterns: istribute exhaustive, virtual centralize exhaustive, an ranom. Simulation results show that the istribute exhaustive pattern has optimal overall performance. Once again the superiority of ecentralization is prove. Inex Terms a hoc networs, bootstrap, Chor, peer-topeer R I. INTRODUCTION esearch effort an real worl application interact in various ways. For PP networs, the interaction is quite positive successful business applications arouse public interest an initiate active research, an research in turn brought in better application software. This is a healthy pattern. In the case of MANETs, theoretical research ominate the area for a ecae; however, except Bluetooth, no application has been wiely applie. This has set off a warning signal in the MANETs community. On the other han, the inherent homogeneity between PP systems an MANETs implies promising propobility of synergy an transplantation. Majority of research in synergy an transplantation eals with problems occurring after a stable PP networ or system has been set up over MANETs. They usually as questions lie how to transfer proven PP approaches in wire networs to MANETs. [-5] Little effort has been reflecte in publications to explore the mechanism of bootstrapping a PP networ over MANETs. Bootstrapping has largely been circumvente via unrealistic assumptions. Bootstrapping basically o two things: () configuration of noes aresses (an IDs), () setting up overlay topology. This paper focuses on the secon tas. For structure PP networs, overlay topology lays founation for other functions lie routing, file sharing, looing up, retrieval, an ata issemination. It is one of ominant factors that affect efficiency, robustness, an Wei Ding (corresponing author) is with the University of Maine at Fort Kent. Fort Kent, ME 4743, USA (phone: ; fax: ; wei.ing@maine.eu). S. S. Iyengar is with Louisiana State University, Baton Rouge, LA 783, USA ( iyengar@csc.lsu.eu). feasibility of algorithms. There are two options for bootstrapping a structure PP networ in wire networs. One is to jumpstart a networ from one or few preefine noes, in which the only way to expan the networ is noe joining. Many structure PP systems require the manual creation of a see networ in their bootstrapping protocols. A long time may be neee before a topology is reay to use. Another approach is to construct an overlay topology for each connecte component. With this option, a PP system coul avance to normal woring status immeiately after bootstrapping. Remarable avance has been achieve in topology generation in wire networs. Present state-of-art generators in wire networs can construct basic networ topologies such as line, ring, mesh, star, an tree. General topology generator, which coul construct any topology if a mathematical expression of preferre selection criteria coul be inputte, is alreay available. However, to best of our nowlege, no such topology construction protocol in MANETs has been recore in previous publications. Our proposal probably is the first successful attempt in the specific area. This paper presents Ring A-hoc Networ (RAN) protocol suite, a novel solution for bootstrapping structure PP networs over MANETs an builing a ring topology in noe ID space. On this ring, Chor [6, 7] coul be put into normal operation without lengthy stabilization. The suite inclues three patterns: istribute exhaustive, virtual centralize exhaustive, an ranom. Simulation results show that the istribute exhaustive pattern has optimal overall performance. II. RELATED WORKS Cramer an Fuhrmann s pessimistic verict [8] on bootstrapping Chor over MANETs, which almost sentence eath to the topic, has been an incentive of this research. We completely isagree with their conclusion. Serious problems coul be foun in [8]. The whole paper is built upon some unrealistic, far-fetche assumptions. For example, they assume that all noes can reach a common bootstrap noe immeiately after they power up. To mae it possible, either all noes in the MANET have to be only one away; or every noe alreay has a route to that super noe. The most unrealistic assumption states that at the time of power up an ID space ring has been set up an all noes have alreay

2 joine the this ring. This research has benefite from previous research in T- Man [9], T-Chor [], an Ring Networs (RN) []. T-Man is esigne as a general purpose istribute protocol for builing an maintaining topology in overlay networ. It is intuitive, aaptive, scalable, robust, an flexible. T-Man follows a stepwise refining proceure to increase the quality of the current set of neighbors. Key concept of T-Man is raning function, which specifies the preference for a noe to choose its neighbors in the target topology. A noe uses the raning function to calculate its neighbor set. This simple an elegant abstraction results in an effective algorithm which prouces various topologies with efficiency. It graually evolves the current topology towars the target. The convergence is fast an scalable to networ size. T-Chor efficiently bootstraps Chor from a ranom unstructure overlay using T-Man. T-Chor creates a perfect Chor topology in O(log(N)) steps. N is networ size. It shows optimize message latency. The generate networ is immeiate operable for Chor. The ol pattern of bootstrapping structure PP system uses a jumpstart noe an noe joining proceure. Noes have to be boote one by one in a slow, linear manner. T-Chor completely breas away from the ol pattern. The RN protocol is an asynchronous message-passing istribute protocol. Noes use traitional message passing in communication. Peers o not nee to be informe of any global networ state. The RN protocol is fully istribute. All peers perioically call the Closer Peer Search proceure to fin a closer successor caniate. The most serious problem with RN is that it requires a wealy connecte initial networ calle minimal bootstrapping system. It oes not specify the scale of the bootstrapping system an how the system is foun or configure. III. TOPOLOGY CONSTRUCTION OVER MANETS In wire networs lie Internet, all noes are connecte. Being neighbor is equivalent to nowing aress, which in turn is equivalent to being able to sen a message. In MANETs, not any two noes are guarantee to be connecte. Neighbor relation in MANETs is usually efine by raio range in lowest layer. It has nothing to o with structure PP ID space or overlay layer. Moreover, the neighborhoo relation in wire networs is uniirectional, while in MANETs it is biirectional an symmetric, since it is efine by raio range. In MANETs, a noe s neighbor set is fixe at a given time, while for a noe in a wire networ, it coul have countless variation. Both PP over wire networs an PP over MANETs have proximity concerns, but in MANETs this issue has more serious impact. A in MANETs is more costly than in Internet. Hence proximity optimization has more urgent, more realistic significance in MANETs. A PP networ over wire networ usually oes not inclue all intermeiate noes on its path on the Networ layer. Otherwise the networ may have too many unrelate noes. In a PP networ over a MANET, the situation is poles apart: all intermeiate noes shoul be inclue to secure connectivity on the overlay layer. IV. RAN PROTOCOL SUITE A. Introuction RAN is a protocol to buil a ring topology over MANETs. RAN has integrate merits of T-Man an Ring Networ. RAN is completely istribute, using only neighborhoo information. RAN buils an ieal ring topology for each connecte component. Upon this ring, Chor coul run immeiately without stabilization. Each noe first converts its connecte component into a component tree with itself as the root. At each step, if a noe has shorter istance from root than the current successor, it is selecte as the new successor. The process repeats till the tree is traverse. Fig. Left shows only neighborhoo relation. Mile shows original successor relation. Right is successor relation after running RAN A component tree is a spanning tree erive from the connecte component. We use the assumption of ieal networ, which is a networ with only one complete connecte component. In an ieal networ, all noes have same one noe time complexity an same one noe message complexity. The networ message complexity is the sum of one noe message complexities of all noes. Suppose M is one noe message complexity; MNet is networ message complexity. For a complete component tree with N noes, ownwar egree, an epth, + N = () = log ( N N + ) () = N N + (3) M Net = N M (4) B. Three Patterns an Three Options We esigne three patterns for RAN, namely istribute exhaustive pattern, virtual centralize exhaustive pattern, an ranom pattern. The primary concern is the trae-off between the completeness of ring an complexities of time an message. Two exhaustive patterns exhaustively search closer successor at each level of component tree. The ieal Chor ring is guarantee, because all noe IDs are compare. However, this exhaustion may suffer from high cost. Measures are neee to mitigate the overhea. These two exhaustive patterns are equally excellent in effectiveness. In

3 3 virtual centralize exhaustive pattern the searching noe serves as a central controller. The istribute exhaustive pattern has better performance for only neighbors exchange messages. The ranom pattern has its root in Ring Networ. We eliminate the minimal bootstrapping system an use a breath-first search scheme in lieu of it. All noes in a component tree of the searching noe are traverse in a cascaing manner. Three options are also efine to improve the efficiency. Plain option means no aitional option. The approximation option coul be applie to all three patterns. It loosens the en conition of search. A small fraction of noes are allowe to be left out of the final rings. In multicast option a noe sens message to all irect chilren by multicasting. It consierably improves time an message complexity. It can not be applie to the ranom pattern. C. Pattern In the istribute exhaustive pattern, the searching noe sens a Closest Successor Request message to each chil. Each chil concurrently forwars the request message to its chilren. At following levels, noes eep forwaring the request message to chilren at next level until leaf noes are reache. Then, from leaf noes up, the closest successor of the root in the subtree is calculate at the root of the subtree an returne to the parent noe in a Closest Successor message. The calculation is one by comparing the istance of returne caniates from chilren. The message complexity of noe M + satisfies ( ) M = + N, where + is the number of sippe messages of leaf noes, for they have no chilren. Let T, T u be ownwar an upwar Time cost, plug in (3), we get M = 4N 4 M Net = 4N 4N T = T u = T = T + Tu = ( +) T = ( + )(log ( N N + ) ) = O(log N ) In multicast option, M = ( + 3) N ( + ) M = ( / + 3)( N ) M Net = MN = ( / + 3)( N ) N The Closest Successor Request message nees time unit to move from one level to next, so T = Tu = T = T = log ( N N + ) = O(log N ) D. Pattern In the virtual centralize exhaustive pattern, all irect chilren noes of the root form the first level set. Direct chilren of noes in first level form the secon level, an so on. Current level noes sen their ownwar chilren set to root, so root get information of the next level. Then root sets the next level as new current level an repeats the same proceure till leaves are reache. This algorithm is most expensive in terms of overhea. However, it gives the root noe tremenous power to control whole process upon istribute networ. In real worl application, iniviualize service coul be implemente if this pattern is use. If we count a multi- message as one message, both MNet an M are inepenent of an epth ; they only epen on N. M = ( N ) M Net = ( N ) N Unlie in the istribute exhaustive pattern, almost all messages have to go through multi-s. To get precise comparison with the istribute exhaustive pattern, the message per M shoul be use. A roun trip of the getallneighbors message an AllNeighbors message at first level taes + time units. At secon level, it is +, an so on, till +. M 3 = L + M Net = NM = N i= i i = 3 T = ( + ) + ( + ) + ( + 3) + L+ ( T = N + ( + ) / i= i + i ) E. Pattern pattern is lie a RN in MANETs. To it suitable for MANETs, several changes are mae to mae it completely ecentralize an self-organize. The minimal bootstrapping system is eliminate. As its substituent, all noes in the component are mae available using a breath-first traversal. In worst case, all noes will be covere. In fact only small number of simulations really use all noes. In worst case, M consists of Ms (to launch noes into the search) an Msearch. (to search each noe). To launch noes each noe except the root receives a Start message with root inclue, so M S = N. The secon part is the sum of istance to bottom for each noe except root, M = M S + M search = ( + + L+ In each roun, ) [( + + L+ ( ) T = roun L4 + + ] + ( N ), same as in the

4 4 istribute exhaustive pattern. T = Troun N = ( + ) N = O( N log N) 9 8 Due to the limit of the page number, etaile algorithms for three patterns an their variants are not given in this paper. Please refer to full paper if intereste. V. SIMULATION Parameters teste inclue completeness (percentage of noes covere in the output ring), time, an numbers of sent an receive messages. Result with message processing rate at an per time unit are given below..9 Completeness Fig.3 Completeness in approximation option with message processing rate Completeness Fig.6 Messages receive in approximation option with message rate Fig.7 Completeness in approximation option with message processing rate Time Fig.4 Time in approximation option with message processing rate Time Fig.5 Messages sent in approximation option with message processing rate Fig.8 Time complexity in approximation option with message processing rate

5 5 Fig.9 Messages sent in approximation option with message processing rate Fig. Messages receive in approximation option with message processing rate Obviously, the winner is the istribute exhaustive pattern. It shows perfect effectiveness, at the same time an unlie the other two patterns, it has no serious sie effect to enanger its avantage. The other two, however, suffer from ifferent fatal problems. For ranom pattern, it is the effectiveness. For virtual centralize exhaustive pattern, it is efficiency. The benefit of ecentralization has shown by the istribute exhaustive pattern. This result also raises a question: coul centralization be implemente above ecentralize infrastructure? networs, the Secon WWW Wors on Emerging Applications for Wireless an Mobile Access (MobEA 4), New Yor City, NY, May 4. [4] Y. C. Hu, H. Pucha, an S. M. Das, Exploiting the Synergy between Peer-to-Peer an Mobile A Hoc Networs, in Proceeings of HotOS- IX: Ninth Wors on Hot Topics in Operating Systems, Lihue, Kauai, Hawaii, May 8-, 3. [5] Himabinu Pucha, Saumitra M. Das, Y. Charlie Hu, Eta: An Efficient DHT Substrate for Applications in Mobile A Hoc Networs, Sixth IEEE Wors on Mobile Computing Systems an Applications, pp , 4. [6] Ion Stoica, Robert Morris, Davi Karger, M. Frans Kaashoe, an Hari Balarishnan, Chor: A Scalable Peer-to-peer Looup Service for Internet Applications, In Proceeing of ACM SIGCOMM, pp. 49-6, San Diego, CA, August. [7] Fran Dabe, Emma Brunsill, M. Frans Kaashoe, Davi Karger, Robert Morris, Ion Stoica, Hari Balarishnan, Builing Peer-to-Peer Systems with Chor, a Looup Service, In the Proceeings of the 8th Wors on Hot Topics in Operating Systems (HotOS-VIII), Schloss Elmau, Germany, May. [8] Curt Cramer an Thomas Fuhrmann, Bootstrapping Chor in A Hoc Networs: Not Going Anywhere for a While, Fourth Annual IEEE International Conference on Pervasive Computing an Communications Worss (PERCOMW'6), pp. 68-7, Pisa, Italy, 6. [9] M. Jelasity an O. Babaoglu, T-Man: Gossip-base overlay topology management, In Engineering Self-Organising Applications (ESOA'5), 5. [] Alberto Montresor, Már Jelasity, Ozalp Babaoglu, "Chor on Deman," Fifth IEEE International Conference on Peer-to-Peer Computing (PP'5), pp , 5. [] Ayman Shaer an Douglas S. Reeves, Self-Stabilizing Structure Ring Topology PP Systems, Proceeing of Fifth IEEE International Conference on Peer-to-Peer Computing (PP'5), pp , 5. VI. CONCLUSION This paper proposes a novel ring construction protocol for builing Chor over MANETs. It can be extene to other popular PP systems lie Pastry. This approach inherite successful topology construction methos in PP over Internet. We believe this approach is the first successful attempt to buil ring in PP ID space over MANETs. Our RAN protocol suite is an algorithm family for ring topology construction. RAN buils perfect ring in PP ID space using only simplest multi- unicast an multicast communication primitives. No unerlying routing protocols are neee. Upon ring generate by RAN, popular PP networs lie Chor coul be immeiately starte an put into normal running without usual lengthy stabilization. RAN family inclues a variety of algorithms for ring builing. We showe the pros an cons of these algorithms, both in theory an in simulation experiments, an illustrate that the istribute exhaustive pattern is the best in terms of effectiveness an efficiency in time an messages overhea. REFERENCES [] [HGRW6] T. Heer, S. Gotz, S. Rieche, an K. Wehrle, Aapting Hash Tables for Mobile A Hoc Networs, Proceeing of Fourth Annual IEEE International Conference on Pervasive Computing an Communications Worss, pp.73 78, 6. [] [LJLQC4] Sei-yon Lee, Ju-woo Jang, Kyung-Geun Lee, Lan Quan, Tae-young Cho, A Peer-to-Peer Search Scheme over Mobile A hoc Networs, (ISPC) International Scientific-Practical Conference 4, Institute of Mathematics of National Acaemy of Sciences (IM NAS, Bishe, Kyrgyz Republic), 4. [3] [LLS4] Mei Li, Wang-Chien Lee, Anan Sivasubramaniam, Efficient peer to peer information sharing over mobile a hoc