VIETNAM NATIONAL UNIVERSITY, HANOI UNIVERSITY OF TECHNOLOGY AND ENGINEERING Khanh Toan Do TRACKERLESS BITTORRENT ADAPTED TO MOBILE AD HOC NETWORKS GRADUATION THESIS Faculty: Information technology HA NOI – 2010 HA NOI - 2010 VIETNAM NATIONAL UNIVERSITY, HANOI UNIVERSITY OF TECHNOLOGY AND ENGINEERING Khanh Toan Do TRACKERLESS BITTORRENT ADAPTED TO MOBILE AD HOC NETWORKS GRADUATION THESIS Faculty: Information technology Instructor: Dr. Dai Tho Nguyen HA NOI – 2010 HA NOI - 2010 Abstract Of the many P2P file sharing prototypes in existence, BitTorrent is one of the few that have managed to attract millions of users. It is known to perform very well over wired networks where end-to-end performance is almost guaranteed. However, in mobile ad hoc networks (MANETs), BitTorrent with its default configuration hardly leads to the best performances because of appearance of many constraints such as the scarcity of resources and their shared nature. There are several researches proposing solutions to adapt BitTorrent to MANETs but still too few studies seek to combine the research ideas in these two areas together. Therefore, in this thesis, we propose to improve the original BitTorrent by combining a presence detection mechanism for MANETs with the BitTorrent downloading mechanism to achieve better performances. With the help of extensive NS-2 simulations, we show that these enhancements to BitTorrent significantly improve the file completion time while fully profiting from the incentives implemented in BitTorrent to enforce fair sharing. Acknowledgements First, I would like give my sincere thank to my instructor, Dr. Dai Tho Nguyen, Department of Networks and Computer Communications - who has give me guidance and support during the time I work on this thesis. Next, I would like to thank the University of Technology and Engineering - Hanoi National University, the school that has given me a perfect environment to study and train myself for four years. Finally, thanks to my family and friends who have always supported and encouraged me a lot throughout my student life. They were, are, and will be the endless source of encouragement, ambition of my life. Ha Noi, June 2010 Khanh Toan Do TABLE OF CONTENTS INTRODUCTION 1 CHAPTER 1: PEER TO PEER NETWORKS 3 1.1 Overview 3 1.2 Definitions 3 1.3 Comparison with client/server architecture 4 1.4 Benefits and weaknesses of P2P networks 5 1.5 Classifying P2P networks 6 1.5.1 Pure P2P networks 6 1.5.2 Hybrid P2P networks 7 CHAPTER 2: BITTORRENT FILE SHARING SYSTEM 10 2.1 Overview 10 2.2 Benefits of the BitTorrent protocol 11 2.3 Limitations 13 2.4 Comparison with other file sharing protocols 13 2.5 Original BitTorrent for wired networks 14 2.5.1 Description 14 2.5.2 Operation 15 2.5.3 Creating and publishing torrents 16 2.5.4 Downloading torrents and sharing files 17 2.6 BitTorrent variant for wireless ad hoc networks 18 2.6.1 Trackerless BitTorrent 18 2.6.2 Packets exchanged between peers 18 2.6.3 Downloading mechanism 19 2.6.4 Selecting a neighbor at random 20 2.6.5 Piece selection strategy 21 2.7 Performance metrics 21 CHAPTER 3: AN IMPROVEMENT OF BITTORRENT ADAPTATION TO MANETS 24 3.1 General ideas 24 3.2 Node presence detection mechanism 24 3.2.1 Soft state bloom filter 25 3.2.2 Bloom filter operations 26 3.2.3 Decoupling information decay and BEACON Intervals 27 3.3 Integration of node presence detection mechanism into BitTorrent 28 3.4 Conclusion 30 CHAPTER 4: SIMULATION RESULTS 31 4.1 Network simulator (NS-2) 31 4.2 Main scenario 31 4.2.1 Estimate the average finish time 34 4.2.2 Estimate the average sharing ratio 35 4.2.3 Estimate the network traffic 36 4.2.4 Impact of the number of network nodes 37 CONCLUSIONS AND PERSPECTIVES 38 REFERENCES 39 TABLE OF FIGURES Figure 1: P2P network 4 Figure 2: A pure P2P network 7 Figure 3: A hybrid P2P network 8 Figure 4: An example of the BitTorrent file sharing system 11 Figure 5: A soft state Bloom filter 25 Figure 6: Update Bloom filter 27 Figure 7: Problem when updating Bloom filter 28 Figure 8: Flowchart of new implementation 30 Figure 9: Network topology 33 Figure 10: Average finish time for our enhanced BitTorrent compared to ordinary BitTorrent with limited neighborhood 34 Figure 11: Average sharing ratio for our enhanced BitTorrent compared to ordinary BitTorrent with limited neighborhood 35 Figure 12: Number of control packets sent between 2 versions 36 Figure 13: Average finish time for N = 30, 40 and 50 37 TABLE OF ACRONYMS DSDV Destination-Sequenced Distance Vector FNT Far Neighbor Table HTTP Hypertext Transfer Protocol ID Identifier IP Internet Protocol MAC Media Access Control MANETs Mobile Ad Hoc Networks NNT Nearby Neighbor Table P2P Peer to Peer PDA Personal Digital Assistant TCP Transmission Control Protocol TTL Time To Live UDP User Data Protocol 1 INTRODUCTION MANETs and P2P file sharing systems are two areas that have long been studied based on a same principle: P2P paradigm. This paradigm aims to build the services of large-scale distributed systems without any infrastructure. In this model, users have an equal role. Global services are guaranteed thanks to the collaboration of users with each other. For wireless ad hoc networks, the network is a collection of wireless nodes without any central control or any base station. The network node acts as both router and host. Multi-hop routing method is used to ensure connectivity between nodes. For P2P file sharing applications, peers work together to share data and multimedia content. Each participating node will share a portion of its upload capacity to serve other nodes. The global productivity of the system increases exponentially with the number of nodes involved. Gnutella, Freenet, and BitTorrent are examples of P2P file sharing applications on the Internet. Both the file-sharing applications and ad hoc networks are all long been studied. They have been studied very much, but are independent of each other. Only very few studies try to find out if they work well together. These studies only focus on finding contents in MANETs without attention to the efficiency of content sharing. Studying the performances of file-sharing applications on mobile ad hoc networks is really challenging because of wireless channels’ diverse constraints. In fact, when the peers play a role of both routers and end users, then the routing overhead must be considered. Moreover, the performance of the transport layer protocol such as TCP decreases markedly when multi-hop paths are used. That is why file-sharing applications are not expected to work well when deployed on mobile ad hoc networks. Designing an efficient solution for the file sharing problem in wireless ad hoc networks is an important part of our study. In this work, we try to develop a file sharing application for wireless ad hoc networks. My aim is to come up with solutions that reduce the content download time while at the same time improving the distribution ratio in the network by enforcing fair sharing among peers. As efficient and fair content sharing is targeted, we choose BitTorrent given its large usage. We are interested in two main parts of the BitTorrent protocol, which are node discovering and downloading mechanisms. 2 The main framework of our study is based on [8], but the solution proposed in this paper still contains some problems with its node discovery mechanism: - Cannot detect if a node has left the network or not. - Node discovery mechanism need too much time. Because of these limitations, we replace the old presence detection method with another one introduced in [3]. The performances of our approach are proven through the ns-2 simulator to be better than the one in [8]. The remaining of this thesis is divided into 4 chapters:  Chapter 1: P2P networks We present an overview of P2P networks, their architecture, benefits and disadvantages.  Chapter 2: BitTorrent file sharing system This chapter describes about BitTorrent protocol and its installation over wired networks and mobile ad hoc networks  Chapter 3: An improvement in BitTorrent on MANETs Here is the main part of this thesis, which offers an innovative solution to BitTorrent over MANETs.  Chapter 4: Simulation results The last chapter shows the results of our simulation, in order to check the correctness arguments made above.  Conclusion and perspectives In this section, we draw a summary of our work and some plans to do in the future. [...]... Original BitTorrent for wired networks 2.5.1 Description BitTorrent protocol defines a method to disseminate and share files online Before having BitTorrent protocol, there were some P2P protocols, which allow a computer in the network to share files with other computers without having a centralized server BitTorrent is an improvement from the previous P2P protocol BitTorrent protocol has a principle to. .. IMPROVEMENT OF BITTORRENT ADAPTATION TO MANETS 3.1 General ideas BitTorrent uses a centralized node (called a tracker) to solve node discovery problems This means that each node participating in the BitTorrent system must know the address of the tracker and contact the tracker to get the addresses of other nodes in the network This cannot be done in mobile ad hoc networks because this kind of networks is... is probably the main reason for using this protocol instead of using traditional downloading from HTTP or FTP servers For those sharing and downloading copyrighted files, BitTorrent is profitable because it is decentralized 10 Figure 4: An example of the BitTorrent file sharing system 2.2 Benefits of the BitTorrent protocol The BitTorrent protocol helps to improve the previous generation of P2P software... sharing between peers 2.6.1 Trackerless BitTorrent According to the feature of MANETs that peers themselves linking into a network, a centralized tracker cannot install To adapt BitTorrent over wireless ad hoc network, we need a new mechanism to replace tracker's role: discovering and identifying the other peers M.K Sbai gave a method using HELLO message to solve such problem [8] To discover new peers,... course, the peer can be attacked Another disadvantage of the BitTorrent protocol is less encouraging peer into seeder after file downloading is complete Consequently, seeders and peers in swarm will disappear gradually, which means that more older torrents to download the file, then the probability of success lower BitTorrent has the advantage in the broadband environment, such as DSL, cable, satellite... case of equality Rarest first is supposed to grow up the entropy of pieces in the network that enforces cooperation and hence improves global performance [14] 17 2.6 BitTorrent variant for wireless ad hoc networks Some works have tried to adapt to the BitTorrent network to MANETs (eg, [1] and [13]) They focus only improved phase detection node without resolve to improve the efficiency of content sharing... location) as of February 2009 [14] BitTorrent is one of the most popular protocols for transferring large files There are many famous applications using BitTorrent protocol such as uTorrent or Podcast Besides legal distribution of files, BitTorrent is often used to illegally share and download copyrighted material The technology within the protocol makes it possible to distribute large amounts of data... 2.6.3 Downloading mechanism To profit from the advantages of the limit neighborhood, M Sbai gave an idea that modified the original BitTorrent to adapt to MANETs [8] A few TCP connections are created to distant peers in addition to those with close peers Pieces can then spread over the network and they will be propagated in different directions, which improve the sharing ratio and the download completion... the client, BitTorrent will continue sharing the file to other clients Effective use of limited upload bandwidth Home broadband connections have quite limited upload bandwidth available is a big problem of P2P systems To solve this, the BitTorrent protocol uses a few mechanisms to mitigate for this problem When a client has received a few initial blocks, it can then use its upload bandwidth to forward... clients without access to tracker The flag was requested to be included in the formal specification in August, in 2008, but it has not been accepted 2.5.4 Downloading torrents and sharing files Using any Internet browser, like Firefox, browse the site has a list of torrents, download it then use BitTorrent client open out there After opening the torrent file, BitTorrent will connect to the trackers, the . AND ENGINEERING Khanh Toan Do TRACKERLESS BITTORRENT ADAPTED TO MOBILE AD HOC NETWORKS GRADUATION THESIS Faculty: Information technology Instructor: Dr. Dai Tho Nguyen . HANOI UNIVERSITY OF TECHNOLOGY AND ENGINEERING Khanh Toan Do TRACKERLESS BITTORRENT ADAPTED TO MOBILE AD HOC NETWORKS GRADUATION THESIS Faculty: Information technology . solutions to adapt BitTorrent to MANETs but still too few studies seek to combine the research ideas in these two areas together. Therefore, in this thesis, we propose to improve the original BitTorrent