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Download miễn phí Khóa luận Trackerless bittorrent adapted to mobile ad hoc networks
TABLE OF CONTENTS
INTRODUCTION .1
CHAP TER 1: PEER TO PEER NETWORKS .3
1.1 Overvie w .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
CHAP TER 2: BITTORRENT FILE SHARING SYSTEM .10
2.1 Overvie w .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 Do wnlo ading 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 betwee n peers .18
2.6.3 Do wnlo ading mechanism .19
2.6.4 Selecting a neighbor at random .20
2.6.5 Piece selection strategy .21
2.7 Performance metrics .21
CHAP TER 3: AN IMPROVEMENT OF BITTORRENT ADAP TATION 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 Inte gration of node presence detection mechanism into BitTorrent .28
3.4 Conclusion .30
CHAP TER 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 P ERSPECTIVES .38
REFERENCES .39
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there are many nodes involvement. In return we have a more quickly and more
efficiently searching mechanism. The nature of P2P interaction directly between the
nodes that still offers significant advantages through utilization of network resources.
But here arises a problem concerning the organization of storage the information about
the location of the file shared on network. Usually they organize the information into a
database. Each record includes a file with file name and address of the node currently
hosting the file. This is a popular way to organize applications using P2P file-sharing
hybrid model like Napster or OpenNap. However, limitations of this method is that it
only allows users to search by file name (or general file identifiers). This is suitable
only for sharing music file or photo libraries. With more complex libraries of
documents related to the character (text files, books, articles, ...), demand does not stop
from looking at the name or identity criteria. Currently almost all file-sharing
applications commonly found on the web do not allow to search features of the content
within document files. It can be seen that to put this searching feature function into a
file-sharing applications, we found it necessary to apply the methods and techniques
used in information retrieval . When that information about the documents not only of
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the name (identification) of documents but also include further information on the
keywords contained in the document. Information on the searching server must be
organized as a system indexing by keyword.
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CHAPTER 2: BITTORRENT FILE SHARING SYSTEM
In this chapter, we present an overview of the BitTorrent file sharing system and
its implementation over wired networks and mobile ad hoc networks.
2.1 Overview
File sharing is very well known in the entire community due to its popular usage.
A large amount of bandwidth on the Internet is used by different file sharing
applications/protocols. It has been estimated that it may account for as much as 43% of
all Internet traffic (depending on geographical 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 without the need of a high capacity server, and expensive bandwidth. This 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.
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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 with a number of significant initiatives, which shall be discussed in next
subsections.
High speed downloading
Simply put, BitTorrent is quite popular due to its parallel file transfer process.
Unlike the typical network behavior, which bottlenecks cause performance to
plummet; BitTorrent actually increases the demand to improve the performance of a
computer network. This behavior increases the stability ratio for the distribution of
large, popular content on the internet, for servers of limited capacity. The protocol
achieves this by splitting large files into smaller blocks, such as 128 kilobytes, by
splitting into blocks, the source components may be required from many sources, but
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not need to set the complete file to be able to load up the block, which means
downloading the software can quickly start contributing as uploaders for other users
Simplicity, easy to use
Unlike other complex previous P2P protocols, the BitTorrent protocol works on a
web based distribution model built over the HTTP protocol. Users simply download a
client, which to a user act as an extension of their internet browser. By opening the
files ‘.Torrent’, client will allow the users to save files to a location of their choice on
the hard drives in the same fashion as original file transfer applications. Until the user
closes 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 those blocks to other machines.
Another aspect is that transfers are limited to four open sessions, and the number of
files hosted is limited to a few users; by focusing on a small number of activities, the
network can reduces overhead. By reducing the number of uploads per machine, and
having considerably more machines uploading content, the time required by a client
for downloading a large file is considerably less than tr aditional means.
Overcoming the Free-Rider problem
In typical P2P systems, the performance of the overall system downs when users
trying to obtain service without contributing anything to the system. This is an old
problem, and BitTorrent was designed with an approach of local optimization by
allocating the most upload bandwidth to peers, which are supplying the greatest
amount of content. Because of the design of the current BitTorrent Protocol, free riders
can only get 20% of the total system bandwidth.
High content integrity
BitTorrent employs two mechanisms, which make it more reliable. First, to be
accepted on a file tracking server, typically new content must be accepted and
managed by moderators who manually inspect it. To reduce the overload for
moderators, regular suppliers of content can be promoted to immoderate submitters
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after gaining enough trust. Once the original content is considered trusted, a validation
checksum of file will be presented from the server to guarantee the content integrity.
2.3 Limitations
BitTorrent protocol does not Giúp users to hide their identifiers. Because the
tracker maintains a list of files being shared, it also contains a list of IP addresses of
the computers are downloading the file, and the list of the files that have been
downloaded previously. Based on the BitTorrent protocol also ascertains the address
of the peer in the swarm and of 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 ... but for dial-up Internet users using the
BitTorrent protocol will not work, because dial-up connection or disconnection and
speed not load high.
2.4 Comparison with other file sharing protocols
The method used to distribute files between eDonkey2000 and BitTorrent
networks is similar, but the clients in the eDonkey network usually share and
download many files, making the bandwidth per carrier becomes less. In contrast,
transporting in BitTorrent is much faster by focusing on a file or a specific group of
files. Original eDonkey2000 protocol provides very little resistance to fraud machines
(download more, upload very little), the new phiên bản of eDonkey2000 client has
installed the system which encourages more uploads. For example, systematic program
eMule (credits system) have a score system to encourage uploaders. One client will
prioritize the shipment to its previous position by moving the client to the top of the
queue to wait for less time. This system proved effective because a queue for each
client using eMule often has hundreds, even thousand entries.
KaZaA is a protocol similar to BitTorrent protocol, but it has another point that
is its distinguishing workstations by dedication level (Participation Level).
Contribution level increases when you upload and decreases when you download.
Once you upload a resource, it devotes to the person with the highest-level first and
then this person devote to the lower contribution level one and so on. This model is
similar to the pyramid model; the most uploader is at the top position of the pyramid,
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and the less one is on the bottom. KaZaA is only appropriate model distribution of
resources for a large number of use...