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Peer To Peer P2P | Part 2

Peer To Peer P2P | Part 2

Other Peer To Peer Applications

The concept of peer-to-peer is also declined in other software such as Skype, which is a type of telephony software.

P2P Software Architectures

The server peer-to-peer work in almost all cases in synchronous mode: the transfer of information is limited to elements concurrently connected to the network. They can use TCP as transport layer data (runs in duplex, data reception is confirmed and their integrity is assured).

However, some use as the continuous (streaming) require the use of a protocol lighter and faster, like UDP, although less reliable, even self-sufficient in the integrity of data transmitted. UDP is also the most used protocol for transmitting messages between servers in the system partly centralized.

The Peer-to-peer systems fall into several broad categories according to their organization:

Centralized Architecture

Examples: Napster, Audiogalaxy, and eDonkey2000.

In this architecture, a client (a software used by members) to connect to a server that manages the sharing, searching, inserting information, although they pass directly from one user to another.

Some believe that such architectures are not a peer-to-peer, as a central server is involved in the process. Others respond that the transferred files does not pass through the central server. This is the most fragile since the central server is essential to the network. Thus, it is removed, following a lawsuit by example, as was the case with Napster and Audiogalaxy, the whole network collapses.

Decentralized Architecture

Such a structure can withstand such attacks since the client software does not connect to a single server, but several. The system is thus more robust, but information retrieval is more difficult. It can be done in unstructured decentralized systems, like Gnutella where research requires a large number of messages proportional to the number of network users (and exponentially with depth research). In decentralized systems structured organization of a connection is maintained between nodes. Most are based on the distributed hash table, to conduct research in a number of messages increasing logarithmically with the number of system users, such as CAN, Chord, Freenet, GNUnet, Tapestry, Pastry, and Symphony.

Another solution was proposed, consisting in the use of “super-nodes, network elements chosen for their computing power and their bandwidth, making the system useful functions such as indexing information and intermediary role in the queries. This solution, making the system somewhat less robust (the target of “attacking” the network for the system to become inoperative are fewer than in a system like Gnutella, for example), is used in systems FastTrack, KaZaA as . The nodes of the network can then become super-nodes and vice versa, depending on system requirements or their own choice.

Similarly, the system uses eDonkey2000 servers fixed, more vulnerable because fewer and less flexible than the super-nodes FastTrack.

Network Protocols

The connections are via TCP / IP as used on the Internet that includes a reception control data, or UDP when the application chooses to control itself the right to receive.

Several peer to peer systems are offered as a network abstraction, even if not all, in 2009, widespread. The proposed applications to the end user are to operate using protocols such networks.

Among them, there are Mnet, Chord, Tapestry, Freenet, I2P (used by Imule), or Koorde Tor (en).

Peer To Peer Security

Most security issues in P2P networks are due to file sharing. Users looking for:

  • Anonymity (to avoid possible prosecution);
  • Interference with the protocol (to avoid the filtering of internet service provider);
  • Encryption (“we can know who I am but not what I download).

To ensure the anonymity of the users, one or more of these concepts are put into practice in peer-to-peer:

Peer To Peer Random Routing

The requests pass through several nodes to make their tracing difficult. These nodes are by passing the information to other network users, different fragments of the same file then pass through different machines, and are copied (for caching), before reaching the end computer that requested the download.

This caching mechanism is often used in conjunction with data encryption so that intermediaries can not see what passes. This method is implemented in Freenet, I2P, Tor, StealthNet.

Immediacy Of Access To The Resource

One of the advantages of client-server access is the immediacy with which we get the resource. Therefore downloading via http, ftp or via newsgroups are still used even though they are typically client-server systems.

Use of the software to transfer files from the Napster era to that of BitTorrent is to wait for the file several hours to several days. Several initiatives are attempting to fill this gap. This is for example the case of Freenet, but also Wuala who wants to access files stored in the network as fast as accessing a local file.

Optimization By Geographical Proximity

Proactive network Provider Participation for P2P P4P Working Group is aimed at developing technologies to maximize the exchange peer-to-peer. They assume that geographically close peers are more likely to exchange data.

Note: P3P, despite its name, has nothing to do with P2P and is not an evolution. This is the Platform for Privacy Preferences: An Initiative of the W3C which aims to improve the security of exchanges on the Web.

Evolution of Scientific Research

The peer-to-peer and, more broadly distributed systems, are the subject of much academic research in computer science.

P2P Terminology

  • The term system peer-to-peer can name a set consisting of users (not necessarily defined in number nor fixed, but generally speaking), the protocol that allows them to communicate (Gnutella, BitTorrent, CAN etc.), and operation of the protocol between these machines;
  • The term network peer-to-peer allows you to designate machines and their interconnection to one point with a set number of machines / users;
  • The term node can refer to the software on a machine, so often a user (but possibly more);
  • The term link is a connection (usually TCP) between two nodes;
  • The term object refers to what is shared in a Peer-to-peer.

Study: From Wikipedia, the free encyclopedia. The text is available under the Creative Commons.

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