Peer-to-peer

 
(abbreviated to P2P) refers to a computer network in which each computer in the network can act as a client or server for the other computers in the network, allowing shared access to files and peripherals without the need for a central server. P2P networks can be set up in the home, a business or over the Internet. Each network type requires all computers in the network to use the same or a compatible program to connect to each other and access files and other resources found on the other computer. P2P networks can be used for sharing content such as audio, video, data or anything in digital format. P2P is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application. Each computer in the network is referred to a node. The owner of each computer on a P2P network would set aside a portion of its resources, such as processing power, disk storage or network bandwidth, directly available to other network participants, without the need for central coordination by servers or stable hosts.Peers are both suppliers and consumers of resources, in contrast to the traditional client–server model where only servers supply (send), and clients consume (receive). The first peer-to-peer application was the file sharing system Napster, originally released in 1999. The concept has inspired new structures and philosophies in many areas of human interaction. Peer-to-peer networking is not restricted to technology, but covers also social processes with a peer-to-peer dynamic. In such context, social peer-to-peer processes are currently emerging throughout society. •  

Architecture of P2P systems

 Peer-to-peer systems often implement an abstract overlay network, built at Application Layer, on top of the native or physical network topology. Such overlays are used for indexing and peer discovery and make the P2P system independent from the physical network topology. Content is typically exchanged directly over the underlying Internet Protocol (IP) network. Anonymous peer-to-peer systems are an exception, and implement extra routing layers to obscure the identity of the source or destination of queries. In structured peer-to-peer networks, peers (and, sometimes, resources) are organized following specific criteria and algorithms, which lead to overlays with specific topologies and properties. They typically use distributed hash table-based (DHT) indexing, such as in the Chord system (MIT). Unstructured peer-to-peer networks do not impose any structure on the overlay networks. Peers in these networks connect in an ad-hoc fashion. Ideally, unstructured P2P systems would have absolutely no centralized system, but in practice there are several types of unstructured systems with various degrees of centralization. Three categories can easily be seen. • In pure peer-to-peer systems the entire network consists solely of equipotent peers. There is only one routing layer, as there are no preferred nodes with any special infrastructure function. • Hybrid peer-to-peer systems allow such infrastructure nodes to exist, often called supernodes. • In centralized peer-to-peer systems, a central server is used for indexing functions and to bootstrap the entire system. Although this has similarities with a structured architecture, the connections between peers are not determined by any algorithm. The first prominent and popular peer-to-peer file sharing system, Napster, was an example of the centralized model. Freenet and early implementations of the gnutella protocol, on the other hand, are examples of the decentralized model. Modern gnutella implementations, Gnutella2, as well as the now deprecated Kazaa network are examples of the hybrid model. A pure P2P network does not have the notion of clients or servers but only equal peer nodes that simultaneously function as both "clients" and "servers" to the other nodes on the network. This model of network arrangement differs from the client–server model where communication is usually to and from a central server. A typical example of a file transfer that does not use the P2P model is the File Transfer Protocol (FTP) service in which the client and server programs are distinct: the clients initiate the transfer, and the servers satisfy these requests. The P2P overlay network consists of all the participating peers as network nodes. There are links between any two nodes that know each other: i.e. if a participating peer knows the location of another peer in the P2P network, then there is a directed edge from the former node to the latter in the overlay network. Based on how the nodes in the overlay network are linked to each other, we can classify the P2P networks as unstructured or structured.  

Structured systems

Structured P2P networks employ a globally consistent protocol to ensure that any node can efficiently route a search to some peer that has the desired file, even if the file is extremely rare. Such a guarantee necessitates a more structured pattern of overlay links. By far the most common type of structured P2P network is the distributed hash table (DHT), in which a variant of consistent hashing is used to assign ownership of each file to a particular peer, in a way analogous to a traditional hash table's assignment of each key to a particular array slot. Though the term DHT is commonly used to refer to the structured overlay, in practice, DHT is a data structured implemented on top of a structured overlay.

 Distributed hash tables

Distributed hash tables (DHTs) are a class of decentralized distributed systems that provide a lookup service similar to a hash table: (key, value) pairs are stored in the DHT, and any participating node can efficiently retrieve the value associated with a given key. Responsibility for maintaining the mapping from keys to values is distributed among the nodes, in such a way that a change in the set of participants causes a minimal amount of disruption. This allows DHTs to scale to extremely large numbers of nodes and to handle continual node arrivals, departures, and failures. DHTs form an infrastructure that can be used to build peer-to-peer networks. Notable distributed networks that use DHTs include BitTorrent's distributed tracker, the Kad network, the Storm botnet, YaCy, and the Coral Content Distribution Network. Some prominent research projects include the Chord project, the PAST storage utility, the P-Grid, a self-organized and emerging overlay network and the CoopNet content distribution system (see below for external links related to these projects). DHT-based networks have been widely utilized for accomplishing efficient resource discovery for grid computing systems, as it aids in resource management and scheduling of applications. Resource discovery activity involves searching for the appropriate resource types that match the user’s application requirements. Recent advances in the domain of decentralized resource discovery have been based on extending the existing DHTs with the capability of multi-dimensional data organization and query routing. Majority of the efforts have looked at embedding spatial database indices such as the Space Filling Curves (SFCs) including the Hilbert curves, Z-curves, k-d tree, MX-CIF Quad tree and R*-tree for managing, routing, and indexing of complex Grid resource query objects over DHT networks. Spatial indices are well suited for handling the complexity of Grid resource queries. Although some spatial indices can have issues as regards to routing load-balance in case of a skewed data set, all the spatial indices are more scalable in terms of the number of hops traversed and messages generated while searching and routing Grid resource queries. More recent evaluation of P2P resource discovery solutions under real-workloads have pointed out several issues in DHT-based solutions such as high cost of advertising/discovering resources and static and dynamic load imbalance.

 Unstructured systems

An unstructured P2P network is formed when the overlay links are established arbitrarily. Such networks can be easily constructed as a new peer that wants to join the network can copy existing links of another node and then form its own links over time. In an unstructured P2P network, if a peer wants to find a desired piece of data in the network, the query has to be flooded through the network to find as many peers as possible that share the data. The main disadvantage with such networks is that the queries may not always be resolved. Popular content is likely to be available at several peers and any peer searching for it is likely to find the same thing. But if a peer is looking for rare data shared by only a few other peers, then it is highly unlikely that search will be successful. Since there is no correlation between a peer and the content managed by it, there is no guarantee that flooding will find a peer that has the desired data. Flooding also causes a high amount of signaling traffic in the network and hence such networks typically have very poor search efficiency. Many of the popular P2P networks are unstructured. In pure P2P networks: Peers act as equals, merging the roles of clients and server. In such networks, there is no central server managing the network, neither is there a central router. Some examples of pure P2P Application Layer networks designed for peer-to-peer file sharing are gnutella (pre v0.4) and Freenet. There also exist hybrid P2P systems, which distribute their clients into two groups: client nodes and overlay nodes. Typically, each client is able to act according to the momentary need of the network and can become part of the respective overlay network used to coordinate the P2P structure. This division between normal and 'better' nodes is done in order to address the scaling problems on early pure P2P networks. As examples for such networks can be named modern implementations of gnutella (after v0.4) and Gnutella2. Another type of hybrid P2P network are networks using on the one hand central server(s) or bootstrapping mechanisms, on the other hand P2P for their data transfers. These networks are in general called 'centralized networks' because of their lack of ability to work without their central server(s). An example for such a network is the eDonkey network (often also called eD2k).  

Indexing and resource discovery

 Older peer-to-peer networks duplicate resources across each node in the network configured to carry that type of information. This allows local searching, but requires much traffic. Modern networks use central coordinating servers and directed search requests. Central servers are typically used for listing potential peers (Tor), coordinating their activities (Folding@home), and searching (Napster, eMule). Decentralized searching was first done by flooding search requests out across peers. More efficient directed search strategies, including supernodes and distributed hash tables, are now used. Many P2P systems use resource-rich peers (namely superpeers, super-nodes) as servers and client-peers are connected in a star-like fashion to a single superpeer.  

Peer-to-peer-like systems

In modern definitions of peer-to-peer technology, the term implies the general architectural concepts outlined in this article. However, the basic concept of peer-to-peer computing was envisioned in earlier software systems and networking discussions, reaching back to principles stated in the first Request for Comments, RFC 1.A distributed messaging system that is often likened as an early peer-to-peer architecture is the USENET network news system that is in principle a client–server model from the user or client perspective, when they read or post news articles. However, news servers communicate with one another as peers to propagate Usenet news articles over the entire group of network servers. The same consideration applies to SMTP email in the sense that the core email relaying network of Mail transfer agents has a peer-to-peer character, while the periphery of e-mail clients and their direct connections is strictly a client–server relationship. Tim Berners-Lee's vision for the World Wide Web, as evidenced by his WorldWideWeb editor/browser, was close to a peer-to-peer design in that it assumed each user of the web would be an active editor and contributor creating and linking content to form an interlinked web of links. This contrasts to the broadcasting-like structure of the web as it has developed over the years.  

Advantages and weaknesses

In P2P networks, clients provide resources, which may include bandwidth, storage space, and computing power. This property is one of the major advantages of using P2P networks because it makes the setup and running costs very small for the original content distributor. As nodes arrive and demand on the system increases, the total capacity of the system also increases, and the likelihood of failure decreases. If one peer on the network fails to function properly, the whole network is not compromised or damaged. In contrast, in a typical client–server architecture, clients share only their demands with the system, but not their resources. In this case, as more clients join the system, fewer resources are available to serve each client, and if the central server fails, the entire network is taken down. The decentralized nature of P2P networks increases robustness because it removes the single point of failure that can be inherent in a client-server based system. Another important property of peer-to-peer systems is the lack of a system administrator. This leads to a network that is easier and faster to setup and keep running because a full staff is not required to ensure efficiency and stability. Decentralized networks introduce new security issues because they are designed so that each user is responsible for controlling their data and resources. Peer-to-peer networks, along with almost all network systems, are vulnerable to unsecure and unsigned codes that may allow remote access to files on a victim's computer or even compromise the entire network. A user may encounter harmful data by downloading a file that was originally uploaded as a virus disguised in an .exe, .mp3, .avi, or any other filetype. This type of security issue is due to the lack of an administrator that maintains the list of files being distributed. Harmful data can also be distributed on P2P networks by modifying files that are already being distributed on the network. This type of security breach is created by the fact that users are connecting to untrusted sources, as opposed to a maintained server. In the past this has happened to the FastTrack network when the RIAA managed to introduce faked chunks into downloads and downloaded files (mostly MP3 files). Files infected with the RIAA virus were unusable afterwards or even contained malicious code. The RIAA is also known to have uploaded fake music and movies to P2P networks in order to deter illegal file sharing. Consequently, the P2P networks of today have seen an enormous increase of their security and file verification mechanisms. Modern hashing, chunk verification and different encryption methods have made most networks resistant to almost any type of attack, even when major parts of the respective network have been replaced by faked or nonfunctional hosts. There are both advantages and disadvantages in P2P networks related to the topic of data backup, recovery, and availability. In a centralized network, the system administrators are the only forces controlling the availability of files being shared. If the administrators decide to no longer distribute a file, they simply have to remove it from their servers, and it will no longer be available to users. Along with leaving the users powerless in deciding what is distributed throughout the community, this makes the entire system vulnerable to threats and requests from the government and other large forces. For example, YouTube has been pressured by the RIAA, MPAA, and entertainment industry to filter out copyrighted content. Although server-client networks are able to monitor and manage content availability, they can have more stability in the availability of the content they choose to host. A client should not have trouble accessing obscure content that is being shared on a stable centralized network. P2P networks, however, are more unreliable in sharing unpopular files because sharing files in a P2P network requires that at least one node in the network has the requested data, and that node must be able to connect to the node requesting the data. This requirement is occasionally hard to meet because users may delete or stop sharing data at any point. In this sense, the community of users in a P2P network is completely responsible for deciding what content is available. Unpopular files will eventually disappear and become unavailable as more people stop sharing them. Popular files, however, will be highly and easily distributed. Popular files on a P2P network actually have more stability and availability than files on central networks. In a centralized network, only the loss of connection between the clients and server is simple enough to cause a failure, but in P2P networks, the connections between every node must be lost in order to fail to share data. In a centralized system, the administrators are responsible for all data recovery and backups, while in P2P systems, each node requires its own backup system. Because of the lack of central authority in P2P networks, forces such as the recording industry, RIAA, MPAA, and the government are unable to delete or stop the sharing of content on P2P systems.

 Social and economic impact

The concept of P2P is increasingly evolving to an expanded usage as the relational dynamic active in distributed networks, i.e., not just computer to computer, but human to human. Yochai Benkler has coined the term commons-based peer production to denote collaborative projects such as free and open source software and Wikipedia. Associated with peer production are the concepts of: • peer governance (referring to the manner in which peer production projects are managed) • peer property (referring to the new type of licenses which recognize individual authorship but not exclusive property rights, such as the GNU General Public License and the Creative Commons licenses) • peer distribution (or the manner in which products, particularly peer-produced products, are distributed) Some researchers have explored the benefits of enabling virtual communities to self-organize and introduce incentives for resource sharing and cooperation, arguing that the social aspect missing from today's peer-to-peer systems should be seen both as a goal and a means for self-organized virtual communities to be built and fostered. Ongoing research efforts for designing effective incentive mechanisms in P2P systems, based on principles from game theory are beginning to take on a more psychological and information-processing direction.

How to clean ramnit?

Ramnit :
Viruses that inject file. Html,. Exe and. Etc.The virus is transmitted through a removable disk (UFD) by way of copying files. Cpl and. Exe is always growing and changing namanya.Yang exact file is located in the Recycler folder. and the fourth copy of the shortcut file that will run the file *. Cpl infektor recycler folder contained in the UFD.When the virus has to infect a computer system, the virus will create and run the svchost.exe file that will do various things: a. create a file named: watermark.exe located in the folder: C: \ programfiles \ mikrosoft \ watermark.exe. b. becoming run userinit.exe registry change: watermark.exe, so that the virus has mastered the system permanently, by infecting files ending in. exe,. dll and. htmlIf the properties, UFD will look much used by the file. Cpl and. Exe in the folder recycler.
The effect:
Ramnit virus will create a program does not run normally, for example: mozilla firefox, winamp, etc.we can not remove the existing file watermark.exe difolder c: \ programfiles \ microsoft \ watermark.exe, because the file is locked by svchost.exe file its ramnit virus.
when we delete files / folders that are in the UFD recycler folder, file. cpl and. exe will come back .. and continued to write back.


for a particular file system is infected . wherewith for example: explorer.exe will be replaced explorermgr.exewhen we clean the virus is not complete (there are not cleared), this virus will come back when we run the application (eg: right click).
To clean:
Prepare Anti Virus cleaner (I use NOD32 stand alone) by> download here <and save it in a zip file / RAR to exe file is not infected.Save the file on the UFD, or copy and paste on an infected computer's hard drive.Use task manager, select the task / processes tab and end task all the svchost.exe file and also all that can end task (except for: task manager)
   
 Open file cleaner that has been shaped NOD32 zip / RAR, using the file open in the task manager. change choice program in order to open the file into allfiles file zip / rar of NOD32 can be seen.after teropen NOD32 with winrar or other application . please double click the file Nod *. exe after the next. next action, select the left and right side select Clean delete. Then run Scan & clean after walking close / close winrar / application made to open NOD32 zip / RAR.
 
   Please be supervised by the task manager when the svchost.exe file in / out processes appear in the task immediately at the end. and as usual when there is no display windows warning that the computer will shutdown in 60 seconds / 1 minute. Please type in the file menu open / run: shutdown-a-a meaning that is the shutdown command to cancel the action.
  
  Warning!! , While NOD 32 clean file on your computer, not to open / run any file. because it let alone run the exe file, right-click aja we are meant to run a virus / her svchost.exe Virus Ramnit.
    Remember we need turn off / end task svchost.exe file for NOD32 clean the file on your computer .