The application of P2P technology

Team Member:LIU Chang, ZHANG jianing

Presentation:

LIU Chang

Introduction

This article discusses the peer-to-peer technologies in common use today and takes a look at possible future applications in this area. The architectures and protocols are examined in enough detail to give a basic understanding of their pros and cons and to highlight the difficulties that must be overcome for future generations of peer-to-peer.

The comparison between traditional C/S and P2P model

A client does not share any of its resources, but requests a server's content or service function. Clients therefore initiate communication sessions with servers which await incoming requests.

P2P model:

These shared resources are available to every computer in the network. Each computer acts as both the client and the server which means all the computers on the network are equals, that is where the term peer-to-peer comes from.

The comparison between traditional C/S and P2P model ：

（ 1 ） On the one hand, all data is stored on the servers, which generally have far greater security controls than most clients.

（ 2 ） On the other hand, as the number of simultaneous client requests to a given server increases, the server can become overloaded.

According to the following picture, we can see the some of mainly differences between C/S and P2P:

  P2P C/S

Data publish Good Bad

Data receive Ordinary Good

Data security Bad Good

Data update Good Bad

Data quality Ordinary Good

Data coverage Bad Good

Data cost control Good Bad

Data manage Bad Good

The P2P technology in Cloud Computing

1. Cloud computing has become a hot buzzword recently. Infrastructure construction and operation cost is high. Google, Microsoft, yahoo, Amazon have spent large sums of money into this market.

2. Google's cloud computing services such as Gmail and Amazon’s S3 and Microsoft's AZURE are very large. Due to the scale of these services is very huge, so your problems easily can lead to the end user, and then the quality of cloud services will be doubted.

In view of this, the ancient P2P technology together with this new technology revealed its unique advantages, show a new vitality for the development of cloud computing.

Together with P2P and Cloud Computing technology, we have something called P2P Cloud:(1) P2P is a great fit for Cloud storage systems offering the much needed reliability.(2) Another area where P2Pcan play a major role is Content Delivery Networks (CDN) which is usually offered as an extension to Cloud storage offerings.

The advantages of a P2P Cloud

Improved reliability than the “client-server” cloud. Much more cost effective because there is no need to

build expensive datacenters. The very fact that expensive datacenters are not needed

means even startups can be Cloud infrastructure players. This eliminates the possibility of few players holding the monopoly control over Cloud infrastructure services.

Easy scalability.（ Well, P2P based Cloud is a realistic possibility but it is not

clear if it will be more effective than the current “client-server” model. However, its reliability cannot be questioned and Skype is a good example for this. The technology is still inside the academic labs and it is a long way to go before we see its adoption on the commercial side.）

The application of P2P in File Sharing

The widely use of P2P file sharing system, such as Gnutella and Napster, is a hot buzzword recently. As a result, a lot of research has been done in the area of architectures. There are two types of P2P systems:1. One is the centralized peer-to-peer. Such as Napster and Seti@Home.2. The other one is decentralized Peer –to- Peer. The main representatives of this structure are Freenet and GNUtella.

Application layer security technology solutions

We will choose GNUtella as a typical example to explain how P2P file sharing system is worded.1.GNUtella's architecture is similar to Freenet's in that it is completely decentralized and distributed.(meaning that there are no central servers and that all computations and interactions happen between clients.) 2. All connections on the network are equal. (When a client wishes to connect to the network they run through a list of nodes that are most likely to be up or take a list from a website and then connect to how ever many nodes they want. This produces a random unstructured network.)

Routing

1. When a search request arrives into a client that client searches itself for the file and broadcasts the request to all its other connections2. all packets on the network start with a TTL (time to live)

How to download a file

1. Sending a HTTP packet requesting the file2. The client with the file interprets this and sends a standard HTTP response.To download a file the client creates a direct connection to the client with the file it wants

Mobile host as a serve

In P2P data networks, the mobile can be as a server that can be accessed by other peers. Hence, several problems attributed to wireless and mobile environment have to be solved differently.

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Solution--Role reversal

The problem of mobile host as a server primarily impacts connections either when the mobile host uses PSM or when the mobile host moves.Essentially, for both the problems in this category, the TCP connection ‘‘suffers‘‘ due to delays or disruptions, and the impact of the delays or disruptions can have a non-trivial impact even on the overall performance of the connection, especially when the file size or the remaining file size is small.

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Under role reversal, a mobile host acting as a server, upon detecting a connect request delayed by the PSM or a hand-off, explicitly issues a TCP-Reset to the corresponding peer for previous connection. Further, the mobile host re-initiates a new connection to that same peer, thus acting as the client. Once the new connection is setup, because of the bi-directional nature of the application semantics and the bi-directional nature of the TCP connection, the mobile host can serve the content as a server

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Failure of incentives

While P2P data networks heavily rely on incentives based mechanisms to encourage peers to contribute to the network, such mechanisms are not tailored for the unique characteristics of wireless and mobile environments. Specifically, the problems of upload-download self-contention and identity loss after mobility fall under this category of problems.

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Incentive aware operations

The problem of failure of incentives stems from the two distinct conditions of the self-contention in a wireless link and mobility-related identity loss. The incentive-aware operations principle in wP2P is used to address both problems.

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Essentially, one technique under incentive aware operations in wP2P involves the adaptation of the upload rate in order to find the smallest upload rate possible to achieve the maximum download rate. While this value for the upload rate is trivial to determine in a wired setting, a more sophisticated algorithm is required in a wireless environment.

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Thank you