A New Web Service Structure of Combining P2P and CDN Technologies

Transcription

1 A New Web Service Structure of Combining P2P and CDN Technologies Junjie Tong Ke Xu Renjie Pi Abstract Nowadays, streaming media and web pages have occupied the most bandwidth on the Internet. And it s important to remain the scalability, performance, fairness and resources management potential while providing the Web Service. In this paper, we have proposed a new Web Service Structure of Combining P2P and CDN Technologies. By building a P2P Content Distribution Network (CDN), peers collaborate to distribute the content of under provisioned websites and to serve queries for larger audiences on behalf of the websites. This can reveal very challenging, given the highly dynamic and autonomous participation of peers. And it also can be used to implement in Cloud Computing and Cloud Storage. Keywords Web Service, P2P, CDN 1. Introduction The motivation behind basing applications on peerto-peer technology derives to a large extent from their ability to function, scale, and self-organize in the presence of a highly transient population of nodes, network, and computer failures, without the need of a central server and the overhead of its administration. Such peer-to-peer architectures typically have as inherent characteristics scalability, resistance to censorship and centralized control, and increased access to resources. [1]These architectures sharing of computer resources (content, storage, and CPU cycles) by direct exchange, rather than requiring the intermediation or support of a centralized server or authority. Peer-to-peer architectures are characterized by their ability to adapt to failures and accommodate transient populations of nodes while maintaining acceptable connectivity and performance. But there also many challenges or drawbacks to implement P2P applications to afford efficient and comfortable web service for the users. A key challenge pertains to the conflicting interests faced by network and content service providers and the costs between different ISP. [2]It also lacks controllability and manageability. The CDN technology is to insert a new network overlay between the Internet and the clients by deploying a large number of CDN servers at the edge of the Internet. And publish the contents to the nearest and proper servers to provide service for the users by deploying its intelligent statistics. By using this technology, the contents on the Internet can be accelerated, and we can provide low latency Web Service exceeding the limits of the bandwidth, adapting to dynamic interviewing and accelerating distant websites under control. CDN servers are expensive to deploy and maintain. The storage space and out-bound bandwidth allocated to each media file are limited and incur a cost. Current solutions to lowering such cost usually compromise the media quality delivered. [3] In the following Table1, we can see the compassion between CDN technology and P2P technology. Table1. Comparison CDN P2P Scalability High-cost Low-cost Server Bandwidth Large Consumption Low Consumption Cost High Low Concurrent Clients Limited Unlimited Content Copyright Controllable Uncontrollable QoS service Under Control No Advantage Web Multimedia Acceleration Distributing Although there are drawbacks both in P2P technology and CDN technology, but by building a P2P Content Distribution Network with a new This work is financially supported by Program for New Century structure, Excellent we Talents can combine University, the No.NCET ; two technologies and National Key project of Scientific and Technical Supporting Programs of China (2008BAH24B04); and the innovation technology star program of Beijing under grant No.2007A /10/$ IEEE 475

2 advantages well. In this paper, we propose a new web service structure of combining P2P and CDN technologies. And we also propose corresponding mechanisms and technologies for combining the two technologies to provide efficient and robust web services for the users. 2. A New Web Service Structure In this section, we have proposed a new web service structure and given a comprehensive exposition. At last, we ll describe a specific architecture basing on this new 2.1 The New Structure This new structure has combining P2P technology and CDN technology oriented to providing efficient and good web service for the users. In this structure, it has three layers. We can see it clearly through the following figure 1. Communicating Module Applications Virtual Disk API Accelerating Module Figure 1. The Structure Layers First, we have to define several roles or entities for the User who is the client of the application is served by the edge servers which are in an overlay networks basing on certain DHT algorithm. Then let s start to explain the structure from the bottom to the top. The communicating module is to providing the communicating function for the users and the servers in the Internet. For the users, its functions are to provide normal communication between the users and the edge servers. Users can also use it to request and retrieve the contents and manage the buffer. For the edge servers, it has to manage the communications between the servers. And in the acceleration module, our purpose is to use the CDN to accelerate various data communication. It has to implement the DHT algorithm and provide the interfaces for the communicating module for the communication between the servers and web services for the users through the CDN. The next layer is the virtual disk API which is provided for the developers. We can develop various applications basing on this API without thinking about the specific implementation of the lower lays. It s efficient for the developers and another important feature is that it is a disk API. So we can operator it like a local file and we can get the web pages as getting a local page. The application layer is open, and that means it is open to all developers. We can develop the applications for our own needs. Here we suppose that the application on the user node is a file system which using this virtual disk API. Although we have described this structure, it s hard to understand it fully and deeply. So in the next part, we ll try to probe a specific design basing on this new 2.2 A Specific Architecture basing on it There are many ways to combine the P2P technology and the CDN technology. In this part, we ll probe a specific architecture basing on the given new There many schemes have been proposed [4]. And we adjust one of them. It is described as that at first construct the P2P overlay networks over the servers in the CDN, and the source servers deliver the contents to the CDN servers. Then the users can retrieve the contents from the edge servers. We can see it clearly from the figure 2. Figure 2. Overview of the Architecture As is described ahead, we have implemented the DHT algorithm to construct the peer-to-peer overlay networks in the CDN. And it s a real question to choose which algorithm to use. We can see the comparisons between different algorithms in reference [5]. And beside the Chord algorithm, CAN algorithm, Pastry system and Tapestry referred in that article, there are also Kademlia algorithm [6] based on the 476

3 XOR metric, DSHT (Distributed Sloppy Hash Table) [7] and so on. During these algorithms, Kademlia algorithm and the DSHT have been used in the business field. Kademlia algorithm has been used in emule and the DSHT has been used in the CoralCDN. Here we adopt the former one. So the communications between the CDN servers have implemented the P2P technology while the CDN servers can accelerate the contents through the networks. 3. Corresponding Mechanisms and Technologies Although we have proposed the structure and given a specific design basing on it, it s important to give the corresponding mechanisms and technologies to provide efficient and robust web service for the users. In this section we have proposed several mechanisms and technologies for this 3.1 Caching Mechanism on the CDN Server While the CDN edge server is serving a user, if there is a content request from the user. The CDN edge server will look for the sources for the user. And it will try to download the contents for the user or return the list of the specific CDN servers to the user. As the contents are published to the P2PCDN overlay networks through the specific algorithm or a random strategy. There will not be a whole file memorized in a single CDN server as we have to balance the overloads on the CDN servers. So we have to exchange the file fragment or block information between the CDN servers. We can use the Gossip algorithm, and this algorithm is described and explored in reference [8]. After finding the CDN servers which have the requested contents fragments or blocks, the CDN edge server will try to retrieve the contents and may cache some parts or not. By using this cache mechanism on the CDN servers, we have considered the distance between the CDN edge servers and the CDN servers which have the resources. As the P2PCDN overlay networks is built on the existing networks which may across several different ISP or sites, if we find that the CDN edge server is not in the same site as the CDN servers which have the resources and the content is request first time. There will be a fail record set up in the edge server while the edge server doesn t cache any part of the contents. The fail record has a timeout and a counter which record the content failing times. When the counter has reached a specific number which means there will be many users downloading the same file at the same time. It will be necessary and efficient to cache parts of the contents on the edge server. The size of the parts depends on the resources of this CDN edge server. 3.2 Technology of Publishing the Web Service In recent years, Service Oriented Architecture (SOA) has raised a new round of net-revolution. And it is important and meaningful to implement the Web Service in our structure and design. There is a model [9] which defined a web service as a triple, p= {I, S, R}, such that: I is the implementation of p represented as a finite automaton, S is the service finite automaton, and R is the set of request finite automata. And then the web services will be published to the CDN. We can adjust this technology to implement it in our structure or design. By using the technology of publishing the Web service, first we give every Web service an individual tag or definition. And every Web service contains a series of operations. Supposing that we adopt the Kadmedia to construct the P2PCDN overlay networks. Then we can hash the Web service s definition and then publish it to the nearest CDN server. While the Web Service lies in its using of centralized UDDI service publish and search mechanism before, now we can use the DHT algorithm to publish and search it easily. And we can clearly see the differences between the two computing model Web Service and P2P in the Service Oriented Architecture [10]. The users can only use the authorized Web Services which are published in the P2PCDN overlay networks. And when the Web Service is first published to the P2PCDN overlay networks, we cache it to the one of the nearest CDN serves of the first one. So if the first one is failed or break down, we can use that one to serve the users. And when the first one is on a heavy load, we can use the excessive one to do the load balancing. And here we have pointed out that the Web Service is not the same with the contents downloading and accelerating. We just use the CDN servers resources to compute for the service providers, and the Web Services can t be cached in the CDN servers. It is considered as an entirety in this network. And the CDN servers should recognize the operations of the Web Service. So we can implement a Web Service platform on the P2PCDN overlay networks. And then open the interface to provide the service, which will reduce the additional overhead to implement the specific interfaces of the Web Service on the CDN servers. It will be good for the extendibility and controllability. 477

4 3.3 Web Page Accelerating Mechanism The web pages can be divided into two main kinds static and dynamic. The difference between is that there is whether communication between the web site and the users or not. We use our namespace in this First, we have to identify all the web pages by giving an individual tag or identity. For the static web pages, we can consider it as a file on the P2PCDN overlay. And we hash the web page s tag to publish it on the P2PCDN overlay networks. And the web page file can t be divided into fragments or blocks, which means that we can t cache it partially. And for the dynamic web page which means that the users may communicate with web servers. Many CDN overlay networks have adopt the technology of redirection to accelerate the web pages. But if a large number of the users are interviewing the same pages at the same time, it s hard to do the load balance and provide the accelerating service well. In this structure, we first publish the static part to the P2PCDN overlay networks by using the DHT algorithm. The key point of communication between the web servers and the users is that we have to use the database which located on the web servers. When the web page is published to the CDN servers, we have the database information added in the static part. So the CDN servers can obtain the authority to obtain data from the database on the web server. That may cause the latency as interviewing the database from a random distant server, but it will reduce the load of the web sites, and make it much more scalability, fault-torrent and efficient relatively. An important problem which is not described clearly is how to identify the tag or identity of the web pages. By using this technology, people can use this overlay to publish their web pages which have to name their pages under our own regulations. It likes a private web page publishing and interviewing protocol. And we can even develop our tools for writing or design the web pages as we can pass them to the users as a file. But it needs us to provide a integrate platform for the web pages, and it can be discussed further. In this part, we have illustrated the web page accelerating mechanism. We can provide the accelerating service well by implementing this 4. Features of This Structure We have proposed a new web service structure and then give a specific design basing on this At last we propose corresponding mechanisms and technologies of this In this section, we list the features of this structure by considering the abovementioned things. Localize the contents. The P2PCDN overlay networks receive the contents from the source servers by using the DHT algorithm. Caching and copying the contents on the CDN servers too. This makes the overlay scalability, fault tolerance capability and high performance. And users can interview the contents or files like getting the local files. Using the opening API simply. As the virtual disk API is open to the users, people can easy to develop their applications by using the integrate interfaces. And this virtual disk API makes users can interview the file or contents like getting or interviewing the local files. It provides the almost the same interfaces as the local disk s. So it s simple for people to understand and use this API. Compatible and meaningful to the SOA. As we can publish the Web Service or a whole serve platform to the P2PCDN overlay networks. We just use the resources of the CDN servers to provide the computing and memorize functions for the users when we provide the web services for the users. We consider the Web Service as a series of operations and these operations can t be separated. Users can obtain the integrate Web Service through this Easy to extension. We can implement the whole structure on the users while we implement the structure on the CDN servers without the virtual disk API layer. But the users don t join the P2PCDN overlay networks as we have closed corresponding functions ahead. But if we want to construct P2P overlay on the edge of the P2PCDN s edge or between the users to extent the overlay or accelerate the contents on the edge, we can open corresponding functions to the users. But we have to set up corresponding mechanism to make it easy to manage and control. At this section, we propose the four main features of this structure and describe them briefly. As the openness and scalability of this structure, we can add functions or ideas to it easily. And that means the unpredictable functions and growing features of this 5. Outlooks of This Structure Recently, the cloud computing and cloud storage have raised and are given a lot of attention. Many works have been done by many universities and research centers. And the number of the universities and the research centers grows fast as more and more people recognize the advantages of the two technologies and consider them as the potential web service mode in the future. 478

5 There have been the architectures which combine the P2P technology or orient for the Web Service. There has proposed a cloud computing platform [11]. And it gives a new cloud storage architecture based on P2P and designs a prototype system. And a Service- Oriented Cloud Computing Architecture (SOCCA) has been proposed after survey the current cloud computing architectures [12]. We have proposed this new web service structure which can publish the web service and provide the computing ability for the web service and storage ability for the contents. It s potential and easy to construct a cloud computing platform basing on this new As the cloud computing emphasizes the computing capability and storage capability, we can provide the computing capability through providing the web service and storage capability through storing the contents on the P2PCDN overlay networks. 6. Conclusion In this paper, we have proposed a new web service structure of combining the P2P and CDN technologies. By implementing this structure and the corresponding mechanisms and technologies, we can optimize and facilitate most of web services provided for the users. We have listed the features of using this And it can be easily extended to construct a cloud computing platform basing on it. And it can provide both the computing ability and the storage ability for the users and service providers. 7. Reference [1] Stephanos Androutsellis-Theotokis and Diomidis Spinellis, A survey of peer-to-peer content distribution technologies, ACM Computing Surveys (CSUR), volume 36, Dec.2004, pp [2] Jiangchuan Liu, Sanjay G.Rao, Bo Li and Hui Zhang, Opportunities and Challenges of Peer-to-Peer Internet Video Broadcast, Proceedings of the IEEE, volume 96, No.1, January [3] Dongyan Xu, Heung-Keung Chai, Catherine Rosenberg, and Sunil Kullarni, Analysis of a Hybrid Architecture for Cost-Effective Steaming Media Distribution, Multimedia Systems, volume 11, number 4, 17 March [4] Yihui Ma, Hongbo Wang, and Shirui Cheng, Combining P2P with CDN Technology in Streaming Media Services, Information and Communications Technologies, 2008(06), pp [5] Ke Xu, Yongqiang Xiong, and Jianping Wu, Research of Peer-to-Peer Network: A Survey, 20p2p.pdf. [6] Petar Maymounkov and David Mazieres, Kademlia: A Peer-to- peer Information System Based on the XOR Metric, In Proceedings of the 1st International Workshop on Peer-to-Peer Systems(IPTPS 02), March 2002, pp [7] Michael J.Freedman, and David Mazieres, Sloppy hashing and self-organizing clusters, In Proc.2nd Intl. Workshop on Peer-to-Peer Systems (IPTPS 03) Berkeley, CA, February [8]Stephen Boyd, Arpita Ghosh, Balaji Prabhakar, and Devavrat Shah, Gossip Algorithms: Design, Analysis and Applications, Computer and Communications Societies. Proceedings IEEE, volume 3, 2005, pp [9] Fatih Emekci, Oagur D.Sahin, Divyakant Agrawal and Amr El Abbadi, A peer-to-peer framework for Web service discovery with ranking, IEEE International Conference on Web Services, 2004, pp [10] Baohua Jin and Dongyao Zou, Research of Web Service Based on P2P, ICCSN 10 Second International Conference on Communication Software and Networks, March 2010, pp [11] Ke Xu, Meina Song, Xiaoqi Zhang and Junde Song, A Cloud Computing Platform Based on P2P, IEEE International Symposium on IT in Medicine & Education, Aug 2009, pp [12] Wei-Tek Tsai, Xin Sun and Janaka Balasooriya, Service-Oriented Cloud Computing Architecture, ITNG Seventh International Conference on Information Technology, April 2010, pp