Content Delivery Network and Optimal Content Replication

• Main Authors: Chi-Hsuan Chao, 趙圻軒
• Other Authors: Shi-Chung Chang
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/w8svsn

碩士 === 國立臺灣大學 === 電機工程學研究所 === 92 === Client/Server Content Delivery Network (C/S CDN) is now commonly used by many Internet users. A C/S CDN replicates multimedia contents from an Origin Server to each surrogate scattered over the Internet. A request from a client for content is directed by a Request Routing System to a surrogate, which finds and delivers the requested content, and is located close to the client to reduce the client’s waiting time. Furthermore, the performance of content delivery improves as the traffic congestion at the Origin Server decreases. Issues of C/S CDN include content management and network performance. One aspect of content management is the design of the optimal number of “multimedia content replication” among surrogates. The architecture of network is crucial to the network performance. In this thesis, we first improve and design in detail the infrastructure of C/S CDN. We then focus on determining the optimal number of multimedia content replication. We improve the infrastructure of CDN in and design delicately each entity in the architecture. We simplify operating steps of clients. Clients can then get the requested content quickly. Unpopular multimedia content, which is does not have a copy at surrogates, is delivered from Origin Server to clients and is replicated in the Distribution System once a client requested for it. This procedure is advantageous to subsequent clients in getting multimedia content. In addition, we design that C/S CDN replicates popular multimedia content among surrogates so that clients can get the requested content immediately from surrogate close to clients after sending popular content requests. In this approach, the time for clients to get multimedia content decreases, and the loads of both internet and Origin Server are reduced so that internet bandwidth can be used effectively, and service efficiency increases. We present a model describing the tradeoff between delay and storage costs with respect to the number of replicating popular content in C/S CDN multimedia content replication problem. This problem is formulated as a convex optimization problem. Then, we solve the problem by numerical simulation and exhaustive search. Results are used to investigate the relationship between the number of replicating popular content, surrogates and service time for clients. In our analysis, we found that total cost and the ratio that a request gets the content from the surrogates increase as the number of replicating popular content become larger. At the same time, the load of Origin Server and Service Time decrease. With the increase in number of Surrogates, the total cost will increase, and service time will tend to decrease rapidly. If multimedia content replication is optimized, CDN service providers can make it easier and faster for clients to access the content without significant cost. We have constructed a simple C/S CDN and perform an experimental implementation design according to the architecture, which we improved and designed delicately. This simple C/S CDN, which provides non-streaming content, satisfies clients’ demand and content provides’ expectation. Request Routing System, Distribution System and Surrogates are implemented with Linux operation system. On the other hand, Origin Server is implemented with Window XP operation system. Every entity connects with each other by Secure Shell (SSH) or transfer data by File Transfer Protocol (FTP). Request Routing System, Distribution System and Surrogates have MySQL databases which store multimedia files’ name. Experimental result shows that this network architecture can work and reduce waiting time for clients