A Review On Content Delivery Network

With the advent of services and applications such as media streaming over the Internet, speed and reliability have become critical issues for users. Content delivery networks (CDNs) are (overlay) networks that are designed to distribute files to a set of clients. Through approaches such as replication of content at multiple servers (proxies) and redirection of user requests to closer servers, content delivery networks (CDNs) attempt to minimize latency at the user-end while reducing bandwidth consumption and load at the origin server. By sharing the load among various locations closer to the user-end, CDNs can deliver content to users in a timely manner. Content replication enhances robustness so that CDNs can maintain reliable service in case of failures. As streaming media is already a multi-billion dollar industry and will probably be a dominant application in the future, the amount and nature of traffic it generates should be considered during the design of content-delivery networks. The delivery of streaming media causes new problems that did not apply to the distribution of HTTP objects: streaming objects are much larger than web objects and hence create much more traffic [1]. Furthermore, it is no longer possible to assume infinite storage size at the replica locations which makes calculations less trivial [2]. If implemented over existing network architectures, CDNs are a form of overlay network; their design consists of resource allocation decisions and the development of a combination of intelligent routing, performance monitoring and careful caching strategies. It is questionable whether even the best such design is scalable to scenarios where millions of geographically-distributed users are requesting on-demand video. When it is possible to augment or replace the existing underlying network, new challenges present themselves; ideally, the CDN traffic should be explicitly considered during topology design. We plan to address the two challenges of (i) designing a CDN that operates over an existing network with known architectural properties, and (ii) performing the dual design of a metro-area agile all-photonic network (AAPN) [3] and CDN. As a first step, it is valuable to review the solutions proposed in the literature regarding the delivery of multimedia objects. This technical report serves that purpose and is organized as follows. Section II presents the parameters, constraints and various algorithms to solve the replica location and content allocation problem. Section III surveys various traffic models and file popularity distributions. Section IV covers the techniques used for request routing and content delivery. Finally, section V discusses the implementation of content delivery in an AAPN. II. TOPOLOGY DESIGN