Abstract: Content Delivery Networks (CDNs) have evolved to overcome the inherent limitations of the Internet in terms of user perceived Quality of Service (QoS) when accessing Web content. A CDN replicates content from the origin server to cache servers, scattered over the globe, in order to deliver content to end-users in a reliable and timely manner from nearby optimal surrogates. Content distribution on the Internet has received considerable research attention. It combines development of high-end computing technologies with highperformance networking infrastructure and distributed replica management techniques. Therefore, our aim is to categorize and analyze the existing CDNs, and to explore the uniqueness, weaknesses, opportunities, and future directions in this field. In this paper, we provide a comprehensive taxonomy with a broad coverage of CDNs in terms of organizational structure, content distribution mechanisms, request redirection techniques, and performance measurement methodologies. We study the existing CDNs in terms of their infrastructure, request-routing mechanisms, content replication techniques, load balancing, and cache management. We also provide an indepth analysis and state-of-the-art survey of CDNs. Finally, we apply the taxonomy to map various CDNs. The mapping of the taxonomy to the CDNs helps in “gap ” analysis in the content networking domain. It also provides a means to identify the present and future development in this field and validates the applicability and

Intermediary-based services and performance optimizations are increasingly being considered, by network service providers, with a view towards offering value-added services and improving the user experience of wireless mobile clients at reduced costs. However, in the presence of an end-to-end security mechanism such as IPsec, it is impossible to offer such services without fully compromising end-to-end security. We propose a new architecture to enable intermediarybased services for wireless mobile users while maintaining an acceptable level of end-to-end security. As a part of our architecture, we present a new IPsec option called Encapsulating Security Variable Payload (ESVP). We identify several important issues related to the architecture and discuss methods for addressing them.