We recently showed for peer-to-peer networks, that having the number of replicas of each object proportional to the request rate for these objects has many per-node advantages. In this paper we complement those results to show that this distribution has network-wide advantages as well. Given these benefits of proportional replication, the next issue is achieving proportional replication in a decentralized manner. We show that local storage management algorithms like LRU automatically achieve near-proportional replication and that the system performance with the replica distribution achieved by LRU is very close to optimal. We also show that the LRU responds to a change in user access pattern quickly (the number of accesses taken to reach the new steady-state replica distribution with LRU is close to the minimum possible with any cache replacement algorithm). Analytical models are provided for computing the steady-state network-wide replica distribution and the transient period for LRU.

Video-on-demand (VoD) service providers are intensely interested in transport, storage, streaming and caching in content delivery networks. Today’s 5,000-hour library may grow toward the 750,000-hour “Long Tail ” movie and TVseries catalog. We propose a method to calculate how much of a library should be cached. Much previous work focused on theoretical caching concepts, or the dynamics of cache filling and reclamation. Our method explicitly considers the impact of the available video server equipment; we present a VoD design tool comprising a novel cost function, hit ratio estimation and heuristic. 1.

IP network based deployments of interactive video-on-demand (VoD) systems are today very limited in scope, but there is a strong belief among telecommunication companies that this market will expand exponentially in the next few years. In this article, we outline the components of VoD architectures and survey the current approaches to their design. We strive to identify the research challenges that must be addressed in the development of design tools that can determine how to expand upon an existing network infrastructure to support video-on-demand. The long tail of content and extensive growth in usage are expected to have a major impact on the streaming and storage requirements of such systems. Hybrid VoD architectures that incorporate peer-to-peer exchange are an extremely promising paradigm, but there are many challenges in developing operational and economically feasible peer-to-peer systems. VoD networks generate sufficient traffic that their impact should be considered in planning general network infrastructure expansions.

Abstract. Large-scale Video-on-Demand (VoD) systems with high storage and high bandwidth requirements need a substantial amount of resources to store, distribute and transport all of the content and deliver it to the clients. We define an extension to the VoD equipment allocation problem as determining the number and model of VoD servers to install at each potential replica location to minimize deployment costs for a given set of distributed demand and available VoD server models. We propose three novel heuristics that generate near-optimal solutions and show that the number of replica sites for networks where the load is unevenly distributed is low (35 − 45 % of potential locations), but that the hit ratios at deployed replicas are high (> 85%). 1

Content Distribution Networks (CDNs) have gained considerable attention in the past few years. As such, there is need for developing frameworks for carrying out CDN simulations. In this paper, we present a modeling and simulation framework for CDNs, called CDNsim. CDNsim has been designated to provide a realistic simulation for CDNs, simulating the surrogate servers, the TCP/IP protocol and the main CDN functions. The main advantages of this tool are its high performance, its extensibility and its user interface which is used to configure its parameters. CDNsim provides an automated environment for conducting experiments and extracting client, server and network statistics. The purpose of CDNsim is to be used as a testbed for CDN evaluation and experimentation. This is quite useful both for the research community (to experiment with new CDN data management techniques) and for CDN developers (to evaluate profits on prior certain CDN installations).

Video-on-Demand (VoD) services are very user-friendly, but also complex and resource demanding. Deployments involve careful design of many mechanisms where content attributes and usage models should be taken into account. We define, and propose a methodology to solve, the VoD Equipment Allocation Problem of determining the number and type of streaming servers with directly attached storage (VoD servers) to install at each potential location in a metropolitan area network topology such that deployment costs are minimized. We develop a cost model for VoD deployments based on streaming, storage and transport costs and train a parametric function that maps the amount of available storage to a worst-case hit ratio. We observe the impact of having to determine the amount of storage and streaming co-jointly, and determine the minimum demand required to deploy replicas as well as the average hit ratio at each location. We observe that common video-on-demand server configurations lead to the installation of excessive storage, because a relatively high hit-ratio can be achieved with small amounts of storage so streaming requirements dominate.