Techno-Economic Evaluation of CDN Deployments in Metropolitan Area Networks

The explosion of Video-on-Demand (VoD) traffic has been a main driving force behind the Internet's evolution from a traditional connection-centric network architecture towards the new content-centric network architecture. To support this evolution, operators are deploying caches of VoD contents closer to users across network equipments deployed in core, metro and even access network segments to mitigate the traffic growth and improve the VoD quality of service. The deployment of storage elements (caches) across the network to deliver contents to end users is known as a Content Delivery Network (CDN). For a CDN operator, it is important to minimize the cache-deployment cost while satisfying end users performance requirements. On one hand, deploying a high number of large caches closer to users improves the performance of a CDN (e.g., decreasing latency) but introduces huge capital and operational costs. On the other hand, deploying fewer caches in higher network segments introduces high operational costs due to high data traffic and might not satisfy future traffic demands, thus failing to meet users requirements. In this paper, we aim to identify the most cost-efficient cache deployment in CDN and to study the tradeoff between the CDN performance and cost. We propose a CDN cost model which takes into consideration the capital and operational expenditures of CDN devices (e.g., caches and video interfaces) and of traffic required to serve the end users. We examine the effect of the content popularity on the cost of CDN deployment strategies, showing that there are different optimal cache deployment strategies for different popularity distributions. Results show that deploying a huge number of large caches in the access segment optimizes the quality of service for end users but increases the operational expenditure. Instead, a CDN deployment which utilizes caches across both the access and metro segments achieves a more balanced solution in terms of both the overall performance and cost.