On the detection of network traffic anomalies in content delivery network services

Today´s Internet traffic is largely dominated by major content providers and highly distributed Content Delivery Networks (CDNs). Internet-scale applications like Facebook and YouTube are served by large CDNs like Akamai and Google CDN, which push content as close to end-users as possible to improve the overall performance of the applications, minimize the effects of peering point congestion and enhance the user experience. The load is balanced among multiple servers or caches according to non-disclosed CDN internal policies. As such, adopting space and time variant policies, users´ requests are served from different physical locations at different time. Cache selection and load balancing policies can have a relevant impact on the traffic routed by the underlying transport network, as well as on the end-user experience. In this paper, we analyze the provisioning of two major Internet applications, namely Facebook and YouTube, in two datasets collected at major European Internet Service Providers (ISPs). First, we show how the cache selection performed by Akamai might result in higher transport costs for the ISP. Second, we present evidence on large-scale outages occurring in the Facebook traffic distribution. Finally, we characterize the variation of YouTube cache selection strategies and their impact on the users´ quality of experience. We argue that it is important for the ISP to rapidly and automatically detect such events. Therefore, we present an Anomaly Detection (AD) system for detecting unexpected cache-selection events and changes in the traffic delivered by CDNs. The proposed algorithm improves over traditional AD approaches by analyzing the complete probability distribution of the monitored features, providing higher visibility and better detection capabilities.