Editorial for special issue Internet-based Content Delivery

We are in the midst of an Internet computing revolution. One vision of 21st century computing is that users will access Internet services and ‘‘resource-hungry’’ applications (e.g. gaming, streaming media, video on demand, and voice-over-IP) over lightweight portable devices rather than through some descendant of the traditional desktop PCs. In this context, distributing and processing Internetbased data in an efficient and cost-effective manner is a challenging issue in Internet technology. Content Delivery Networks (CDNs) have emerged to overcome the inherent limitations of the Internet in terms of user perceived Quality of Service (QoS) when accessing Web data. They offer infrastructure and mechanisms to deliver content and services in a scalablemanner, and enhance users’Web experience. Specifically, a CDN is an overlay network across the Internet, which consists of a set of servers (distributed around the world), routers and network elements. Edge servers are the key elements in a CDN, acting as proxy caches that serve directly cached content to users. With CDNs, content is distributed to edge cache servers located close to users, resulting in fast, reliable applications andWeb services for the users. Once a user requests content on aWebprovider (managed by a CDN), the user’s request is directed to the appropriate CDN server. The perceived high end-user performance and cost savings of using CDNs have already urged many Web entrepreneurs to make contracts with CDNs. For instance, Akamai – one of the largest CDN providers in the world – claims to be delivering 20% of the world’s Web traffic. While the real numbers are debatable, it is clear that CDNs play a crucial role in the modern Internet infrastructure. The main value proposition for traditional CDN services has shifted over time. Initially, the focus was on improving end-user perceived experience by decreasing response time, especially when the customer Web site experiences unexpected traffic surges. Nowadays, CDN services are treated by content providers as away to use a shared infrastructure to handle their peak capacity requirements, thus allowing reduced investment cost in their own Web site infrastructure. Moreover, recent trends in CDNs indicate a