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 userswill access Internet services and ‘‘resource-hungry’’ applications(e.g. gaming, streaming media, video on demand,and voice-over-IP) over lightweight portable devices ratherthan through some descendant of the traditional desktopPCs. In this context, distributing and processing Internetbaseddata in an efficient and cost-effective manner is achallenging issue in Internet technology.Content Delivery Networks (CDNs) have emerged toovercome the inherent limitations of the Internet in termsof user perceived Quality of Service (QoS) when accessingWeb data. They offer infrastructure and mechanisms to delivercontent and services in a scalable manner, and enhanceusers’ Web experience. Specifically, a CDN is an overlay networkacross 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, actingas proxy caches that serve directly cached content to users.With CDNs, content is distributed to edge cache servers locatedclose to users, resulting in fast, reliable applicationsand Web services for the users. Once a user requests contenton a Web provider (managed by a CDN), the user’s request isdirected to the appropriate CDN server. The perceived highend-user performance and cost savings of using CDNs havealready urged many Web entrepreneurs to make contractswith CDNs. For instance, Akamai – one of the largest CDNproviders in the world – claims to be delivering 20% of theworld’s Web traffic.1 While the real numbers are debatable,it is clear that CDNs play a crucial role in the modern Internetinfrastructure.