4.1 Delivery Networks as Virtual Networks Conceptually, a delivery network is a virtual network built as a software layer over the actual Internet, deployed on widely distributed hardware, and tailored to meet the specific systems requirements of distributed applications and services Figure 2]. A delivery network provides enhanced reliability, performance, scalability and security that is not achievable by directly utilizing the underlying Internet. A CDN, in the traditional sense of delivering static Web content, is one type of delivery network. A different but complimentary approach to addressing challenges facing Internet applications is a clean-slate redesign of the Internet [32]. While a re-architecture of the Internet might be beneficial, its adoption in the real world is far from guaranteed. With hundreds of billions of dollars in sunk investments and entrenched adoption by tens of thousands of entities, the current Internet architecture will change slowly, if at all. For example, consider that IPv6—a needed incremental change—was first proposed in 1996 but is just beginning to ramp up in actual deployment nearly 15 years later. The beauty of the virtual network approach is that it works over the existing Internet as-is, requiring no client software and no changes to the underlying networks. And, since it is built almost entirely in software, it can easily be adapted to future requirements as the Internet evolves. Figure 2: A delivery network is a virtual network built as ab bsoftware layer over the Internet that is deployed on widely
