The Case for Service Overlays

The Internet was designed as a packet-switched network in the 1960's and 1970's, with the explicit intent of sacrificing quality-of-service guarantees for an individual application in order to optimize channel usage and provide optimal median service for all applications. This approach was successful, since the application mix of the Internet heretofore has been dominated by applications with low quality-of-service needs: primarily bulk data transfer and low-bandwidth text- based interactive applications. As the Internet absorbs other networks and applications with strong quality-of-service requirements (television, voice over IP) , this tradeoff changes. We are faced with the problem of introducing the quality- of-service guarantees of circuit-switching into packet-switched networks. Fundamental change to the lower layers of the Internet stack have proven infeasible; even strongly-motivated, well-designed modifications which made transition a first-class design consideration have had difficult introductions. ATM and IPv6 are two recent examples. One effective transition strategy for new networking techniques has been the use of overlays. In this paper, we introduce the concept of a service overlay network, to offer circuit-switched behavior on legacy IP networks, and establish the requirements on the underlying IP network to make this strategy effective.