Pathlet Routing

Source-controlled multipath routing can be highly beneficial to both sources and to network providers. For a source, the flexibility to choose among multiple paths can improve reliability and path quality. To a network provider, source-controlled routing could be a salable service. Unfortunately, the Internet's interdomain routing protocol, BGP, offers no multipath routing mechanism. Several proposals offer multiple paths, but are limited in the paths they can expose. This paper introduces a new scheme, pathlet routing, in which networks advertise fragments of end-to-end paths from which a source can assemble an end-to-end route. Pathlet routing is a flexible mechanism that, we show, can emulate a number of existing routing protocols, including BGP and unrestricted source routing. It also enables a new type of routing policy, local transit (LT) policies, which allows networks to control the portions of routes which transit across them, while giving a large amount of flexibility to sources. Finally, we show that LT policies have much better scalability than BGP.