We propose a novel alternative to application-level overlays called VIOLIN, or Virtual Internetworking on OverLay INfrastructure. Inspired by recent advances in virtual machines, VIOLINs are virtual and isolated networks created on top of an overlay infrastructure such as PlanetLab. Entities in a VIOLIN include virtual routers, switches, and end-hosts, all implemented in software and hosted by physical overlay hosts. The salient features of VIOLIN include: (1) Each VIOLIN is a ‘virtual world’ with its own IP address space. And its activities and communications are strictly confined within the VIOLIN. (2) All VIOLIN entities can be created, deleted, or migrated on-demand. (3) It provides a new playground to deploy, leverage, and evaluate value-added network services which are not widely deployed in the real Internet. An application can simply connect to a VIOLIN and leverage the network services provided. (4) It releases application developers from network service implementation d...