Abstract: Placement of computation inside the network is a powerful computation model that can improve the overall performance of network applications. In this paper, we address the problem of providing sound and efficient system support for placing computation in a network router. We identify a set of requirements, related to protection, resource control, scheduling and efficiency, that are relevant to the design of this system support. We have developed a system that attempts to meet these requirements, and have used it to write a router application that performs aggregated congestion control.