J. Sterbenz et al. (Eds.): IWAN 2002, LNCS 2546, pp. 253-266, 2002.  Springer-Verlag Berlin Heidelberg 2002 Flexible, Dynamic, and Scalable Service Composition for Active Routers Stefan Schmid, Tim Chart, Manolis Sifalakis, Andrew C. Scott Distributed Multimedia Research Group Computing Department Lancaster University, U.K. {sschmid, chart, mjs, acs}@comp.lancs.ac.uk Abstract. This paper describes a novel model for the provision of service com- posites for active routers. The service composition framework enables flexible programmability of the router’s data path through dynamically loadable soft- ware components, called ’active components’. The composition model promotes transparent and dynamic creation of network-side services and allows inde- pendent users to partake in this process. A prototype implementation has re- vealed that the composition model using packet filters and a classification graph structure as a means to integrate active components into the forwarding path enables the dynamic alteration of the elements of a composite at run-time and permits scalability in the generation of such composites. Furthermore, it allows the flexible provision of a unique service profile for each packet passing through an active router. We show that the overhead of this composition model does not significantly affect the performance of the router. 1 Introduction In recent years, many diverse and variously-focused frameworks sporting elements of active network solutions have emerged and established themselves. The majority of those platforms address only a subset of the issues that determine their utility outside of a laboratory environment, resulting in many being inflexible, poorly-performing, unscalable or insecure. Few active network solutions have considered the magnitude of the service composition model for real-life network environments and hence pro- vide only a limited flexibility for the composition of network services. Yet, in order for active networking to be considered a suitable technology for wide deployment over inter-networks, these issues must be addressed. A recent study by Hicks and Nettles [10] has revealed that even most extensible active router platforms lack sufficient flexibility in order to allow for true evolution. Such modular or plug-in based architectures typically limit the scope of future changes through pre-defined interfaces. Instead, true extensibility should not be limited to a fixed set of modules or plug-ins, but should rather allow modification and replacement of all components contributing to a service composite. This paper presents the service composition framework  a key component of the LARA++ [6] active router architecture  which attempts to provide a secure, safe,