The next step in the evolution of active networks-one that will support radical new uses of the network and increased scalability-is to package the power of a programmable network platform into customizable active services that are easy for applications to use. The Activecast project has developed and is evaluating a set of active services that will not only enhance the "application-friendliness" of active networks, but will also improve the scalability and usability of networks in general.

This paper discusses the challenges of programming active net-works and then presents four new active network services, PAM-cast, Concast, ESP, and LWP, that simplify the task of programming active networks. PAMcast services allow messages to be sent to any node(s) satisfying a set of user-supplied selection criteria. The Concast service provides the logical inverse of multicast, gathering and merging data from a set of senders. Finally, the ESP and LWP services provide extremely lightweight building-blocks on which additional higher-level semantic services can be constructed. For each service, we describe the service abstraction, the ways in which users can customize the service, and its ease of use (i.e., how the customized service is automatically distributed across and "programmed" into the network on the user's behalf). We also present results from simulation models and actual Implementations of the new services that demonstrate the scalability And performance of the services.