Past work on the active network architectural framework has focused on the NodeOS and Execution Environment (EE), which offer rather standard programming environments. As a result, Active Applications (AAs) must build the desired service from the ground up. Ideally, active applications could be built on higher-level active services that could themselves be "programmed". In this paper, we examine the issues involved in the design and implementation of higherlevel active network services. We

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... ibe the issues that arise when using AAs to implement these services and then present our experiences implementing one such service, namely concast, as an AA running on the ASP EE. The paper concludes with performance numbers obtained from an example audio-merge application that shows the viability of using AAs as specialized execution environments. ¡