Experiences building a communication-oriented JavaOS

Mobile code makes it easier to maintain, debug, update, and customize a sys tem. Active networks are one of the more interesting applications of mobile code: code Is injected into the nodes of a network to customize the networ k's functionality, such as routing, and to add new features, such as specia l-purpose congestion control and filtering algorithms. The challenge is to develop a communication-oriented platform for such systems, We refer to mob ile code targeted at low-level, communication-oriented systems like active networks as liquid software, the key distinction being that liquid software is focused on the efficient transfer of data, not high-performance computa tion. To this end, we have designed and implemented Joust, which consists o f a complete re-implementation of the Java virtual machine (including both the runtime system and a just-in-time compiler), running on the Scout opera ting system (a configurable, communication-oriented OS). The result is a co nfigurable, high-performance platform for running liquid software. We prese nt the results of implementing two different applications of liquid softwar e on Joust, including a prototype architecture for active networks. Copyrig ht (C) 2000 John Wiley & Sons, Ltd.