Experiences building a communication-oriented JavaOS

Mobile code makes it easier to maintain, debug, update, and customize a system. Active networks are one of the more interesting applications of mobile code: code is injected into the nodes of a network to customize the network's functionality, such as routing, and to add new features, such as special-purpose congestion control and filtering algorithms. The challenge is to develop a communication-oriented platform for such systems. We refer to mobile 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 computation. To this end, we have designed and implemented Joust, which consists of a complete re-implementation of the Java virtual machine (including both the runtime system and a just-in-time compiler), running on the Scout operating system (a configurable, communication-oriented OS). The result is a configurable, high-performance platform for running liquid software. We present the results of implementing two different applications of liquid software on Joust, including a prototype architecture for active networks.