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. Copyright © 2000 John Wiley & Sons, Ltd.

This paper reports on a set of experiments that measure the amount of CPU processing needed to decode MPEGcompressed video in software. These experiments were designed to discover indicators that could be used to predict how many cycles are required to decode a given frame. Such predictors can be used to do more accurate CPU scheduling. We found that by considering both frame type and size, it is possible to construct a linear model of MPEG decoding with R 2 values of 0.97 and higher. Moreover, this model can be used to predict decoding times at both the frame and packet level that are almost always accurate to within 25% of the actual decode times. This is a surprising result given the large variability in MPEG decoding times, and suggests that it is feasible to design systems that make quality of service guarantees for MPEG-encoded video. 1 Introduction The ability of modern processors to decode MPEG compressed video in realtime has led to users wanting to run a mix of application...

Scout is new communication-centric operating system. The principle scout abstraction (the path) is an attempt to capture all of the operating system infrastructure necessary to insure that a given network connection can achieve high and predictable performance in the face of other connections and other system loads.

USC is a new stub compiler that generates stubs that perform many data conversion operations. USC is flexible and can be used in situations where previously only manual code generation was possible. USC generated code is up to 20 times faster than code generated by traditional argument marshaling schemes such as ASN.1 and Sun XDR. This paper presents the design of USC and a comprehensive set of experiments that compares USC performance with the best manually generated code and traditional stub compilers.