Dag Johansen

NAP: practical fault-tolerance for itinerant computations

One use of mobile agents is support for itinerant computation (D. Chess et al., 1995). An itinerant computation is a program that moves from host to host in a network. Which hosts the program visits is determined by the program. The program can have a pre-defined itinerary or can dynamically compute the next host to visit as it visits each successive host; it can visit the same host repeatedly or it can even create multiple concurrent copies of itself on a single host. Itinerant computations are susceptible to processor failures, communications failures, and crashes due to program bugs. NAP is a protocol for supporting fault tolerance in itinerant computations. It employs a form of failure detection and recovery, and it generalizes the primary backup approach to a new computational model. The guarantees offered by NAP as well as an implementation for NAP in TACOMA are discussed.

Mobile Agent Applicability

In this paper, we present experiences from building several mobile agent based distributed applications using the agent system TACOMA. Our hope is to demonstrate mobile agent applicability potential through some real and concrete examples. We conclude that mobile agents, even if they simplify remote installation of software, basically complement other structuring techniques in distributed applications.

Distributed event stream processing with non-deterministic finite automata

Efficient matching of incoming events to persistent queries is fundamental to event pattern matching, complex event processing, and publish/subscribe systems. Recent processing engines based on non-deterministic finite automata (NFAs) have demonstrated scalability in the number of queries that can be efficiently executed on a single machine. However, existing NFA based systems are limited to processing events on a single machine. Consequently, their event processing capacity cannot be increased by adding more machines. In this paper, we present an experimental evaluation of different methods for distributing an event processing system that is based on NFAs across multiple machines in a cluster. Our results show that careful input stream partitioning gives close to linear performance scaleup for CPU bound workloads.

A TACOMA retrospective

For seven years, the TACOMA project has investigated the design and implementation of software support for mobile agents. A series of prototypes has been developed, with experiences in distributed applications driving the effort. This paper describes the evolution of these TACOMA prototypes, what primitives each supports, and how the primitives are used in building distributed applications. Copyright

DAVVI: a prototype for the next generation multimedia entertainment platform

In this demo, we present DAVVI, a prototype of the next generation multimedia entertainment platform. It delivers multi-quality video content in a torrent-similar way like known systems from Move Networks, Microsoft and Apple do. However, it also provides a brand new, personalized user experience. Through applied search, personalization and recommendation technologies, end-users can efficiently search and retrieve highlights and combine arbitrary events in a customized manner using drag and drop. The created playlists of video segments are then delivered back to the system to improve future search and recommendation results. Here, we demonstrate this system using a soccer example.

Bagadus: an integrated system for arena sports analytics: a soccer case study

Sports analytics is a growing area of interest, both from a computer system view to manage the technical challenges and from a sport performance view to aid the development of athletes. In this paper, we present Bagadus, a prototype of a sports analytics application using soccer as a case study. Bagadus integrates a sensor system, a soccer analytics annotations system and a video processing system using a video camera array. A prototype is currently installed at Alfheim Stadium in Norway, and in this paper, we describe how the system can follow and zoom in on particular player(s). Next, the system will playout events from the games using stitched panorama video or camera switching mode and create video summaries based on queries to the sensor system. Furthermore, we evaluate the system from a systems point of view, benchmarking different approaches, algorithms and tradeoffs.

Low overhead container format for adaptive streaming

Current segmented HTTP streaming systems provide scalable and quality adaptive video delivery services to a huge number of users. However, while they support a wide range of bandwidths and enable arbitrary content-based composition, their current formats have shortcomings like large overheads, live streaming delays, etc. We have therefore developed an adaptive media player that works around these problems while still using standard components like H.264/AVC for video, and MP3 for audio. The systems adaptivity allows the player to pick a quality level that makes good use of available bandwidth and CPU resources while at the same time maintaining smooth uninterrupted playback, as well as offering near instant seek and startup times. This paper presents an appropriate way of coding the segments and a simple multimedia container format that is optimized for adaptive streaming and video composition over HTTP. We show that our format is sufficiently advanced to contain any payload type, while being trivial to parse and translate to other container formats. Additionally, we show that our format is second to none in terms of overhead, without incurring any penalties on live streaming.

Bagadus: An integrated real-time system for soccer analytics

The importance of winning has increased the role of performance analysis in the sports industry, and this underscores how statistics and technology keep changing the way sports are played. Thus, this is a growing area of interest, both from a computer system view in managing the technical challenges and from a sport performance view in aiding the development of athletes. In this respect, Bagadus is a real-time prototype of a sports analytics application using soccer as a case study. Bagadus integrates a sensor system, a soccer analytics annotations system, and a video processing system using a video camera array. A prototype is currently installed at Alfheim Stadium in Norway, and in this article, we describe how the system can be used in real-time to playback events. The system supports both stitched panorama video and camera switching modes and creates video summaries based on queries to the sensor system. Moreover, we evaluate the system from a systems point of view, benchmarking different approaches, algorithms, and trade-offs, and show how the system runs in real time.

Ubiquitous devices united: enabling distributed computing through mobile code

A problem with a ubiquitous device like a cellular phone is that it is not properly integrated with contemporary distributed systems. Our goal is to improve this, by enabling cellular phones as interacting clients in a distributed system. We have devised an architecture with two main components: 1) A cellular phone, and 2) a remote extensible server based on a mobile code system. The cellular phone link provides a communication channel to the remote extensible server. This channel is used both for extending remote servers with mobile code and for event notification from remote servers. We have built a prototype weather alarm system, to illustrate the functionality of the architecture. Our prototype system is in daily use, and may be accessed and used by anyone from the World Wide Web.

Muithu: Smaller footprint, potentially larger imprint

We describe our experience with the Muithu sports notational analysis system, a novel digital information system in the popular sports domain. The system integrates real-time coach notations with related video sequences, and is configured with small, off-the-shelf and cheap components. Muithu requires little or no human post-processing, which is in strong contrast to state of the art resource-intensive competing systems. Muithu also provides a novel social network for athletes and their coaches for information management and interactive e-learning experiences based on video footage. This next generation notational analysis system is already in operational use by a Norwegian elite soccer club, both for training and game events.