Patterns of Network and User Activity in an Inhabited Television Event

Inhabited television takes traditional broadcast television and combines it with multiuser virtual reality to give new possibilities for interaction and participation in and around shows or channels. Out of This World was an experimental inhabited TV show, staged in Manchester in September of 1998, using the MASSIVE-2 system. During this event, we captured comprehensive records of network traffic and additional logs of user activity (in particular, movement and speaking). In this paper, we present the results of our analyses of network and user activity in these shows. We contrast our results with those obtained from previous analyses of teleconferencing-style scenarios. We find that the inhabited television scenario results in much higher levels of user activity and significant bursts of coordinated activity. We show how these characteristics must be taken into account when designing a system and infrastructure for applications of this kind. In particular, it is clear that any notion of strict turn-taking (and associated assumptions about resource sharing) is completely unfounded in this domain. We also show that the concept of “levels of participation” is a powerful tool for understanding and managing the bandwidth requirements of an inhabited television event

A domain specific language for dynamic interest management within virtual environments

Interest management is a widely used term within the area of virtual environments. It is so widely used that there even exist many synonyms for the concept. Thus both the terminology, and meaning of the concept are currently not well defined. The typical aim of interest management techniques within virtual environments has been to increase scalability. However, this thesis argues that the concept of interest management should not be so tightly coupled with the goal of scalable virtual environments, but be a concept in its own right, i.e. the management of interests. The main focus of this thesis is the representation of expressions of interest. The various techniques for expressing interest are surveyed and evaluated, providing the basis for the research into a suitable representation. This representation is achieved in two stages. The first part of this thesis introduces a novel dynamic interest management technique based upon set theory. It describes how it is expressive enough to implement most of the static interest management techniques currently available such as categorisation, locales, and interacting locales. By de-coupling the logic that implements these interests from the virtual environment, it can also describe how interests can be changed during the virtual environment's execution, thus making the technique dynamic. Enforcing and denying interests is also considered, allowing for the enforcement of interests integral to the requirements of the virtual environment. An example of this is denying the user the ability to be interested in artefacts that aren't visible. The new approach presented is implemented with SQL, and evaluated. The second part of this thesis focusses on the limitations of using SQL as an implementation language, focussing on issues of readability and succinctness and a lack of any abstraction mechanisms. Overcoming these limitations is treated as the primary design goal for a new domain specific language for representing interests. The thesis introduces this language, Wish, and evaluates it within the domain, demonstrating that it is as expressive as SQL yet is more readable, conceptually succinct and allows for arbitrary abstraction of complexity.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Scaleable audio for collaborative environments

This thesis is concerned with supporting natural audio communication in collaborative environments across the Internet. Recent experience with Collaborative Virtual Environments, for example, to support large on-line communities and highly interactive social events, suggest that in the future there will be applications in which many users speak at the same time. Such applications will generate large and dynamically changing volumes of audio traffic that can cause congestion and hence packet loss in the network and so seriously impair audio quality. This thesis reveals that no current approach to audio distribution can combine support for large number of simultaneous speakers with TCP-fair responsiveness to congestion. A model for audio distribution called Distributed Partial Mixing (DPM) is proposed that dynamically adapts both to varying numbers of active audio streams in collaborative environments and to congestion in the network. Each DPM component adaptively mixes subsets of its input audio streams into one or more mixed streams, which it then forwards to the other components along with any unmixed streams. DPM minimises the amount of mixing performed so that end users receive as many separate audio streams as possible within prevailing network resource constraints. This is important in order to allow maximum flexibility of audio presentation (especially spatialisation) to the end user. A distributed partial mixing prototype is realised as part of the audio service in MASSIVE-3. A series of experiments over a single network link demonstrate that DPM gracefully manages the tradeoff between preserving stable audio quality and being responsive to congestion and achieving fairness towards competing TCP traffic. The problem of large scale deployment of DPM over heterogeneous networks is also addressed. The thesis proposes that a shared tree of DPM servers and clients, where the nodes of the tree can perform distributed partial mixing, is an effective basis for wide area deployment. Two models for realising this in two contrasting situations are then explored in more detail: a static, centralised, subscription-based DPM service suitable for fully managed networks, and a fully distributed self-organising DPM service suitable for unmanaged networks (such as the current Internet)

Scaleable audio for collaborative environments

This thesis is concerned with supporting natural audio communication in collaborative environments across the Internet. Recent experience with Collaborative Virtual Environments, for example, to support large on-line communities and highly interactive social events, suggest that in the future there will be applications in which many users speak at the same time. Such applications will generate large and dynamically changing volumes of audio traffic that can cause congestion and hence packet loss in the network and so seriously impair audio quality. This thesis reveals that no current approach to audio distribution can combine support for large number of simultaneous speakers with TCP-fair responsiveness to congestion. A model for audio distribution called Distributed Partial Mixing (DPM) is proposed that dynamically adapts both to varying numbers of active audio streams in collaborative environments and to congestion in the network. Each DPM component adaptively mixes subsets of its input audio streams into one or more mixed streams, which it then forwards to the other components along with any unmixed streams. DPM minimises the amount of mixing performed so that end users receive as many separate audio streams as possible within prevailing network resource constraints. This is important in order to allow maximum flexibility of audio presentation (especially spatialisation) to the end user. A distributed partial mixing prototype is realised as part of the audio service in MASSIVE-3. A series of experiments over a single network link demonstrate that DPM gracefully manages the tradeoff between preserving stable audio quality and being responsive to congestion and achieving fairness towards competing TCP traffic. The problem of large scale deployment of DPM over heterogeneous networks is also addressed. The thesis proposes that a shared tree of DPM servers and clients, where the nodes of the tree can perform distributed partial mixing, is an effective basis for wide area deployment. Two models for realising this in two contrasting situations are then explored in more detail: a static, centralised, subscription-based DPM service suitable for fully managed networks, and a fully distributed self-organising DPM service suitable for unmanaged networks (such as the current Internet)