Collaboration within a distributed interactive application (DIA) requires that a high level of consistency be maintained between remote hosts. However, this can require large amounts of network resources, which can negatively affect the scalability of the application, and also increase network latency. Predictive models, such as dead reckoning, provide a sufficient level of consistency, whilst reducing network requirements. Dead reckoning traditionally uses a spatial error threshold metric to operate. In previous work, it was shown how the use of the spatial threshold could result in potentially unbounded local absolute inconsistency. To remedy this, a novel time-space threshold was proposed, that placed bounds on local absolute inconsistency. However, use of the time-space threshold could result in unacceptably large spatial inconsistency. A hybrid approach that combined both error threshold measures was then shown to place bounds on both levels of inconsistency. However, choosing suitable threshold values for use within the hybrid scheme has been problematic, as no direct comparisons can be made between the two threshold metrics. In this paper, a novel comparison scheme is proposed. Under this approach, an error threshold look-up table is generated, based on entity speed and equivalent inconsistency measures. Using this look-up table, it is shown how the performance of comparable thresholds is equal on average, from the point of view of network packet generation. These error thresholds are then employed in a hybrid threshold scheme, which is shown to improve overall consistency in comparison to the previous solution of simply using numerically equal threshold values

Dead reckoning is widely employed as an entity update packet reduction technique in distributed interactive applications (DIAs). Such techniques reduce network bandwidth consumption and thus limit the effects of network latency on the consistency of networked simulations. A key component of the dead reckoning method is the underlying error threshold metric, as this directly determines when an entity update packet is to be sent between local and remote users. The most common metric is the spatial threshold, which is simply based on the distance between a local user's actual position and their predicted position. Other, recently proposed, metrics include the time-space threshold and the hybrid threshold, both of which are summarised within. This paper investigates the issue of user movement in relation to dead reckoning and each of the threshold metrics. In particular the relationship between the curvature of movement, the various threshold metrics and absolute consistency is studied. Experimental live trials across the Internet allow a comparative analysis of how users behave when different threshold metrics are used with varying degrees of curvature. The presented results provide justification for the use of a hybrid threshold approach when dead reckoning is employed in DIAs

Collaboration and competition are important factors of Networked Virtual Environments (NVE). Both require a certain level of consistency in order for the interaction to be fruitful and compelling. However, finite network bandwidth and communication delay are key factors affecting this aspect of interactivity. A popular method in their mitigation for dynamic entities is the IEEE DIS standard dead reckoning mechanism [1].

Human-to-human interaction across distributed applications requires that sufficient consistency be maintained among participants in the face of network characteristics such as latency and limited bandwidth. Techniques and approaches for reducing bandwidth usage can minimize network delays by reducing the network traffic and therefore better exploiting available bandwidth. However, these approaches induce inconsistencies within the level of human perception. Dead reckoning is a well-known technique for reducing the number of update packets transmitted between participating nodes. It employs a distance threshold for deciding when to generate update packets. This paper questions the use of such a distance threshold in the context of absolute consistency and it highlights a major drawback with such a technique. An alternative threshold criterion based on time and distance is examined and it is compared to the distance only threshold. A drawback with this proposed technique is also identified and a hybrid threshold criterion is then proposed. However, the trade-off between spatial and temporal inconsistency remains.

The hybrid strategy-based modeling approach is a method for reducing the number of network packets that need to be transmitted to maintain global consistency in Distributed Interactive Applications. It combines a short-term model such as dead reckoning with a long-term strategy model. A key aspect of this approach is to determine strategies that users adopt in navigating the simulated environment to satisfy some objective or goal. Computer-generated artificial entities called BOTS, navigate by employing an Artificial Intelligence technique called path finding. This paper proposes using the A* path finding algorithm to automatically compute strategies that human users might take through the simulated environment. Since the A* algorithm operates on a graph representation of the environment and because of the real-time constraints imposed on Distributed Interactive Applications, the paper also carries out a comparative analysis of two extreme graph representations of the environment — a standard regular grid and a minimal grid representation. The comparison shows that the minimal grid leads to an order of magnitude reduction in real-time computation compared to the regular grid. In addition the paths computed using the minimal grid and the A* algorithm are used to determine strategy models as part of the hybrid strategy-based modeling approach. It is shown that this reduces the network traffic required to maintain global consistency of entity dynamics in two simulated environments.

As Distributed Interactive Applications (DIAs) become increasingly more prominent in the video game industry they must scale to accommodate progressively more users and maintain a globally consistent worldview. However, network constraints, such as bandwidth, limit the amount of communication allowed between users. Several methods of reducing network communication packets, while maintaining consistency, exist. These include dead reckoning and the hybrid strategy-based modelling approach. This latter method combines a short-term model such as dead reckoning with a long-term strategy model of user behaviour. By employing the strategy that most closely represents user behaviour, a reduction in the number of network packets that must be transmitted to maintain consistency has been shown. In this paper a novel method for constructing multiple long-term strategies using dead reckoning and polygons is described. Furthermore the algorithms are implemented in an industry-proven game engine known as Torque. A series of experiments are executed to investigate the effects of varying the spatial density of strategy models on the number of packets that need to be transmitted to maintain the global consistency of the DIA. The results show that increasing the spatial density of strategy models allows a higher consistency to be achieved with fewer packets using the hybrid strategy-based model than with pure dead reckoning. In some cases, the hybrid strategy-based model completely replaces dead reckoning as a means of communicating updates.

Distributed Interactive Applications (DIAs) have been gaining commercial success in recent years due to the widespread appeal of networked multiplayer computer games. Within these games, participants interact with each other and their environment, producing complex behavioural patterns that evolve over time. These patterns are non-linear, and often appear to exhibit dependencies under certain conditions. In this paper, we analyse the behavioural patterns of two users interacting in a DIA. Our motivation behind this analysis is to construct models of user behaviour that can be used within Entity-State-Update (ESU) mechanisms. By representing their behaviour as time-series datasets, we investigate the use of simple statistical dependence measures to help partition the datasets and identify three different types of behavioural states exhibited by the two users. It is our intention that future research on ESU mechanisms can utilize this behavioural partitioning to reduce the network traffic in a DIA based on a hybrid-model approach.