The last years have witnessed a dramatic growth in the number as well as in the variety of distributed virtual environment systems. These systems allow multiple users, working on different client computers that are interconnected through different networks, to interact in a shared virtual world. One of the key issues in the design of scalable and cost-effective DVE systems is the partitioning problem. This problem consists of efficiently assigning the existing clients to the servers in the system and some techniques have been already proposed for solving it. This paper experimentally analyzes the correlation of the quality function proposed in the literature for solving the partitioning problem with the performance of DVE systems. Since the results show an absence of correlation, we also propose the experimental characterization of DVE systems. The results show that the reason for that absence of correlation is the nonlinear behavior of DVE systems with regard to the number of clients in the system. DVE systems reach saturation when any of the servers reaches 100 percent of CPU utilization. The system performance greatly decreases if this limit is exceeded in any server. Also, as a direct application of these results, we present a partitioning method that is targeted to keep all the servers in the system below a certain threshold value of CPU utilization, regardless of the amount of network traffic. Evaluation results show that the proposed partitioning method can improve DVE system performance, regardless of both the movement pattern of clients and the initial distribution of clients in the virtual world.

Distributed virtual environment (DVE) systems allow multiple users working on different client computer's interconnected through different networks to interact in a shared virtual world. In these systems, latency is crucial for providing an acceptable quality of service (QoS), since it determines how fast client computers are reported about changes in the shared virtual scene produced by other client computers. This paper presents in a unified manner a partitioning approach for providing a latency below a threshold to the maximum number of users as possible in DVE systems. This partitioning approach searches the assignment of avatars, which represents the best trade-off among system latency, system throughput, and partitioning efficiency when solving the partitioning problem. Evaluation results show that the proposed approach not only maximizes system throughput, but also allows the system to satisfy, if possible, any specific latency requirement needed for providing QoS. This improvement is achieved without decreasing either image resolution or quality of animation, and it can be used together with other techniques already proposed. Therefore, it can contribute to provide QoS in DVEs.

The design flow of network-on-chip (NoCs) include several key issues. Among other parameters, the decision of where cores have to be topologically mapped and also the routing algorithm represent two highly correlated design problems that must be carefully solved for any given application in order to optimize several different performance metrics. The strong correlation between the different parameters often makes that the optimization of a given performance metric has a negative effect on a different performance metric. In this paper we propose a new strategy that simultaneously refines the mapping and the routing function to determine the Pareto optimal configurations which optimize average delay and routing robustness. The proposed strategy has been applied on both synthetic and real traffic scenarios. The obtained results show how the solutions found by the proposed approach outperforms those provided by other approaches proposed in literature, in terms of both performance and fault tolerance.