Virtual distributed environments in a shared infrastructure

This chapter describes our approach to handle security in a complex Distributed Virtual Environment (DVE). The modules of such an environment all need to be concerned about security. An object-oriented model of a DVE allows us to capture security in an aspect-oriented fashion as a crosscutting concern among the multiple modules. As DVEs become more complex in content, distribution, and capabilities, the security requirement emerges as a key issue in their design and implementation. In order to control the software complexity, our strategy is to model and analyze the impact of security concerns on the functional model of DVEs via an aspect-oriented technique. This approach is appropriate to be applied at both the system design and modeling stages and provides guidance during the implementation stage. This chapter illustrates an aspect-oriented approach to the impact analysis of security concerns upon the functionalities of DVEs. A design-level security model for DVEs is provided to show how to weave security concerns into the models of DVE designs seamlessly.

In this paper, we design and implement a prototype system with an adaptive intra-media synchronization scheme for haptic interactions in distributed virtual environments (DVEs). In order to interact with haptic interfaces in the DVEs, we require a stringent level of QoS service from the network. Especially, network delay jitter and packet loss over the Internet may seriously degrade the output quality of haptic media in the DVEs. The proposed system model consists of three layers (application, synchronization, and network) to support haptic interactions over time-varying IP networks. The intra-media synchronization scheme implemented in the system controls buffering time and transmission rate to enhance the QoS of networked haptic interactions. To demonstrate usefulness of the proposed scheme, we simulate it by using NS-2 simulator and implement simple haptic-based DVEs. According to the simulation results, the proposed scheme provides more stable playout of haptic data under network delay jitter. Moreover, when lots of clients are participating in the DVEs, it can decrease the transmission rate of haptic data so that we can get smaller network delay. According to the experiment results, the proposed scheme can be applied to the real DVEs under network delay jitter.

Security in a peer-to-peer distributed virtual environment

In the large-scale Distributed Virtual Environment (DVE) multimedia systems, one of key challenges is to distributedly preserve causal order delivery of messages in real time. Most of the existing causal order control approaches with real-time constraints use vector time as causal control information which is closely coupled with system scales. As the scale expands, each message is attached a large amount of control information that introduces too much network transmission overhead to maintain the real-time causal order delivery. In this article, a novel Lightweight Real-Time Causal Order (LRTCO) algorithm is proposed for large-scale DVE multimedia systems. LRTCO predicts and compares the network transmission times of messages so as to select the proper causal control information of which the amount is dynamically adapted to the network latency variations and unconcerned with system scales. The control information in LRTCO is effective to preserve causal order delivery of messages and lightweight to maintain the real-time property of DVE systems. Experimental results demonstrate that LRTCO costs low transmission overhead and communication bandwidth, reduces causal order violations efficiently, and improves the scalability of DVE systems.

A distributed virtual environment (DVE) is a shared virtual environment (VE) that allows remote users to interact with each other through networks. DVEs are becoming very popular due to some prominent applications, such as online games and virtual worlds. To support a large number of users, a multi-server DVE architecture may be adopted, with each server managing a subset of users. However, there are two critical problems with this architecture: view inconsistency caused by delays and server overloading caused by uneven distribution of users. While the first problem affects users' perception of the VE and causes user disputes, the second problem affects the system response time. In this paper, we first show that the view inconsistency problem and the load balancing problem are conflicting objectives. We then propose an efficient joint optimization framework to address both problems. Our results show that the proposed method can improve the view inconsistency problem significantly, which is important to the interactivity of DVE applications.

In distributed virtual environment many methods of data distribution management (DDM) are presented to efficiently improve network traffic situation and save system resources, these technologies are based on virtual environment partition. The grid size of the partition affects the data distribution results. This paper aims to present a neural-network based study mechanism, which adjusts the grid size dynamically in the virtual environment. The simulation results indicate that by using this technique, better experimental results and practicability were achieved regardless the DDM used. And there is a significant improvement in system scalability.

Distributed Virtual Environments (DVEs) have grown popular in various fields of application. Apart from providing great collaborational opportunities in an immersive setting, large-scale DVEs pose severe scalability challenges. Although P2P approaches have proven to be effective for tackling many of these issues, still load delay problems remain in regions with high object or avatar density. In this article we present and evaluate a hoarding approach that is suitable to minimize such delays in P2P-based DVEs with a real-time distribution of dynamic data. The prediction of what data shall be hoarded is based on an epidemic aggregation algorithm working solely with local knowledge. Evaluation results that have been obtained using a DVE simulation environment will be presented.

Distributed Virtual Environment (DVE) is a shared application consisting many objects, which can be accessed by many users. There have been many methods used to scale the DVE such as dividing simulation workload, dynamic load balancing among servers, and creating alternative architectures. However, they may not accommodate many objects and users. In this paper, we explore all approaches used to scale the DVE and then determine the characteristics of the existing approaches. With those characteristics, we compared existing approaches based on three parameters: the number of simulation per region, implementation, and the number of objects managed by simulator. The results show that all approaches use the same viewpoint, called present viewpoint, in developing the DVE. It views DVE as a world where all objects and activities are managed by a simulator. The results also show that this viewpoint contributes in terms of limitations of the current DVEs performance. In response to these results, we further propose a new viewpoint, called object-based viewpoint, to generate object-based simulators architecture. The experiment results show that our proposed architecture can provide a large scale DVE with better performances than the previous architectures.

We propose a prereckoning algorithm for distributed virtual environments. First, an overview of dead reckoning techniques used in distributed virtual environments is provided. The benefits and drawbacks of implementing dead reckoning within specific types of distributed virtual environments are discussed. An alternative to traditional dead reckoning techniques used in DIS-compliant distributed virtual environments is proposed. The alternative, referred to as "prereckoning", seeks to significantly reduce prediction error with a minimal increase in the number of entity state update packets issued. The performance of the prereckoning algorithm is compared to one of the DIS standard algorithms for location prediction. The test cases are based upon a game-based environment where the movements of participants are influenced by physical boundaries.

The virtual machine technology as new teaching aids in the teaching of computer network security has very good application prospect. At the same time, the virtual machine technology is adopted to simulate the real network teaching environment and improve teachers' teaching effect and has become a kind of effective means to ensure the quality of teaching. The virtual machine technology is adopted to enhance the teaching effect of Network Security. The installation and use of the virtual machine software VMware,setting a virtual network environment on single computer, and simulating attacks and defense on network safety, the teaching effect in both theory and practice teaching is promoted.The virtual machine technology application in computer network has very broad prospects.

Distributed Virtual Environments (DVEs) can handle large numbers of participants by optimizing the routing of state update messages sent to the computer of the individual participant. Often Area of Interest (AoI) management is used to limit the information an avatar can observe and thus the necessary state update messages that are sent to the client which the avatar represents.

Synchronization in a distributed virtual environment (DVE) involves mechanisms to ensure a consistent view of a virtual world for all participants. Most applications in the DVE are related to collaborative activities that include non-contention and contention cases. Using transmission of update messages is suitable enough to support synchronization for only non-contention activity. The contention activity requires an additional mechanism to control accessing a common object for synchronization. In this paper, we present the compromised synchronization control mechanism to support both non-contention and contention activities. The mechanism employs frequent update event and multiple-lock checking to control the synchronization. Frequent update event is used to support a dynamic virtual world for non-contention activity. Multiple-lock checking is embedded to ensure consistency when accessing the common object is required simultaneously for the contention event. Performance measurement of the compromised synchronization is provided by simulation in terms of locking time, sampling event, number of logical processes, and traffic tolerance. Prototype application is also implemented to compare the result in a small scale level. Based on the simulation and experimental results, the compromised sychronization control mechanism is capable to support up to 100 participants for the non-contention activity. It provides a good performance of supporting the contention activity in a small scale. The mechanism is considered suitable for collaborative application where contention is considered a critical event.

Virtual machine (VM) technologies offer lots of benefits such as users' isolation, server consolidation and live migration. However, owing to the overhead incurred by indirect access to physical resources such as GPU, IO devices and VM technologies have not been widely used in high performance computing area. General purpose graphics processing unit (GPGPU) computing solution for virtual machines makes it possible that high performance computing (HPC) applications running on GPU can be ported to virtual machines (VMs) environment. A novel GPU resources management system built on VMs called VMGPURMS and a novel GPU cluster schedule policy are presented to use VM as computing node, and enable users to run jobs in the whole virtual machine environment transparently. Evaluation demonstrates that the efficiency of GPUs with the GPU cluster schedule policy could be improved by 17% over the traditional cluster schedule policy without taking GPU into consideration.

In distributed simulations, such as multiplayer distributed virtual environments (DVE), power consumption traditionally has not been a major design factor. However, emerging battery operated mobile computing platforms require revisiting DVE implementation approaches for maximizing power efficiency. We explore some implications of power considerations in DVE implementation over mobile handhelds connected by wireless networks. We focus on the state dissemination problem in DVEs and propose a new power aware dead reckoning framework for power efficient state dissemination. We highlight a fundamental tradeoff between state consistency and power consumption, and present an adaptive dead reckoning algorithm that attempts to dynamically optimize the tradeoff at runtime. We present a quantitative evaluation of our approach using a synthetic DVE benchmark application.

In distributed simulations, such as multi-player distributed virtual environments (DVE),power consumption traditionally has not been a major design factor. However, emerging battery-operated mobile computing platforms require revisiting DVE implementation approaches for maximizing power efficiency. In this paper we explore some implications of power considerations in DVE implementation over mobile handhelds connected by wireless networks. We focus on the state dissemination problem in DVEs and propose a new power-aware dead reckoning framework for power-efficient state dissemination. We highlight a fundamental tradeoff between state consistency and power consumption, and present an adaptive dead reckoning algorithm that attempts to dynamically optimize the tradeoff at runtime. We present a quantitative evaluation of our approach using a syntheticDVE benchmark application.