This paper explores the use of rough set theory for feature selection in high dimensional haptic-based handwritten signatures (exploited for user identification). Two rough set-based methods for feature selection are analyzed, the first is a greedy approach while the second relies on genetic algorithms to find minimal subsets of attributes. Also, to further reduce the haptic feature space while maximizing user identification accuracy, a method is proposed where feature vectors are subsampled prior to the feature selection procedure. Rough set-generated minimal subsets are initially exploited to determine the importance of different haptic data types (e.g. force, position, torque and orientation) in discriminating between different users. In addition, a comparison between rough set-based methods and classical machine learning techniques in the selection of minimal information-preserving subsets of features in high dimensional haptic datasets, is provided. The criteria for comparison are the length of the selected subsets of features and their corresponding discrimination power. Support Vector Machine classifiers are used to evaluate the accuracy of the selected minimal feature vectors. The results demonstrated that the combination of rough set and genetic algorithm techniques can outperform well-established machine learning methods in the selection of minimal subsets of features present in haptic-based handwritten signatures.

In this paper, we present an efficient MAC layer scheme using Dynamic Slot Assignment (DSA) in TDMA-based MAC protocols for cluster-based wireless sensor networks. The DSA scheme is presented to analyze the energy efficiency and channel utilization in a bursty traffic environment under low traffic conditions with a large number of sensor nodes in a single cluster. The DSA scheme will allow the network to adapt to the changing traffic load. Based on the network activity, the connection is established between the cluster-head node and those sensor nodes which have data to send, and a TDMA slot is assigned to each of them dynamically. We present the complete system model and model the data traffic by a correlated stochastic process (i.e. Markov chain) for a network where the second and subsequent connection arrival rate is dependent on the first arrival rate. We numerically compare our DSA with a traditionally proposed static TDMA model, the BMA model, and a variant of the BMA model (EA-TDMA), and prove substantial improvement in the energy consumption and channel utilization in low activity sensor networks. Results show that the efficiency of the MAC protocol can be increased significantly using the presented model.

We present a novel analytical framework to investigate the performance of activity based TDMA slot scheduling under varying traffic conditions in cluster-based wireless sensor networks. Dynamic TDMA Slot Scheduling (DTSS) scheme is presented to analyze the channel utilization and packet dropping probability in bursty network environment under low and high traffic conditions with a large number of sensor nodes in a single cluster. DTSS scheme will allow the network to adapt to the changing traffic load. Based on the network activity, the connection is established between the cluster-head node and those sensors nodes which have data to send, and requested number of TDMA slots is assigned to them dynamically. We have modeled the data traffic by a correlated stochastic process (i.e. Markov chain) for a network where the second and subsequent connection arrival rate is dependent on the first arrival rate. We numerically compared DTSS with traditionally proposed static TDMA model and proved substantial improvement in the bandwidth efficiency and decrease in connection blocking probability in low activity networks. The drawback of the proposed system is also investigated. Results show that the efficiency of the MAC protocol can be increased significantly using the proposed model with reasonably low packet dropping probability.

Undesired physical fatigue reduces the overall Quality of Experience (QoE) of virtual reality haptics applications. Detecting fatigue is the first step in rectifying this problem. Fatigue in usability analysis is usually detected through conducting questionnaires and observations. This paper introduces an objective indirect discovery of user's fatigue through analyzing data of a haptic writing application. Our results show that if users are feeling tired their kinetic energy would decrease. We can compute this kinetic energy from the velocity of the arm movement during the usage of the haptic device.

In cluster-based two-tier Wireless Sensor Networks (WSNs), the cluster-head nodes (CHs) gather data from sensors and then transmit to the base station. When these cluster head nodes start to die, the coverage of the respective clusters is lost and it leaves the region unmonitored. Even if the CHs are rotated and reassigned after some time, until the next rotation that cluster in question will be out of cluster head, causing a loss of information and loss of coverage. To select a Backup Cluster Head (BCH) is suggested for those CHs which are close to deplete their energy [1]. When the CH dies, BCH takes over the responsibility and continues to work as a new cluster head. In this paper we present an analytical model of cluster reliability in cluster-based WSN using BCH, based on Markov chain model. We use non-homogeneous Markov process, along with Forward Chapman-Kolmogorov equations to illustrate the cluster monitoring period in a finite three state space model. We test the accuracy of the model by applying the probabilities of failure of CH and BCH nodes, for a fixed number of sensor nodes in a cluster. The results show that the presented model is able to match the behaviour of the cluster state transition accurately and validates the simulation results and analysis published in [1].

In this paper, a study is conducted in order to explore the use of genetic programming, in particular gene expression programming (GEP), in finding analytic functions that can behave as classifiers in high-dimensional haptic feature spaces. More importantly, the determined explicit functions are used in discovering minimal knowledge-preserving subsets of features from very high dimensional haptic datasets, thus acting as general dimensionality reducers. This approach is applied to the haptic-based biometrics problem; namely, in user identity verification. GEP models are initially generated using the original haptic biometric datatset, which is imbalanced in terms of the number of representative instances of each class. This procedure was repeated while considering an under-sampled (balanced) version of the datasets. The results demonstrated that for all datasets, whether imbalanced or under-sampled, a certain number (on average) of perfect classification models were determined. In addition, using GEP, great feature reduction was achieved as the generated analytic functions (classifiers) exploited only a small fraction of the available features.

This paper introduces a haptic data reduction and transmission technique to reduce the packet rate in six degree-of-freedom (6-DoF) haptic-enabled telementoring systems. The presented method relies on the limitations of human haptic perception (i.e. the Just Noticeable Differences) with respect to a user's hand position and orientation in order to reduce the number of packets transmitted without compromising transparency. A haptic prediction model is exploited to further reduce the amount of haptic packets transmitted, and to improve the reconstruction of data samples on the receiver side. Several distance metrics are also discussed to evaluate the acuity of human haptic perception when data reduction is performed in 6-DoF settings. Psychophysical experiments validate the effectiveness of the suggested algorithm as great haptic data reduction is achieved (up to 96%), while preserving the overall quality of the telementoring environment.

In this paper, the importance of the user's primary holding pivot point on the end effector of a haptic interface is discussed. Both theoretical analysis and experimental results demonstrate that this holding pivot point is critical for the correct perception of the haptic properties assigned to the virtual objects. We also study the physical inertia effects of the end effector on the non-uniform stiffness perception of simulated virtual objects. To the best of our knowledge, no such combined consideration of holding pivot point and device structure related inertia has so far been made for works in 6-DOF haptic rendering. We have instrumented the end effector of a haptic interface with a membrane potentiometer to measure the user's primary holding pivot point in real-time. Accordingly, a preliminary adaptive feedback method is developed to render the appropriate forces/torques to compensate for the effects of the end effector's inertia on the haptic stiffness perception.

In this paper, we present a collision detection algorithm and a force response algorithm both for use in dynamic, rigid-bodied, highly-detailed, hapto-visual virtual environments in which the models' geometry is point-based. Our collision detection algorithm partitions the virtual space into a modified octree in a preprocessing step. At runtime, collision detection involves querying the octree for the octant where the end-effector currently is, as well as the indices of neighboring octants. After the world space is narrowed down to a volume of interest, the algorithm checks to see if the end-effector falls inside any axes-aligned bounding box that is centered at the model surface points that reside in the aforementioned volume of interest. A collision is defined as the haptic endeffector being found inside an axes-aligned bounding box centered at a model surface point. After a collision is detected, the force response algorithm calculates a force vector that starts at the end-effector's current position and ends at the model surface point closest to the end-effector. This is an adaptation of the common god/proxy-object approach but for use in point-based models.

Many wake-up calls have been received for emergency response, due to natural disasters such as hurricanes, fires or man-made incidents. The emergency responders need to work in a coordinated, well-planned manner to best mitigate the impact of an emergency incident. Simulation systems provide a wider range of training at a much lower expense for emergency preparedness and response. It is identified as the only feasible approach when it is difficult to emulate real-life experiments. The presented research demonstrates the emergency training simulation for the SITE building at the University of Ottawa, where the real-time interaction and collaboration are achieved over HLA/RTI, the IEEE standard for distributed simulation and modeling.

Haptic Tele-mentoring refers to an educational technique in which the mentor can teach the mentee, in a hand-by-hand manner over communication networks, through the coupling of two haptic devices. Essentially, the realization of tele-mentoring relies on the efficient transmission of haptic information, such that either end of the network can sense and/or impart forces. A few of obstacles in developing the tele-mentoring applications over the internet are network delay, jitter, and packet loss. These impairments potentially affect the stability of the tele-mentoring system and degrade the feeling of guiding. This paper analyzes the design and implementation constraints of the system, as well as the simulation and experimental results. To compensate for the network latency, a novel approach based on the behaviors of the human arm trajectory is proposed to lower the overshoot so as to improve the overall system stability. The experimental results show the effectiveness of the anti-overshoot algorithm.

Wireless Sensor Networks (WSN) are becoming a viable tool for many monitoring applications. These applications may be of critical nature where the transportation of the information of events from the region of interest to some base station is crucial, where the data loss can not be tolerated. In the cluster-based two-tier WSN, where cluster-head nodes gather data from sensors in their clusters and then transmit to base station, when cluster head nodes start to die, the coverage of those clusters is lost and it leaves the region unmonitored. Even if the cluster heads are rotated and reassigned after some time, until the next rotation that cluster in question will be out of cluster head and will lose coverage. A lot of information is lost which is sensed and sent by the sensor nodes of the cluster to the dead cluster head. We propose here to select backup cluster heads (BCHs), for those cluster heads which are close to deplete their energy. The cluster head, when about to die, sends an SOS with the gathered information until then, to the respective BCH which takes over the responsibility and continues to work as a new cluster head. To evaluate the effect and results of BCH we used LEACH-C protocol and compared the data loss ratio with and without a BCH.

This paper introduces a novel generic method aimed at predicting motion and force information in haptic media. An autoregressive (AR) model is presented for the prediction of both, haptic movement and force. The conditional maximum likelihood technique is utilized in order to accurately estimate the adaptive coefficients of the AR model. Furthermore, the incorporation of concepts from haptic perceptibility, i.e. the just noticeable difference (JND), has been demonstrated to optimize the suggested algorithm, while preserving the immersiveness of the haptic-enabled environment. The proposed technique has also proved to provide accurate prediction results for non-linear haptic movement and force information while simultaneously remaining computationally efficient.

For the past decade, there have been numerous research works focusing on the protection of digital images, audio, video, 3D virtual scenes, and software data from unauthorized use and distribution. With the emerging technology of the MPEG-4 standard, MPEG-4 scenes that may include images, video, audio, and 3D objects can easily be built using the text-based MPEG-4 XMT standard. XMT allows content authors to exchange their content with other authors, tools, or service providers and facilitates interoperability with MPEG-4, X3D, and SMIL. In order for owners and designers to protect and/or authenticate their work, some form of security needs to be applied into the MPEG-4 XMT structure and its media content. Unlike images or videos, watermarking an XMT structure is not an easy task, since the structure contains no noise components to embed the watermark. This article is the first one proposing a novel robust algorithm for the authentication of a given MPEG-4 XMT structured scene and the location of its multimedia content.

This paper presents a new locally refined collision detection approach for large scale complex meshes in distributed virtual environments (DVEs) where exact and interactive interference detection is required. Transmitting models with millions of polygons is time consuming in comparison with transmitting simple models. Even if the models are transmitted in progressive manner, the earlier received models are in low level-of-detail (LOD) because the models are refined globally. Increasing the accuracy of collision detection (CD) at the client still takes time because increasing the LOD of the model is a slow process. The new approach is composed of an AB-tree collision query algorithm and a new mesh refinement algorithm on a space partitioned mesh (SPM) representation. It deals with this problem by selectively refining the models at certain areas that are predicted to collide with other objects and transmitting the refined parts instead of the entire model from server to client. The accuracy of CD is increased quickly at the predicted contact areas. An interactive rate is guaranteed by reducing network response time and dynamically adjusting the complexity and the space cost of the collision query algorithm

3D mesh compression and segmentation are two active areas of 3D object modeling. Most existing 3D compression algorithms compress the whole object to reduce the local storage requirement and the delays in transmitting objects over the Internet. However, in some interactive applications, the client may be interested in particular section(s) of the object. The server needs to segment the object into pans and send them individually or sequentially. This paper presents a segmentation based 3D mesh compression scheme that can meet this requirement. We propose an efficient eXtend Multi-Ring neighborhood (XMR) based 3D mesh segmentation algorithm that decomposes the object into meaningful regions. Then we compress them separately and put them into one stream. The common boundary triangles that are used for adhering the regions together are processed and appended to the end of the stream. We call this a region-conquer-and-stitch scheme.

10.1145/1101149.1101297

In wireless sensor networks, one of the main design challenges is to save severely constrained energy resources and obtain a long system lifetime. Low cost of sensors enables us to initially deploy a large number of sensor nodes in a very high density. Thus, a potential approach to solve a lifetime problem arises. That is to schedule sensor nodes work alternatively by configuring some of them an off-duty status that has lower energy consumption than the normal on-duty one. In a single wireless sensor network, sensors assume two main functionalities: sensing and communication. Minimizing energy consumption in a highly dense wireless sensor network needs to maximize off-duty nodes in both domains. Most of the previous work addressed only one kind of redundancy: sensing or communication alone. Based on our previous conclusion: "the communication range is twice the sensing range" is the sufficient condition and the tight lower bound to ensure that complete coverage preservation implies connectivity among active nodes, if the original network topology (consisting of all the deployed nodes) is connected, we study a node status configuration strategy in a tightly integrated two-phase mode for those sensor networks where the communication range is more than twice the sensing range by comparing this strategy with the other two in the term of off-node number, the experimental results show that it leads to more off-duty nodes in double domains without incurring the reduction of off-duty nodes in a single domain.

No abstract available.

A collaborative, haptic, audio and visual environment (C-HAVE) consists of a network of nodes. Each node in the C-HAVE world contributes to the shared environment with some virtual objects. These can be static, e.g., a sculpture or the ground, or dynamic, e.g., an object that can be virtually manipulated. We aim at developing a heterogeneous scalable architecture for large collaborative haptics environments where a number of potential users participate with different kinds of haptic devices. The main objective of the presented research is the development of three prototypes to demonstrate quantitatively the effects of adding haptics to a task. The experimental results reveal the effects of the different implementations on the performance and time delay of a particular task through objective measurement results.

Abstract The IEEE 1516 Standard ‘High Level Architecture (HLA)’ and its implementation ‘Run‐Time Infra‐structure (RTI)’ defines a general‐purpose network communication mechanism for Distributed Interactive Simulation (DIS). However, it does not address real‐time requirements of DIS. Current operating system technologies can provide real‐time processing through some real‐time operating systems (RTOSs) and the Internet is also moving to an age of Quality of Service (QoS), providing delay and jitter bounded services. With the availability of RTOSs and IP QoS, it is possible for HLA to be extended to take advantage of these technologies in order to construct an architecture for Real‐Time DIS (RT‐DIS). This extension will be a critical aspect of applications in virtual medicine, distributed virtual environments, weapon simulation, aerospace simulation and others. This paper outlines the current real‐time technology with respect to operating systems and at the network infrastructure level. After summarizing the requirements and our experiences with RT‐DIS, we present a proposal for HLA real‐time extension and architecture for real‐time RTI. Similar to the growth of real‐time CORBA (Common Object Request Broker) after the mature based CORBA standard suite, Real‐Time HLA is a natural extension following the standardization of HLA into IEEE 1516 in September 2000. Copyright © 2004 John Wiley & Sons, Ltd.

In this paper, we propose a novel watermarking algorithm that makes use of a secret sharing scheme to address the problem of joint ownership verification for a digital image without a trusted dealer, which has not be addressed so far. Given that multiple owners create an image jointly, they collaboratively compute their own distinct keys without anyone else involved. For the watermarking detection, only when certain number of owners present their keys, can the ownership of the image be verified. Any owner alone can not verify the image ownership. In addition, experimental results show that the proposed algorithm has the desired properties such as invisibility, reliable detection and robustness against a wide range of imaging processing operations.

In this work, we investigate the problem of bit rate adaptation transcoding for transmitting video over burst-error wireless channels. In particular, we consider a scenario consisting of packet-based transmission with an automatic repeat request (ARQ) error control scheme. We first analyze the buffering implications of inserting a video transcoder at the wireless access point with the variable bit rate channel as the target. We derive the conditions that both the source encoder and transcoder buffers have to satisfy for preventing the decoder buffer from underflowing. Furthermore, we propose a bit rate adaptation algorithm for VBR transcoders used in the wireless access point. Our experimental results demonstrate that visual quality can be improved by the proposed algorithm without violating the end-to-end delay requirements.

Virtual environments (VEs) are interactive computer simulations that immerse users in an alternate reality. Distributed VE (DVE) applications simulate the experience of real-time interaction among multiple users in a shared three-dimensional (3-D) virtual world. In this paper, we identify the network service requirements for highly interactive DVEs and show the limitations of IPv4 in satisfying them. We propose a transport system for DVE applications, which incorporates a scalable network architecture and dynamic QoS adaptation over IPv6. The network communication architecture combines the advantages of anycasting, unicasting and multicasting while the dynamic QoS adaptation assists the DVE applications in adapting to fluctuations in the network. The network-specific issues are hidden from the application by means of a networking module. The traffic measurements are performed on a DVE application using the proposed architecture.

Videoconferencing in the context of 3D virtual environments promises better spatial consistency and mutual awareness for its participants. However, in the absence of IP Multicast and limited upload bandwidth of today's DSL connections, the feasibility of such systems in supporting even a small group of users is in question. This paper presents the design and implementation of an awareness driven 3D videoconferencing application that runs on a peer-to-peer architecture and our own End System Multicast protocol. The paper highlights the unique requirements of multiparty videoconferencing applications and presents a solution that can support 4-10 bandwidth-limited users without the need for IP Multicast capability.

High delivery ratio with low energy consumption is one of design challenges for wireless sensor network routing protocols. In this paper, we identify the drawbacks of pure single path routing scheme and multipath routing scheme, in terms of guaranteed delivery with low energy consumption. Accordingly, we describe a scheme, in which data is forwarded along a pre-established single path to save energy, and a high delivery ratio is achieved by path repair whenever a break is detected. We propose a simple, quick, local path repairing approach, whereby a pivot node can skip over path break by only using the already existing routing information in its neighborhood. We implement this scheme and compare its performance with those of pure single path without repair and two multipath routing schemes. Simulation results show that in the same network topology with the same failed nodes, our single-path with repair routing scheme (SWR) has the highest delivery ratio among all the compared schemes in almost all the test cases. The energy consumed by SWR for one data delivery test is relatively low compared with the other schemes.

Abstract In wireless sensor networks that consist of a large number of low‐power, short‐lived, unreliable sensors, one of the main design challenges is to obtain long system lifetime without sacrificing system original performances (sensing coverage and sensing reliability). In this paper, we propose a node‐scheduling scheme, which can reduce system overall energy consumption, therefore increasing system lifetime, by identifying redundant nodes in respect of sensing coverage and then assigning them an off‐duty operation mode that has lower energy consumption than the normal on‐duty one. Our scheme aims to completely preserve original sensing coverage theoretically. Practically, sensing coverage degradation caused by location error, packet loss and node failure is very limited, not more than 1% as shown by our experimental results. In addition, the experimental results illustrate that certain redundancy is still guaranteed after node‐scheduling, which we believe can provide enough sensing reliability in many applications. We implement the proposed scheme in NS‐2 as an extension of the LEACH protocol and compare its energy consumption with the original LEACH. Simulation results exhibit noticeably longer system lifetime after introducing our scheme than before. Copyright © 2003 John Wiley & Sons, Ltd.

Collaborative virtual environment (CVE) concepts have been used in many systems. The architectures available today provide support for a number of users but they fail if too many users are together in a small "space" in the virtual world. This paper introduces VELVET, an adaptive hybrid architecture which allows a greater number of users to interact through a CVE. VELVET introduces a novel adaptive area of interest management, which supports heterogeneity amongst the various participants.

Though many image watermarking schemes have been proposed, none of them can resolve the problem of joint ownership. This paper proposes two novel algorithms that make use of a secret sharing scheme in cryptography to address this problem. The first one applies Shamir's (2, 2) threshold scheme to the watermarking algorithm. A watermark, which is a gaussian distributed random vector determined by two keys, is embedded to selected coefficients in all middle bands in the wavelet domain of an image, so that only when the two keys are put together can the ownership be verified. The second algorithm is a modification of the first one. Three random watermarks are embedded to middle bands in the wavelet domain of an image. For the watermark detection, two thresholds are set, so the watermark detector can verify partial ownership as well as full ownership. Experimental results show that both algorithms have the desired properties such as invisibility, reliable detection and robustness against a wide range of imaging processing operations.

In order to transmit pre-encoded digital video over heterogeneous networks, it is necessary to employ transcoding techniques that convert pre-encoded video streams into streams having different bit rates and quality. The specified problem is referred to as rate shaping or rate adaptation. In this work, we propose a new rate control scheme for H.263+ based video transcoding. The proposed rate control scheme is comprised of Frame-Layer bit allocation and Macroblock-Layer rate control. At the frame layer, scene context statistics from the incoming video stream are utilized to detect scene changes and determine frame type. The bit budget is allocated to frames according to their energy and frame types. At the macroblock layer, a novel linear Rate-Quantization model is used for selecting quantization parameters for macroblocks. Implementation and experimental results show that the proposed algorithm can provide accurate bit allocation, and can effectively alleviate visual quality degradation after scene changes. This rate adaptation scheme can be used to provide flexible video bit rate adaptation for transmission of pre-encoded video over heterogeneous networks.

The growing complexity of Virtual Reality simulations and the inclusion of a greater range and number of events and interactions in such simulations precipitates the need for the recording of these events to allow their subsequent viewing, discussion and perhaps modification. Furthermore, storage of such recordings in a format defined by an international standard allows their easy use and accessibility as well as distribution. This paper presents a framework for MPEG-4 based recording and replay of Virtual Reality sessions.

In this paper, we describe an experimental performance-driven animation system for an avatar face using model-based video coding and audio-track driven lip animation.

In this paper, we present a protocol that allocates resources in communication networks in order to assure specific QoS characteristics as requested by new connections. The design takes into consideration the possibility for the network allocation to adapt to application requirements.The proposed protocol uses a Bandwidth Preemptive Algorithm that permits adaptive bandwidth allocation in multicast, multi-stream environments. This design has been inspired by the one proposed by Sakate [1] where a centralized methodology is used. In our approach, we use a distributed methodology where we change the behavior of the communication service and allow the continuation of the service under more severe conditions. In other words, when there is a lack of bandwidth for a new connection, the communication service will try to find the missing bandwidth within the existent connections (or streams) when looking for a feasible path on a hop-by-hop basis, starting from the destination to an a on-tree node.

As the cost of training individuals to learn how to use new technologies increases, the need for virtual environments that facilitate training becomes more noticeable. More specifically, the use of Collaborative Virtual Environments for training in industrial applications is of special interest. What follows is a discussion of two prototypes designed and implemented for the purpose of using Collaborative Virtual Environments in training scenarios.

Many critics of the Java language have pointed performance deficiencies as a barrier to acceptable support of Collaborative Multimedia Systems. This paper presents four MCRLab products, fully written in Java that support collaboration amongst a group of users, and successfully demonstrate that Java collaboration frameworks are not only possible but also can perform at acceptable levels of quality, if designed correctly.

Existing electronic commerce applications only provide the user with a relatively simple browser-based interface to access products. Buyers, however, are not provided with the same shopping experience, as they would have in an actual store or shopping mall. With the creation of a virtual shopping mall, simulations of most of the actual shopping environments and user interactions can be achieved. The virtual mall brings together the services and inventories of various vendors. Users can either navigate through the vendors, adding items into a virtual shopping cart, or perform intelligent searches through "user and vendor agents". The electronic mall prototype also allows the user to communicate with an "intelligent assistant" (IA) using simple voice commands. This assistant interacts with the shopper using voice synthesis and helps him or her use the interface to navigate efficiently in the mall. Real-time interactions among entities in the virtual environment are implemented over the Run Time Infrastructure of the High Level Architecture (RTI/HLA), an OMG and IEEE standard for distributed simulations and modeling developed by the US Department of Defense.

Many educational resources and objects have been developed as Java applets or applications, which can accessed by simply downloading them from various repositories. It is often necessary to share these resources in real time, for instance when an instructor teaches remote students how to use a certain resource explains the theory behind it. We have developed some tools for this purpose that emulate a virtual classroom, and are primarily designed for synchronous sharing of resources. They enable participants to share Java objects in real time and also allow the instructor to dynamically manage the telebearing session.

This panel will discuss a recommendation for curricula guidelines for courses about multimedia. Based on conference input, the guidelines will be modified for review prior to future publication by ACM (with other groups). The recommendation will be one of the main results of a June 2000 Dagstuhl workshop led by 4 of the panelists. Dr. Heller, the 5th panelist, also attended that workshop, and is co-PI with the panel moderator on a directly related NSF project, Curriculum Resources in Interactive Multimedia, CRIM, see http://ei.cs.vt.edu/~crim. Each of the panelists has taught courses about multimedia. Each is interested in developing tools/demonstrations/resources to help in those course. Each has a particular area of interest in the multimedia field. Together they constitute a representative group among those who will contribute to and benefit from curricula resources in multimedia.

The concept of collaborative virtual environments has been deployed in many systems in the past few years. Applications of such technology have been used anywhere from military combat simulations to various civilian commercial applications. We present a specific system developed for industrial teletraining. The system, which aims to reduce the cost of training, consists of an interactive 3D environment with collaboration and management capabilities that allows a trainer to lead and control a session attended by many trainees.

We introduce an architecture for performing closely-coupled collaborative tasks in virtual environments. Our architecture consists of an application-layer model based on higher-level user interactions with shared objects, and a communication protocol for dissemination of collaborative update messages among participants.

This paper reviews and discusses the known definitions and properties of second-order self-similar discrete-time processes and supplements them with some more general conditions of self-similarity. A model for ATM cell traffic is presented and self-similarity conditions of this model are found. This study is motivated by observations that traffic in many real communication networks is self-similar in nature.

Real measurements in high-speed communications networks have recently shown that traffic may demonstrate properties of long-range dependency peculiar to self-similar stochastic processes. Measurements have also shown that, with increasing buffer capacity, the resulting cell loss is not reduced exponentially fast as it is predicted by Markov-model-based queueing theory but, in contrast, decreases very slowly. Presenting a theoretical understanding to those experimental results is still a problem. The paper presents mathematical models for self-similar cell traffic and analyzes the overflow behavior of a finite-size ATM buffer fed by such a traffic. An asymptotical upper bound to the overflow probability, which decreases hyperbolically, h/sup -a/, with buffer-size-h is obtained. A lower bound is also described, which demonstrates the same h/sup -a/ asymptotical behavior, thus showing an actual hyperbolical decay of overflow probability for a self-similar-traffic model.

Recent traffic measurements in corporate local-area networks (LANs), variable-bit-rate video sources, ISDN control-channels, and other communication systems, have indicated traffic behaviour of self-similar nature. This paper first discusses some definitions and properties of (second-order) self-similarity and gives simpler criteria for it. It then gives a model of self-similar traffic suitable for queuing system analysis of an asynchronous transfer mode (ATM) queue. A lower bound to the overflow probability of a finite ATM buffer is obtained, as also a lower bound to the cell loss probability. Finally, the stationary distribution of the cell delay in an infinite ATM buffer is obtained.

We present a complete software control architecture for synchronizing multiple data streams generated from distributed media-storing database servers without the use of a global clock. Independent network connections are set up to remote workstations for multimedia presentations. Based on the document scenario and traffic predictions, stream delivery scheduling is performed in a centralized manner. Certain compensation mechanisms at the receiver are also necessary due to the presence of random network delays. A stream synchronization protocol (SSP) allows for synchronization recovery, ensuring a high quality multimedia display at the receiver. SSP uses synchronization quality of service parameters to guarantee the simultaneous delivery of the different types of data streams. In the proposed architecture, a priority-based synchronization control mechanism for MPEG-2 coded data streams is also provided. A performance modeling of the SSP is presented using the DSPN models. Relevant results such as the effect of the SSP, the number of synchronization errors, etc., are obtained.

A real-time multimedia communication system over broadband networks is introduced in the paper. This system consists of distributed database servers which store and retrieve data objects of different types of media and in different coding formats. The multimedia document is transmitted over the network as streams through different connections and presented to the user simultaneously. A set of stream synchronization control schemes is designed to control the multiple data streams (either in coded or uncoded format) to achieve multimedia synchronization during progressive presentation. A centralized scheduler derives a stream delivery schedule to compensate variable network delay. The synchronization controller at a user's workstation performs synchronization error recovery by adjusting the presentation schedule according to the temporal requirements in the scenario. Skew tolerance parameters are employed as one of the synchronization requirements. In particular, MPEG-2 coded stream sync...

Multimedia information management and communications systems for medical applications have been undergoing design and development. The aim of these activities has been the development of distributed computer systems providing storage, processing, and communication services required by the medical community. One of the main critical issues of such systems is the handling of multimedia information (i.e., text, images, graphics, and voice) in a uniform way and the fast access to images through the network. We present the design architecture and concepts used in our multimedia database system, along with its performance evaluation. The evaluation focuses on the response times of a multimedia medical database server, as seen by remote workstations for various retrieval and image transfer requests. For this purpose, a queueing network model was developed and simulated. Communications between the workstations and the database server are governed by the client-server model using TCP/IP and appropriate application protocols on a 10 Mb/s Ethernet LAN.>

An asynchronous transfer mode (ATM) packet switch should be capable of handling delay sensitive as well as loss sensitive traffic. The authors consider delinking handling of these two types of priorities in a switching system, and present an analysis of two classes of delay sensitive traffic in an N*N nonblocking switch with input queues. In such a switch, two variations of nonpreemptive priority are studied. A packet switch with input buffers has inadequate throughput. To enhance the performance and to provide low delay to high priority traffic, a dual plane switch architecture is examined, where each plane is a nonblocking switch with input buffers. The two planes are connected in parallel to form a load sharing arrangement. The analysis of a single plane nonblocking switch is extended to this architecture. In both cases, the performance is compared with the simulation results of a 64*64 switch.>

The authors present a study whose main objective has been to explore the use of high-bandwidth multimedia communications technology for medical applications physically distributed among hospitals, that is to say an interhospital multimedia communications system. The design and development issues of a prototype are described, as well as the results of an in-field trial. From the results of this trial, a performance study has been developed for evaluating the expected communications requirements of a large-scale configuration of the system.>

A nonblocking N*N switch for high speed packet switching networks is considered. In practice such a switch may operate L times faster than the input/output trunk. When 1>

The problem of communicating the radiologist's findings to the attending physician is introduced, and it is shown why it is essentially a multimedia communication problem. A multimedia communications system that was designed with a focus on database and medical reports organization and architecture is described. A report is presented of some of the key results of an in-house trial linking the Department of Radiological Sciences and the Emergency Department at the Ottawa Civic Hospital, Canada, a 950-bed tertiary-care teaching hospital.>

The commenter points out an error made in the paper by P. Nain et al. (see ibid., vol.36, p.806-15, July 1988) and shows that correcting this error requires a state space that has an exponential size. The authors reply that the errors cannot easily be corrected and that their model provides a good approximation model for HYMAP.>

A performance study is presented of the proposed IEEE 802.6 standard (DQDB MAN) used as a backbone loop network in packet-switching mode to interconnect token rings that operate as specified in the ANSI/IEEE 802.5 standard. Interconnection between DQDB and token rings is provided by gateways that use assembly and segmentation processors and limited buffer sizes. The authors consider a network architecture in which Type 2 of the IEEE 802.2 logical-link-control (LLC) standard is used as end-to-end protocol between stations on the token rings. The use of the former and current DQDB slot formats are compared. Several window sizes, different policy schemes, and various traffic intensities and bit rates in token rings are also considered. Using the current DQDB slot size, results show that higher access priority should be allocated to the gateways in the token rings and also show the importance of reducing the time caused by the segmentation of packets in the gateways.>

The authors present a multimedia medical communications system based on packet local area networks. This system is intended to facilitate the communications between radiologists and physicians within a hospital. Radiographs are taken, digitized, and then stored in the database. Radiologists retrieve radiographic images from the database for diagnosis, and make diagnostic reports to be stored in the database. Physicians can then consult these radiographic images and diagnostic reports. A real-time conference can be set up between a radiologist and a physician who are in different locations, for discussing a particular case or radiographic images can be retrieved from the database for diagnosis and conferencing. Simulations indicate the delay for displaying an image of 1 Mb from the local storage (hard disk) at a workstation is approximately 6.5 s.>

A simple protocol is presented for establishing and terminating circuit-switched communications within a metropolitan area network (MAN) that supports both circuit-switched communication (for voice and video) and packet-switched communication (for data and file transfers). A mathematical model of the MAN is used to study its performance with respect to the circuit-switched communication and its effects on the pocket-switched communication. The models are numerically solved by the mean-value-analysis algorithm.>

A hybrid multiple access protocol (HYMAP) was proposed by M. Rios and N.D. Georganas (1985), combining the best features of CSMA/CD and of a conflict-free protocol. Control is transferred from one protocol to the other according to state information sensed on the channel. The performance of HYMAP was evaluated by computer simulation. An exact analysis of this hybrid protocol is presented. Since HYMAP permits free access of new arrivals during collision resolution, the mean length of the conflict-free period is determined by solving a large system of linear equations. The basic mean performance measures (throughput, delay) can then be easily computed and compared to the performance of CSMA/CD.>

The class of product-form semi-homogeneous queueing networks is introduced as a generalization of the class of homogeneous networks, which has been considered by Balbo et al for the performance modeling of local area networks. In semi-homogeneous networks, the relative traffic intensity at the various shared resources may depend on the routing chain to which a customer belongs. We develop an efficient algorithm for the exact analysis of this class of networks. It is based on the equations which form the foundation of RECAL, a general purpose exact algorithm for multiple-chain closed queueing networks. The complexity of the algorithm is shown to be of order less than exponential in (P-1)1/2, where P is the number of processors (workstations) in the network. It is therefore, in general, more efficient than a direct application of either convolution, MVA or RECAL to the class of semi-homogeneous queueing networks. The algorithm presented here may be situated between the algorithms of Balbo et al and the general purpose algorithms, both in terms of its generality and efficiency.

RECAL, a Re cursion by C hain Al gorithm for computing the mean performance measures of product-form multiple-chain closed queuing networks, is presented. It is based on a new recursive expression that relates the normalization constant of a network with r closed routing chains to those of a set of networks having ( r - 1) chains. It relies on the artifice of breaking down each chain into constituent subchains that each have a population of one. The time and space requirements of the algorithm are shown to be polynomial in the number of chains. When the network contains many routing chains, the proposed algorithm is substantially more efficient than the convolution or mean value analysis algorithms. The algorithm, therefore, extends the range of queuing networks that can be analyzed efficiently by exact means.

A method is described whereby a multiple-class closed network of first-come first-served (FCFS) queues can be analyzed exactly by a decomposition and aggregation procedure that proceeds class by class, rather than node by node. First, the FCFS network is transformed into an equivalent network of processor-sharing queues in which a hierarchy of subsystems associated with subsets of the classes may be identified. This decomposition and aggregation procedure reduces the multiple-class queuing networks into a hierarchy of single-class queueing network problems. The reduced system is constructed containing one particular class of customers. A parametric analysis of this class with respect to the routing can then be made. The time and space requirements of this parametric analysis technique are derived and compared to the requirements of a straightforward repetitive analysis of the network using the convolution algorithm. An example parametric analysis of a store-and-forward communication network model is given.

article Free Access Share on Strategies for optimal capacity allocations in DAMA satellite communication systems Authors: Kevin Wong Canadian Astronautics Limited, Ottawa, Canada Canadian Astronautics Limited, Ottawa, CanadaView Profile , Nicolas D. Georganas Department of Electrical Engineering, University of Ottawa, Ottawa, Ontario, Canada Department of Electrical Engineering, University of Ottawa, Ottawa, Ontario, CanadaView Profile Authors Info & Claims ACM SIGCOMM Computer Communication ReviewVolume 15Issue 4Sept. 1985 pp 93–99https://doi.org/10.1145/318951.319021Online:01 September 1985Publication History 1citation427DownloadsMetricsTotal Citations1Total Downloads427Last 12 Months3Last 6 weeks0 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

RECAL, a Recursion by Chain Algorithm for computing the mean performance measures of product-form multiple-chain closed queueing networks, is presented. It is based on a new recursive expression which relates the normalization constant of a network with r closed routing chains to those of a set of networks having (r-l) chains. It relies on the artifice of breaking down each chain into constituent sub-chains that each have a population of one. The time and space requirements of the algorithm are shown to be polynomial in the number of chains. When the network contains many routing chains the proposed algorithm is substantially more efficient than the convolution or mean value analysis algorithms. The algorithm therefore extends the range of queueing networks which can be analyzed efficiently by exact means. A numerical example is given.

This correspondence presents HYMAP, a hybrid multiple access protocol for local area networks. The protocol combines features of both CSMA/CD and a collision-free protocol. Control is transferred from one protocol to the other according to state information sensed on the channel. The performance of HYMAP is evaluated by computer simulation for both data and voice packets. It compares favorably to other well-known multiple-access protocols. The number of packet-voice terminals that can be supported by HYMAP is higher than that obtained by using other protocols. Statistical analysis of the simulation results is also given.

Adaptive quantizers for PCM and DPCM coding of speech have been of great interest, and several excellent quantization strategies have evolved [1], [2]. In this paper we propose another algorithm for the step-size change in a quantizer. In the present strategy the quantizer is always a linear one except for the fact that the step size can be changed by a fixed amount at each sampling instant. This fixed value is also the minimum allowed step size. Hence, we have the name incremental adaptive quantizer. The quantizer has been simulated on a computer and its performance has been compared with that of Jayant's adaptive quantizer (JAQ), both in PCM and DPCM coders. The figure of merit used in the comparison is the signal-to-noise ratio (SNR) with a correlated sequence as the input. The preliminary results indicate that the new design can perform very well. However, it has the drawback of not being able to respond to very fast changes in the input. It can be easily realized in an integrated form using ROM's.

This paper presents a simulation study of a cellular highcapacity land-mobile radio system using the hybrid channel assignment scheme with Erlang-Cservice. The performance of this system in regard to the probability of queueing, the average queueing time, and the average number of queued calls is evaluated and compared with that of the systems employing either the fixed or the dynamic channel assignment scheme.

A message-switched computer network with end-to-end window flow control is considered. Using recently developed heuristics for the numerical solution of such networks, an algorithm for the selection of “good” flow-control window settings is developed. The criterion of performance is the ratio of the network average throughput versus average network delay. An example network demonstrates the results.

This correspondence presents expressions for the Mean Error-Free Interval in a packet-oriented data transmission system. In particular, the case of transmission through a random-error channel is studied, with some results also given for more general noisy channels.

This paper considers the problem of congestion in message-switched, or packet-switched, networks, which employ probabilistic routing schemes. A queueing model for the analysis of a local congestion control scheme is presented. Analytic study of the model shows that local congestion control with random routing is superior to similar control with deterministic routing for a particular example worked out here.

This concise paper extends the results of Pennotti and Schwartz by proposing a queueing model of a communication network with random routing and end-to-end congestion control. Using conventional performance criteria, the performance of this model is compared with that of a previously published model, where fixed routing was employed.