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There exists a common view that the brain acts like a Turing machine: The machine reads information from an infinite tape (sensory data) and, on the basis of the machine's state and information from the tape, an action (decision) is made. The main problem with this model lies in how to synchronize a large number of tapes in an adaptive way so that the machine is able to accomplish tasks such as object classification. We propose that such mechanisms exist already in the eye. A popular view is that the retina, typically associated with high gain and adaptation for light processing, is actually performing local preprocessing by means of its center-surround receptive field. We would like to show another property of the retina: The ability to integrate many independent processes. We believe that this integration is implemented by synchronization of neuronal oscillations. In this paper, we present a model of the retina consisting of a series of coupled oscillators which can synchronize on several scales. Synchronization is an analog process which is converted into a digital spike train in the output of the retina. We have developed a hardware implementation of this model, which enables us to carry out rapid simulation of multineuron oscillatory dynamics. We show that the properties of the spike trains in our model are similar to those found in vivo in the cat retina. Index Terms--Brain computation, quasi-periodic oscillations, synchronization, universal Turing machine, visual system.

An iterative, distributed approach for linear minimum mean-square-error (LMMSE) estimation using the embedded subgraphs algorithm (ESA) is proposed. ESA is proved to be robust to temporary communication faults such as failing links and sleeping nodes, and enjoys guaranteed convergence under relatively mild conditions.

The carrier-frequency offset effect on the performance of asynchronous multicarrier direct-sequence code-division multiple-access (MC-DS-CDMA) systems with aperiodic random spreading and correlated Rayleigh fading is studied in this paper. We obtain the optimum combining filter that maximizes the signal-to-interference-plus-noise ratio (SINR) of the combined statistics and exploits correlated information among subchannels. A closed-form expression for the unconditional covariance matrix of the interference-plus-noise vector, which forms the basis of our theoretical analysis of the maximum SINR and the average bit error probability formula, is derived by averaging several random parameters including asynchronous delays, correlated Rayleigh fading, and signature sequences. The analytic results obtained are applicable to MC-CDMA with appropriate modifications. Furthermore, we show that the MC-CDMA system with a common random signature sequence over all subcarriers for a given user outperforms that with distinct sequences over different subcarriers. Finally, the performance of MC-CDMA systems using the optimum combining technique is compared with that of different combining filters in the simulation. Index Terms--Asynchronous transmission, carrier-frequency offset (CFO), code-division multiple access (CDMA), multicarrier CDMA (MC-CDMA), random signature sequence.

Abstract Facilitating a collaborative community in an online class takes a delicate balance of technology and personal communication. This article explores the use of asynchronous communication tools, including threaded discussions, [...]

A solution to vector consensus problem for Byzantine asynchronous systems augmented with wormholes is presented. Wormholes prefigure a hybrid distributed system model, embodying the notion of an enhanced part of the system with good properties otherwise not guaranteed by the normal weak environment.

An error-concealment technique for shape in MPEG-4 object-based video coating is presented. The method is based on using global motion estimation and compensation techniques for boundary recovery.

The ATM VP-based leased line network communication demands varied combination of configurations that link the routes to the actual facilities. An integer programming formulation of the problem and an algorithm to solve it are proposed. It is proved that an algorithm can be used to solve problems with small computing lines.

Some asymmetric traveling salesman problem (ATSP) instances are approximable within bounds equal to 3 and 9/5. Two preprocessing linear programs to reformulate ATSP instances into equivalent ones achieving data-dependent bounds by the same approximation algorithms are discussed.

Our growing reliance on online services accessible on the Internet demands highly available systems that provide correct service without interruptions. Software bugs, operator mistakes, and malicious attacks are a major cause of service interruptions and they can cause arbitrary behavior, that is, Byzantine faults. This article describes a new replication algorithm, BFT, that can be used to build highly available systems that tolerate Byzantine faults. BFT can be used in practice to implement real services: it performs well, it is safe in asynchronous environments such as the Internet, it incorporates mechanisms to defend against Byzantine-faulty clients, and it recovers replicas proactively. The recovery mechanism allows the algorithm to tolerate any number of faults over the lifetime of the system provided fewer than 1/3 of the replicas become faulty within a small window of vulnerability. BFT has been implemented as a generic program library with a simple interface. We used the library to implement the first Byzantine-fault-tolerant NFS file system, BFS. The BFT library and BFS perform well because the library incorporates several important optimizations, the most important of which is the use of symmetric cryptography to authenticate messages. The performance results show that BFS performs 2% faster to 24% slower than production implementations of the NFS protocol that are not replicated. This supports our claim that the BFT library can be used to build practical systems that tolerate Byzantine faults. Categories and Subject Descriptors: C.2.0 [Computer-Communication Networks]: General--Security and protection; C.2.4 [Computer-Communication Networks]: Distributed Systems--Client/server; D.4.3 [Operating Systems]: File Systems Management; D.4.5 [Operating Systems]: Reliability--Fault tolerance; D.4.6 [Operating Systems]: Security and Protection--Access controls; authentication; cryptographic controls; D.4.8 [Operating Systems]: Performance--Measurements General Terms: Security, Reliability, Algorithms, Performance, Measurement Additional Key Words and Phrases: Byzantine fault tolerance, state machine replication, proactive recovery, asynchronous systems, state transfer

A self-organizing protocol is proposed for small ad hoc networks. Among this protocol's original features is the initial creation of an asynchronous sparse tree topology followed by a transition to a more fully connected network and synchronous scheduling. An efficient address bundling technique and unique reliability simulation results for this protocol are also presented.

In this paper, an asynchronous transfer mode (ATM),based network is applied as the communication backbone between geographical information system (GIS) and supervisory control and data acquisition (SCADA). Because the ATM network is a true multiservice network that provides broadband services and meets the different quality of service requirements, this technique is increasingly important in a modern communication system. The paper begins with the event generator that brings different messages to the ATM network from various local area networks. A statistical evaluation is then employed to examine the amount of message flow and the quality of service, where the outcome is assessed based on traffic, capacity and performance of the proposed method. Test results help solidify the effectiveness of the approach for power system communication applications. Index Terms--Asynchronous transfer mode (ATM), geographical information system (GIS), supervisory control and data acquisition (SCADA).

Byline: Raquel Benbunan-Fich (1), Starr Roxanne Hiltz (2) Keywords: asynchronous learning networks; computer-mediated communication systems; group communication; groups versus individuals; field experiment Abstract: An Asynchronous Learning Network (ALN) is a Computer-Mediated Communication System designed to support 'anytime/anywhere' interaction among students and between students and instructors. A field experiment compared groups and individuals solving an ethical case scenario, with and without an ALN, to determine the separate and joint effects of communication medium and teamwork. Dependent variables include quality and length of the reports, and subjective perceptions of learning and satisfaction. The results indicate that that an ALN enhances the quantity and quality of the solutions to an ethical case scenario. The combination of teamwork with ALN-support increases the students' perception of learning. Although the perception of collaborative learning was similar between ALN-supported and unsupported groups, participants in computer-mediated groups reported lower perceptions of discussion quality than participants in manual groups. Author Affiliation: (1) Stillman School of Business, Seton Hall University, South Orange, NJ, 07079 (2) CIS Department, New Jersey Institute of Technology, Newark, NJ, 07102 Article History: Registration Date: 29/09/2004

Byline: M. Thoennessen (1), E. Kashy (1), Y. Tsai (2), N.E. Davis (3) Keywords: asynchronous learning networks; CAPA; computer assisted homework systems; technology in traditional lecture classes Abstract: The evolution of the computer-assisted personalized approach (CAPA) system and its use in large lecture classes is described. Increased individual student contact in these large classes of over 400 students has been established by implementing an asynchronous learning network (ALN). The two systems complement each other and provide the means to monitor and promote individual student performance at any time during the semester. During one semester poorly performing students were individually contacted by personalized e-mail to inform them of their standing and to encourage better performance. Results of this combined technological approach are presented. Author Affiliation: (1) Department of Physics &amp Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI, 48824 (2) Computer Science Department, Michigan State University, East Lansing, MI, 48824 (3) College of Natural Science, Michigan State University, East Lansing, MI, 48824 Article History: Registration Date: 29/09/2004

Byline: Gregory W. Hislop (1) Keywords: Asynchronous Learning Networks; online education Abstract: This paper describes experiences at Drexel University with use of an Asynchronous Learning Network to provide an online graduate degree for information systems professionals. Students in this program never gather for face-to-face classes but students and faculty engage in an active learning experience online. This paper provides an overview of the project's fundamental strategies, presents some evaluation data relevant to these strategies, and concludes with some observations based on the project experience. Author Affiliation: (1) Drexel University, 3141 Chestnut Street, Philadelphia, PA, 19104 E-mail Article History: Registration Date: 29/09/2004

This paper presents a global optimization of the transmission chain for video on asynchronous transfer mode (ATM) channels. This optimum control includes compression, transmission, and decoding. First, the gain in statistical multiplexing is put forward to demonstrate that transmitting at variable rates on asynchronous multiplexing links is more efficient than exploiting the constant rate on synchronous links. The joint optimization relies on both the entropy rate and the end-to-end image quality. This requires the characterization of the video sources as entropy generators, and the development of the entropy rate-distortion functions in the coder and the transmission channel. Quantizers and variable-length entropy coders in coding, traffic, and queues in transmission multiplexing each lead to performance functions expressing quality in terms of entropy rate. The objective measures of quality are, respectively, the PSNR in terms of the output data rate and the cell loss in terms of the network loads. The main advantage of transmitting on variable bit-rate channels is to permit the generation of image sequences at constant subjective quality on the coding side, and the saving of transmission bandwidth through a gain in statistical multiplexing on the network side. Mirrored control actions are described for coding and multiplexing; they lead to a unique global optimum of the transmission chain. Since the decoders are generally slaved to the coding and transmission performances, they are restricted to perform independent optimum signal reconstruction. Index Terms - ATM network, optimum coding, optimum transmission, packet-switched transmissions, video coding.

A new processing strategy for the ATLAS event selection system is proposed for use downstream of the first level trigger. It aims to achieve a reduction of the event rate to a level suitable for recording on permanent storage via a sequential treatment of the 'regions of interest' selected by the level 1 trigger. A possible Trigger/DAQ architecture which exploits this concept is presented. It is based on a single processing farm and a network which transports data and protocol traffic. The resources necessary for the implementation of this architecture are estimated. A set of performance figures obtained by calculations and computer simulations are given assuming the use of ATM networking technology.

Rate control is considered an important issue in video coding, since it significantly affects video quality. In this paper, we will discuss joint encoder and channel rate control for variable bit-rate (VBR) video over packet-switched ATM networks. Since variable bit-rate traffic is allowed in such networks, an open-loop encoder without rate control can generate consistent quality video. However, in order to improve statistical multiplexing gain (SMG), an encoder buffer is essential to meet traffic constraints imposed by networks and to smooth the highly variable video bitstream. Due to the finite buffer size, some forms of encoder rate control have to be enforced, and consequently, video quality varies. We argue that a rate control scheme has to balance both issues of consistent video quality on the encoder side and bitstream smoothness for SMG on the network side. We present a joint encoder and channel rate control algorithm for ATM networks with leaky buckets as open-loop source flow control models. The algorithm considers constraints imposed by the encoder and decoder buffers, the leaky bucket control, traffic smoothing, and rate control. The encoder rate control is separated into a sustainable-rate control and a unidirectional instantaneous-rate control. It can improve the problem of leaky bucket saturation exhibited in previous works. Experimental results with MPEG video will be presented. The results verify our analysis and show the effectiveness of the proposed algorithm. Index Terms - Asynchronous transfer mode, digital video compression, encoding, leaky bucket, MPEG, quantization, rate control, variable bit-rate video.

Byline: Nen-Fu Huang (1), Rui-Chi Wang (1) Keywords: ATM; NP-hardness; PCN Abstract: The wireless personal communication networks (PCN) will play an important role throughout the 1990s and into the next century. Due to the demand for extending the wireless services to integrated services such as data, voice, images and video, a high-speed backbone network to connect the base stations in the microcells is required. One of the possible solutions is to apply the ATM-based backbone network. In such an ATM-based PCN, the communication path between a pair of mobile terminals might be elongated due to the mobility of terminals. Generally, there are two ways to resolve this problem. The first is to migrate the elongated path to a better one when necessary. The other is to design an appropriate backbone network by considering the mobile environment. Recently, several mechanisms based on the former approach have been proposed. In this paper, the latter approach is considered and the design problem of allocating the backbone links among the ATM switches so that the network performance affected by the terminal mobility is kept as less as possible is investigated. We show that this link allocation problem is NP-hard. A simple and efficient heuristic is also proposed for this problem. Simulation results show that based on the backbone obtained by the heuristic, the average length of each communication path is kept as short as possible even under the mobile environment. As a result, the number of successfully established paths in the network is increased significantly. Author Affiliation: (1) Department of Computer Science, National Tsing Hua University, Hsinchu, 30043, Taiwan, Republic of China Article History: Registration Date: 27/09/2004

ATM switching fabrics are good candidates to implement high performance parallel event builders for the future data acquisition systems in particle physics experiments. We are studying their feasibility through simulations and implementation of event builder demonstrators. We present results from performance measurements made with a demonstrator based on a commercial ATM switch and on network interfaces that we have developed. The measurements are compared with the simulation studies and their scalability is discussed.