Unpredictable Delays Research Articles

Soft real-time communication over ethernet with adaptive traffic smoothing

Due to the low price and robustness resulting from its wide acceptance and deployment, Ethernet has become an attractive candidate for real-time control networks. However, it is difficult to build a real-time control network using the standard Ethernet because the Ethernet MAC protocol-1-persistent CSMA/CD protocol-may cause unpredictable access delay. When both real-time and nonreal-time packets are concurrently transported over an ordinary Ethernet, real-time (RT) packets from a node may experience a large delay due to 1) contention with nonRT packets in the local node where they originate and 2) collision with RT and nonRT packets from the other nodes. To resolve this problem, we design, implement, and evaluate an adaptive traffic smoother. Specifically, we design two adaptive traffic smoothers, one at the kernel level and the other at the user level. The kernel-level traffic smoother is installed between the IP layer and the Ethernet MAC layer for better performance, and the user-level traffic smoother is installed on top of the transport layer for better portability. The kernel-level traffic smoother first gives RT packets priority over nonRT packets in order to eliminate contention within the local node. Second, it smoothes nonRT traffic so as to reduce collision with RT packets from the other nodes. This traffic smoothing can dramatically decrease the packet-collision probability on the network. The traffic smoother, installed at each node, regulates the node's outgoing nonRT traffic to maintain a certain rate. In order to provide a reasonable nonRT throughput while providing probabilistic delay guarantees for RT traffic, the nonRT traffic-generation rate is allowed to adapt itself to the underlying network load condition. Our implementation of the traffic smoother requires only a minimal change in the OS kernel without any modification to the current standard of Ethernet MAC protocol or the TCP or UDP/IP stack. The traffic smoother has been implemented on the Linux OS and is shown to reduce the RT message deadline-miss ratio up to two orders of magnitude under a heavily loaded condition, while the nonRT throughput drops only by half. For better portability, we also implemented and evaluated a user-level traffic smoother on top of the transport layer. Moreover, we emulate a switch using a kernel-level traffic smoother to evaluate the performance of traffic smoother in a switched Ethernet environment that can scale to a large control network.

Distance Estimation Error Compensation of a Direct Control Type, Internet-based Mobile Robot System

This research is concerned with the development of an Internet-based mobile robot system, which is insensitive to the unpredictable Internet time delay in data transmission. For this purpose, the PPS (Position Prediction Simulator) is suggested and implemented to compensate for the time delay problem of the Internet. The PPS is divided into two parts, including the 3D virtual simulator and the robot position prediction part. The proposed PPS shows the visual information of a remote site, which is obtained from image processing and predicted position considering the time delay. The simulation results showed that the direct control using the PPS is insensitive to the time delay problem as in the indirect control. For the verification of the proposed PPS, the robot was moved and stopped following the planned path under various traffic conditions. The experimental results showed that the distance error could be reduced using the developed PPS.

Time synchronization in a local area network

In this article we examine the problem of synchronizing the time-of-day clock in one node of an automation network system with a reference clock. The emphasis of this article is on switched, highly loaded networks, where unpredictable delays introduce excessive synchronization noise. PC clocks are accurate enough when connected within a network, but a new requirement is for them to be synchronized, which means that they should show the same time at the same instant. The most prominent time-synchronization method is the network time protocol proposed by Mills and Internet engineering task force group. A complete solution of the high-precision time-synchronization problem must reduce the randomness associated with the RTOS. The methods discussed in this article can help determine the frequency and time offset of a local time-of-day clock. The next challenge is to construct a local time-of-day clock and apply the synchronization information to it.

Prenatal cocaine exposure does not alter working memory in adult rats

The present study was designed to assess working memory in adult rats exposed to intravenous cocaine in utero, as part of an examination of various cognitive and affective functions. The study included four groups: a saline control and three groups exposed to ascending doses of cocaine from gestational days 8 to 21 (0.5, 1.0, or 3.0 mg/kg). This exposure regimen (route of administration and dose) has been shown to accurately reproduce the pharmacokinetic profile and physiological effects of human recreational cocaine use. This report describes the results of a series of automated alternation tasks, in which the animals were rewarded for alternating their responses between two response ports on successive trials. In the final task, the delay between trials varied randomly between 0, 20, 40, and 80 s, thereby varying the retention interval. Although performance declined dramatically as the retention interval increased, the rate of this decline did not differ across treatment groups. These results suggest that prenatal cocaine exposure, at doses that model recreational use, does not produce lasting changes in explicit memory or working memory. However, subtle, sex-specific effects of prenatal cocaine exposure were seen on measures that indicate impairments in sustained attention and “readiness”, as well as altered reactivity to task-related stressors such as waiting for long and unpredictable delays.

Cross-correlation between gravitational wave detectors for detecting association with gamma ray bursts

Cross-correlation of the outputs of two gravitational wave (GW) detectors has recently been proposed as a method for detecting statistical association between GWs and gamma ray bursts (GRBs). Unfortunately, the method can be effectively used only in the case of stationary noise. In this work a different cross-correlation algorithm is presented, which may effectively be applied also in nonstationary conditions for the cumulative analysis of a large number of GRBs. The value of the cross-correlation at zero delay, which is the only one expected to be correlated to any astrophysical signal, is compared with the distribution of cross-correlation of the same data for all nonzero delays within the integration time interval. This background distribution is Gaussian, so the statistical significance of an experimentally observed excess is well defined. Computer simulations using real noise data of the cryogenic GW detectors Explorer and Nautilus with superimposed deltalike signals were performed to test the effectiveness of the method, and theoretical estimates of its sensitivity were compared to the results of the simulation. The effectiveness of the proposed algorithm is compared to that of other cumulative techniques, showing that the algorithm is particularly effective in the case of non-Gaussian noise and of a large (100\char21{}1000 s) and unpredictable delay between GWs and GRBs.

Unilateral lesions of the pedunculopontine nucleus do not alleviate subthalamic nucleus-mediated anticipatory responding in a delayed sensorimotor task in the rat

Lesions of the subthalamic nucleus (STN) in the rat are known to cause anticipated movements in behavioral tasks requiring a preparatory period before the execution of externally cued conditioned movements. In the present study, we describe the effects of lesions of the pedunculopontine nucleus (PPN), a structure located on the outflow of the STN to lower brainstem and spinal motor nuclei, on the anticipatory responding caused by a unilateral lesion of the STN in a delayed sensorimotor task. Rats were instructed to keep a lever pressed down by the presentation of a composite visual and acoustic signal, and were required to hold the lever pressed until a trigger stimulus occurred after an unpredictable delay. The trigger stimulus required the animals to release the lever and to press a second lever for food reinforcement. The task was evaluated according to analysis of movement parameters and errors made by the animals during the preparative and executive phases of the conditioned movement. An ibotenate lesion was placed into the STN in either side of the brain. This lesion was followed 3 weeks later by an ibotenate lesion of the PPN ipsilaterally to the STN previously lesioned. The results indicate that the anticipatory responding induced by the STN lesion was not alleviated by the subsequent PPN lesion. However, the animals bearing the combined lesion were severely impaired in conditioned responding to salient stimuli involved in the paradigm and showed side-specific lengthening of reaction and movement times without global motor impairments. The results suggest that the anticipatory responses caused by STN lesions do not require the intervention of the PPN and that the disruption of the dopaminergic nigrostriatal pathway following the combined lesion may be responsible for impairments observed.

Optimizing controllability of an interactive videoconferencing system with Web-based control interfaces

With the rapid advances in computing and communications technologies, interactive multimedia applications, such as videoconferencing, over wide-area networks are becoming feasible. We developed an ATM-based multipoint videoconferencing (AMV) system, which can support continuous presence with high-quality audio/video and provide Web-based control interfaces for conferees to conduct interactive videoconferences in wide-area networks. On the basis of a well-developed multimedia distribution platform, we developed an application development platform, on which we can prototype videoconferencing applications quickly. Through running a prototype AMV system, we obtained many valuable experiment results. This paper reports the practical experience and studies the controllability of the AMV system on basis of a proposed videoconference model. Since there is unpredictable delay in transmitting conferees' interaction requests, in general, we cannot simultaneously achieve high controllability and high interactivity. To gain more insight into this issue, we develop an approach which can dynamically adjust, according to network conditions, the interval for collecting interaction requests to achieve either high controllability or high interactivity. We conduct experiments to validate and evaluate the approach and, moreover, determine the proper parameter values that achieve optimum tradeoff between controllability and interactivity.

Cooperative Evaluation of XML Queries in Mediators

As XML becomes the de facto standard for data representation and exchange over Internet, there are ever increasing applica tions using XML as a middleware model. Network-computing paradigm is also changing; it shifts to mobile agent paradigm. Building a mediated query system by combining both XML and mobile agent technologies is very promising. In this paper, we address the problem of cooperative evaluation of XML queries by exploiting mobile agent technologies. Our contribu tions are as follows: By introducing a new operator—the variable binding operator, we represent XML queries' pattern body as a special operator tree, and an evaluation method of the variable binding operator is presented to match the XML queries' pattern body with the XML data graph by exploiting automaton theory. In the case of XML data involving XML-Link, by introducing a proxy operator, a novel al gorithm is given to evaluate the XML queries cooperatively, that is, by representing the subquery operator tree with XML, it can be sent to the remote site or brought along with a mobile agent to execute at the remote site. Under the new computing paradigm, how to reduce data shipment and cope with unpredictable network delay is a critical issue, we explore the opportunities that our strategies can bring to optimize the wide-area query processing as well.

Dopamine denervation of specific striatal subregions differentially affects preparation and execution of a delayed response task in the rat

In the present study, the effects of unilateral or bilateral dopamine denervation of either the dorsal or ventral striatum on the preparation and execution of a delayed response task in the rat were investigated. Animals were instructed to hold a lever pressed down by the presentation of a visual and/or acoustic signal, and were required to hold the lever until a trigger stimulus occurred after an unpredictable delay ranging from 2 to 4 s. The trigger stimulus required animals to release the lever and to press a second lever for food reinforcement. The time between instruction and trigger signal represented the preparation phase preceding movement. The motor performance was evaluated by using reaction and movement times in addition to correct responses in each session. Dopaminergic denervation of either the dorsal or ventral striatum ipsilaterally to the side in which the second lever to be pressed was located did not significantly change reaction and movement times, although it reduced the percentage of correct trials. A significant increase of both reaction and movement times was recorded only after bilateral denervation of the ventral striatum. The analysis of incorrect responses indicated that dopaminergic innervation of the two striatal subregions had different functions in the correct execution of the behavioral paradigm. In the group of animals with dorsal lesions the most frequent incorrect response was represented by a lack of the conditioned response to the presentation of the instruction stimulus starting the trial. If the animals reacted properly to this signal, the performance thereafter was correct in the majority of trials. Conversely, animals with ventral lesions exhibited a large repertoire of incorrect responses throughout the paradigm, including premature release or delayed press of levers, and omission of the second lever press. Histological verification of brain coronal sections by tyrosine-hydroxylase immunoreactivity showed that the lesions were confined in either the dorsal or ventral striatum, sparing the lateral region. The data support the hypothesis that dopaminergic innervation enables the two striatal regions to differently participate in the preparation and execution of complex delayed sensorimotor tasks. Indeed, the dorsal striatum seems to be involved in the correct utilization of external sensory information for the initiation of conditioned behavior, whereas, the ventral striatum appears to be mainly concerned with the temporal expectation of impending stimuli that trigger reward-reinforced movements.

The function of the pedunculopontine nucleus in the preparation and execution of an externally-cued bar pressing task in the rat

In the present study the role of the pedunculopontine nucleus (PPN) in the preparation and execution of an externally-cued rewarded motor act was investigated. Animals were instructed to press down a lever at the presentation of a combined visual and acoustic signal and were required to hold down the lever until a trigger stimulus occurred after an unpredictable delay ranging from 2 to 4 s. The trigger stimulus required animals to release the lever and to press a second lever for food reinforcement. The time between instruction and trigger signals represented the preparation phase preceding movement. Unilateral ibotenic acid-induced focal degeneration of pedunculopontine neurons did not influence either reaction and movement times, or capacity of the animals to correctly respond to presentation of stimuli of behavioral significance. On the contrary, bilateral lesions increased both reaction and movement times, and dramatically reduced the percentage of correct responses. The analysis of incorrect responses suggested that the most striking deficit exhibited by the animals following the bilateral lesion was a lack of conditioned response to the signal initiating each trial. However, the animals retained the capability to respond correctly in some trials, and were able to collect the reward when delivered outside the behavioral context. Histological analysis of lesions showed that in addition to loss of neurons within the pedunculopontine region, reduction of tyrosine-hydroxylase positive neurons had occurred in the pars compacta of the substantia nigra. The data suggest that the PPN is involved in the preparation and execution of externally-cued movements, and demonstrate that its destruction mimics the main effects produced by the dopaminergic denervation of the dorsal striatum.

Teleoperating a mobile robot — A solution based on java language

This article describes a computational framework, which can run almost on every computer connected to a IP-based network, to study teleoperation techniques. The paper discusses the teleoperation of a mobile platform from a remote computer, both connected by the Internet communication network. To obtain a cheap and portable solution, the user interface and communication management was developed using Java language. The development based on this language gave a cheap, portable and easy to improve software package that is useful to test new control techniques with large time delays. Since the real time control over the Internet can suffer from unpredictable delays and bandwidth constraints, the authors use the RTP protocol to overcome some of these problems.

Temporal aspects of interaction in shared virtual worlds

In this paper we examine the problems of usability and related temporal issues in shared virtual environments. Shared virtual environments involve physically distributed users interacting with each other and with distributed objects via complex highly graphical user interfaces. These factors can result in interaction which suffers from serious and unpredictable delays in system response times. Careful interaction design can alleviate the problems resulting from such delays. We look at several areas of shared virtual world design, including object interaction, avatars and scene rendering, investigating ways of dealing with communicating information, preserving world coherence and providing users with effective real-time interaction. Our medium of analysis is the Extended User Action Notation (XUAN), a variant of the User Action Notation that enables us to express explicitly and clearly the temporal features of our examples. Finally, we discuss the implications of our temporal analysis for further research and development of shared virtual worlds, and the implications for the further development and use of XUAN.

Response properties of saccade-related burst neurons in the central mesencephalic reticular formation.

We studied the activity of saccade-related burst neurons in the central mesencephalic reticular formation (cMRF) in awake behaving monkeys. In experiment 1, we examined the activity of single neurons while monkeys performed an average of 225 delayed saccade trials that evoked gaze shifts having horizontal and vertical amplitudes between 2 and 20 degrees . All neurons studied generated high-frequency bursts of activity during some of these saccades. For each neuron, the duration and frequency of these bursts of activity reached maximal values when the monkey made movements within a restricted range of horizontal and vertical amplitudes. The onset of the movement followed the onset of the burst by the longest intervals for movements within a restricted range of horizontal and vertical amplitudes. The range of movements for which this interval was longest varied from neuron to neuron. Across the population, these ranges included nearly all contraversive saccades with horizontal and vertical amplitudes between 2 and 20 degrees. In experiment 2, we used the following task to examine the low-frequency prelude of activity that cMRF neurons generate before bursting: the monkey was required to fixate a light-emitting diode (LED) while two eccentric visual stimuli were presented. After a delay, the color of the fixation LED was changed, identifying one of the two eccentric stimuli as the saccadic target. After a final unpredictable delay, the fixation LED was extinguished and the monkey was reinforced for redirecting gaze to the identified saccadic target. Some cMRF neurons fired at a low frequency during the interval after the fixation LED changed color but before it was extinguished. For many neurons, the firing rate during this interval was related to the metrics of the movement the monkey made at the end of the trial and, to a lesser degree, to the location of the eccentric stimulus to which a movement was not directed.

Architectures for shared haptic virtual environments

The lack of force feedback in visual-only simulations may seriously hamper user proprioception, effectiveness and sense of immersion while manipulating virtual environments. Haptic rendering, the process of feeding back force to the user in response to interaction with the environment is sensitive to delay and can become unstable. In this paper we will describe various techniques to integrate force feedback in shared virtual simulations, dealing with significant and unpredictable delays. Three different implementations are investigated: static, collaborative and cooperative haptic virtual environments.

Dependable Transaction Management over a Network of Real-Time Databases

Transaction management consists of many components, such as scheduling, concurrency control, recovery, and distributed commit. These components are designed independently and introduce varying levels of delays. For example, concurrency control based on distributed locking, requires additional efforts for deadlock detection and elimination. The possibility of a deadlock leads to unpredictable delays, and repeated restarts of transactions in distributed systems. On the contrary, real-time transactions require a response within a time limit. In this study, an effort has been made for countering the delay problems.

Asynchronous analysis of parallel dynamic programming algorithms

We examine a very simple asynchronous model of parallel computation that assumes the time to compute a task is random, following some probability distribution. The goal of this model is to capture the effects of unpredictable delays on processors, due to communication delays or cache misses, for example. Using techniques from queueing theory and occupancy problems, we use this model to analyze two parallel dynamic programming algorithms. We show that this model is simple to analyze and correctly predicts which algorithm will perform better in practice. The algorithms we consider are a pipeline algorithm, where each processor i computes in order the entries of rows i, i+p, and so on, where p is the number of processors; and a diagonal algorithm, where entries along each diagonal extending from the left to the top of the table are computed in turn. It is likely that the techniques used here can be useful in the analysis of other algorithms that use barriers or pipelining techniques.

Complex Deficits on Reaction Time Performance following Bilateral Intrastriatal 6‐OHDA Infusion in the Rat

The present study examined the ability of rats subjected to bilateral 6-hydroxydopamine lesions of the terminal area of the nigrostriatal dopamine system to perform a prelearned reaction time task. This lesion model, the induction of a partial dopamine denervation of the striatum (74% depletion of dopamine striatal tissue content) with a retrograde degeneration of dopamine cell bodies in the substantia nigra, sparing the mesolimbic dopaminergic pathway, closely approximates the neuronal degeneration observed in human idiopathic Parkinson's disease. Rats were trained previously to release a lever, within a reaction time limit, after the presentation of a visual cue through reinforcement with food pellets. The onset of the light stimulus varied randomly after an unpredictable delay period of 0.25-1.0 s. Rats with dopaminergic lesions showed moderate to extensive performance deficits which were not compensated for the five postoperative weeks. More than half of the lesioned animals (64%) showed severe deficits, characterized by a concomitant increase in the number of anticipated (premature release of the lever before the visual cue) and delayed responses (lever release after the reaction time limit) with shortened reaction times in some cases. A smaller proportion (36%) of lesioned animals exhibited mild impairment of performance with a large increase in delayed responses and lengthening of reaction times but with no change in the number of anticipated responses. Asymmetric lesions had no effect on the reaction time performance. Examination of tyrosine hydroxylase immunostaining revealed that in the most impaired animals dopamine depletion was extensive in the medial striatum, whereas it was restricted to the dorsolateral striatum in the least impaired animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Real-time communication in multihop networks

Communication in real-time systems has to be predictable, because unpredictable delays in the delivery of messages can adversely affect the execution of tasks dependent on these messages. We develop a scheme for providing predictable interprocess communication in real-time systems with (partially connected) point-to-point interconnection networks, which provide guarantees on the maximum delivery time for messages. This scheme is based on the concept of a real-time channel, a unidirectional connection between source and destination. A real-time channel has parameters that describe the performance requirements of the source-destination communication, e.g., from a sensor station to a control site. Once such a channel is established, the communications subsystem guarantees that these performance requirements will be met. We concentrate on methods to compute guarantees for the delivery time of messages belonging to real-time channels. We also address problems associated with allocating buffers for these messages and develop a scheme that preserves delivery time guarantees. >

A Time Analysis of a Technical Services Workflow in a Representative Library

In September 1990, the Sterling C. Evans Library at Texas A&M university implemented the NOTIS acquisitions module. The cataloging, OPAC, circulation, and serials records functions were already operational. The researchers examined the changes in workflow by tracking 641 social science firm orders (excluding serials) to identify possible bottlenecks and unpredicted delays in the process from selection to availability to the library patrons. All of the orders were tracked for eight months, at which time the researchers analyzed the results. Initially, researchers noted that training, staff adjusting to changes in procedures, and new equipment resulted in processing delays. The continued lack of adequate equipment and high turnover in calaloging personnel had the greatest effect later in the study.

Compiler support for object-oriented real-time software

The suitability of compile-time code analysis and rearrangement to improve the predictability of object-oriented software in dynamic real-time environments is discussed. The techniques combine the abstraction of object-oriented software design with the power of static, compiler-based code analysis to develop and enhance the predictability of real-time software. They also counteract the effects of unpredictable delays caused by the arrival, servicing, and execution of dynamic tasks, and give the application latitude to react to delays caused by hardware, external events, and the loading of communication media. >