Home About us Contact
|
Home About us Contact | ||
|
|
||
Congestion
Kinds of Congestion Terms modified by Congestion Selected AbstractsScale, Congestion and GrowthECONOMICA, Issue 267 2000Theo Eicher This paper explores the relationship between aggregate and relativecongestion, returns to scale and economic growth. Aggregate congestionreduces the effective productivity of capital; relative congestion reducesthe effective productivity of labour. Both forms of congestion adverselyaffect the equilibrium growth rate, although their relative effects dependupon aggregate returns to scale. The two forms of congestion havecontrasting effects on the transitional dynamics. Relative congestionretards the rate of adjustment; aggregate congestion accelerates it. Theexternalities generated by congestion and non-optimal expenditure can befully corrected, both during the transition and in steady state, by atime-invariant income tax. [source] Generalized window advertising for TCP congestion control,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2002Mario Gerla Congestion in the Internet is a major cause of network performance degradation. The Generalized Window Advertising (GWA) scheme proposed in this paper is a new approach for enhancing the congestion control properties of TCP. GWA requires only minor modifications to the existing protocol stack and is completely backward compatible, allowing GWA-hosts to interact with non-GWA hosts without modifications. GWA exploits the notion of end-host-network cooperation, with the congestion level notified from the network to end hosts. It is based on solid control theory results mat guarantee performance and stable network operation. GWA is able to avoid window oscillations and the related fluctuations in offered load and network performance. This makes it more robust to sustained network overload due to a large number of connections competing for the same bottleneck, a situation where traditional TCP implementations fail to provide satisfactory performance. GWA-TCP is compared with traditional TCP, TCP with RED and also ECN using the ns-2 simulator. Results show that in most cases GWA-TCP outperforms the traditional schemes. In particular, when compared with ECN, it provides smoother network operation and increased fairness. [source] Effects of club size in the provision of public goods.PAPERS IN REGIONAL SCIENCE, Issue 4 2002Network, congestion effects in the case of the French municipalities Congestion; public goods; urban economics; local governments Abstract The article formalizes and measures the impact of club size on the quality of the public good provided to its members. Under a general framework we describe various functional forms that allow either network or crowding effects. Mechanisms of provision are that of a political process in which both the demand and the supply sides are considered. Estimations use the whole set of French municipalities. The supply model performs better than the demand model in the case of small municipalities, while for large cities the demand model has higher explanatory power. In so far as impact of city size on the quality of club goods is concerned, crowding does appear, but it does so in different patterns. For small towns marginal congestion first decreases then increases with population. Marginal congestion is decreasing for cities of intermediate size. For larger cities no significant effects are observed. [source] Social Optimal Location of Facilities with Fixed Servers, Stochastic Demand, and CongestionPRODUCTION AND OPERATIONS MANAGEMENT, Issue 6 2009Ignacio Castillo We consider two capacity choice scenarios for the optimal location of facilities with fixed servers, stochastic demand, and congestion. Motivating applications include virtual call centers, consisting of geographically dispersed centers, walk-in health clinics, motor vehicle inspection stations, automobile emissions testing stations, and internal service systems. The choice of locations for such facilities influences both the travel cost and waiting times of users. In contrast to most previous research, we explicitly embed both customer travel/connection and delay costs in the objective function and solve the location,allocation problem and choose facility capacities simultaneously. The choice of capacity for a facility that is viewed as a queueing system with Poisson arrivals and exponential service times could mean choosing a service rate for the servers (Scenario 1) or choosing the number of servers (Scenario 2). We express the optimal service rate in closed form in Scenario 1 and the (asymptotically) optimal number of servers in closed form in Scenario 2. This allows us to eliminate both the number of servers and the service rates from the optimization problems, leading to tractable mixed-integer nonlinear programs. Our computational results show that both problems can be solved efficiently using a Lagrangian relaxation optimization procedure. [source] The effect of inferior turbinate hypertrophy on nasal spray distribution to the middle meatus,CLINICAL OTOLARYNGOLOGY, Issue 6 2001A.C. Dowley The effect of inferior turbinate hypertrophy on nasal spray distribution to the middle meatus The distribution of topical nasal sprays is suboptimal, the main obstruction to adequate delivery in normal volunteers being the nasal valve. We aimed to test the hypothesis that, in patients with rhino-sinusitis, hypertrophy of the inferior turbinate also limits the distribution of administered drug to the middle meatus. We modelled the effect of inferior turbinate hypertrophy and reduction by effecting congestion (by ipsilateral isometric exercise) and decongestion (topical oxymetazoline) in normal volunteers. The method chosen to estimate drug delivery to the middle meatus used endoscopic photography after the administration of dyed aqueous spray. A randomized cross-over study design was used and 20 nasal cavities were studied. The congestion/decongestion manoeuvres significantly altered nasal airflow, as measured by peak inspiratory nasal flow (P < 0.001). Congestion diminished significantly drug delivery to the middle meatus, as compared with decongestion (P = 0.026). This may support a clinical role for inferior turbinate reduction to improve the efficacy of topical nasal therapy, as well as improving nasal airflow. [source] Role of natriuretic hormones in the diagnosis of patent ductus arteriosus in newborn infantsACTA PAEDIATRICA, Issue 4 2001E Pesonen Haemodynamically significant patent ductus arteriosus worsens respiratory distress by initiating pulmonary congestion and inactivating of surfactant. Excepting size of the ductus, several factors influence ductal flow. Conclusion: Atrial natriuretic hormones provide clinically useful data, especially in serial follow-up of the patient. [source] A Behavioral Component Analysis of Route Guidance Systems Using Neural NetworksCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2003Khaled Hamad This article focuses on the behavioral component, one of the three components (the other two being dynamic traffic component and information supply strategy component) of a practical RGS developed through a 4-year project at the University of Delaware. Development of the behavioral model is based on the premise that different drivers perceive and behave differently in response to the information provided. Understanding the behavior of RGS-equipped drivers' acceptance or nonacceptance of provided information is essential for understanding the reliability of the system. Backpropagation neural network with its ability to map complex input,output relationships has been used to structure the model. This model was tested on two networks under both recurring and nonrecurring congestion. A comparative analysis of the measures of effectiveness revealed that the performance of the developed RGS is significantly better than the performance under existing non-RGS conditions. [source] Network-aware selective job checkpoint and migration to enhance co-allocation in multi-cluster systems,CONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 13 2009William M. Jones Abstract Multi-site parallel job schedulers can improve average job turn-around time by making use of fragmented node resources available throughout the grid. By mapping jobs across potentially many clusters, jobs that would otherwise wait in the queue for local resources can begin execution much earlier; thereby improving system utilization and reducing average queue waiting time. Recent research in this area of scheduling leverages user-provided estimates of job communication characteristics to more effectively partition the job across system resources. In this paper, we address the impact of inaccuracies in these estimates on system performance and show that multi-site scheduling techniques benefit from these estimates, even in the presence of considerable inaccuracy. While these results are encouraging, there are instances where these errors result in poor job scheduling decisions that cause network over-subscription. This situation can lead to significantly degraded application performance and turnaround time. Consequently, we explore the use of job checkpointing, termination, migration, and restart (CTMR) to selectively stop offending jobs to alleviate network congestion and subsequently restart them when (and where) sufficient network resources are available. We then characterize the conditions and the extent to which the process of CTMR improves overall performance. We demonstrate that this technique is beneficial even when the overhead of doing so is costly. Copyright © 2009 John Wiley & Sons, Ltd. [source] Loop Diuretics Can Cause Clinical Natriuretic Failure: A Prescription for Volume ExpansionCONGESTIVE HEART FAILURE, Issue 1 2009Syed S. Ali MD Ultrafiltration enhances volume removal and weight reduction vs diuretics. However, their differential impact on total body sodium, potassium, and magnesium has not been described. Fifteen patients with congestion despite diuretic therapy had urine electrolytes measured after a diuretic dose. Ultrafiltration was initiated and ultrafiltrate electrolytes were measured. The urine sodium after diuretics (60±47 mmol/L) was less than in the ultrafiltrate (134±8.0 mmol/L) (P=.000025). The urine potassium level after diuretics (41±23 mmol/L) was greater than in the ultrafiltrate (3.7±0.6 mmol/L) (P=.000017). The urine magnesium level after diuretics (5.2±3.1 mg/dL) was greater than in the ultrafiltrate (2.9±0.7 mg/dL) (P=.017). In acute decompensated heart failure patients with congestion despite diuretic therapy, diuretics are poor natriuretics and cause significant potassium and magnesium loss. Ultrafiltration extracts more sodium while sparing potassium and magnesium. The sustained clinical benefits of ultrafiltration compared with diuretics may be partly related to their disparate effects on total body sodium, potassium, and magnesium, in addition to their differential efficacy of volume removal. [source] An environment for prosperity and quality living accommodating growth in the Thames ValleyCORPORATE SOCIAL RESPONSIBILITY AND ENVIRONMENTAL MANAGEMENT, Issue 1 2004Hugh Howes The Thames Valley is seen as the powerhouse of the British economy, and one of the best performing regions in Europe. This economic base offers opportunities for expansion with the potential for it to become the knowledge capital of Europe. Business interests view the area as a highly desirable location, not only because of its markets, skills and proximity to the City and Heathrow but also because of its high quality environment. Companies, however, complain of skills shortages, traffic congestion, lack of suitable premises and housing that is affordable to the workforce. Much of the Thames Valley is either Green Belt or Areas of Outstanding Natural Beauty. Furthermore, the availability of future water supplies, the maintenance of the quality of water in the rivers and managing flood risk are also likely to act as constraints on development in the future. How economic growth is to be achieved with minimal additional development and without detriment to the environment is the central question that is likely to dominate planning in the this region over the next few years. Is it possible to achieve more with existing resources? Copyright © 2004 John Wiley & Sons, Ltd and ERP Environment. [source] Road pricing: lessons from LondonECONOMIC POLICY, Issue 46 2006Georgina Santos SUMMARY Road pricing LESSONS FROM LONDON This paper assesses the original London Congestion Charging Scheme (LCCS) and its impacts, and it simulates the proposed extension which will include most of Kensington and Chelsea. It also touches upon the political economy of the congestion charge and the increase of the charge from £5 to £8 per day. The possibility of transferring the experience to Paris, Rome and New York is also discussed. The LCCS has had positive impacts. This was despite the considerable political influences on the charge level and location. It is difficult to assess the impacts of the increase of the charge from £5 to £8, which took place in July 2005, because no data have yet been released by Transport for London. The proposed extension of the charging zone does not seem to be an efficient change on economic grounds, at least for the specific boundaries, method of charging and level of charging that is currently planned. Our benefit cost ratios computed under different assumptions of costs and benefits are all below unity. Overall, the experience shows that simple methods of congestion charging, though in no way resembling first-best Pigouvian taxes, can do a remarkably good job of creating benefits from the reduction of congestion. Nevertheless, the magnitude of these benefits can be highly sensitive to the details of the scheme, which therefore need to be developed with great care. , Georgina Santos and Gordon Fraser [source] Scale, Congestion and GrowthECONOMICA, Issue 267 2000Theo Eicher This paper explores the relationship between aggregate and relativecongestion, returns to scale and economic growth. Aggregate congestionreduces the effective productivity of capital; relative congestion reducesthe effective productivity of labour. Both forms of congestion adverselyaffect the equilibrium growth rate, although their relative effects dependupon aggregate returns to scale. The two forms of congestion havecontrasting effects on the transitional dynamics. Relative congestionretards the rate of adjustment; aggregate congestion accelerates it. Theexternalities generated by congestion and non-optimal expenditure can befully corrected, both during the transition and in steady state, by atime-invariant income tax. [source] Power flow congestion relief by using customer-side energy storage systemsELECTRICAL ENGINEERING IN JAPAN, Issue 1 2007Ken Furusawa Abstract In recent years, energy storage systems have increasingly been expected as a means of load leveling of the annual load factor. Of course there is an effect of installing the energy storage systems at the substation. But some customers operate their storage system in an integrated way and it also has an effect of increasing the load factor. In this paper the authors proposed that the energy storage systems on the customer side be used for congestion relief on transmission networks. However, it is not clear which kind of customer has the effect of relieving transmission line congestion. First, this paper assumes the authors determine the optimal configuration of energy equipment including energy storage systems. We propose a new contract whereby electric utility subsidizes a part of the entrance cost of the energy storage systems and customers change the output pattern of energy storage according to the request of the electric utility. This paper evaluates the possibility that the contract gives merit to both the electric utility and the customer. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(1): 36,45, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20299 [source] Expression of caspase and apoptotic signal pathway induced by sulfur dioxideENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 2 2010Juli Bai Abstract Sulfur dioxide (SO2) is a common air pollutant that is released in low concentrations into the atmosphere and in higher concentrations in some work places. In the present study, male Wistar rats were housed in exposure chambers and treated with 14.00 ± 1.01, 28.00 ± 1.77, and 56.00 ± 3.44 mg/m3 SO2 for 7 days (6 hr/day), while control rats were exposed to filtered air under the same conditions. The mRNA and protein levels of caspase-3, caspase-8, and caspase-9 were analyzed using a real-time reverse transcription-polymerase chain reaction (real-time RT-PCR) assay and an immunohistochemistry method. Activities of caspases were detected using colorimetric and fluorescent assays. Chromatin degradation and cell morphological changes were investigated by TUNEL assay and H&E staining in livers and lungs, respectively. The results showed that mRNA levels, protein levels and activities of caspase-3, caspase-8, and caspase-9 were increased in a dose-dependent manner in livers and lungs of rats after SO2 inhalation. In addition, livers were infiltrated with lymphocytes, congestion and inflammation occurred in lungs, and eosinophil cells and apoptotic cells increased in both livers and lungs after SO2 inhalation. These results suggest that SO2 exposure increases the expression and activity of both initiator and and effector caspases, and may induce apoptosis in liver and lung of rats through both death receptor and mitochondrial pathways. Environ. Mol. Mutagen. 2010. © 2009 Wiley-Liss, Inc. [source] Performance of TCP on low-bandwidth wireless links with delay spikesEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2008Pasi Lassila We model the goodput of a single TCP source on a wireless link experiencing sudden increases in Round Trip Time (RTT), that is delay spikes. Such spikes trigger spurious timeouts that reduce the TCP goodput. Renewal reward theory is used to derive a straightforward expression for TCP goodput that takes into account limited sending rates (limited window size), lost packets due to congestion and the delay spike properties such as the average spike duration and distribution of the spike intervals. The basic model is for independent and identically distributed (i.i.d.) spike intervals, and correlated spike intervals are modelled by using a modulating background Markov chain. Validation by ns2 simulations shows excellent agreement for lossless scenarios and good accuracy for moderate loss scenarios (for packet loss probabilities less than 5%). Numerical studies have also been performed to assess the impact of different spike interval distributions on TCP performance. Copyright © 2007 John Wiley & Sons, Ltd. [source] TCP-friendly transmission of voice over IPEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2003F. Beritelli In the last few years an increasing amount of attention has been paid to technologies for the transmission of voice over IP (VoIP). At present, the UDP transport protocol is used to provide this service. However, when the same bottleneck link is shared with TCP flows, and in the presence of a high network load and congestion, UDP sources capture most of the bandwidth, strongly penalizing TCP sources. To solve this problem some congestion control should be introduced for UDP traffic as well, in such a way that this traffic becomes TCP-friendly. In this perspective, several TCP-friendly algorithms have been proposed in the literature. Among them, the most promising candidates for the immediate future are RAP and TFRC. However, although these algorithms were introduced to support real-time applications on the Internet, up to now the only target in optimizing them has been that of achieving fairness with TCP flows in the network. No attention has been paid to the applications using them, and in particular, to the quality of service (QoS) perceived by their users. The target of this paper is to analyze the problem of transmitting voice over IP when voice sources use one of these TCP-friendly algorithms. With this aim, a VoIP system architecture is introduced and the characteristics of each its elements are discussed. To optimize the system, a multirate voice encoder is used so as to be feasible to work over a TCP layer, and a modification of both RAP and TFRC is proposed. Finally, in order to analyze the performance of the proposed system architecture and to compare the modified RAP and TFRC with the original algorithms, the sources have been modeled with an arrival process modulated by a Markov chain, and the model has been used to generate traffic in a simulation study performed with the ns-2 network simulator. Copyright © 2003 AEI. [source] Isolation of a Carnobacterium maltaromaticum- like bacterium from systemically infected lake whitefish (Coregonus clupeaformis)FEMS MICROBIOLOGY LETTERS, Issue 1 2008Thomas P. Loch Abstract Herein we report on the first isolation of a Carnobacterium maltaromaticum -like bacterium from kidneys and swim bladders of lake whitefish (Coregonus clupeaformis) caught from Lakes Michigan and Huron, Michigan. Isolates were Gram-positive, nonmotile, facultatively anaerobic, asporogenous rods that did not produce catalase, cytochrome oxidase, or H2S, and did not grow on acetate agar. Except for carbohydrate fermentation, many phenotypic characteristics of lake whitefish isolates coincided with those of C. maltaromaticum, the causative agent of pseudokidney disease. Partial sequencing of 16S and 23S rRNA genes, as well as the piscicolin 126 precursor gene, yielded 97% and 98% nucleotide matches with C. maltaromaticum, respectively (accession numbers EU546836 and EU546837; EU643471). Phylogenetic analyses showed that lake whitefish isolates of this study are highly related, yet not fully identical to C. maltaromaticum. The presence of the C. maltaromaticum -like bacterium was associated with splenomegaly, renal and splenic congestion, and thickening of the swim bladder wall with accumulation of a mucoid exudate. Examination of stained tissue sections revealed renal and splenic congestion, vacuolation and bile stasis within the liver, and hyperplasia within the epithelial lining of the swim bladder. The concurrent presence of pathological changes and the C. maltaromaticum -like bacteria suggests that this bacterium is pathogenic to lake whitefish. [source] Urban Form and Household Activity-Travel BehaviorGROWTH AND CHANGE, Issue 2 2006RON N. BULIUNG ABSTRACT Cities and metropolitan regions face several challenges including urban sprawl, auto dependence and congestion, and related environmental and human health effects. Examining the spatial characteristics of daily household activity-travel behavior holds important implications for understanding and addressing urban transportation issues. Research of this sort can inform development of urban land use policy that encourages the use of local opportunities, potentially leading to reduced motorized travel. This article examines the potential household activity-travel response to a planned metropolitan polycentric hierarchy of activity centers. Behavioral observations have been drawn from an activity-travel survey conducted in the Portland, Oregon, metropolitan area during the mid-1990s. Evidence presented from exploratory analysis indicates an urban/suburban differential, with less daily travel and smaller activity spaces for urban households. Investigation of the travel reduction potential of the proposed land-use strategy suggests that location effects could be offset by adjustments to household sociodemographic and mobility characteristics. [source] Reconstruction of the columella using the prefabricated reverse flow submental flap: A case reportHEAD & NECK: JOURNAL FOR THE SCIENCES & SPECIALTIES OF THE HEAD AND NECK, Issue 7 2006Onder Tan MD Abstract Background. The reconstruction of columellar defects is still a challenging procedure because of limited local and regional flap options and the characteristics of the anatomy of this site. Although a number of methods are available to repair nasal columella defects, no treatment of choice ensuring an excellent texture- and color-matched tissue in one stage has been determined to date. Method. In this case, we used a reverse-flow submental island flap prefabricated with the costal cartilage for the reconstruction of a complex columellar defect. Result. The flap survived completely with reversible venous congestion. The cosmetic result and nasal respiratory function were acceptable during the follow-up time of 6 months. Conclusion. We propose that the prefabricated reverse submental flap may be an alternative among the surgical options for columellar defects. This flap may also be considered in the reconstructive repertoire of other composite defects of the head and neck region. © 2006 Wiley Periodicals, Inc. Head Neck, 2006 [source] Upper and Lower Cluster Headache: Clinical and Pathogenetic Observations in 608 PatientsHEADACHE, Issue 7 2002Carola Cademartiri MD Objective, Background, and Methods.,Ever since it was proposed by Ekbom and Kugelberg back in 1968 on the basis of the different location of head pain during attacks, the differentiation of cluster headache into an upper syndrome (US) and a lower syndrome (LS) has been regarded as a purely academic distinction. To evaluate whether this differentiation is indeed well founded and to understand its possible significance in the light of current pathogenetic knowledge, we rigorously applied Ekbom and Kugelberg's classification criteria to a sample of 608 patients with cluster headache (CH; 440 men and 168 women), including 483 with episodic CH, 69 with chronic CH, and 56 with CH periodicity undetermined. Results.,Of these patients, 278 could be classified as US sufferers and 330 as LS sufferers. Our data analysis showed statistically significant clinical differences between the two syndromes: pain location was more common in the ocular, temporal, and nuchal regions among LS sufferers; in addition, patients with LS reported not only a higher rate of autonomic symptoms, but also a higher predominance of nasal congestion, ptosis, and forehead and facial sweating among these symptoms. Conclusions.,Based on current anatomofunctional knowledge and on the most recent pathogenetic findings, we believe that changes in hypothalamic activity posteroinferiorly may lead to activation of the caudal part of the spinal trigeminal nucleus by way of the hypothalamus, midbrain, and trigeminal nerve fibers and consequently to activation of the trigeminovascular system with a different location in the two syndromes. More specifically, there seems to be a larger and more extensive involvement of the subnucleus caudalis in LS compared with US, where only its ventrocaudal portions are likely to be affected. [source] "Tower, Am I Cleared to Land?": Problematic Communication in Aviation DiscourseHUMAN COMMUNICATION RESEARCH, Issue 3 2008John W. Howard III This study examined problematic communication in pilot,air traffic controller (ATC) interaction. More than 15 hours of pilot,ATC dialogue were collected by monitoring control tower frequencies at 15 U.S. airports. The transcribed data yielded a total of 34 ATCs, 270 pilots, and 1,799 turns of talk. Analyses revealed that (a) communication problematics manifested in pilot turns more than ATC turns, (b) higher amounts of information led to increased problematic communication in the subsequent turn, and (c) linguistic violations of ATC protocol increased problematic communication in the subsequent turn. Partial support was found for the effect of frequency congestion on problematic communication. No effect was observed for airport size on problematic communication. The discussion addresses the significance of protocol deviations and system constraints for problematic communication. Applications for the findings in pilot,ATC radio interaction are also suggested. Résumé « Tour de contrôle, suis-je autoriséà atterrir? » : Communication à problèmes dans le discours de l,aviation Cette recherche a étudié la communication à problèmes en interaction pilote-contrôleur aérien. Plus de 15 heures de dialogue pilote-contrôleur aérien furent recueillies grâce au suivi des fréquences des tours de contrôle de 15 aéroports des États-Unis. Un total de 34 contrôleurs aériens, 270 pilotes et 1799 tours de parole se retrouvent dans les données retranscrites. Les analyses ont révélé que a) les problèmes de communication se sont manifestés dans les tours de parole des pilotes plutôt que dans les tours de parole des contrôleurs aériens, b) une plus grande quantité d'information menait à plus de communication à problèmes dans le tour de parole subséquent et c) les violations linguistiques du protocole des contrôleurs aérien augmentaient la communication à problèmes au tour de parole subséquent. L,analyse appuie en partie l'effet de l,encombrement des fréquences sur la communication à problèmes. La taille de l'aéroport n,a pas eu d'effet observable sur la communication à problèmes. La discussion aborde l'importance des déviations du protocole et des contraintes de système pour la communication à problèmes. Il est aussi suggéré des applications des résultats aux interactions radio entre pilotes et contrôleurs aériens. Abstract "Tower, darf ich landen?" Problematische Kommunikation im Luftfahrtsdiskurs Diese Studie befasst sich mit der Untersuchung von problematischer Kommunikation zwischen Pilot und Fluglotse. Durch die Beobachtung der Luftüberwachung an 15 U.S.-amerikanischen Flughäfen konnten mehr als 15 Stunden Dialog zwischen Pilot und Fluglotse zusammengetragen werden. Die transkribierten Daten lieferten 34 Fluglotsen, 270 Piloten und 1799 Gesprächsfolgen. Die Auswertung zeigte, dass (a) Kommunikationsprobleme eher auf Seiten der Piloten als der Fluglotsen zu finden waren, (b) eine größere Informationsmenge zu vermehrter problematischer Kommunikation im darauf folgenden Dialogteil führte und c) linguistische Übertretungen des Fluglotsenprotokolls ebenfalls zu vermehrter problematischer Kommunikation beim darauf folgenden Dialogteil führte. Die Flughafengröße hatte keinen Einfluss auf problematische Kommunikation. In der Diskussion wird die Bedeutsamkeit von Protokollabweichungen und Bedingungen des Systems für die problematische Kommunikation erörtert und die Anwendungsmöglichkeiten der Ergebnisse für die Funkinteraktion zwischen Pilot und Fluglotse vorgeschlagen. Resumen "Torre, ¿Está Despejado Para Aterrizar?": La Comunicación Problemática en el Discurso de la Aviación Este estudio examina la comunicación problemática en la interacción entre el piloto y la torre de control de tráfico de aire (ATC). Más de 15 horas de diálogos entre pilotos y ATC fueron coleccionados mediante el monitoreo de las frecuencias de la torre de control de 15 aeropuertos en los Estados Unidos. Los datos transcriptos resultaron en un total de 34 ATC, 270 pilotos, y 1799 turnos de conversación. Los análisis revelaron que (a) la comunicación problemática se manifestaba más en los turnos de los pilotos que en los turnos de los ATC, (b) mayores niveles de información llevaron a un incremento de la comunicación problemática en los turnos subsecuentes, y (c) las violaciones lingüísticas al protocolo del ATC incrementó la comunicación problemática en los turnos subsecuentes. Se encontró apoyo parcial para el efecto de frecuencia de congestión en la comunicación problemática. No se observó efecto alguno entre el tamaño del aeropuerto y la comunicación problemática. En la discusión, se trata la significancia de las desviaciones del protocolo y las constricciones del sistema sobre la comunicación problemática. Las aplicaciones de estos hallazgos en la interacción entre pilotos y la radio del ATC son sugeridas también. ZhaiYao Yo yak [source] Hybrid adaptive predictive control for a dynamic pickup and delivery problem including traffic congestionINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 2 2008Cristián E. Cortés Abstract This paper presents a hybrid adaptive predictive control approach to incorporate future information regarding unknown demand and expected traffic conditions, in the context of a dynamic pickup and delivery problem with fixed fleet size. As the routing problem is dynamic, several stochastic effects have to be considered within the analytical expression of the dispatcher assignment decision objective function. This paper is focused on two issues: one is the extra cost associated with potential rerouting arising from unknown requests in the future, and the other is the potential uncertainty in travel time coming from non-recurrent traffic congestion from unexpected incidents. These effects are incorporated explicitly in the objective function of the hybrid predictive controller. In fact, the proposed predictive control strategy is based on a multivariable model that includes both discrete/integer and continuous variables. The vehicle load and the sequence of stops correspond to the discrete/integer variable, adding the vehicle position as an indicator of the traffic congestion conditions. The strategy is analyzed under two scenarios. The first one considers a predictable congestion obtained using historical data (off-line method) requiring a predictive model of velocities distributed over zones. The second scenario that accepts unpredictable congestion events generates a more complex problem that is managed by using both fault detection and isolation and fuzzy fault-tolerant control approaches. Results validating these approaches are presented through a simulated numerical example. Copyright © 2007 John Wiley & Sons, Ltd. [source] Corruption-aware adaptive increase and adaptive decrease algorithm for TCP error and congestion controls in wireless networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2009Lin Cui Abstract The conventional TCP tends to suffer from performance degradation due to packet corruptions in the wireless lossy channels, since any corruption event is regarded as an indication of network congestion. This paper proposes a TCP error and congestion control scheme using corruption-aware adaptive increase and adaptive decrease algorithm to improve TCP performance over wireless networks. In the proposed scheme, the available network bandwidth is estimated based on the amount of the received integral data as well as the received corrupted data. The slow start threshold is updated only when a lost but not corrupted segment is detected by sender, since the corrupted packets still arrive at the TCP receiver. In the proposed scheme, the duplicated ACKs are processed differently by sender depending on whether there are any lost but not corrupted segments at present. Simulation results show that the proposed scheme could significantly improve TCP throughput over the heterogeneous wired and wireless networks with a high bit error rate, compared with the existing TCP and its variants. Copyright © 2008 John Wiley & Sons, Ltd. [source] Competitive flow control in general multi-node multi-link communication networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2008Ismet Sahin Abstract In this paper, we consider the flow control in a general multi-node multi-link communication network with competing users. Each user has a source node, a destination node, and an existing route for its data flow over any set of links in the network from its source to its destination node. The flow rate for each user is a control variable that is determined by optimizing a user-specific utility function which combines maximizing the flow rate and minimizing the network congestion for that user. A preference parameter in the utility function allows each user to adjust the trade-off between these two objectives. Since all users share the same network resources and are only interested in optimizing their own utility functions, the Nash equilibrium of game theory represents a reasonable solution concept for this multi-user general network. The existence and uniqueness of such an equilibrium is therefore very important for the network to admit an enforceable flow configuration. In this paper, we derive an expression for the Nash equilibrium and prove its uniqueness. We illustrate the results with an example and discuss some properties and observations related to the network performance when in the Nash equilibrium. Copyright © 2007 John Wiley & Sons, Ltd. [source] Performance of delay-sensitive traffic in multi-layered satellite IP networks with on-board processing capabilityINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 12 2007Suzan Bayhan Abstract In this article, performance of delay-sensitive traffic in multi-layered satellite Internet Protocol (IP) networks with on-board processing (OBP) capability is investigated. With OBP, a satellite can process the received data, and according to the nature of application, it can decide on the transmission properties. First, we present a concise overview of relevant aspects of satellite networks to delay-sensitive traffic and routing. Then, in order to improve the system performance for delay-sensitive traffic, specifically Voice over Internet Protocol (VoIP), a novel adaptive routing mechanism in two-layered satellite network considering the network's real-time information is introduced and evaluated. Adaptive Routing Protocol for Quality of Service (ARPQ) utilizes OBP and avoids congestion by distributing traffic load between medium-Earth orbit and low-Earth orbit layers. We utilize a prioritized queueing policy to satisfy quality-of-service (QoS) requirements of delay-sensitive applications while evading non-real-time traffic suffer low performance level. The simulation results verify that multi-layered satellite networks with OBP capabilities and QoS mechanisms are essential for feasibility of packet-based high-quality delay-sensitive services which are expected to be the vital components of next-generation communications networks. Copyright © 2007 John Wiley & Sons, Ltd. [source] A study on a receiver-based management scheme of access link resources for QoS-controllable TCP connectionsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 7 2006Kazuhiro Azuma Abstract Although the bandwidth of access networks is rapidly increasing with the latest techniques such as DSL and FTTH, the access link bandwidth remains a bottleneck, especially when users activate multiple network applications simultaneously. Furthermore, since the throughput of a standard TCP connection is dependent on various network parameters, including round-trip time and packet loss ratio, the access link bandwidth is not shared among the network applications according to the user's demands. In this thesis, we present a new management scheme of access link resources for effective utilization of the access link bandwidth and control of the TCP connection's throughput. Our proposed scheme adjusts the total amount of the receive socket buffer assigned to TCP connections to avoid congestion at the access network, and assigns it to each TCP connection according to characteristics in consideration of QoS. The control objectives of our scheme are (1) to protect short-lived TCP connections from the bandwidth occupation by long-lived TCP connections, and (2) to differentiate the throughput of the long-lived TCP connections according to the upper-layer application's demands. One of the results obtained from the simulation experiments is that our proposed scheme can reduce the delay of short-lived document transfer perceived by the receiver host by up to about 90%, while a high utilization of access link bandwidth is maintained. Copyright © 2006 John Wiley & Sons, Ltd. [source] Reorder notifying TCP (RN-TCP) with explicit packet drop notification (EPDN)INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2006Arjuna Sathiaseelan Abstract Numerous studies have shown that packet reordering is common, especially in networks where there is high degree of parallelism and different link speeds. Reordering of packets decrease the TCP performance of a network, mainly because it leads to overestimation of the congestion in the network. In this paper, we analyse the performance of networks when reordering of packets occur. We propose a proactive solution that could significantly improve the performance of the network when reordering of packets occurs. We report results of our simulation experiments, which support this claim. Our solution is based on enabling the senders to distinguish between dropped packets and reordered packets. Copyright © 2005 John Wiley & Sons, Ltd. [source] A perceptual quality model intended for adaptive VoIP applications,INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2006Christian Hoene Abstract Quality models predict the perceptual quality of services as they calculate subjective ratings from measured parameters. In this article, we present a new quality model that evaluates Voice over IP (VoIP) telephone calls. In addition to packet loss rate, coding mode and delay, it takes into account the impairments due to changes in the transmission configuration (e.g. switching the coding mode or re-scheduling the playout time). Moreover, this model can be used at run time to control the transmission of such calls. It is also computationally efficient and open source. To demonstrate the potential of our model, we apply it to select the ideal coding and packet rate in bandwidth-limited environments. Furthermore, we decide, based on model predictions, whether to delay the playout of speech frames after delay spikes. Delay spikes often occur after congestion and cause packets to arrive too late. We show a considerable improvement in perceptual speech quality if our model is applied to control VoIP transmissions. Copyright © 2005 John Wiley & Sons, Ltd. [source] Combined fair packet scheduling policy and multi-class adaptive CAC scheme for QoS provisioning in multimedia cellular networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2006Tarek Bejaoui Abstract In this paper, we propose a combined multi-class adaptive connection admission control algorithm and a new fair packet scheduling policy, based on an enhanced weighted fair queuing algorithm. It takes into account a realistic behaviour of traffic while considering the spatial variation of the system characterizing both the user mobility and the signal propagation impairments due to the surrounding effects. The proposed allocation scheme provides enhanced traffic performance in heterogeneous environments and achieves a good level of capacity gain. The new adaptive quality of service (QoS) oriented connection admission control (CAC) function is proposed to meet the rapidly increasing demand for providing multimedia services with diversified quality requirements. It decides whether the connection request is to be admitted into the system, on the basis of the generated interference level and the waiting time before access. This CAC scheme, based on service class differentiation, aims at maximizing the use of available radio resource and meeting the QoS requirement of higher priority users as much as possible while maintaining the minimum requirements of lower priority users, especially when the system suffers from congestion. The results indicate that significantly increased traffic performance can be achieved in comparison with other conventional investigated policies. Copyright © 2006 John Wiley & Sons, Ltd. [source] Characterizing user-perceived impairment events using end-to-end measurementsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 10 2005Soshant Bali Abstract Measures of quality of service (QoS) must correlate to end-user experience. For multimedia services, these metrics should focus on the phenomena that are observable by the end-user. Metrics such as delay and loss may have little direct meaning to the end-user because knowledge of specific coding and/or adaptive techniques is required to translate delay and loss to the user-perceived performance. Impairment events, as defined in this paper, are observable by the end-users independent of coding, adaptive playout or packet loss concealment techniques employed by their multimedia applications. Time between impairments and duration of impairments are metrics that are easily understandable by a network user. Methods to detect these impairment events using end-to-end measurements are developed here. In addition, techniques to identify Layer 2 route changes and congestion events using end-to-end measurements are also developed. These are useful in determining what caused the impairments. End-to-end measurements were conducted for about 26 days on 9 different node pairs to evaluate the developed techniques. Impairments occurred at a high rate on the two paths on which congestion events were detected. On these two paths, congestion occurred for 6,8 hours during the day on weekdays. Impairments caused by route changes were rare but lasted for several minutes. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||