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Traffic Load (traffic + load)

Distribution by Scientific Domains

Engineering	75%
Information Science and Computing	25%

Selected Abstracts

Anpassung des Verkehrslastmodells des DIN FB 101 für kommunale Brücken

BETON- UND STAHLBETONBAU, Issue 5 2007
Balthasar Novák Prof. Dr.-Ing.
Für den Verantwortungsbereich des BMVBS ist das kürzlich eingeführte Lastmodell LM1 für die Verkehrslasten auf Brücken ohne weitere Reduktionen für alle neuen Brückenbauwerke anzusetzen. Dies führt jedoch leider gerade im Bereich der Kommunen zu teilweise konservativen Ergebnissen, da die geometrischen Abmessungen von kommunalen Brücken deutlich von den "üblichen" Abmessungen von Autobahnen und Bundesstraßen abweichen können und die Belastung aus dem LM1 durch den realen Verkehr nicht erzeugt werden kann. Es werden Vorschläge präsentiert, wie bei bestimmten geometrischen Randbedingungen und abhängig vom statischen System eine weitere Abminderung des LM1 möglich ist, ohne das Sicherheitsniveau zu verlassen. Die Arbeit entstand in enger Zusammenarbeit mit den Städten Frankfurt/Main, Leipzig und Stuttgart. Adjusted Traffic Load for Bridges under Communal Responsibility Recently the traffic loads of bridges of the EC1 have been introduced in Germany under the responsibility of the Federal Ministry of Transport, Building and Urban Affairs. Usually the Load Model LM1 has to be used for all new bridge structures with the adjusted values of ,Q1 = 0, 8, ,Q2 = 0, 8, ,Q3 = 0. A further classification has not been defined. This makes sense for the highway bridges and federal road bridges, because usually they have longer spans where a further reduction of the ,-values is not justified. In the sphere of influence of cities and villages the situation is totally different, because many bridges are short and are buildt as single span girder bridges or single frame bridges. In case of those bridges the LM1 leads to conservative results because the geometry and the total weight and the axle weight of the real lorries are limited and cannot develop those high inner forces and moments. The authors developed a proposal for further reduction of the ,-values dependent on the geometry and the statical system of the bridge without leaving the safety level of the Eurocode. Also for strengthening existing bridges these values can be used. The development has been undertaken in colaboration with the civil engineering offices in Frankfurth/Main, Leipzig and Stuttgart. [source]

An opportunistic cross-layer architecture for voice in multi-hop wireless LANs

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2009
Suhaib A. Obeidat
Abstract We propose an opportunistic cross-layer architecture for adaptive support of Voice over IP in multi-hop wireless LANs. As opposed to providing high call quality, we target emergencies where it is important to communicate, even if at low quality, no matter the harshness of the network conditions. With the importance of delay on voice quality in mind, we select adaptation parameters that control the ratio of real-time traffic load to available bandwidth. This is achieved in two ways: minimizing the load and maximizing the bandwidth. The PHY/MAC interaction improves the use of the spectral resources by opportunistically exploiting rate-control and packet bursts, while the MAC/application interaction controls the demand per source through voice compression. The objective is to maximize the number of calls admitted that satisfy the end-to-end delay budget. The performance of the protocol is studied extensively in the ns-2 network simulator. Results indicate that call quality degrades as load increases and overlonger paths, and a larger packet size improves performance. For long paths having low-quality channels, forward error correction, header compression, and relaxing the delay budget of the system are required to maintain call admission and quality. The proposed adaptive protocol achieves high performance improvements over the traditional, non-adaptive approach. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Analytical approach to the optimal adaptation rate of reconfigurable radio networks

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 7 2008
R. Fraile
Abstract Flexible radio resource management schemes are nowadays used within a wide range of systems. However, the optimal selection for their adaptation rate is still an open research issue. This paper presents an analytical approach to such problem, which consists in a combined analysis of the dynamics of the session-arrival process and the estimation of the mean traffic load from network measurements. From this study, it is concluded that both aspects pose an upper limit on the optimal system adaptation rate, being the most restrictive the one depending on the mean traffic load estimation. A specific procedure for deriving such limit on adaptation rate is provided. It is shown that the derived value directly depends on the mean service duration. The application of the whole analysis is illustrated with an example based on a set of measurements from a live network. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Resource allocation for statistical quality of service provision in buffered crossbar switches,

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2008
Qiang Duan
Abstract The buffered crossbar switch is a promising switching architecture that plays a crucial role for providing quality of service (QoS) in computer networks. Sufficient amount of resources,bandwidth and buffer space,must be allocated in buffered crossbar switches for QoS provision. Resource allocation based on deterministic QoS objectives might be too conservative in practical network operations. To improve resource utilization in buffered crossbar switches, we study the problem of resource allocation for statistical QoS provision in this paper. First, we develop a model and techniques for analyzing the probabilistic delay performance of buffered crossbar switches, which is described by the delay upper bound with a prescribed violation probability. Then, we determine the required amounts of bandwidth and buffer space to achieve the probabilistic delay objectives for different traffic classes in buffered crossbar switches. In our analysis, we apply the effective arrival envelope to specify traffic load in a statistical manner and characterize switch service capacity by using the service curve technique. Instead of just focusing on one specific type of scheduler, the model and techniques developed in this paper are very flexible and can be used for analyzing buffered crossbar switches with a wide variety of scheduling algorithms. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Performance of delay-sensitive traffic in multi-layered satellite IP networks with on-board processing capability

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 12 2007
Suzan 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]

Dynamic bandwidth recycle algorithm for OVSF,CDMA systems

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2006
Peng-Jung Wu
Abstract This paper presents a dynamic bandwidth recycle algorithm in the downlink of a WCDMA system using orthogonal variable spreading factor codes (OVSF). It consists of a bandwidth recycle algorithm and a bandwidth reservation algorithm. The bandwidth recycle algorithm is used to recycle bandwidth from current serviced connections when the system does not have enough available bandwidth to support a bandwidth request. The bandwidth reservation algorithm is used to reduce transmission delay caused by suddenly increasing bandwidth requests. Four traffic classes, conversational, streaming, interactive, and background classes, defined by universal mobile telecommunication system (UMTS) are considered. Simulation results show that the bandwidth utilization and block rate are improved, the bandwidth guaranteed to conversational and streaming classes are protected, and the delay time of interactive and background classes are kept under an acceptable value even when the traffic load is heavy. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Resource allocation in satellite networks: certainty equivalent approaches versus sensitivity estimation algorithms

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 1 2005
Franco Davoli
Abstract In this paper, we consider a resource allocation problem for a satellite network, where variations of fading conditions are added to those of traffic load. Since the capacity of the system is finite and divided in finite discrete portions, the resource allocation problem reveals to be a discrete stochastic programming one, which is typically NP-hard. We propose a new approach based on the minimization over a discrete constraint set using an estimation of the gradient, obtained through a ,relaxed continuous extension' of the performance measure. The computation of the gradient estimation is based on the infinitesimal perturbation analysis technique, applied on a stochastic fluid model of the network. No closed-forms of the performance measure, nor additional feedback concerning the state of the system, and very mild assumptions on the probabilistic properties about the statistical processes involved in the problem are requested. Such optimization approach is compared with a dynamic programming algorithm that maintains a perfect knowledge about the state of the satellite network (traffic load statistics and fading levels). The comparison shows that the sensitivity estimation capability of the proposed algorithm allows to maintain the optimal resource allocation in dynamic conditions and it is able to provide even better performance than the one reached by employing the dynamic programming approach. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Study of MANET routing protocols by GloMoSim simulator

INTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 6 2005
Ashwini K. Pandey
This paper compares ad hoc on-demand distance vector (AODV), dynamic source routing (DSR) and wireless routing protocol (WRP) for MANETs to distance vector protocol to better understand the major characteristics of the three routing protocols, using a parallel discrete event-driven simulator, GloMoSim. MANET (mobile ad hoc network) is a multi-hop wireless network without a fixed infrastructure. Following are some of our key findings: (1) AODV is most sensitive to changes in traffic load in the messaging overhead for routing. The number of control packets generated by AODV became 36 times larger when the traffic load was increased. For distance vector, WRP and DSR, their increase was approximately 1.3 times, 1.1 times and 7.6 times, respectively. (2) Two advantages common in the three MANET routing protocols compared to classical distance vector protocol were identified to be scalability for node mobility in end-to-end delay and scalability for node density in messaging overhead. (3) WRP resulted in the shortest delay and highest packet delivery rate, implying that WRP will be the best for real-time applications in the four protocols compared. WRP demonstrated the best traffic scalability; control overhead will not increase much when traffic load increases. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Performance evaluation on a double-layered satellite network

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 6 2005
Feng-Ge Wu
Abstract How to evaluate the performance of satellite networks is a prerequisite to the construction of satellite networks, and is also one of challenges in the researches on satellite networks. In this paper, generalized stochastic Petri net (GSPN) models are presented to carry out the performance analysis of a double-layered satellite network. Firstly, the GSPN model of a double-layered satellite network is simplified by proper analysis. Then, two sets of experiments are conducted to analyse the performance of the satellite networks, and show that the double-layered satellite network outperforms single-layered ones on the heavy traffic load. Finally, the feasibility and effectiveness of the proposed approach is verified by simulation experiments. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Performance evaluation of adaptive routing algorithms in packet-switched intersatellite link networks

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2002
Mihael Mohor
Abstract This paper addresses the performance evaluation of adaptive routing algorithms in non-geostationary packet-switched satellite communication systems. The dynamic topology of satellite networks and variable traffic load in satellite coverage areas, due to the motion of satellites in their orbit planes, pose stringent requirements to routing algorithms. We have limited the scope of our interest to routing in the intersatellite link (ISL) segment. In order to analyse the applicability of different routing algorithms used in terrestrial networks, and to evaluate the performance of new algorithms designed for satellite networks, we have built a simulation model of a satellite communication system with intersatellite links. In the paper, we present simulation results considering a network-uniform source/destination distribution model and a uniform source,destination traffic flow, thus showing the inherent routing characteristics of a selected Celestri-like LEO satellite constellation. The updates of the routing tables are centrally calculated according to the Dijkstra shortest path algorithm. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Content storage architectures for boosted IPTV service

BELL LABS TECHNICAL JOURNAL, Issue 3 2008
Marc Verhoeyen
Television (TV) consumers adore interactivity and personalization. Internet Protocol television (IPTV) systems help satisfy this desire by providing different services including video-on-demand (VoD), network personal video recording (NPVR), and time shift TV (TSTV). However, these services place a heavy traffic load on the network by requiring a unicast video stream for each active customer. This paper discusses means to reduce the network traffic load by introducing storage deep in the network-thus avoiding the need for unicast traffic support over the metro or core network-and algorithms to place content intelligently on those storage devices. An algorithm for intelligent redistribution is described that endeavors to place the most appropriate content close to consumers. The paper discusses further how this new paradigm of network storage can help improve quality of experience for the IPTV consumer and can assist in the deployment of Internet video and sharing of user-generated content (UGC). © 2008 Alcatel-Lucent. [source]

Prioritized e-mail servicing to reduce non-spam delay and loss: A performance analysis

INTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 4 2008
Muhammad N. Marsono
This paper proposes a prioritized e-mail servicing on e-mail servers to reduce the delay and loss of non-spam e-mails due to queuing. Using a prioritized two-queue scheme, non-spam e-mails are queued in a fast queue and given higher service priority than spam e-mails that are queued in a slow queue. Four prioritized e-mail service strategies for the two-queue scheme are proposed and analyzed. We modeled these four strategies using discrete-time Markov chain analysis under different e-mail traffic loads and service capacities. Non-spam e-mails can be delivered within a small delay, even under heavy e-mail loadings and high spam-to-non-spam a priori. Results from our analysis of the two-queue scheme show that it gives non-spam delay and loss probability two orders of magnitude smaller than the typical single-queue approach during heavy spam traffic. Moreover, prioritized e-mail servicing protects e-mail servers from spam attacks. Copyright © 2007 John Wiley & Sons, Ltd. [source]

A tutorial on using genetic algorithms for the design of network topology

INTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 4 2006
Bassam Al-Bassam
The design of network topology is an important part of network design, since network topology is directly associated with network operational behavior, capacity, reliability, and cost. This paper is a tutorial paper concerned with illustrating how the optimization capabilities of genetic algorithms can be used to design suitable network topologies considering basic topology problems. Simple genetic algorithms have been developed for the topology problem of mesh networks, considering single node and single link failure tolerance. The algorithms are based on criteria of two important measures: minimizing the length of communication links; and minimizing traffic flow through these links for given traffic loads. The first measure contributes to minimizing the cost of cabling, while the second measure contributes to minimizing the cost of link capacity. The work provides a useful approach and tools to network students and professionals concerned with the topology design of backbone networks. The developed software is made available on the Internet.,Copyright © 2006 John Wiley & Sons, Ltd. [source]

Zur maßgebenden Verkehrslaststellung bei Schrägseilbrücken

BAUTECHNIK, Issue 4 2004
Harald Unterweger ao.
Als Grundlage der Bemessung erfordert die Systemberechnung im Brükkenbau auch die Auffindung der ungünstigsten Verkehrslaststellung für jeden betrachteten Brückenquerschnitt. Insbesondere beim Fahrbahnbalken von Schrägseilbrücken ergibt sich die Gesamtbeanspruchung aus einem komplexen Zusammenwirken aus Normalkräften, Querkräften und Biegemomenten. In der Praxis erfolgt üblicherweise eine Selektion jener Verkehrslaststellungen, die eine der Teil beanspruchungen am Querschnitt (meist ausgedrückt durch Schnittkräfte) maximieren, wodurch jedoch für die nachfolgend betrachteten Stahl- bzw. Verbundbrücken nicht immer die höchsten Beanspruchungen entstehen. Einleitend erfolgt die Darstellung eines einfachen und anschaulichen Verfahrens, um , unabhängig von der Komplexität der Grenzzustandsfunktion, die auch das Beulen des Hauptträgerstegs beinhalten kann , die ungünstigste Verkehrslaststellung am Querschnitt zu finden. Dies stellt eine Verallgemeinerung des in [1] vorgestellten Verfahrens dar. Der Hauptteil beinhaltet ein Anwendungsbeispiel einer Schrägseilbrücke mit Verbundquerschnitt, wobei zwei repräsentative Fahrbahnquerschnitte näher untersucht werden. Einerseits werden die Gesamtbeanspruchungen der konventionellen und der genauen Vorgehensweise anhand von Einflußlinien erläutert, und andererseits lassen sich daraus Hinweise für die Praxis ableiten. Die dargestellte ingenieurmäßige Vorgehensweise kann alle Arten der Einwirkungen beinhalten und ist grundsätzlich auch auf andere Bauwerke sowie Baustoffe (z. B. Stahlbeton) direkt anwendbar. Appropriate traffic load cases for steel and composite cable , stayed bridges. A significant problem in the global analysis of bridge structures is to find the most unfavourable position of the traffic loads for each cross-section. In practice usually those traffic load cases are chosen which maximise one part of stresses at the cross-section (often expressed in form of internal forces). First of all a simple method is presented to find out the most unfavourable traffic load position, also applicable for complex interaction formulae including web buckling. Secondly an example of a cable-stayed bridge is analysed. For two significant sections of the bridge deck the results are presented. The stresses due to the conventional practical procedure are compared with the more accurate ones. The behaviour is explained by the corresponding influence lines. Based on these results some proposals for practical work are given. The presented procedure is also applicable to other types of construction works and materials (e.g. reinforced concrete). [source]

Versuche zur Ermüdungsfestigkeit alter Betonstähle

BETON- UND STAHLBETONBAU, Issue 7 2009
Patrick Fehlmann Dipl.
Baustoffe; Bewehrung; Versuche; Brückenbau Abstract Die Frage der Ermüdungssicherheit hat im Zusammenhang mit der Überprüfung bestehender Stahlbetonbauwerke, insbesondere Brücken, an Aktualität gewonnen. Während auf der Einwirkungsseite die Anzahl der Lastwechsel und die Lasten, die die Brücke im Laufe ihres Lebens erfahren hat, von Bedeutung sind, sind es auf der Widerstandsseite die Genauigkeit des Tragwerkmodells und die Materialkennwerte. Mit Letzteren befasst sich dieser Aufsatz. Der wichtigste Parameter auf der Widerstandsseite ist die Ermüdungsfestigkeit des Betonstahls. Mittels Dauerschwingversuchen wurde die Ermüdungsfestigkeit von vier Betonstahlsorten ermittelt. Zwei Sorten stammen von abgebrochenen Brücken aus den 1950er Jahren; zwei weitere sind kürzlich produzierte Sorten von Ring- und Stabmaterial der Betonstahlsorte B 500 B. Das Ziel der Versuche bestand darin, festzustellen, ob das Alter einer Stahlbetonkonstruktion einen Einfluss auf die Ermüdungsfestigkeit des Betonstahls hat. Im Aufsatz werden die Problematik beim Nachweis der Ermüdungssicherheit bestehender Brücken kurz geschildert, die Versuche beschrieben und deren Resultate diskutiert. Fatigue Tests with Old Reinforcing Steels Recently, fatigue safety has become an issue with respect to surveying the condition of existing structures, in particular bridges. While questions considering traffic loads and frequencies dominate the calculations of the appropriate load scenarios, the accuracy of the structural model and material properties play a vital role for the calculation of the resistance. This article deals with the latter. The most important parameter on the resistance side is the fatigue strength of the reinforcement. Therefore, fatigue strength of four brands of reinforcing steel was determined in fatigue tests. Two brands of reinforcement bars could be gathered during demolition work of two bridges which were built in the 1950ies. Another two brands of new reinforcing steel B 500 B, a rod-steel and a steel from the roll, were tested. The aim of the tests was to prove whether age and environment of the built-in reinforcement bars affect their fatigue resistance or not. The article briefly describes the difficulties with verifying the fatigue safety of existing bridges while the main part deals with the experimental work and the discussion of the test results. [source]