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We study the reliability of large networks of coupled neural oscillators in response to fluctuating stimuli. Reliability means that a stimulus elicits essentially identical responses upon repeated presentations. We view the problem on two scales: neuronal reliability, which concerns the repeatability of spike times of individual neurons embedded within a network, and pooled-response reliability, which addresses the repeatability of the total synaptic output from the network. We find that individual embedded neurons can be reliable or unreliable depending on network conditions, whereas pooled responses of sufficiently large networks are mostly reliable. We study also the effects of noise, and find that some types affect reliability more seriously than others.

High bandwidth DDoS attacks consume more resources and have direct impact at ISP level in contrast to low rate DDoS attacks leading to graceful degradation of network and being mostly undetectable. Although an array of detection schemes have been proposed, current requirement is a real time DDoS detection mechanism that adapts itself to varying network conditions to give minimum false alarms. We treat DDoS attacks as events that disturb the distribution of traffic features in ISP domain reflected by entropic variations on in stream samples. Next we propose to calibrate the detection mechanism for minimum false alarm rate by varying tolerance factor in real time. Simulations are carried out in ns-2 at different attack strengths. We also report our experimental results over KDD 99 dataset. Results show that the proposed approach is comparable to previously reported approaches with an advantage of variable rate attack detection and minimum false alarms.

A large class of applications require real-time processing of continuous stream data resulting in the development of data stream management systems (DSMS). Since many of these applications are distributed, distributed DSMSs are starting to receive attention. In this paper, we focus on an important issue in distributed DSMS operation, namely load distribution to minimize end-to-end latency. We identify the often conflicting requirements of load distribution, and propose a "potential-driven" load distribution approach to mimic the movements of objects in the physical world. Our approach also takes into account heterogeneous machines, different network conditions, and resource constraints. We present experimental results that investigate our algorithms from various aspects, and show that they outperform existing techniques in terms of end-to-end latency.

Chronic network conditions are caused by performance impairing events that occur intermittently over an extended period of time. Such conditions can cause repeated performance degradation to customers, and sometimes can even turn into serious hard failures. It is therefore critical to troubleshoot and repair chronic network conditions in a timely fashion in order to ensure high reliability and performance in large IP networks. Today, troubleshooting chronic conditions is often performed manually, making it a tedious, time-consuming and error-prone process.In this paper, we present NICE (Network-wide Information Correlation and Exploration), a novel infrastructure that enables the troubleshooting of chronic network conditions by detecting and analyzing statistical correlations across multiple data sources. NICE uses a novel circular permutation test to determine the statistical significance of correlation. It also allows flexible analysis at various spatial granularity (e.g., link, router, network level, etc.). We validate NICE using real measurement data collected at a tier-1 ISP network. The results are quite positive. We then apply NICE to troubleshoot real network issues in the tier-1 ISP network. In all three case studies conducted so far, NICE successfully uncovers previously unknown chronic network conditions, resulting in improved network operations.

Many of applications in vehicular ad hoc networks (VANET) are based on dissemination of information, so broadcasting is a fundamental service in these networks. Broadcasting is a difficult task since vehicular networks often lack continuous end-to-end connectivity and have large variations in node densities. In this paper we present a method that improves the reception rates of broadcast messages by overcoming problem of connectivity gaps. In our method, every forwarder of message when facing a gap sends small messages periodically. These methods are used to understand entrance of a new vehicle that can be selected as the next forwarder of message. We have evaluated the performance of proposed protocol in NS2 under various network conditions.

This letter presents an analytical model that jointly exploits the buffer dynamics of both the sending and receiving nodes to find the optimum number of byte-level and packet-level forward error correction (FEC) units for real-time multimedia transmission over wireless networks. The proposed analytical model first provides an optimum number of FEC units required at the byte-level, and then chooses the number of FEC units at the packet-level based on current channel and network conditions. The accuracy of the proposed model is dependent on two parameters: the variable deadline-time at the byte-level and fixed round-trip time (RTT) delay at the packet-level. Numerical results demonstrate the effectiveness of the model in reducing the unrecoverable error probability, which is achieved when the byte-level FEC scheme is supplemented by the packet-level FEC scheme.

In the future mobile networks, a mobile terminal is able to select the best suitable network for each data transmission. The selection of a network connection to be used has been under a lot of study. In this paper, we consider a more extensive case in which we do not select a network connection but use several network connections simultaneously to transfer data. When data is transferred using multiple network connections, a network connection has to be selected for each component of the data. We have modelled this problem as a multiobjective optimization problem and developed a heuristic to solve the problem fast in a static network environment. In this paper, we discuss solving the problem in a dynamic network environment in which the availability as well as the rate and prizing of connections vary. We introduce an improved version of the heuristic that reacts to changing network conditions and improves the solution when possible.

This paper deals with the performance evaluation of handling streaming traffic in IP best effort networks using TFRC protocol. In our studies we check and discuss an influence of video on demand traffic and different network conditions on TFRC congestion control mechanism. Moreover, we check TFRC performance when it is sharing bottleneck with different versions of TCP. We illustrate our studies by simulation results performed in ns-2 simulation tool and compare results with those obtained for UDP.

Dimirovski, Georgi M. (Dogus Author) -- Conference full title: 2008 47th IEEE Conference on Decision and Control (CDC): Cancun, Mexico: 9-11 December 2008 A robust active queue management (AQM) scheme based on H-infinty theory is presented for the problem of congestion control in TCP communication networks. In TCP/IP networks, the packet-dropping probability function is considered as a control input, and network parameters are time-varying. Thus a TCP/AQM controller is modeled as a uncertain time-delay system with a saturated input. The corresponding existence condition of the observer and controller are obtained by applying Lyapunov-Krasovskii function approach and the linear matrix inequality technique. Simulation results show that the proposed scheme can track the desired queue length very quickly under various network conditions, and avoid the problem of dynamic network congestion.

Distributed Coordination Function (DCF) in IEEE 802.11 WLANs cannot guarantee per-station TCP fairness among wireless stations. In order to satisfy users, and guarantee to allocate fair bandwidth among wireless users regardless of the number and direction of flows, the Weighted Window method is proposed. This method can be simply implemented in mobile stations without having to modify the MAC layer. In this paper, the proposed method and its properties will be presented in detail using ns2 simulation tool under various network conditions. The simulation results are shown that the proposed method achieves fair throughput among stations as compared with previous methods.

Wireless reconfigurable networks are prone to several security attacks such as selective forwarding, black holes, and wormholes. In this paper, we introduce a network coding method that detects security attacks related to routing. The proposed method works on a distributed fashion performing random network coding over nodes composing a given route, not only to distribute content, but also to provide data confidentiality by cooperation as a mechanism of detection. The method presents a robust, accurate and fast response under security attacks for varying network conditions, such as density and interference, and it also increases successfully received packets without a significant sacrifice of the bandwidth usage.

This paper provides some efficient algorithms for calculating the stochastic network equilibrium (SUE) assignment problem. First, the paper shows the linkbased formulation of the SUE problem, which is represented by path variables in conventional formulation. Then, the new solution algorithms are presented and implemented in various network conditions. The numerical results exhibit that the methodsachieve fast convergence to rigorous solution. The paper also discusses the reason for efficient calculation of the new algorithms. Finally, the guide lines forselecting an algorithm in practical applications are given.

In this paper, we present the design of a VoIP conferencing system that enables the voice communication of multiple users in the Internet. After studying the conversational dynamics in multi-party conferencing, we identify user-observable metrics that affect the perception of conversational quality and their trade-offs. Based on the dynamics and the behavior on delays, jitters, and losses of Internet traces collected in the PlanetLab, we design the transmission topology and schemes for loss concealments and play-out scheduling. Last, we compare the performance of our system and Skype (version 3.5.0.214) using repeatable experiments that simulate human participants and network conditions in a multi-party conferencing scenario.

In almost all of multiplayer network games, dead-reckoning (DR) is used to predict movement of game players. According to received DR vectors, game clients can predict future' movement of other players. However, DR does not work well under bad network conditions. In this paper, we propose a solution to achieve much more prediction accuracy. Personal habits influence path prediction of players. However, our method introduces extra computation burden and searching delay. So, a hybrid method, which is a combination of DR and personal habits, is introduced. We use a 2D tank game for experiment and compare the results of our solution with those of traditional methods. To obtain habitual movement, we carry out 30 minutes playing observation on each participator. Simulation shows that our method achieves significant improvement in path prediction.

Among the many ways of improving the performance of a wireless sensor network (WSN) in terms of crucial metrics such as its lifetime and data latency, exploiting the mobility of some of the network components has been recently observed to be among the most promising. In this paper we demonstrate how two very different schemes for WSN mobility leads to different benefits for network performance. More specifically, we consider the data MULEs kind of random, uncontrolled mobility with single-hop data collection and we compare it with the controllable mobility of the data collection point (sink) where sensor-to-sink data routing follows multi-hop paths. Through quite thorough ns2-based simulations we show that data MULEs are to be used in those WSNs deployed for delay tolerant applications. Benefits of this scheme include low energy consumption and easier protocol and nodal design. Data latency, however, can be unbearably high. We therefore show that a good tradeoff between network lifetime gains and data latency increases can be obtained by using those solutions where the mobility of the sink is controlled by the network conditions.

The spread of viruses and worms has severe implications on the performance of virtually any network. Current methods to stop the propagation of malicious code rely on anti-virus signature recognition to prevent hosts from being infected. Unfortunately, the latency between the introduction of a new virus into a network and the implementation/distribution of a patch can be significant. Within this period, a network can be crippled by the abnormally high rate of traffic generated by infected hosts. Previous research has provided a mechanism for controlling the rate at which a host can make new network connections when exhibiting virus-like behavior. Extending this technology to network routers provides the benefit of network protection without the need for individual client support, and serves as an initial step in developing a virus-resilient network. This paper/presentation reflects on the unique challenge of adapting the Virus Throttle mechanism to HP ProCurve network switch routers. Also discussed is the method of proving that it works in realistic network conditions to protect against worms without interfering with normal network traffic.

The paper proposes the framework for investigation of prospective adaptive and cooperative defense mechanisms against the Internet attacks. The approach suggested is based on the multi-agent modeling and simulation. According to the approach the defense and attack systems are represented as interacting teams of intelligent agents that act under some adaptation criterion. They adjust their configuration and behavior in compliance with the network conditions and attack (defense) severity. The paper represents the architecture and software implementation of simulation environment that combines discrete-event simulation, multi-agent approach and packet-level simulation of various Internet protocols. The environment allows to simulate complex attack and defense scenarios. The paper describes the experiments aimed on the investigation of adaptive "Distributed Denial of Service" attacks and defense mechanisms.

Advanced phones, such as Smartphones and Pocket PC phones, can be useful tools for real world field trials and data collection, because they have capable hardware, are inexpensive, and ready for everyday use. We have employed Windows Mobile Smartphones and Pocket PC phones in our research for more than a year. We employed these phones as measurement tools to sample the network conditions our subjects encountered in their daily life. We also conducted multiple field trials with these phones for usability studies. Our methods included in situ logging, in situ surveys, interviews, and focus groups. We present the lessons we have learned from this experience, in particular on the instrumentation of the phones and the use of human subjects.

Wireless Sensor Networks (WSN) have the potential of significantly enhancing our ability to monitor and interact with our physical environment. Realizing a fault-tolerant operation is critical to the success of WSN. The main challenge is providing fault-tolerance (FT) while conserving the limited resources of the network. Our main contribution in this paper is to propose a general framework for fault-tolerance in WSN. The proposed framework can be used to guide the design and development of FT solutions and to evaluate existing ones. We present a comparative study of the existing schemes and identify potential enhancements. A primary module of the framework is the learning and refinement module which enables a FT solution to be adaptive and self-configurable based on changes in the network conditions. We view this as vital to the resource-constrained and highly dynamic WSN. Up to our knowledge, we are the first to propose the implementation of such module in FT solutions for WSN.

Reliable server pooling (RSerPool) is a protocol framework for server redundancy and session failover, currently still under standardization by the IETF RSerPool WG. An important property of RSerPool is its lightweight architecture: server pool and session management can be realized with small CPU power and memory requirements. That is, RSerPool-based services can also be managed and provided by embedded systems. Currently, there has already been some research on the performance of the data structures managing server pools. But a generic, application- independent performance analysis - in particular also including measurements in real system setups - is still missing. Therefore, the aim of this paper is - after an outline of the RSerPool framework, an introduction to the pool management procedures and a description of our pool management approach - to first provide a detailed performance evaluation of the pool management structures themselves. Afterwards, the performance of a prototype implementation is analysed in order to evaluate its applicability under real network conditions.

In wireless sensor networks (WSNs), address-based routing approaches often lead to severe problems due to node mobility, energy-saving sleep-cycles, and often missing or unreliable address information. Data-centric routing schemes such as flooding or gossiping solve these problems but may lead to congestion or starvation. Based on biologically inspired mechanisms known from cellular signaling pathways, we discovered potentials in enhancing the communication required for self-organization in network environments suffering from datapaths with low reliability and time variations of the reliability. Using an importance factor for particular transmissions in combination with feedback loops, the overall quality of the global system can be increased. The resulting algorithm, Weighted Probabilistic Data Dissemination (WPDD), includes an inherent adaptation to changing network conditions. Congestion control is supported as well as prioritized data communication. This paper outlines the working behavior of WPDD and demonstrates its applicability based on selected simulation results.

Sudden changes on road networks, including new roads, bridge construction, road blockage or traffic accidents cause travelers to switch their routes to less costly ones as compared to alternative routes. Travelers, however, tend to take higher cost routes due to insufficient information and errors in perceived travel time. This may cause severe congestion on a certain route. Conventional models, however, are unable to adequately simulate travelers' behavior under such suddenly changing network conditions. The objective of this paper is to analyze travelers' daily travel behavior in such cases via a stochastic process, the Markov-chain approach, which is considered to be a suitable method for representing sudden changes in states. This model is based on agent and we assumes that travelers select their route via learning process of travel time that they had previously experienced.

Testing of communication protocols and applications using simulated networks is necessary. In this paper, we show the development of a network emulator called as "Lenet". Since our objective is to provide a network emulator as a user can use it more convenient, Lenet is developed as a userland application which is typically used by end users. Even though a userland application, Lenet has similar functions and accuracy to the existing software emulators of an in-kernel implementation type. Lenet gives two kinds of emulation. One is by parameters to simulate specific network conditions for an end-to-end. Another type of emulation is to replay the behavior of a real network using a replay scenario created by packet capture or written by a user. We present some evaluation results of Lenet on performance and convenience

In this work we propose a traffic management mechanism to support real-time flows in highly unpredictable sensor network environments. The mechanism is based on a joint traffic regulation and end-to-end scheduling approach; a traffic regulation component adjusts the incoming packet rate to implicitly control the channel load and intelligently rejects packets that are more likely to miss their deadline while a laxity-based scheduling component projects the packets? per-hop delay and compensates for network endto- end delays. Thus, high success ratios without severely degrading the fidelity are achieved. Our mechanism attempts to maintain accuracy in a resource-efficient manner even under extremely unstable network conditions where delays are difficult to model and compute. Furthermore, the adoption of a component-based approach allows for substantial independence from both the MAC and routing layers. We thoroughly evaluate our mechanism and demonstrate its accuracy and performance merits.

An important stage of wide-area systems and networking research is to prototype a system to understand its performance when deployed in the real Internet. A key requirement of prototyping is that results obtained from the prototype experiments be representative of the behavior if the system were deployed over nodes connected to commercial ISPs. Recently, distributed testbeds such as PlanetLab and RON have become increasingly popular for performing wide-area experimentation. However, such testbeds typically consist of a significant fraction of nodes with connectivity to research and education networks which potentially hinder their usability in prototyping systems.In this paper, we investigate the impact of testbeds with connectivity to research and education networks on the applications and network services so that such testbeds can be leveraged for evaluation and prototyping. Specifically, we investigate when the representativeness of wide-area experiments deployed on such testbeds is affected by studying the routing paths that applications use over such testbeds. We then investigate how the representativeness of wide-area experiments is affected by studying the performance properties of such paths. We further measure the impact of using such testbeds on application performance via application case studies. Finally, we propose a technique that uses the currently available testbeds but reduces their bias by exposing applications evaluated to network conditions more reflective of the conditions in the commercial Internet.

Analysis of the 802.11 CSMA/CA mechanism has received considerable attention recently. Bianchi [3] presents an analytic model under a saturated traffic assumption. Bianchi's model is accurate, but typical network conditions are non-saturated heterogenous. We present an extension of his model to a non-saturated environment. The model's predictions, validated against simulation, accurately capture many interesting features of non-saturated operation. For example, the model predicts that peak throughput occurs prior to saturation. Our model also allows stations to have different traffic arrival rates, enabling us to address the question of fairness between competing flows.

VRC algorithm is a new active queue management (AQM) arithmetic based on rate. The response rate of VRC algorithm is rapider than traditional AQM arithmetic. A new VRC algorithm based on the fuzzy immune adaptive PID control and Smith predictor is proposed. PID parameters’ online self-adapting was implemented by immune feedback mechanism. Moreover the Smith predictor was successfully introduced into feedback to compensate the time delay in network. Contrasted with traditional PID algorithm, fuzzy immune PID-Smith is validated by simulation results. It can adjust itself to new network conditions rapidly and stably, can converge to queue size-setting value, and can get better robustness.

This paper presents an analysis of a 500 kV bulk power transmission system and the dimensioning of proper shunt reactors to be applied under steady state and transient aspects in particular. Therefore, the behavior of single-pole auto-reclosing under line-to-ground fault conditions is analyzed. Hence is described the necessity and influence of factors such as phase and neutral reactors, capacitive and inductive couplings on the extinction of secondary arc. Those are investigated in order to justify the feasibility of single-pole auto-reclosing. A practical example of the system is developed with respect to an investigation of the impact of neutral reactors. The considerations have been firstly done analytically and verified subsequently based on transient simulations using ATP/EMTP.

This paper presents advanced protection co-ordination methods to be applied for the integration of IPP units to the transmission grid. A typical system configuration of an IPP unit installation is considered. The protection system is also assumed to be commonly which is based on the distance protection principle. The changing network conditions and their impacts on the protection system caused by the IPP are described. Thus the topics of co-ordination of different characteristics, teleprotection schemes, distance grading and relay loadability are investigated and methods for covering their adverse impacts are given. It can be seen that only modern relay technology is not leading to a proper protection system. Only well co-ordinated and adapted protection relays will result in a system of high reliability of the IPP in-feed and in an economic benefit for the IPP investors finally.

CTCP, an innovative TCP congestion control algorithm developed by Microsoft, is evaluated and compared to HSTCP and StandardTCP. Tests were performed on the production Internet from Stanford Linear Accelerator Center (SLAC) to various geographically located hosts to give a broad overview of the performances. We find that certain issues were apparent during testing (not directly related to the congestion control algorithms) which may skew results. With this in mind, we find that CTCP performed similarly to HSTCP across a multitude of different network environments. However, to improve the fairness and to reduce the impact of CTCP upon existing StandardTCP traffic, two areas of further research were investigated. Algorithmic additions to CTCP for burst control to reduce the aggressiveness of its cwnd increments demonstrated beneficial improvements in both fairness and throughput over the original CTCP algorithm. Similarly, {gamma} auto-tuning algorithms were investigated to dynamically adapt CTCP flows to their network conditions for optimal performance. While the effects of these auto-tuning algorithms when used in addition to burst control showed little to no benefit to fairness nor throughput for the limited number of network paths tested, one of the auto-tuning algorithms performed such that there was negligible impact upon StandardTCP. With thesemore » improvements, CTCP was found to perform better than HSTCP in terms of fairness and similarly in terms of throughput under the production environments tested.« less

P2P data stores excel if availability of inserted data items must be guaranteed. Their inherent mechanisms to counter peer population dynamics make them suitable for a wide range of application domains. This paper presents and analyzes the fusion maintenance operation. It aims at reorganizing parts of our P2P data store in case the peer population shrinks so much that data availability is threatened. To this end, we present a formal cost model that peers use to estimate the optimal invocation point of a fusion. Finally, we present experimental results that validate our cost model by simulating various network conditions.

Simulation-based planning by emergency management agencies for region-scale evacuation scenarios requires fast execution of large vehicular traffic models. The planning problem is behaviors of population as well as the far-reaching dependencies inherent in heavily stressed network conditions spanning wide spatial scales. Parallel execution is, thus, required to sustain the required detail, size and speed. However, few parallel simulators exist for such applications, partly due to the challenges underlying their development. While most existing simulators are limited in size to a few hundred thousand road segment intersections, region-scale scenarios can involve millions of intersections. Moreover, many simulators are based on time-stepped models, which can be computationally inefficient for the purposes of modeling evacuation traffic. We are addressing the speed and scalability problems using a two-fold approach.

Temporal Scaling and Quality Scaling are both widely-used techniques to reduce the bitrate of streaming video. However, combinations and comparisons of Temporal and Quality Scaling have not been systematically studied. This research extends previous work to provide a model for combining Temporal and Quality Scaling, and uses an optimization algorithm to provide a systematic analysis of their combination over a range of network conditions and video content. Analytic experiments show: 1) Quality Scaling typically performs better than Temporal Scaling, with performance differences correlated with the motion characteristics of the video. In fact, when the network capacity is moderate and the loss rate is low, Quality Scaling performs nearly as well as the optimal combination of Quality and Temporal Scaling; 2) when the network capacity is low and the packet loss rate is high, Quality Scaling alone is ineffective, but a combination of Quality and Temporal Scaling can provide reasonable video quality; 3) adjusting the amount of Forward Error Correction (FEC) provides significantly better performance than video streaming without FEC or video streaming with a fixed amount of FEC.

Time-constrained error recovery is an integral component of reliable low-delay video applications. Regardless of the error-control method adopted by the application, unacknowledged or missing packets must be quickly identified as lost or delayed, so that necessary timely actions can be taken by the server/client. Historically, this problem has been referred to as the retransmission timeout (RTO) estimation. Earlier studies show that existing RTO estimators suffer from either long loss detection times or a large number of pre-mature timeouts. The goal of this study is to address these problems by developing an adaptive RTO estimator for high-bitrate low-delay video applications. By exploiting the temporal dependence between consecutive delay samples, we propose an adaptive linear delay predictor. This way, our RTO estimator configures itself based on the video characteristics and varying network conditions. Our approach also features a controller that optimally manages the trade-off between the amount of overwaiting and redundant retransmission rate. The skeleton implementation shows that the proposed RTO estimator discriminates lost packets from excessively-delayed packets faster and more accurately than its rivals, which consequently enables the applications to recover more packets under stringent delay requirements.

Travel choices are made according to people’s personal preferences and knowledge of the system. Since increase, improvement and updating of knowledge is achieved through information, consequentially information itself is a crucial issue in transportation problems. If information was perfect, users could easily choose the best path from their point of view, but unfortunately complete and precise information about network conditions is rarely available, therefore uncertainty can cause anxiety and stress in decision makers.

Seamless interoperability between two dissimilar networks require handoff from one network to the other. Such handoffs are known as vertical handoffs. Vertical handoff introduces a shift in the approach to handoffs. It deals with handoffs between dissimilar networks, such as from an access point to a base station or vice versa. A horizontal handoff, on the other hand, involves the scenario wherein the handoff is within the same network such as handoffs between cells. Most of the existing research proposes to implement vertical handoff on an overlay network, wherein a user moves from one geographic location to another, such as moving from a WLAN coverage area to a cellular coverage area, or vice versa. This research discusses the need to trigger a vertical handoff based on changes in the mobile environment independent of geographic changes of a user. We develop a novel framework that executes vertical handoff based on a multilayer approach coupled together with adjunct information such as pricing and user preference. This framework allows changes in applications, variations in network conditions and user preferences to trigger vertical handoffs. We conclude by providing a general evaluation of the framework.

In this paper, we explain an implementation of an accrual failure detector, that we call the . failure detector. The particularity of the . failure detector is that it dynamically adjusts to current network conditions the scale on which the suspicion level is expressed. We have done the experiment in a LAN in a whole day and evaluated the behavior of our . failure detector. Then we discuss on the parameters of the failure detector based on our experimental result.

In this paper we present the Wireless LAN (WLAN) emulator that we design to run on StarBED, the large scale network experiment environment of the Hokuriku Research Centre in Ishikawa, Japan. As WLANs start to spread on an ever wider scale, the need to investigate application deployment on WLANs has become stringent. We develop an emulation environment since it allows using in experiments the real applications that will be deployed in practice. In addition, it offers full control of the network conditions in which the applications will be tested. Our approach is user-oriented in the sense that the input of the system is a user-level scenario representation. This is subsequently converted into a quality degradation description that represents the effect the network will have on application traffic. Finally, the quality degradation description is transformed into an emulator configuration that is effectively used in the emulation environment to enforce network quality degradation on the application traffic.

In this paper, we have developed an estimation technique for send-time flow control scheme. Based on our network dynamics observations, we have refined the estimation techniques used in send-time control. We have developed heuristics to reflect these observations in the estimation process. These heuristics have been validated using simulation. We have used simulation to compare TCP and DTP performance under a variety of network conditions. DTP performs much better in all the scenarios considered. It needs much fewer buffers in the intermediate nodes compared TCP. It has much smaller loss rate than TCP when they have the same buffer capacity. It has smaller average round-trip time and such average PPI than TCP.

While the dynamic performance of thyristor-controlled series capacitor is well recognized, the use of series capacitors (SC) and controllable series capacitor (CSC) for the improvement of transfer capability has also drawn plenty of research interests in recent years. Through simulations based on OPF using a sample network, this study illustrates and compares the savings of the total system production cost under three different scenarios: with no device installed, with SC installed and with CSC installed on the corresponding transmission corridor. The results are based on the accumulation of the production costs over a year while the four seasons are modeled using different generation and load patterns. In particular, the results have shown that, under some network conditions, there is more gain from CSC over SC, because of CSC's ability to make use of the transfer capability in the neighbored area. In addition to the seasonal effects, studies and comparisons are also made for cases with multiple CSC and with CSC operating under constant power flow operation mode. In the multiple CSC case, the effects of installing multiple devices are investigated. In the other case, CSC is set to operate under constant power operation mode, which is in fact the most common way CSC is being used nowadays. The case results demonstrate that there are apparent benefits from using CSC

Recently, user mobility in wireless data networks is increasing because of the popularity of portable devices and the desire for voice and multimedia applications. These applications, however, require fast handoffs among base stations to maintain the quality of the connections. Re-authentication during handoff procedures causes a long handoff latency which affects the flow and service quality especially for multimedia applications. Therefore minimizing re-authentication latency is crucial in order to support real-time multimedia applications on public wireless IP networks.In this paper, we proposed two fast re-authentication methods based on the predictive authentication mechanism defined by IEEE 802.11i security group. We have implemented these methods in an experimental test-bed using freeware and commodity 802.11 hardware and we demonstrate that they provide significant latency reductions compared to already proposed solutions. Conducted measurements show a very low latency not exceeding 50 ms under extreme congested network conditions.

Synchronous groupware applications need to offer each user a consistent view of the interactions represented by the streams exchanged between dispersed groups of users. Using strong ordering such as CAUSAL or TOTAL order to capture and deliver streams' interactions may be too expensive (in terms of delay) due to the variability of the network conditions. This paper builds upon previous work on expressing streams causality and propose a multimodal communication toolkit in order to integrate different delivery modes (e.g. FIFO, CAUSAL, TOTAL) into a single channel (with respect to each of these protocols). Moreover the proposed multimodal channel can handle the mix of any partial or total order protocols. We build an experimental platform for measuring the cost of combining several protocols on various network conditions and show how our communication service can adjust the degree of synchronization according to network variations.

In this paper we analyse different factors affecting players' perception and performance in multiplayer games. We introduce a mean opinion score metric borrowed from the subjective analysis of audio and video content to classify the player's perceived game quality. With a survey we investigated the player's view on network latency for a variety of games. Furthermore, we examine four different games under different network conditions and collect data on game score and subjective perception from every player. During the evaluation, we investigate the effect of latency and jitter on multiplayer games. We use regression analysis methods to identify coherences between delay, jitter, skill, game score, and the subjective impression of the player. Finally, we compare the results from the survey and the experiments.

This paper describes the Remote View system developed by the former Technical Integration Services directorate of the Defense Information Systems Agency. The system facilitates performance analysis of theater-wide Internet protocol circuits by integrating disparate sources of traffic and topology data from different organizations throughout the theater to provide a consolidated view of network health. It is a capability that derived from requirements associated with working in an active, operational military environment with rapidly changing network conditions. United States Central Command relied on Remote View to help manage the unprecedented expansion of their networks during Operations Enduring Freedom and Iraqi Freedom, and they continue to use it today.

The supply transformer neutral is preferably earthed inductively, which means that the network is operated with compensated neutral, in order to reduce fault currents occurring in case of earth faults in electrical distribution networks. The inductance of this arc suppression coil located between the supply transformer neutral and the earth potential is to be readjusted (tuned) to different network configurations after any change in the topology of the network. A newly developed method allows all essential parameters of the zero phase sequence system to be reliably determined, without any adjustment of the arc suppression coil, by feeding non-mains-frequency signals, especially a frequency spectrum, into the zero phase sequence system of the network. This innovative method offers the following advantages: • The degree of detuning, the resonant frequency and the electrical parameters of the zero phase sequence system of the network can be determined exceedingly reliably even in extremely detuned networks. • The method works independently of the amplitude of zero potential. • Supplementary coils in the arc suppression region are identified automatically and are taken into account when the desired degree of compensation is set. • The arc suppression coil itself is only adjusted if tuning is actually required, even under extremely fluctuating network conditions, which results in shorter operating times of the coil drive and thus in increased availability and service life.

CIGRE WG A3.13 is studying the impact of changing network conditions and system requirements on the specification of conventional HV equipment within the scope of SC A3. They see three main developments leading to future networks: the strong increase in distributed generation, the increase in the transmission of bulk power over long distance and the increase in the application of power electronics. The impact of each development is described, conclusions are given or studies going on are highlighted

In this paper we introduce our on-going work on WiFi hotspot throughput optimization using 2-hop relays. We analyse incentives correlations with varying network conditions, node mobility and number of users in the network. Our simulation results provide guidance to optimal network utilization with fair incentive distribution to both users and providers

This research mainly studies the performance improvement of the IEEE 802.11e. IEEE 802.11e is an emerging supplement to the IEEE 802.11 standard in supporting quality-of-service (QoS). It introduces EDCF and HCF, and the former is the focus of this research. In this paper, the EDCF parameters' influences on the performance are studied. A new algorithm, called CW-EDCF, is proposed. This scheme dynamically adjusts the sizes of CWmin, CWmax and the CW parameter of the high priority traffic class, taking into account both the applications requirement; and network conditions. We compare it with the EDCF scheme through simulations. Results show that CW-EDCF outperforms the basic EDCF.

Soft state has been a mantra of Internet protocol design for the past decade. System designers build protocols that implement soft state mechanisms based on intuition or on qualitative arguments that the design is "better", yet there has never been a formal performance evaluation study that draws the same conclusion. In fact, previous attempts [P. Ji et al., 2003 and S. Raman et al., 1999] to build such a quantitative argument have found that pure soft state protocols significantly under-perform their hard state counterparts, and that only soft-hard hybrids can match hard state protocol performance. In this paper, we argue otherwise. We develop models that provide a performance-oriented explanation and justification of the Internet designer's intuition. The novel observation is that, if network conditions are known, a hard state protocol can always be configured to outperform its soft state counterpart. However, in reality, network conditions are unpredictable, and that soft state protocols are much more resilient to unanticipated fluctuations in these conditions.

This paper presents a new control design for VSC transmission systems with special attention to unbalanced ac network conditions. The proposed control strategy contains a main controller and an auxiliary controller. The main controller is implemented in the positive dq frame using decoupling control without involving positive/negative sequence decomposition. The auxiliary controller is implemented in the negative sequence dq frame using cross coupling control of negative sequence current. Simulation results using SIMULINK power system blockset (PSB) show good performance of the proposed control strategy for a 300 MW, 300 kV dc VSC Transmission system during both balanced conditions and unbalanced conditions which may be caused by solid single-phase to ground fault.