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In-depth analysis of network security vulnerability must consider attacker exploits not just in isolation, but also in combination. The general approach to this problem is to compute attack paths (combinations of exploits), from which one can decide whether a given set of network hardening measures guarantees the safety of given critical resources. We go beyond attack paths to compute actual sets of hardening measures (assignments of initial network conditions) that guarantee the safety of given critical resources. Moreover, for given costs associated with individual hardening measures, we compute assignments that minimize overall cost. By doing our minimization at the level of initial conditions rather than exploits, we resolve hardening irrelevancies and redundancies in a way that cannot be done through previously proposed exploit-level approaches. Also, we use an efficient exploit-dependency representation based on monotonic logic that has polynomial complexity, as opposed to many previous attack graph representations having exponential complexity.

We are developing a distributed architecture for massively-multiplayer games. In this paper, we focus on designing a low-latency event ordering protocol, called NEO, for this architecture. Previous event ordering protocols prevent several types of cheats at the expense of operating at the latency of the slowest player. We broaden the definition of cheating to include four common protocol level cheats and demonstrate how NEO prevents these cheats. At the same time, NEO has a playout latency independent of network conditions and adapts to network congestion to optimize performance.

Because of heterogeneous and dynamic changing network environments, content delivery across the network requires system support for coping with different network conditions in order to provide satisfactory user experiences. Despite the existence of many adaptation frameworks, the question of which adaptation approach performs the best under what network configurations still remains unanswered. The performance implication of different adaptation approaches (end-point, proxy-based and path-based approaches) has not been studied yet. This paper aims to address this shortcoming by conducting a series simulation-based experiments to compare performance among these adaptation approaches under different network configurations. The experiment results show that there are well-defined network environments under which each of these approaches delivers its best performance, and among them, the path-based approach, which uses the entire communication path to do adaptation, provides the best and the most robust performance under different network configurations, and for different types of servers and clients.

Interest in measuring available bandwidth has increased in response to the need for fast, accurate, non-intrusive estimation of current network conditions. Several methods have been proposed in recent years with varying degrees of success. This paper presents the details of the algorithm and implementation of PathMon, an active probe method which requires no prior knowledge of the network and no management control over the network to provide an end-to-end measurement of available bandwidth. In comparison to other available bandwidth methods, experiments show that PathMon is more accurate, and converges more quickly with less overhead.

With the growth of computing power and the proliferation of broadband access to the Internet, media streaming has widely diffused. Although the proxy caching technique is one method to accomplish effective media streaming, it cannot adapt to the variations of user locations and diverse user demands. By using the P2P communication architecture, media streaming can be expected to smoothly react to network conditions and changes in user demands for media-streams. We propose efficient methods to achieve continuous and scalable media streaming system. In our mechanisms, a media stream is divided into blocks for efficient use of network bandwidth and storage space. We propose two scalable search methods and two algorithms to determine an optimum provider peer from search results. Through several simulation experiments, we show that the FLS method can perform continuous media play-out while reducing the amount of search traffic to 1/6 compared with full flooding.

As middlewares are more and more spanning over larger networks, towards world-wide grid computing, communicating with mobile objects in a scalable and reliable manner becomes an important and difficult issue. This paper proposes a parametric protocol for such communications. Based on Time To Live (TTL) forwarders, and Time To Update (TTU) mobile objects, it allows to get the best of those two well-known techniques (forwarders, servers). As a parametric protocol, it can be adapted to various network conditions.

It is usually hard to control the network conditions affecting public online game servers when studying the impact of latency, loss and jitter on user experience. This leads to a natural desire for running user-experience trials under controlled network conditions, and hence a requirement for accurate (or at least predictable) emulation of IP level latency, loss and jitter on a localized network testbed. In this short paper we reflect on some experiences with running user-experience trials, and specifically evaluate the utility and limitations of using FreeBSD's kernel-resident dummynet module to introduce controlled jitter. We expect these insights will stimulate further user-experience trials built around low-cost, unix-based networking tools.

The performance of a robot operated over a data network does not only depend on a control algorithm used, but also on network conditions. Providing network QoS (quality-of-service) to a networked robot system could significantly improve its system performances. However, the network QoS can degrade due to several factors, such as congestion and interference, and can affect the overall system performances. We propose a gain adaptation approach to compensate deteriorative changes in network QoS in order to maintain the performances of a robot system as much as possible. The approach is demonstrated by path tracking control of networked differential drive mobile robot over a QoS enabled network. The simulation results show that when the gain adaptation is applied, the robot can effectively tolerate network QoS deterioration, and increase the overall system robustness. The concept of gain adaptation can be easily extended to other network-based control applications.

This paper reports on the quality of service (QoS) requirements and the performance of virtual environment (VE) applications deployed in IP networks. We are interested specifically in systems that support communication with end-user through force feedback devices known as haptic interfaces. Little is known about networked haptic interfaces in VE. Our goal is to understand such application QoS requirements as well as the effect of other traffic when they co-exist in the same network. In this paper, we compare the peer-to-peer model with the client-server model. Our motivation is to deploy distributed haptic VE applications (DHVE) over a network connecting two departments of Queen's University of Belfast. This deployment will be used for educational purposes and for implementing further research in this area, and will be evaluated by end-users; hence, the essential realization of network-based DHVE under realistic network conditions. A set of experiments was conducted to achieve this aim and their results are presented in this paper.

Active networks (AN) have been investigated over several years, attempting to satisfy the increasing needs for highly customizable protocol mechanisms in an era where the Internet is threatened to become immutable due to its huge installed base. AN seem to be particularly useful in the context of QoS support. This paper investigates AN for on-demand QoS routing and proposes an approach called AQR. Simulation experiments are reported which show the (varying) benefits of AQR under various network conditions and traffic characteristics.

This paper presents a study of SSTI related to VSC HVDC. The study was conducted with well established methods, which have been used in the design of SSDC and evaluation of SSTI in classic HVDC. Identical control systems for VSC HVDC as in the real plant are included in the study. The paper will show how the VSC and its control contribute to the electrical damping on subsynchronous oscillations. Different operation modes, load levels, control modes and AC network conditions have been considered in the study.

The growing requirement of TCP-Friendly bandwidth use by streaming video plus the proven advantages of Forward Error Correction (FEC) to combat packet loss presents the opportunity to optimize the amount of FEC in a TCP-Friendly video stream. In this paper, we derive an analytical model for predicting the playable frame rate in a TCP-Friendly MPEG stream with FEC. Our model characterizes the Group Of Pictures (GOP) and Forward Error Correction (FEC) that are part of the MPEG video transmission. Assuming a network estimate for the packet loss probability, our model incorporates TCP-Friendly throughput constraints to calculate a total playable frame rate. For a given packet loss probability, we use our model to search the variable space to find the MPEG configuration that yields the optimal playable frame rate. Analysis over a range of network conditions indicates that adjusting FEC can provide a significant performance improvement, while adjusting a well-chosen GOP will contribute little improvement. Further analysis shows that a poor choice for a GOP can result in a large degradation of the playable frame rate. Overall, by introducing moderate amounts of FEC overhead, frame rates can be improved 10 to 50 times under network conditions with moderate to high loss rates.

An often-claimed benefit of mobile agent technology is the reduction in communication costs. In particular, the area of information filtering has been proposed for the application of mobile filter agents. However, the effective coordination of agents, which takes into account the current network conditions, is difficult to achieve. This paper analyses the situation where data distributed among various remote data servers is examined with mobile filter agents. We present an approach for coordinating the agents' employment, which minimizes communication costs. Validation studies on the possible cost savings for various configurations show that savings of up to 90% can be achieved in the face of actual Internet conditions.

Since the summer of 1997, three natural gas turbocompressors have been driven by adjustable speed supersynchronous motors of 38 MW @ 4200 rpm-the largest LCI drives ever built for that speed up to now. Restrictions on harmonics imposed by the utility, special network conditions, pressure by ecological political groups, and life-cycle economics were decisive in the choice of drive systems. Selection and design criteria for the drivers, network considerations, and first year positive operating experience are addressed by the client and the manufacturer. A subsequent project involving similar high speed electric motor drivers of 25 MW with active magnetic bearings for a "dry" turbocompressor string concludes the paper that primarily addresses prospective users of such systems.

The rate-based flow control for available bit rate (ABR) services in asynchronous transfer mode (ATM) networks is presented. A closed control loop between the source and the destination is performed to implement flow control for ABR services. The source sends resource management (RM) cells with the data cells to be used to indicate the sending station's current transmission rate and the higher rate it would like to use. Based on this information the available cell rate (ACR) which the network can afford is calculated. This is performed in three different ways known as explicit forward congestion identification (EFCI), relative rate marking (RRM) and explicit proportional rate control algorithm (EPRCA). In this paper the combination of the three different schemes is considered. A general formula for evaluating ACR value is given when two network conditions are considered, namely heavy load and moderate load. The new ACR value is calculated based on a feedback acknowledgement from the bottleneck switch. This acknowledgement suggests a new ACR value namely explicit rate (ER)-a rate that the congested switch can afford. A computer simulation is performed to examine the performance of a network consisting of two ATM switches applying the previously mentioned control schemes. High performance is achieved when using the explicit rate (ER) determined by the congested switch.

The capacity of urban road networks is severed by many events such as natural or man-made disasters, accidents, highway reconstruction, and chemical spills, referred to as nonrecurrent incidents. A computer software package, Transportation Emergency Decision Support System, developed to guide emergency vehicles determine the best alternative route to the destination under modified network conditions. The network modification is exercised in the edit and information modules. >

To differentiate services for various traffic categories (TCs) in 802.11eD.2.0 [1], TCs possess different minimum contention window (CWmin) values, which are static over duration. Performances of low priority traffics (FTP) with higher CWmin values are suppressed even during absence of high priority traffics (video and voice). In this paper, we propose a modified backoff scheme called Dynamic Offset Contention Window (DOCW) algorithm, which dynamically adjusts CW values of traffics to network conditions. It is shown by simulations that the proposed algorithm enhances throughputs of low priority traffics where QoS is provided as well.

Publisher Summary The chapter deals with the general framework for meta-search based on query-weighting and numerical aggregation operators. Meta-search is one of the most promising approaches to solve the problem. If the single search-engines store only a portion of all the existing information about some particular domain, various searchers should be queried to increase the search coverage. The meta-search process is modeled as involving two main processes or phases—expansion and aggregation. Expansion means that a query is transformed into a collection of new queries by applying some transformation to the original query. Expansion is used to enrich or refine queries with different purposes and different meanings. Meta-search engines arise to increase the coverage of single search-engines. Meta-search engines offer a unified way to access multiple search engines, avoiding the user to interact with all the underlying engines, but they do not merge results from different sources, neither do they calculate a unique ranking for each item retrieved. It avoids hard computation requirements. The main computation effort is due to the aggregation and sorting algorithms. The overall time cost of the procedure could be high, because the expansion procedures can generate several queries, therefore system performance is very dependent on the network conditions.

When the gap length of a vacuum switch at current zero is too short (i.e. contacts open shortly before current zero), high frequency transients, known as multiple reignitions or virtual current chopping, may occur under certain network conditions. In order to estimate the probability of such transients a mathematical vacuum breaker model, based on numerous measured data, has been developed. It is able to simulate the HF-behaviour in single or three phase networks. To verify the abilities of the breaker model, complex measurements of the interruption of a modern 11 kV dry type transformer with a vacuum breaker under no-load conditions have been carried out. A comparison between the measured data and the results of the simulations, which require an equivalent HF-network for all involved devices (especially the transformer), is presented.

This study develops AVENUE (an Advanced and Visual Evaluator for road Networks in Urban arEas). AVENUE incorporates a driver's route choice model and a traffic flow model that can reproduce over-saturated network conditions as well as under-saturated ones. The development of AVENUE is based on object-oriented programming which affords flexible modifications to users' requirements and graphical environment for easy operations. This model was validated through an application to the Kinshicho area in Tokyo. >

The Tingle suite consists of three programs that monitor remote hosts on a network, perform user-specified actions in response to changing network conditions, and generate reports related to network performance. The first program, Tingle, sends echo requests to user-specified hosts. Echo replies are captured and used to generate one-line reports regarding the state of the remote hosts. The other two programs of the suite process the output of Tingle. The first, twarn, performs user-specified actions in response to network transitions, such as hosts going up or down. The second, tsum, generates summaries of measurements of network performance, such as echo response time and the ratio of echo replies to echo requests. >

A good flow control scheme is crucial for the proper functioning of the available bit rate (ABR) service in asynchronous transfer mode (ATM) networks. To this end, the ABR flow control scheme has been developed by the ATM Forum. In this scheme, resource management (RM) cells are used to carry network feedback to the ABR sources. The ABR sources use the feedback information to adjust their source rates. We examine the response of the congestion control mechanism using a simulation method. It has been found that the flow control scheme is able to achieve low cell loss under extreme traffic conditions, and high link bandwidth utilisation is possible under stable conditions. It has also been found that the feedback to the sources may be inadequate for high bandwidth utilisation under changing network conditions. We propose that the maximum rate of the out-of-rate RM cells be increased, the destination be allowed to generate backward RM cells indicating available bandwidth, and congestion information be modified only in the backward RM cells.

As we addressed in the previous chapter, in single-hop systems of WDM networks a connection is set up by selecting a path of physical links and assigning a (reserved) wavelength to these links. Because of limitations on the number of available wavelengths on the fibers, and hardware constraints at the nodes, it is impossible to set up a lightpath for each of connections between every pair of source-destination nodes. The set of lightpaths that are set up on the physical topology constitutes a logical (also called virtual) topology. One of the major advantages of WDM networks is that it is able to reconfigure its logical topology to adapt to changes of traffic patterns and network conditions.

Switchgear operation is increasingly determined by electronic components. Powerful electronics allow the implementation of functions by means of software rather than hardware and hence the achievement of economic savings. This paper discusses the introduction of new low-power transformers. With these transformers, we are coming closer to achieving universally useable switchgear panels which are independent of load and network conditions, since just one transformer type fulfils all of the protection and measurement requirements, rendering individual transformer selection superfluous. In addition to technical details, this paper focuses on the tasks to be solved, a practical implementation and an application scenario.

Present day continuous media applications have real-time requirements which must be satisfied by the transport service of the network infrastructure used, and the degree to which these requirements are met have a direct impact on performance, perhaps rendering the application inoperative. Therefore it is desirable to perform performance monitoring, through such performance parameters as delay, jitter, packet loss and throughput. Additionally, the awareness of the current values of these performance parameters may be of importance, in that a continuous media application may be able to tolerate the less than perfect satisfaction of its initial real-time requirements, and adapt itself to network conditions within certain limits. This paper describes a simple methodology for measuring these performance parameters using information generated by the RTCP protocol. The use of this methodology is illustrated by results from point-to-point desktop videoconferencing sessions.

Today access to video is available via numerous multimedia enabled devices through a wide variety of network types. What is required is a mechanism to ensure that users can receive different qualities of video proportional to their device capabilities and network conditions. In this thesis, we propose an online adaptive video streaming approach which uses the Peer-to-Peer (P2P) paradigm to not only distribute the content using peers' bandwidth, but also adapt the video using peers' processing power, while taking into account receiver heterogeneity, watermarking, and perceptual encryption.

This paper investigates the problems in explicit rate congestion avoidance algorithms for ABR service in ATM networks. It is found that the performance of the existing algorithms [2, 3, 4] depend on network conditions which vary dramatically in the real condition such as number of traversing sessions, traffic characteristics and propagation delay. In addition, this paper proposes a novel efficient and robust ABR congestion avoidance algorithm called “Fast Rate Allocation Congestion Avoidance (FRACA)”. Some simulation results are presented to illustrate performance in terms of computation accuracy and switch buffer occupancy of the proposed algorithm. Moreover, the simulation results are compared with Explicit Rate Indication Congestion Avoidance (ERICA+) and Enhanced Fast Max-Min Rate Allocation (E-FMMRA) which are the well-known explicit rate switch algorithms and also compatible with ATM Forum Traffic Management Specification 4.0. From comparison, the proposed algorithm works better than both algorithms for all configuration scenarios.

The paper presents a measurement technique for the assessment of the degree of quality of facsimile transmissions over a telephone-type network that can be performed while the communication lines are in use. The main impairments introduced by the telecommunication channel are continuously measured by using a blind equalization technique and a timing recovery system, thus assuring a high accuracy with a reasonable measurement time, even under poor signal-to-noise ratio (SNR) conditions. Experimental results, that confirm the good performance of the proposed method, are reported and discussed.

In contrast to the DUO models with fixed demand, the DUO models with variable demand consider both elastic traffic demand and route choice within a mathematical program framework. The essence of this framework is the existence of feedback on network conditions, where the amount of O-D demand is determined by the corresponding minimal route travel times, which are in turn affected by the O-D demand through the traffic assignment procedure. Since the interactions between the variable demand and route choice decisions are treated within a unified framework, the internal inconsistencies that are apt to characterize conventional transportation planning procedures can be avoided. In consideration of the departure time choices, two types of models can be further identified, i.e., the DUO variable demand/route choice model, and the DUO variable demand/departure time/route choice model.

Current groupware systems do not work well over wireless networks, as a wireless connection is of variable and often poor quality. Our research suggests a number of changes that allow groupware applications to make efficient use of a wireless channel. One fundamental change is providing adaptability, which allows applications to take advantage of favourable network conditions and to react to difficult conditions as they occur. Our experiments with a multi user text editor revealed several strategies for adaptive groupware. Applying these strategies demonstrated a bandwidth reduction in one scenario of over 90%.

In this chapter, the analysis conducted in the previous chapter is advanced by extending the model to a two-link network. In this way, the analysis can be extended to study the impacts of mode-split and route-split effects simultaneously. The models presented are based on the SNDUE framework which was discussed in Chapter 4. Within this framework, the interactions between, on the one hand, the informed and uninformed drivers, and on the other, the drivers and the stochastic network conditions can be properly analysed.

Motorist information systems enhance drivers’ knowledge of the situation in road networks, and thus improve driver’s decision-making (Ben-Akiva et al., 1991; Bonsall et al., 1991; van Berkum and van der Mede, 1993). However, it is far less well understood whether and to what extent the interaction between the drivers themselves and the information and the drivers may reduce potential beneficial effects of these new technologies. A few models have been developed in order to assess the potential of motorist information systems. Whether these are able to capture the main characteristics of these systems is unclear (Watling, 1994). Using simulation experiments, Mahmassani and Chen (1991) and Mahmassani and Jayakrishnan (1991) found that if more than 20 per cent of the drivers are equipped with the motorist information system, the negative effects due to concentration and overreaction (Ben-Akiva et al., 1991), may begin to outweigh the beneficial effects. Concentration takes place if the information reduces the variations among drivers, increases uniformity of perceptions of network conditions and thus increases congestion. Overreaction occurs if drivers do not fully take into account the responses of other drivers provided with the same information, thereby shifting the congestion from one road to another. In these circumstances Mahmassani and Jayakrishnan (1991) argued that provision of coordinated information is necessary.

This report aims at enhancing market acceptance of amorphous core distribution transformers (AMDT) in Europe. PAUWELS TRAFO built several prototypes and trial series, supported by ELECTRABEL in its "Rational Use of Energy" effort. Several units were tested at the laboratories of LABORELEC.

This paper describes XADVANCE, a newly developed tool to analyze the short-term and long-term dynamics of power systems including dynamically changeable components. This paper first outlines XADVANCE, then describes the following features: (1) because no iterative algorithm is used to calculate network conditions, there is no mathematical instability; and (2) a universal dynamics simulation module is used in integral calculation with a user interface using a block diagram and a one-line diagram. Consequently, new power system components such as FACTS equipment can be easily modeled. This paper also evaluates the validation of the developed tool based on studies on (1) frequency regulation by water heaters, and (2) stabilization using an adjustable speed machine (ASM). XADVANCE is shown to be effective in analyzing the dynamics of complex power systems including advanced equipment.

The goal of optimal allocation is to increase stored data availability subject to minimizing the storage budget. Symmetric allocation based on the network coding has been proved to be optimal for distributed storage systems if node availability is not considered. However, because of network conditions and the inherent properties of nodes, each node will have a different availability. This paper focuses on the problem of optimizing distributed data storage when considering node availability. Using a probability model for storage systems, we redefine symmetric allocation in terms of probability-symmetric allocation and propose a probability-symmetric allocation model and strategy based on network coding. These are shown to be optimal in general. Compared with the symmetric allocation scheme proposed by Leong et al., the proposed probability-symmetric allocation scheme not only improves data availability in distributed storage systems but also is more practical.

With the explosion of information highways, network heterogeneity becomes a major issue. It is a challenge to write universal multimedia applications that run over interconnected packet networks with many subnetworks of unevenly distributed resources (processing, bandwidth, storage, and congestion control policies, etc.). Applications generate bursty traffic in today’s packet networks, causing unavoidable congestion, delays and losses. Thus, for applications such as real-time mutimedia, it is desirable for information to be compressed and prioritized so that the application can degrade gracefully under adverse network conditions.

This paper is concerned with the development of strategies for integrated management and control for incident situations, a particular aspect of the TTIC (traffic and travel information centre). The use of VMS (variable message signs) to inform drivers of conditions ahead, when combined with integrated traffic control strategies, can be extremely cost effective in an urban network. However, certain network conditions have to be met for this to happen, and comprehensive and effective monitoring and incident detection systems must be in place. Also, the majority of the benefits are derived from a small number of major incidents and their frequency and location with respect to diversion points can significantly affect the levels of benefit

Due to limited buffers and highly unpredictable traffic loads, the design of effective buffer management policies that minimize cell loss is critical to ATM networks. We outline the important characteristics of optimal buffer control policies for a single node, and using a dynamic programming formulation for a simple two-node network, gain insights into the much harder general multi-node problem. The key result we present is that simple non-work-conserving policies which use limited feedback from adjacent nodes can reduce cell loss significantly. We construct a feedback-based control that uses simple “stop-and-go” rules. This control is then enhanced to react to rapidly changing network conditions. This new control is called the Adaptive HILO policy. Simulation studies of complex networks with large delay-bandwidth product show that the Adaptive HILO policy performs impressively under diverse conditions. Using intuitive arguments, we demonstrate that this policy effectively utilizes unused buffer capacity in upstream buffers during periods of heavy load in downstream buffers.

Congestion control is an important function of traffic management in Asynchronous Transfer Mode (ATM) net works. Available Bit Rate (ABR) is a category of service for ATM networks wherein the source adapts its generation rate to network conditions based on feedback. In this paper we study closed-loop ABR congestion control using special cells called Resource Management (RM) cells to relay feedback to the source. In particular, we investigate both the effectiveness of rate-based ABR congestion control in the presence of bursty source traffic and the relationship between the burst time scale and the ABR control time scale. Two ABR congestion control schemes, the ABR Explicit Forward Congestion Indication (EFCT) and ABR Congestion Indication (CT) schemes, are compared with Unspecified Bit Rate (UBR) transport which makes no effort to control congestion. Traffic sources of various burst lengths of 100, 1000, 10000, and an equal mix of 100 and 10000 cells are used in simulations. It is found that ABR congestion control effectively controls low frequency, medium to long term traffic load transients, but does not control high frequency, short term load transients. In the latter case, ABR control is not necessary since short term transients do not require large amount of buffering. Of the two AABR schemes considered, the more sophisticated ABR CT scheme performs significantly better than the ABR EFCI scheme in terms of delay and buffer occupancy.

In wireless communication systems the resource anagement needs to integrate adaptive techniques to the varying network conditions, due to the eventual dramatic changes that may occur in the link quality. Therefore, it may be desirable to support adaptable resource management techniques that are able to find their decisions in the network configuration information or in the source application description. Accordingly, the paper identifies, explores and proposes adaptive techniques for resource management so as to enhance the transmission quality on wireless systems either through a feedback channel or by making use of the network virtualization concept. Setting up dependencies between the application requests and the radio channel conditions, a feedback loop adaptively configures modulation and coding schemes, calibrates multi-antenna system, controls power per beam allocation or invokes a linear precoding. Finally, when the application requests exceed the network capacity, by the network virtualization process the adaptive potential of the application parameters can be employed, either through source fragmentation or source code adaptation.

Mobile clients face wide variations in network conditions and local resource availability when accessing remote data. Coping with this uncertainty requires the ability to retrieve and present data at varying degrees of fidelity. In this paper we present applicaton-aware adaptation as a solution to this problem. The essence of our solution is a collaborative partnership between applications and the operating system. We describe the Odyssey API for application-aware adaptation and demonstrate its use in accessing two types of data: video and maps.

Protocols for synchronizing data streams should be highly adaptive with regard to both changing network conditions as well as to individual user needs. The Adaptive Synchronization Protocol we are going to describe in this paper supports any type of distribution of the stream group to be synchronized. It incorporates buffer level control mechanisms allowing an immediate reaction on overflow or underflow situations. Moreover, the proposed mechanism is flexible enough to support a variety of synchronization policies and allows to switch them dynamically during presentation. Since control messages are only exchanged when the network conditions actually change, the message overhead of the protocol is very low.

International business scholars increasingly acknowledge the embeddedness of internationalization strategies within global networks of client and supplier relations. Following this paradigm, we inv...

The problem of congestion control in packet-switching networks has been the subject of extensive research over the past two decades [1,2]. A variety of congestion control strategies have been proposed in the literature and some have been applied, more or less successfully, to conventional data networks. Nevertheless, the behavior of network dynamics in the presence of congestion and the proper ways of handling traffic in order to obtain more reliable and predictable performance is not yet sufficiently understood. The difficulty stems mainly from the uncertainties about traffic patterns and the time-varying nature of network conditions.

The learning benefits offered by strategic alliances make the effective governance of knowledge-sharing between collaborative partners a key element of managing partnership networks. This research explored the question of how a firm's governance of its alliance network facilitates knowledge-sharing about effective collaboration between the hub or broker firm and network members. The study examined the operation of Aurora Energy's preferred suppliers alliance network between 1992 and 2005. The Aurora preferred suppliers network operates in Tasmania, an island state located off the south coast of Australia and is a hub-and-spoke network of dyadic alliances between Aurora Energy, an energy company, and 14 retailers of electrical heating appliances. The study found that Aurora's governance of network conditions facilitated knowledge-sharing which generated three distinct forms of value: beneficial alliance outcomes; new knowledge about utilising alliance relationships; and new functional skills.

The author reflects on an article by Ramesh Jain and discusses the major constraints of mobility when producing content for mobile devices.

Random early detection (RED) proposed by Floyd and Jacobson (1993) is an active queue management strategy that has been deployed extensively in routers. However, its effectiveness has been limited owing to the difficulty in tuning its parameters under different network conditions. The authors define the notion of an operating point that an active queue management (AQM) policy should target. They suggest that the RED parameters should be set or varied with the aim of reaching this operating point. Extensive simulations have been performed to understand the effect of max/sub th/ and max/sub p/ on the network dynamics. Based on these simulations, guidelines are given to adapt the RED parameters.

The interactions between adaptive routing algorithms incorporating learning automata and a variable window flow control algorithm are examined. The routing algorithms examined use two new discretised learning automata to choose the minimum delay routes in the network. The first routing algorithm can choose between two possible candidate paths. The second algorithm, using a new fast and accurate multi-action discretised automaton can choose between as many candidate paths as desired. The flow control algorithm is a threshold-based variable window algorithm that decreases the window size when a predefined delay threshold is exceeded and increases it below this threshold. The interactions between the two algorithms are studied. The resulting scheme is compared with similar schemes reported in the literature via simulations. Simulation results are presented which show that the new scheme performs quite well in both normal and abnormal network conditions.

The problem of choosing buffer allocation strategies occurs in the design of any store-and-forward computer network. A good buffer allocation strategy can reduce message blocking; and hence provide more efficient use of network storage resources. We first summarize five buffer allocation strategies and then provide algorithms for determining the minimum buffer sizes required by these strategies given that each outgoing channel must satisfy certain blocking requirements. After that, we compare them under different network conditions such as heavy or light input traffic rate, uniform or non-uniform server utilization and different blocking requirements. Guidelines on which strategy to use under different conditions are also given.

This paper provides a good look at the concept of equivalence in general and at Thevenin's and Norton's theorems in particular. The ain is to investigate simple, general, and comprehensive ways to present and prove these theorems. It is shown that linearity and the absence of external coupling should not be conditions for Thevenin's and Norton's theorems. It is also shown that the traditional open-circuit, short-circuit, and dead network conditions can be replaced by any two distinct conditions at the terinmals. Two-ports and multiterminal networks are also included in the presentation.