While vacation processes are considered to be ordinary behavior for servers, the study of queueing networks with server vacations is limited, interesting, and challenging. In this paper, we provide a unified and effective method of functional analysis for the study of a supermarket model with server multiple vacations. Firstly, we analyze a supermarket model of N identical servers with server multiple vacations, and set up an infinite-dimensional system of differential (or mean-field) equations, which is satisfied by the expected fraction vector, in terms of a technique of tailed equations. Secondly, as N→ ∞ we use the operator semigroup to provide a mean-field limit for the sequence of Markov processes, which asymptotically approaches a single trajectory identified by the unique and global solution to the infinite-dimensional system of limiting differential equations. Thirdly, we provide an effective algorithm for computing the fixed point of the infinite-dimensional system of limiting differential equations, and use the fixed point to give performance analysis of this supermarket model, including the mean of stationary queue length in any server and the expected sojourn time that any arriving customer spends in this system. Finally, we use some numerical examples to analyze how the performance measures depend on some crucial factors of this supermarket model. Note that the method of this paper will be useful and effective for performance analysis of complicated supermarket models with respect to resource management in practical areas such as computer networks, manufacturing systems and transportation networks.

The scalability and mobility issues in current Internet architecture have drawn a lot of attentions from researchers. However, there are still many problems in current solutions. In this paper, we argue that three spaces, i.e., endpoint IDentifier(ID), Endpoint Locator(ELoc) and Routing Locator(RLoc), are necessary to realize two separations, i.e., separating identifier from locator and separating edge networks from the transit core. Following this argument, we design ID-ELoc-RLoc based architecture, i.e., IER, a separation approach to solve both mobility and scalability issues. After separating identifier from locator, mobile endpoints can ensure continuity of communications across IP address changes since their IDs do not change during moving. After separating edge networks from the transit core, the size and dynamics of global routing table would not be affected by traffic engineering, multi-homing, etc. in edge networks. In this paper, we introduce the definitions, framework, and implementation considerations of our IER architecture in details.

Mental workload is a major consideration for the design of emergency operation procedures (EOPs) in nuclear power plants. Continuous and objective measures are desired. This paper compares seven mental workload measurement methods (pupil size, blink rate, blink duration, heart rate variability, parasympathetic/sympathetic ratio, total power and (Goals, Operations, Methods, and Section Rules)-(Keystroke Level Model) GOMS-KLM-based workload index) with regard to sensitivity, validity and intrusiveness. Eighteen participants performed two computerised EOPs of different complexity levels, and mental workload measures were collected during the experiment. The results show that the blink rate is sensitive to both the difference in the overall task complexity and changes in peak complexity within EOPs, that the error rate is sensitive to the level of arousal and correlate to the step error rate and that blink duration increases over the task period in both low and high complexity EOPs. Cardiac measures were able to distinguish tasks with different overall complexity. The intrusiveness of the physiological instruments is acceptable. Finally, the six physiological measures were integrated using group method of data handling to predict perceived overall mental workload.Practitioner Summary: The study compared seven measures for evaluating the mental workload with emergency operation procedure in nuclear power plants. An experiment with simulated procedures was carried out, and the results show that eye response measures are useful for assessing temporal changes of workload whereas cardiac measures are useful for evaluating the overall workload.

When decomposing the total orbit into $N$ sub-orbits (or simply orbits) related to each of $N$ servers and through comparing the numbers of customers in these orbits, we introduce a retrial supermarket model of $N$ identical servers, where two probing-server choice numbers are respectively designed for dynamically allocating each primary arrival and each retrial arrival into these orbits when the chosen servers are all busy. Note that the designed purpose of the two choice numbers can effectively improve performance measures of this retrial supermarket model. This paper analyzes a simple and basic retrial supermarket model of N identical servers, that is, Poisson arrivals, exponential service and retrial times. To this end, we first provide a detailed probability computation to set up an infinite-dimensional system of differential equations (or mean-field equations) satisfied by the expected fraction vector. Then, as N goes to infinity, we apply the operator semigroup to obtaining the mean-field limit (or chaos of propagation) for the sequence of Markov processes which express the state of this retrial supermarket model. Specifically, some simple and basic conditions for the mean-field limit as well as for the Lipschitz condition are established through the first two moments of the queue length in any orbit. Finally, we show that the fixed point satisfies a system of nonlinear equations which is an interesting networking generalization of the tail equations given in the M/M/1 retrial queue, and also use the fixed point to give performance analysis of this retrial supermarket model through numerical computation.

In this paper, we provide a matrix-analytic solution for randomized load balancing models (also known as \emph{supermarket models}) with phase-type (PH) service times. Generalizing the service times to the phase-type distribution makes the analysis of the supermarket models more difficult and challenging than that of the exponential service time case which has been extensively discussed in the literature. We first describe the supermarket model as a system of differential vector equations, and provide a doubly exponential solution to the fixed point of the system of differential vector equations. Then we analyze the exponential convergence of the current location of the supermarket model to its fixed point. Finally, we present numerical examples to illustrate our approach and show its effectiveness in analyzing the randomized load balancing schemes with non-exponential service requirements.

In this paper, we provide a new and effective approach for studying super-exponential solution of a retrial supermarket model with Poisson arrivals, exponential service times and exponential retrial times and with two different probing-server numbers. We describe the retrial supermarket model as a system of differential equations by means of density-dependent jump Markov processes, and obtain an iterative algorithm for computing the fixed point of the system of differential equations. Based on the fixed point, we analyze the expected sojourn time that a tagged arriving customer spends in this system, and use numerical examples to indicate different influence of the two probing-server numbers on system performance including the fixed point and the expected sojourn time. Furthermore, we analyze exponential convergence of the current location of the retrial supermarket model to the fixed point, and apply the Kurtz Theorem to study density-dependent jump Markov process given in the retrial supermarket model, which leads to a Lipschitz condition under which the fraction measure of the retrial supermarket model weakly converges to the system of differential equations. This paper arrives at a new understanding of how the workload probing can help in load balancing jobs in retrial supermarket models.

Email is a crucial part of our daily life, but email systems are facing increasing security threats such as attacks and spam. Because of this, new mechanisms are being provided to defend against the attacks and to reduce the amount of spam in email systems. Up to now, few available works have been reported on the performance evaluation of email systems under attack, which has become necessary for enhancing email security. In this paper, we propose a novel method to study the impact of three types of attacks on email systems. We construct a multiple queueing model to characterize three types of attacks integrally, and study the performance metrics of system security such as system availability, average queue length and information leakage probability. Numerical examples indicate that the approach of this paper is effective and efficient for dealing with the security analysis of email systems under attack. We believe that this work will open a new avenue for the performance evaluation of computer networks under email attack and other forms of attacks.

Multipath routing can adapt to traffic changes, increase reliability and enhance the Quality of Service support in communication networks. This routing algorithm has been recognized as one of the salient features in Mobile Ad hoc Networks (MANETs). However, existing multipath routing protocols are often practically infeasible due to its security venerability if they suffer from attacks in MANETs, such as repudiation attacks, Denial of Service attacks. In this paper we propose a novel secure multipath routing protocol, referred to as SMRP, and investigate its feasibility and performance. SMRP applies a new heuristic algorithm increasing the number of disjoint paths and a smart authentication mechanism to enhance the security against the attacks in MANETs. The performance results from extensive analysis and experiments show that SMRP can efficiently enhance the security in MANETs while preserving the low overhead of computing and communication. Copyright © 2009 John Wiley & Sons, Ltd.

Seamless handover is one of the most attractive research fields in B3G systems. Many mechanisms are proposed to provide certain QoS guarantees in handovers of mobile systems, which would also introduce new threats, such as DoS and DDOS attacks. In this paper, we extend a cookie-based scheme to protect systems from DoS and DDoS attacks. We also adopt a novel queuing network model to analyze our scheme by estimating two essential metrics, i.e. the mean total response time and the mean queue length of MAP. Numerical results indicate that our mechanism works better than the traditional cookie-based scheme and it could effectively help networks defend against abnormal attacks in the handover process.

In this paper, we propose a novel modeling method, Stochastic Game Nets (SGN), and use it to model and analyze the security issues in enterprise networks. Firstly, the definition and modeling algorithm of Stochastic Game Nets are given. And then we apply the Stochastic Game Nets method to describe the attack and defense course in the enterprise networks successfully, and find a Nash equilibrium. Finally we analyze the confidentiality and integrity of the enterprise network quantificationally based on the model. The method can also be applied to other areas with respect to a game.

Future network systems and embedded infrastructure devices in ubiquitous environments will need to consume low power and process large amounts of network packet traffic. In order to meet necessary high processing efficiency requirements, future processors will have many heterogeneous cores with reduced reliability due to low voltage, small transistor sizes, semiconductor wearout, and environmental factors such as noise and interference. It will be necessary for multi-core network infrastructure software to mitigate transient hardware faults to maintain acceptable system reliability. Applications such as packet processing can benefit from the reliability versus performance tradeoff. We propose a model based on stochastic reward nets to evaluate the performance vs. reliability tradeoff of unreliable embedded multi-core network processors, and apply this model to a multi-core packet processing application.

Red water phenomenon occurred in some communities of a city in China after water source switch in recent days. The origin of this red water problem and mechanism of iron release were investigated in the study. Water quality of local and new water sources was tested and tap water quality in suffered area had been monitored for 3 months since red water occurred. Interior corrosion scales on the pipe which was obtained from the suffered area were analyzed by XRD, SEM, and EDS. Corrosion rates of cast iron under the conditions of two source water were obtained by Annular Reactor. The influence of different source water on iron release was studied by pipe section reactor to simulate the distribution systems. The results indicated that large increase of sulfate concentration by water source shift was regarded as the cause of red water problem. The Larson ratio increased from about 0.4 to 1.7-1.9 and the red water problem happened in the taps of some urban communities just several days after the new water source was applied. The mechanism of iron release was concluded that the stable shell of scales in the pipes had been corrupted by this kind of high-sulfate-concentration source water and it was hard to recover soon spontaneously. The effect of sulfate on iron release of the old cast iron was more significant than its effect on enhancing iron corrosion. The rate of iron release increased with increasing Larson ratio, and the correlation of them was nonlinear on the old cast-iron. The problem remained quite a long time even if the water source re-shifted into the blended one with only small ratio of the new source and the Larson ratio reduced to about 0.6.

Two-points-short-term free chlorine plus chloramines disinfection process was used in conventional treatments of water supply. The process is adding chlorine at the start of filtration and clear well respectively, and then after a few minutes chlorine disinfection in clear well adding ammonia to change the chlorine to chloramines. The point of chlorine dosing move up to the filtration process can decrease disinfection by-product yield and control bio-film growth in filtration process. Compared with adding equal quantity chlorine once, this process reduced 51.6% of THMs and 46.7% of HAAs. HPC result also showed advantage in microorganism controlling.

In domains of scientific and engineering computation, many applications share the characteristic that a large amount of batch jobs are included in the problem domain and these jobs can be executed concurrently on distributed resources. A register-based resource representing framework has been devised to allow these applications to be developed and executed independent of any specific resources, while providing them with the vital mechanisms to improve performance and reduce cost. The major strategies include enabling simultaneous accesses to distributed resources, enabling dynamic resource discovery for every jobs, enabling up to thousands of jobs to be submitted in one request, and utilizing every resource's inner parallel computability. A set of tools for developing register-based resource representing frameworks have been implemented. And the promised mechanisms have been evaluated with the application gSVAP running on Peking University Grid.

In this paper, we propose a novel modeling method, Stochastic Game Nets(SGN). SGN is an good method to model and deal with the game issues, which takes advantages of both stochastic game theory and Stochastic Petri Nets. The SGN could inherit the efficient and flexible modeling approach of Stochastic Petri Nets, and also make well use of the game-theoretical framework from game theory. Meanwhile, we apply the SGN method to model and analyze the network attacks, compute the Nash equilibrium and best-response strategies to defend the attacks. We believe that the SGN opens a new avenue to deal with the game issues in computer networks.

Batch-scale experiments were done to quantitatively study the effect of inorganic chemical parameters on iron release in drinking water distribution systems. The parameters include acid-base condition, oxidation-reduction condition, and neutral ion condition. It was found that the iron release rate decreased with pH, alkalinity, the concentration of dissolved oxygen increasing, and the iron release rate increased with the concentration of chloride increasing. The theoretical critical formula of iron release rate was elucidated. According to the formula, the necessary condition for controlling iron release is that pH is above 7.6, the concentration of alkalinity and dissolved oxygen is more than 150 mg/L and 2 mg/L, and the concentration of chloride is less than 150 mg/L of distributed water.

This study investigates the regularity of the change on the physical and chemical water qualities in the distribution system during the process of water source switching in A city. Due to the water source switching, the water quality is chemical-astable. Because of the differences between the two water sources, pH reduced from 7.54 to 7.18, alkalinity reduced from 188 mg x L(-1) to 117 mg x L(-1), chloride (Cl(-)) reduced from 310 mg x L(-1) to 132 mg x L(-1), conductance reduced from 0.176 S x m(-1) to 0.087 S x m(-1) and the ions of calcium and magnesium reduced to 15 mg x L(-1) and 11 mg x L(-1) respectively. Residual chlorine changed while the increase of the chlorine demand and the water quantity decreasing at night, and the changes of pH, alkalinity and residual chlorine brought the iron increased to 0.4 mg x L(-1) at the tiptop, which was over the standard. The influence of the change of the water parameters on the water chemical-stability in the drinking water distribution system is analyzed, and the controlling countermeasure is advanced: increasing pH, using phosphate and enhancing the quality of the water in distribution system especially the residual chlorine.

In most network security analysis, researchers mainly focus on qualitative studies on security schemes and possible attacks, and there are few papers on quantitative analysis in the current literature. In this paper, we propose one queueing model for the evaluation of the denial of service (DoS) attacks in computer networks. The network under DoS attacks is characterized by a two-dimensional embedded Markov chain model. With this model, we can develop a memory-efficient algorithm for finding the stationary probability distribution which can be used to find other interesting performance metrics such as the connection loss probability and buffer occupancy percentages of half-open connections for regular traffic and attack traffic. Different from previous works in the literature, this paper gives a more general analytical approach to the study of security measures of a computer network under DoS attacks. We hope that our approach opens a new avenue to the quantitative evaluation of more complicated security schemes in computer networks.

In this paper, an AntiWorm system based on the Intel IXP Network Processor was implemented using the Parallel Bloom filters technique. The AntiWorm system consists of two components: Bloom filters and Exact Matching engines. The Parallel Bloom filters can identify the suspicious traffic quickly and effectively, and then dispatch them to Exact Matching engines for further investigation. Both the principles and the implementation of the AntiWorm system are introduced in detail. With the consideration of the system performance parameters, two feasible implementation solutions are investigated and the advantages and disadvantages are also compared. The selections of configuration parameters of the AntiWorm system are also discussed. A hash scheme based on MD5's function is proposed for implementing fast hash functions. To test the performance of the AntiWorm system, such as throughput and delay, some experiments are carried out with different simulated traffic condition. The internal statistics of IXP network processor are also collected and analyzed for optimizing the system performance. To demonstrate the operation of the AntiWorm system, assaults by Worm Blaster are used in the test bed, and the experimental results prove the effectiveness of the AntiWorm system. The Software Package WormDetector1.0 is also provided as a software release from the research.

Variation rule of iron in drinking water distribution systems was studied, and it was found that the iron released from the scale to the bulk water was the primary reason for iron overstep. The main chemical composition of the scale in cast iron pipe and galvanized steel pipe was iron in a northern city in China. In the drinking water distribution systems, when the value of dissolved oxygen or chlorine residual was low, the iron release phenomenon was severe. The reason for that was the passivation layer of the corrosion scale was destroyed in reductive condition and the result was a great amount of iron in ferrous form was released. According to the research results, the control methods for iron release and 'red water' phenomenon were indicated.