We consider a single server constant retrial queue,in which a state-dependent service policy is used to control the service rate.Customer arrival follows Poisson process,while service time and retrial time are exponen...We consider a single server constant retrial queue,in which a state-dependent service policy is used to control the service rate.Customer arrival follows Poisson process,while service time and retrial time are exponential distributions.Whenever the server is available,it admits the retrial customers into service based on a first-come first-served rule.The service rate adjusts in real-time based on the retrial queue length.An iterative algorithm is proposed to numerically solve the personal optimal problem in the fully observable scenario.Furthermore,we investigate the impact of parameters on the social optimal threshold.The effectiveness of the results is illustrated by two examples.展开更多
A new weighted fair queueing algorithm is proposed, which uses the novel flow-based service ratio parameters to schedule flows. This solves the main drawback of traditional weighted fair queneing algorithms- the packe...A new weighted fair queueing algorithm is proposed, which uses the novel flow-based service ratio parameters to schedule flows. This solves the main drawback of traditional weighted fair queneing algorithms- the packet-based calculation of the weight parameters. In addition, this paper proposes a novel service ratio calculation method and a queue mangement technology. The former adjusts the service ratio parameters adaptively based on the dynamics of the packet lengths and thee solves the unfairness problem induced by the variable packet length. The latter improves the utilization of the server＇s queue buffer and reduces the delay jitter through restricting the buffer length for each flow.展开更多
By studying the spectral properties of the underlying operator corresponding to the M/G/1 queueing model with optional second service we obtain that the time-dependent solution of the model strongly converges to its s...By studying the spectral properties of the underlying operator corresponding to the M/G/1 queueing model with optional second service we obtain that the time-dependent solution of the model strongly converges to its steady-state solution. We also show that the time-dependent queueing size at the departure point converges to the corresponding steady-state queueing size at the departure point.展开更多
This article examines the effects of reneging, server breakdown and server vacation on the various states of the batch arrivals queueing system with single server providing service to customers in three fluctuating mo...This article examines the effects of reneging, server breakdown and server vacation on the various states of the batch arrivals queueing system with single server providing service to customers in three fluctuating modes. In this queueing system, any batch arrival joins the queue if the server is busy or on vacation or under repair. However, if the server is free, one customer from the arriving batch joins the service immediately while others join the queue. In case of server breakdown, the customer whose service is interrupted returns back to the head of the queue. As soon as the server has is repaired, the server attends to the customer in mode 1. For this queueing system, customers that are impatient due to breakdown and server vacation may renege (leave the queue without getting service). Due to fluctuating modes of service delivery, the system may provide service with complete or reduced efficiency. Consequently, we construct the mathematical model and derive the probability generating functions of the steady state probabilities of several states of the system including the steady state queue size distribution. Further, we discuss some particular cases of the proposed queueing model. We present numerical examples in order to demonstrate the effects of server vacation and reneging on the various states of the system. The study revealed that an increase in reneging and a decrease in server vacation results in a decrease in server utilization and an increase in server’s idle time provided rates of server breakdown and repair completion are constant. In addition, the probability of server vacation, the probability of system is under repair and the probabilities that the server provides service in three fluctuating modes decreases due to an increase in reneging and a decrease in vacation completion rates.展开更多
We study a vacation queueing system with a single server simultaneously dealing with an M/G/1 and an M/D/1 queue. Two classes of units, priority and non-priority, arrive at the system in two independent Poisson stream...We study a vacation queueing system with a single server simultaneously dealing with an M/G/1 and an M/D/1 queue. Two classes of units, priority and non-priority, arrive at the system in two independent Poisson streams. Under a non-preemptive priority rule, the server provides a general service to the priority units and a deterministic service to the non-priority units. We further assume that the server may take a vacation of random length just after serving the last priority unit present in the system. We obtain steady state queue size distribution at a random epoch. Corresponding results for some special cases, including the known results of the M/G/1 and the M/D/1 queues, have been derived.展开更多
An M/G/1 retrial queue with two-phase service and feedback is studied in this paper, where the server is subject to starting failures and breakdowns during service. Primary customers get in the system according to a P...An M/G/1 retrial queue with two-phase service and feedback is studied in this paper, where the server is subject to starting failures and breakdowns during service. Primary customers get in the system according to a Poisson process, and they will receive service immediately if the server is available upon arrival. Otherwise, they will enter a retrial orbit and are queued in the orbit in accordance with a first-come-first-served （FCFS） discipline. Customers are allowed to balk and renege at particular times. All customers demand the first “essential” service, whereas only some of them demand the second “multi-optional” service. It is assumed that the retrial time, service time and repair time of the server are all arbitrarily distributed. The necessary and sufficient condition for the system stability is derived. Using a supplementary variable method, the steady-state solutions for some queueing and reliability measures of the system are obtained.展开更多
A new type of fair service, referred to as Statistically-Fair Service (SFS), is proposed in this paper. The SFS discipline is given based on the SFS criterion. Compared to "strict" fair service available, SF...A new type of fair service, referred to as Statistically-Fair Service (SFS), is proposed in this paper. The SFS discipline is given based on the SFS criterion. Compared to "strict" fair service available, SFS is mainly characterized by its flexible suitability for the nature of statistically-multiplexed networks. By its statistically-fair service to users, therefore, SFS can ensure well end-to-end QoS requirements on a statistical basis with a benefit of enhancement in network utilization. Two useful properties of SFS is presented. One of them, the property of retaining Exponentially Bounded Burstiness(EBB), can facilitate end-to-end delay estimation of EBB-type traffic. Finally, some numerical results obtained from a simulation study on SFS shows that an SFS-equipped node in steady states will in deed retain the EBB attribute of any input flow.展开更多
To safeguard the interests of transacting parties,non-repudiation mechanisms need to assure fairness and timeliness.The non-repudiation service currently implemented usually does not consider the requirement of fairne...To safeguard the interests of transacting parties,non-repudiation mechanisms need to assure fairness and timeliness.The non-repudiation service currently implemented usually does not consider the requirement of fairness and the fair non-repudiation protocols to date can not be suitably applied in real environment due to its complex interaction.This paper discusses the transaction-oriented non-repudiation requirement for Web services transaction,analyzes the constraints of the traditional model for the available fair non-repudiation protocols and designs a new Online-TTP fair non-repudiation protocol.The new protocol provides a fair non-repudiation solution to secure Web services transactions and can be embedded into a single Web service call.The protocol adopts evidence chained to decreasing the overhead of evidence verification and management and alleviates the overhead of certificate revocation checking and time-stamp generation for signatures.The protocol has strong fairness,timeliness,efficiency and practicability.展开更多
Semi-Markovian model of operation of a single-server queue system with losses and immediate service quality control has been built. In case of unsatisfactory request service quality, its re-servicing is carried out. R...Semi-Markovian model of operation of a single-server queue system with losses and immediate service quality control has been built. In case of unsatisfactory request service quality, its re-servicing is carried out. Re-servicing is executed till it is regarded satisfactory. Time between request income, and request service time are assumed to be random values with distribution functions of general kind. An explicit form of the system stationary characteristics has been defined.展开更多
This paper considers a Geo/Geo/1 queueing system with infinite capacity, in which the service rate changes depending on the workload. Initially, when the number of customers in the system is less than a certain thresh...This paper considers a Geo/Geo/1 queueing system with infinite capacity, in which the service rate changes depending on the workload. Initially, when the number of customers in the system is less than a certain threshold L, low service rate is provided for cost saving. On the other hand, the high service rate is activated as soon as L customers accumulate in the system and such service rate is preserved until the system becomes completely empty even if the number of customers falls below L. The steady-state probability distribution and the expected number of customers in the system are derived. Through the first-step argument, a recursive algorithm for computing the first moment of the conditional sojourn time is obtained. Furthermore, employing the results of regeneration cycle analysis, the direct search method is also implemented to determine the optimal value of L for minimizing the long-run average cost rate function.展开更多
The sharing of operation and management information is required by smart grid.The amount of information transmitted in electric power communication systems will increase greatly in the near future.The integrated infor...The sharing of operation and management information is required by smart grid.The amount of information transmitted in electric power communication systems will increase greatly in the near future.The integrated information transmission technology is an important method for transmitting various kinds of information via the existing broadband channels and networks in power systems.To implement integrated information transmission in power systems,the problem about how to guarantee the quality of service(QoS)of the communication services must be dealt with.展开更多
This paper considers an efficient priority service model with two-level-polling scheme which the message packets conform to the discrete-time Geom/G/1 queue with multiple vacations and bulk arrival. By the embedded Ma...This paper considers an efficient priority service model with two-level-polling scheme which the message packets conform to the discrete-time Geom/G/1 queue with multiple vacations and bulk arrival. By the embedded Markov chain theory and the probability generating function method, we set up the mathematics functions and give closed form expressions for obtaining the mean cyclic period （MCP）, the mean queue length （MQL） and the mean waiting time （MWT） characteristics, the analytical results are also verified through extensive computer simulations. The performance analysis reveals that this priority polling scheme can gives better efficiency as well as impartiality in terms of system characteristics, and it can be used for differentiating priority service to guarantee better QoS and system stability in design and improvement of MAC protocol.展开更多
Service-Oriented Architecture (SOA) is a computer systems design concept which aims to achieve reusability and integration in a distributed environment through the use of autonomous, loosely coupled, interoperable abs...Service-Oriented Architecture (SOA) is a computer systems design concept which aims to achieve reusability and integration in a distributed environment through the use of autonomous, loosely coupled, interoperable abstractions known as services. In order to interoperate, communication between services is very important due to their autonomous nature. This communication provides services with their functional strengths, but also creates the opportunity for the loss of privacy. In this paper, a Privacy Protection Framework for Service-Oriented Architecture (PPFSOA) is described. In this framework, a Privacy Service (PS) is used in combination with privacy policies to create privacy contracts that outline what can and cannot be done with a consumer’s personally identifiable information (PII). The privacy policy consists of one-to-many privacy rules, with each rule created from a set of six privacy elements: collector, what, purpose, retention, recipient and trust. The PS acts as an intermediary between the service consumer and service provider, to establish an unbiased contract before the two parties begin sending PII. It is shown how many Privacy Services work together to form the privacy protection framework. An examination of what current approaches to protecting privacy in an SOA environment is also presented. Finally, the operations the PS must perform in order to fulfill its tasks are outlined.展开更多
Active queue management(AQM) is essentially a router buffer management strategy supporting TCP congestion control.Since existing AQM schemes exhibit poor performance and even instability in time delay uncertain networ...Active queue management(AQM) is essentially a router buffer management strategy supporting TCP congestion control.Since existing AQM schemes exhibit poor performance and even instability in time delay uncertain networks,a robust buffer management(RBM) mechanism is proposed to guarantee the quality of service(QoS).RBM consists of a Smith predictor and two independent controllers.The Smith predictor is used to compensate for the round trip time(RTT) delay and to restrain its negative influence on network performance.The main feedback controller and the disturbance rejection controller are designed as proportional-integral (PI) controller and proportional(P) controller by internal model control(IMC) and frequency-domain analysis respectively.By simulation experiments in Netwrok-Simulator-2(NS2),it is demonstrated that RBM can effectively manage the buffer occupation around the target value against time delay and system disturbance. Compared with delay compensation-AQM algorithm(DC-AQM),proportional-integral-derivative(PID) algorithm and random exponential marking(REM) algorithm,the RBM scheme exhibits the superiority in terms of stability, responsiveness and robustness.展开更多
Workload of each service class varies dynamically in the grid environment, making the static service pool size allocation scheme unable to guarantee the QoS requirement of each service class. In this paper, we link th...Workload of each service class varies dynamically in the grid environment, making the static service pool size allocation scheme unable to guarantee the QoS requirement of each service class. In this paper, we link the issue of dynamical service pool size allocation scheme with QoS requirement under the varying workload, and formulate the QoS performance of service requests in the grid environment by queue theory. Combined Lagrangian optimization with a bisearch approach, the problem of optimally allocating service pool size scheme is resolved. Simulation results show efficiency of the optimal service pool size allocation scheme.展开更多
Internet routers generally see packets from a fast flow more often than a slow flow. This suggests that network fairness may be improved without per-flow information. In this paper, we propose a scheme using Most Rece...Internet routers generally see packets from a fast flow more often than a slow flow. This suggests that network fairness may be improved without per-flow information. In this paper, we propose a scheme using Most Recently Used List (MRUL)-a list storing statistics of limited active flows that sorted in most recently seen first mode-to improve the fairness of RED. Based on the list, our proposed scheme jointly considers the identification and punish of the fast and unresponsive fast flows, and the protection of slow flows. Its performance improvements are demonstrated with extensive simulations. Different from the previous proposals, the complexity of our proposed scheme is proportional to the size of the MRUL list but not coupled with the queue buffer size or the number of active flows, so it is scalable and suitable for various routers. In addition, another issue we address in this paper is queue management in RED. Specifically, we replace the linear packet dropping function in RED by a judicially designed nonlinear quadratic function, while original RED remains unchanged. We call this new scheme Nonlinear RED, or NLRED. The underlying idea is that, with the proposed nonlinear packet dropping function, packet dropping becomes gentler than RED at light traffic load but more aggressive at heavy load. As a result, at light traffic load, NLRED encourages the router to operate in a range of average queue sizes rather than a fixed one. When the load is heavy and the average queue size approaches the pre-determined maximum threshold (i.e. the queue size may soon get out of control), NLRED allows more aggressive packet dropping to back off from it. Simulations demonstrate that NLRED achieves a higher and more stable throughput than RED and REM. Since NLRED is fully compatible with RED, we can easily upgrade/replace the existing RED implementations by NLRED.展开更多
In a manufacturing company, certain departments can be characterized as production departments and others as service departments. This paper expands and simplifies the results by the author and his co-author （Lowenth...In a manufacturing company, certain departments can be characterized as production departments and others as service departments. This paper expands and simplifies the results by the author and his co-author （Lowenthal ＆ Malek, 2005; 2013）, by explaining in a simple way how to obtain the fair-price per unit to pay to external suppliers that replace service departments. The paper also proves that replacing several service departments at once produces exactly the same fair-price per unit if they were replaced sequentially.展开更多
The two-stage tandem queueing system M(z)/M/c→/PH(r)/1/K is studied in this paper. Customers arrive at stage-Ⅰ system in batches according to a Poisson process, and the size of the batch, x , is a r. v. within a ran...The two-stage tandem queueing system M(z)/M/c→/PH(r)/1/K is studied in this paper. Customers arrive at stage-Ⅰ system in batches according to a Poisson process, and the size of the batch, x , is a r. v. within a range of a finite number of positive integers. The stage- Ⅱ ststem has finite capacity, where customers are served in batches with a PH-distribution and the size of the batch is a positive integer r. Only after served in stage- Ⅰ system, and then served in stage- Ⅱ system, can the customers depart from the whole system. Several definitions such as the stage- Ⅰ service blocked time, the first-class and the second-class batch waiting times, and the batch sojourn time are introduced, and their distributions are obtained respectively.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.11971486)。
文摘We consider a single server constant retrial queue,in which a state-dependent service policy is used to control the service rate.Customer arrival follows Poisson process,while service time and retrial time are exponential distributions.Whenever the server is available,it admits the retrial customers into service based on a first-come first-served rule.The service rate adjusts in real-time based on the retrial queue length.An iterative algorithm is proposed to numerically solve the personal optimal problem in the fully observable scenario.Furthermore,we investigate the impact of parameters on the social optimal threshold.The effectiveness of the results is illustrated by two examples.
基金National Natural Science Foundation of China ( No.60572157)Sharp Corporation of Japanthe Hi-Tech Research and Development Program(863) of China (No.2003AA123310)
文摘A new weighted fair queueing algorithm is proposed, which uses the novel flow-based service ratio parameters to schedule flows. This solves the main drawback of traditional weighted fair queneing algorithms- the packet-based calculation of the weight parameters. In addition, this paper proposes a novel service ratio calculation method and a queue mangement technology. The former adjusts the service ratio parameters adaptively based on the dynamics of the packet lengths and thee solves the unfairness problem induced by the variable packet length. The latter improves the utilization of the server＇s queue buffer and reduces the delay jitter through restricting the buffer length for each flow.
基金supported by the National Natural Science Foundation of China(11371303)Natural Science Foundation of Xinjiang(2012211A023)Science Foundation of Xinjiang University(XY110101)
文摘By studying the spectral properties of the underlying operator corresponding to the M/G/1 queueing model with optional second service we obtain that the time-dependent solution of the model strongly converges to its steady-state solution. We also show that the time-dependent queueing size at the departure point converges to the corresponding steady-state queueing size at the departure point.
文摘This article examines the effects of reneging, server breakdown and server vacation on the various states of the batch arrivals queueing system with single server providing service to customers in three fluctuating modes. In this queueing system, any batch arrival joins the queue if the server is busy or on vacation or under repair. However, if the server is free, one customer from the arriving batch joins the service immediately while others join the queue. In case of server breakdown, the customer whose service is interrupted returns back to the head of the queue. As soon as the server has is repaired, the server attends to the customer in mode 1. For this queueing system, customers that are impatient due to breakdown and server vacation may renege (leave the queue without getting service). Due to fluctuating modes of service delivery, the system may provide service with complete or reduced efficiency. Consequently, we construct the mathematical model and derive the probability generating functions of the steady state probabilities of several states of the system including the steady state queue size distribution. Further, we discuss some particular cases of the proposed queueing model. We present numerical examples in order to demonstrate the effects of server vacation and reneging on the various states of the system. The study revealed that an increase in reneging and a decrease in server vacation results in a decrease in server utilization and an increase in server’s idle time provided rates of server breakdown and repair completion are constant. In addition, the probability of server vacation, the probability of system is under repair and the probabilities that the server provides service in three fluctuating modes decreases due to an increase in reneging and a decrease in vacation completion rates.
文摘We study a vacation queueing system with a single server simultaneously dealing with an M/G/1 and an M/D/1 queue. Two classes of units, priority and non-priority, arrive at the system in two independent Poisson streams. Under a non-preemptive priority rule, the server provides a general service to the priority units and a deterministic service to the non-priority units. We further assume that the server may take a vacation of random length just after serving the last priority unit present in the system. We obtain steady state queue size distribution at a random epoch. Corresponding results for some special cases, including the known results of the M/G/1 and the M/D/1 queues, have been derived.
基金Research sponsored by BJTU Research Foundation (2005SM064),the Scientific Research Foundation for the Returned Overseas Chinese Scholars,Education Ministry and the National Natural Science Foundation of China (10526004,60504016).
文摘An M/G/1 retrial queue with two-phase service and feedback is studied in this paper, where the server is subject to starting failures and breakdowns during service. Primary customers get in the system according to a Poisson process, and they will receive service immediately if the server is available upon arrival. Otherwise, they will enter a retrial orbit and are queued in the orbit in accordance with a first-come-first-served （FCFS） discipline. Customers are allowed to balk and renege at particular times. All customers demand the first “essential” service, whereas only some of them demand the second “multi-optional” service. It is assumed that the retrial time, service time and repair time of the server are all arbitrarily distributed. The necessary and sufficient condition for the system stability is derived. Using a supplementary variable method, the steady-state solutions for some queueing and reliability measures of the system are obtained.
基金Supported by the Electronics Preresearch Foundation of China Academy of Electronics and Information Technology
文摘A new type of fair service, referred to as Statistically-Fair Service (SFS), is proposed in this paper. The SFS discipline is given based on the SFS criterion. Compared to "strict" fair service available, SFS is mainly characterized by its flexible suitability for the nature of statistically-multiplexed networks. By its statistically-fair service to users, therefore, SFS can ensure well end-to-end QoS requirements on a statistical basis with a benefit of enhancement in network utilization. Two useful properties of SFS is presented. One of them, the property of retaining Exponentially Bounded Burstiness(EBB), can facilitate end-to-end delay estimation of EBB-type traffic. Finally, some numerical results obtained from a simulation study on SFS shows that an SFS-equipped node in steady states will in deed retain the EBB attribute of any input flow.
基金Supported by the National High Technology Research and Development Program of China (863 Program) (2006AA01Z405)
文摘To safeguard the interests of transacting parties,non-repudiation mechanisms need to assure fairness and timeliness.The non-repudiation service currently implemented usually does not consider the requirement of fairness and the fair non-repudiation protocols to date can not be suitably applied in real environment due to its complex interaction.This paper discusses the transaction-oriented non-repudiation requirement for Web services transaction,analyzes the constraints of the traditional model for the available fair non-repudiation protocols and designs a new Online-TTP fair non-repudiation protocol.The new protocol provides a fair non-repudiation solution to secure Web services transactions and can be embedded into a single Web service call.The protocol adopts evidence chained to decreasing the overhead of evidence verification and management and alleviates the overhead of certificate revocation checking and time-stamp generation for signatures.The protocol has strong fairness,timeliness,efficiency and practicability.
文摘Semi-Markovian model of operation of a single-server queue system with losses and immediate service quality control has been built. In case of unsatisfactory request service quality, its re-servicing is carried out. Re-servicing is executed till it is regarded satisfactory. Time between request income, and request service time are assumed to be random values with distribution functions of general kind. An explicit form of the system stationary characteristics has been defined.
文摘This paper considers a Geo/Geo/1 queueing system with infinite capacity, in which the service rate changes depending on the workload. Initially, when the number of customers in the system is less than a certain threshold L, low service rate is provided for cost saving. On the other hand, the high service rate is activated as soon as L customers accumulate in the system and such service rate is preserved until the system becomes completely empty even if the number of customers falls below L. The steady-state probability distribution and the expected number of customers in the system are derived. Through the first-step argument, a recursive algorithm for computing the first moment of the conditional sojourn time is obtained. Furthermore, employing the results of regeneration cycle analysis, the direct search method is also implemented to determine the optimal value of L for minimizing the long-run average cost rate function.
文摘The sharing of operation and management information is required by smart grid.The amount of information transmitted in electric power communication systems will increase greatly in the near future.The integrated information transmission technology is an important method for transmitting various kinds of information via the existing broadband channels and networks in power systems.To implement integrated information transmission in power systems,the problem about how to guarantee the quality of service(QoS)of the communication services must be dealt with.
基金Supported by the National Natural Science Foundation of China （No. 69862001, F0424104, 60362001 and 61072079）.
文摘This paper considers an efficient priority service model with two-level-polling scheme which the message packets conform to the discrete-time Geom/G/1 queue with multiple vacations and bulk arrival. By the embedded Markov chain theory and the probability generating function method, we set up the mathematics functions and give closed form expressions for obtaining the mean cyclic period （MCP）, the mean queue length （MQL） and the mean waiting time （MWT） characteristics, the analytical results are also verified through extensive computer simulations. The performance analysis reveals that this priority polling scheme can gives better efficiency as well as impartiality in terms of system characteristics, and it can be used for differentiating priority service to guarantee better QoS and system stability in design and improvement of MAC protocol.
文摘Service-Oriented Architecture (SOA) is a computer systems design concept which aims to achieve reusability and integration in a distributed environment through the use of autonomous, loosely coupled, interoperable abstractions known as services. In order to interoperate, communication between services is very important due to their autonomous nature. This communication provides services with their functional strengths, but also creates the opportunity for the loss of privacy. In this paper, a Privacy Protection Framework for Service-Oriented Architecture (PPFSOA) is described. In this framework, a Privacy Service (PS) is used in combination with privacy policies to create privacy contracts that outline what can and cannot be done with a consumer’s personally identifiable information (PII). The privacy policy consists of one-to-many privacy rules, with each rule created from a set of six privacy elements: collector, what, purpose, retention, recipient and trust. The PS acts as an intermediary between the service consumer and service provider, to establish an unbiased contract before the two parties begin sending PII. It is shown how many Privacy Services work together to form the privacy protection framework. An examination of what current approaches to protecting privacy in an SOA environment is also presented. Finally, the operations the PS must perform in order to fulfill its tasks are outlined.
基金the National Natural Science Foundation of China(No.60574081)
文摘Active queue management(AQM) is essentially a router buffer management strategy supporting TCP congestion control.Since existing AQM schemes exhibit poor performance and even instability in time delay uncertain networks,a robust buffer management(RBM) mechanism is proposed to guarantee the quality of service(QoS).RBM consists of a Smith predictor and two independent controllers.The Smith predictor is used to compensate for the round trip time(RTT) delay and to restrain its negative influence on network performance.The main feedback controller and the disturbance rejection controller are designed as proportional-integral (PI) controller and proportional(P) controller by internal model control(IMC) and frequency-domain analysis respectively.By simulation experiments in Netwrok-Simulator-2(NS2),it is demonstrated that RBM can effectively manage the buffer occupation around the target value against time delay and system disturbance. Compared with delay compensation-AQM algorithm(DC-AQM),proportional-integral-derivative(PID) algorithm and random exponential marking(REM) algorithm,the RBM scheme exhibits the superiority in terms of stability, responsiveness and robustness.
基金Project supported by the National-High-Technology Research and Development Program of China (Grant No.2004AA111110)
文摘Workload of each service class varies dynamically in the grid environment, making the static service pool size allocation scheme unable to guarantee the QoS requirement of each service class. In this paper, we link the issue of dynamical service pool size allocation scheme with QoS requirement under the varying workload, and formulate the QoS performance of service requests in the grid environment by queue theory. Combined Lagrangian optimization with a bisearch approach, the problem of optimally allocating service pool size scheme is resolved. Simulation results show efficiency of the optimal service pool size allocation scheme.
文摘Internet routers generally see packets from a fast flow more often than a slow flow. This suggests that network fairness may be improved without per-flow information. In this paper, we propose a scheme using Most Recently Used List (MRUL)-a list storing statistics of limited active flows that sorted in most recently seen first mode-to improve the fairness of RED. Based on the list, our proposed scheme jointly considers the identification and punish of the fast and unresponsive fast flows, and the protection of slow flows. Its performance improvements are demonstrated with extensive simulations. Different from the previous proposals, the complexity of our proposed scheme is proportional to the size of the MRUL list but not coupled with the queue buffer size or the number of active flows, so it is scalable and suitable for various routers. In addition, another issue we address in this paper is queue management in RED. Specifically, we replace the linear packet dropping function in RED by a judicially designed nonlinear quadratic function, while original RED remains unchanged. We call this new scheme Nonlinear RED, or NLRED. The underlying idea is that, with the proposed nonlinear packet dropping function, packet dropping becomes gentler than RED at light traffic load but more aggressive at heavy load. As a result, at light traffic load, NLRED encourages the router to operate in a range of average queue sizes rather than a fixed one. When the load is heavy and the average queue size approaches the pre-determined maximum threshold (i.e. the queue size may soon get out of control), NLRED allows more aggressive packet dropping to back off from it. Simulations demonstrate that NLRED achieves a higher and more stable throughput than RED and REM. Since NLRED is fully compatible with RED, we can easily upgrade/replace the existing RED implementations by NLRED.
文摘In a manufacturing company, certain departments can be characterized as production departments and others as service departments. This paper expands and simplifies the results by the author and his co-author （Lowenthal ＆ Malek, 2005; 2013）, by explaining in a simple way how to obtain the fair-price per unit to pay to external suppliers that replace service departments. The paper also proves that replacing several service departments at once produces exactly the same fair-price per unit if they were replaced sequentially.
基金This paper is supported by the National Natural Science Foundation of China
文摘The two-stage tandem queueing system M(z)/M/c→/PH(r)/1/K is studied in this paper. Customers arrive at stage-Ⅰ system in batches according to a Poisson process, and the size of the batch, x , is a r. v. within a range of a finite number of positive integers. The stage- Ⅱ ststem has finite capacity, where customers are served in batches with a PH-distribution and the size of the batch is a positive integer r. Only after served in stage- Ⅰ system, and then served in stage- Ⅱ system, can the customers depart from the whole system. Several definitions such as the stage- Ⅰ service blocked time, the first-class and the second-class batch waiting times, and the batch sojourn time are introduced, and their distributions are obtained respectively.
