Sharif Digital Repository

Hidden-terminal is one of the main problems in ad hoc wireless networks. In addition, there are scenarios where the desired destination is located in the range of other transmitters, so that the efforts on setting up communication with this terminal will fail due to collisions that may occur between transmitted control frames and undesired received control and data frames. This phenomenon becomes a bottleneck when most of data transmissions experience packet fragmentation. In such scenarios, the desired destination becomes unreachable during the data transfer of neighboring nodes. Using the same PHY of IEEE 802.11 and making slight modifications in its MAC, a new medium access control scheme... 

Multiprocessor systems have been widely used for the execution of parallel applications. Task scheduling is crucial for the right operation of multiprocessor systems, where the aim is shortening the length of schedules. Fault tolerance is becoming a necessary attribute in multiprocessor systems as the number of processing elements is getting larger. This paper presents a fault tolerant scheduling algorithm for task graph applications in multiprocessor systems. The algorithm is an extension of a previously proposed algorithm with a reduced communications scheme. Simulation results show the efficiency of the proposed algorithm despite its simplicity  

In this study, the authors evaluate the security of the lightweight block cipher KLEIN-64 using biclique cryptanalysis. They first point out some new weaknesses of the diffusion layer and key schedule of this algorithm. Then they exploit them to cryptanalyst the full round version of KLEIN-64 using an asymmetric biclique. The (worst case) computations and data complexity of this cryptanalysis are 262.84 and 239, respectively. A modified version of this cryptanalysis is also presented which is slightly faster at the expense of the data required  

Corner-case analysis is a well-known technique to cope with occasional deviations occurring during the manufacturing process of semiconductors. However, the increasing amount of process variation in nanometer technologies has made it inevitable to move toward statistical analysis methods, instead of deterministic worst-case-based techniques, at all design levels. We show that by statically considering statistical effects of random and systematic process variation on performance and power consumption of a Multiprocessor System-on-Chip (MPSoC), significant power improvement can be achieved by static software-level optimizations such as task and communication scheduling. Moreover, we analyze... 

In this paper, the availability of the Resource Management System (RMS) and computational resources distributed within grid computing environments is studied. Since the RMS acts as a heart of the grid environments, the unavailability of this system can render the entire environment to the inoperable phase. Furthermore, the unavailability of the grid resources may result in degradation of the performance of the grid. Therefore, considering the great importance of the availability issue in grid computing environments, the Stochastic Activity Networks (SANs) are exploited to model and evaluate the availability of grid environments. The proposed SAN models the failure of the resource management... 

Task scheduling algorithms in grid environments strive to maximize the overall throughput of the grid. In order to maximize the throughput of the grid environments, the makespan of the grid tasks should be minimized. In this paper, a new task scheduling algorithm is proposed to assign tasks to the grid resources with goal of minimizing the total makespan of the tasks. The algorithm uses the genetic approach to find the suitable assignment within grid resources. The experimental results obtained from applying the proposed algorithm to schedule independent tasks within grid environments demonstrate the applicability of the algorithm in achieving schedules with comparatively lower makespan in... 

Impossible differential attack is a well-known mean to examine robustness of block ciphers. Using impossible differential cryptanalysis, we analyze security of a family of lightweight block ciphers, named Midori, that are designed considering low energy consumption. Midori state size can be either 64 bits for Midori64 or 128 bits for Midori128; however, both versions have key size equal to 128 bits.In this paper, we mainly study security of Midori64. To this end, we use various techniques such as early-abort, memory reallocation, miss-in-the-middle and turning to account the inadequate key schedule algorithm of Midori64. We first show two new 7-round impossible differential characteristics... 

Diffusion of key schedule algorithm plays an important role in security of block ciphers. In this paper, we present a new approach to key schedule diffusion analysis by taking the advantages of graph theory modeling. This modeling can help to disclose the weaknesses of key schedules. In this line, the key schedule weaknesses of Twine-128 are shown and an improved key schedule is proposed. In order to make a fair comparison, some parameters are introduced to quantify the diffusion property of key schedule, and compare the results for Twine-128 with both key schedules. The results show that the new key schedule made Twine-128 stronger. Also for more reliability, the results of biclique attack... 

While IEEE 802.16 standardizes the PHY and MAC layers of Wireless Metropolitan Area Networks (MAN), optimal scheduling which is crucial in providing QoS, remains to be an open issue. In this paper, we propose an optimization based uplink scheduling algorithm which aims at maximizing the throughput while guaranteeing the negotiated QoS parameters for all connections. Unlike typical strict priority schedulers the proposed scheduler is able to satisfy the requirements of higher priority connections while not letting the lower priority connections to be neglected. Additionally, a parameter is defined to ensure fairness among rtPS connections. The scheduler's performance is then evaluated through... 

The general approach to fault tolerance in uniprocessor systems is to maintain enough time redundancy in the schedule so that any task instance can be re-executed in presence of faults during the execution. In this paper a scheme is presented to add enough and efficient time redundancy to the Earliest-Deadline-First (EDF) scheduling policy for periodic real-time tasks. This scheme can be used to tolerate transient faults during the execution of tasks. We describe a recovery scheme which can be used to re-execute tasks in the event of transient faults and discuss conditions that must be met by any such recovery scheme. For performance evaluation of this idea a tool is developed. © 2007 IEEE  

In the last decade, the scale of heterogeneous computing (HC) systems such as heterogeneous cloud computing environments was growing like never before. So network failures are unavoidable in such systems, which affect system reliability. Since the task scheduling algorithm in HC is challenging, we investigate a new reliability-aware task scheduling algorithm (RATSA) in this paper. RATSA is designed to schedule tasks on directed acyclic graphs (DAGs) by using the shuffled frog-leaping algorithm (SFLA) and genetic algorithm (GA) as evolutionary algorithms. The population-based SFLA-GA is applied to optimize makespan in the RATSA as an NP-complete problem. Moreover, the proposed algorithm... 

In the last decade, the scale of heterogeneous computing (HC) systems such as heterogeneous cloud computing environments was growing like never before. So network failures are unavoidable in such systems, which affect system reliability. Since the task scheduling algorithm in HC is challenging, we investigate a new reliability-aware task scheduling algorithm (RATSA) in this paper. RATSA is designed to schedule tasks on directed acyclic graphs (DAGs) by using the shuffled frog-leaping algorithm (SFLA) and genetic algorithm (GA) as evolutionary algorithms. The population-based SFLA-GA is applied to optimize makespan in the RATSA as an NP-complete problem. Moreover, the proposed algorithm... 

In this paper, we present a new Start-time Fair Queuing (SFQ) algorithm called Weighted Start-time Fair Queuing (WSFQ) which is more efficient and achieves better fairness than SFQ in the presence of small and huge elastic traffic flows. WSFQ scheduler, like SFQ uses a start time eligibility criterion to select packets and when the start-time of two packets in two flows are the same, it acts like Weighted Fair Queuing (WFQ) which selects the smallest virtual finish time first. Afterward, we compared the performance of our model with that of the applied scheduling algorithms such as First-In-First-Out (FIFO), SFQ as well as WFQ on the end-to-end delay and the throughput in small and... 

A bicriteria two-machine flowshop scheduling problem is addressed to minimize the number of setups and makespan. The jobs have sequence dependent setup times. Scheduling problems considering either of these objectives are NP-hard. Two multi-objective metaheurisctics based on genetic algorithms (MOGA) and simulated annealing (MOSA) are proposed to find approximations of Pareto-optimal frontiers. The performances of these approaches are compared with lower bounds for small problems. In larger problems, their performance is compared with each other. Experimentations revealed that both algorithms perform very similar on small problems and that MOGA outperforms MOSA in terms of the quality of... 

This paper introduces an analytical method for approximating the performance of a firm real-time system consisting of a number of parallel infinite-capacity single-server queues. The service discipline for the individual queues is earliest-deadline-first (EDF). Real-time jobs with exponentially distributed relative deadlines arrive according to a Poisson process. Jobs either all have deadlines until the beginning of service or deadlines until the end of service. Upon arrival, a job joins a queue according to a state-dependent stationary policy, where the state of the system is the number of jobs in each queue. Migration among the queues is not allowed. An important performance measure to...