Permission-based fault tolerant mutual exclusion algorithm for mobile Ad Hoc networks

This study focuses on resolving the problem of mutual exclusion in mobile ad hoc networks. A Mobile Ad Hoc Network (MANET) is a wireless network without fixed infrastructure. Nodes are mobile and topology of MANET changes very frequently and unpredictably. Due to these limitations, conventional mutual exclusion algorithms presented for distributed systems (DS) are not applicable for MANETs unless they attach to a mechanism for dynamic changes in their topology. Algorithms for mutual exclusion in DS are categorized into two main classes including token-based and permission-based algorithms. Token-based algorithms depend on circulation of a specific message known as token. The owner of the token has priority for entering the critical section. Token may lose during communications, because of link failure or failure of token host. However, the processes for token-loss detection and token regeneration are very complicated and time-consuming. Token-based algorithms are generally non-fault-tolerant (although some mechanisms are utilized to increase their level of fault-tolerance) because of common problem of single token as a single point of failure. On the contrary, permission-based algorithms utilize the permission of multiple nodes to guarantee mutual exclusion. It yields to high traffic when number of nodes is high. Moreover, the number of message transmissions and energy consumption increase in MANET by increasing the number of mobile nodes accompanied in every decision making cycle. The purpose of this study is to introduce a method of managing the critical section,named as Ancestral, having higher fault-tolerance than token-based and fewer message transmissions and traffic rather that permission-based algorithms. This method makes a tradeoff between token-based and permission-based. It does not utilize any token, that is similar to permission-based, and the latest node having the critical section influences the entrance of the next node to the critical section, that is similar to token-based algorithms. The algorithm based on ancestral is named as DAD algorithms and increases the availability of fully connected network between 2.86 to 59.83% and decreases the number of message transmissions from 4j-2 to 3j messages (j as number of nodes in partition). This method is then utilized as the basis of dynamic ancestral mutual exclusion algorithm for MANET which is named as MDA. This algorithm is presented and evaluated for different scenarios of mobility of nodes, failure, load and number of nodes. The results of study show that MDA algorithm guarantees mutual exclusion,dead lock freedom and starvation freedom. It improves the availability of CS to minimum 154.94% and 113.36% for low load and high load of CS requests respectively compared to other permission-based lgorithm.Furthermore, it improves response time up to 90.69% for high load and 75.21% for low load of CS requests. It degrades the number of messages from n to 2 messages in the best case and from 3n/2 to n in the worst case. MDA algorithm is resilient to transient partitioning of network that is normally occurs due to failure of nodes or links

TrainNet: a novel transport infrastructure for non real-time data delivery

To date, researchers have proposed many vehicular networks in which cars or buses act as a mechanical backhaul for transporting data. For example, a bus can be retrofitted with a computer and wireless card to automatically ferry data to/from rural villages without Internet connectivity. Alternatively, a person carrying a portable storage device can be used to link geographically disparate networks. These examples of challenged networks are characterized by frequent disruptions, long delays, and/or intermittent connectivity. This thesis proposes TrainNet, a vehicular network that uses trains to transport latency insensitive data. TrainNet augments a railway network by equipping stations and trains with mass storage devices; e.g., a rack of portable hard disks. TrainNet has two applications. First, it provides a low cost, very high bandwidth link that can be used to deliver non real-time data. In particular, cable TV operators can use TrainNet to meet the high bandwidth requirement associated with Video on Demand (VoD) services. Moreover, TrainNet is able to meet this requirement easily because its links are scalable, meaning their capacity can be increased inexpensively due to the continual fall of hard disk price. Secondly, TrainNet provides an alternative, economically viable, broadband solution to rural regions that are reachable via a railway network. Therefore, using TrainNet, rural communities will be able to gain access to bandwidth intensive digital contents such as music, video, television programs, and movies cheaply. A key problem in TrainNet is resource scheduling. This problem arises because stations compete for the fixed storage capacity on each train. To this end, this thesis is the first to propose three max-min scheduling algorithms, namely LMMF, WGMMF and GMMF, for use in challenged networks. These algorithms arbitrate the hard disk space among competing stations using local traffic information at each station, or those from other stations. To study these algorithms, the Unified Modeling Language (UML) is first used to construct a model of TrainNet, before a simulator is constructed using the DESMO-J framework. The resulting TrainNet simulator is then used to investigate the behavior of said max-min algorithms in scenarios with realistic traffic patterns. Results show that while LMMF is the fairest algorithm, it results in data loss and has the longest mean delay, the lowest average throughput, and the lowest hard disk utilization. Furthermore, Jain’s fairness index shows WGMMF to be the least fair algorithm. However, it avoids data loss as is the case with GMMF, and achieves the best performance in terms of mean delay, averaged throughput, and hard disk utilization

Availability Analysis of Predictive Hybrid M-Out-of-N Systems

In m-out-of-n system, if m-out-of-n modules agree, system can report consensus; otherwise, the system fails. On the other hand, in predictive hybrid system if there is no agreement, a history record of previous successful result(s) is used to predict the output. In order to analyze the availability of predictive hybrid redundancy system, Markov modeling is utilized. By using Markov model of the system in steady state, the availability is derived and compared with m-out-of-n system. The results of simulation demonstrated that the availability of predictive hybrid system is higher than m-out-of-n system especially for large m

Evaluating reliability and predictive validity of the persian translation of quantitative checklist for autism in toddlers (Q-CHAT)

Objective: Early screening of autism increases the chance of receiving timely intervention. Using the Parent Report Questionnaires is effective in screening autism. The Q-CHAT is a new instrument that has shown several advantages than other screening tools. Because there is no adequate tool for the early screening of autistic traits in Iranian children, we aimed to investigate the adequacy of the Persian translation of Q-CHAT. Method: At first, we prepared the Persian translation of the Quantitative Checklist for Autism in Toddlers (Q-CHAT). After that, an appropriate sample was selected and the check list was administered. Our sample included 100 children in two groups (typically developing and autistic children) who had been selected conveniently .Pearson's r was used to determine test-retest reliability, and Cronbach's alpha coefficient was used to explore the internal consistency of Q-CHAT. We used the receiver operating characteristics curve (ROC) to investigate whether Q-CHAT can adequately discriminate between typically developing and ASD children or not. Data analysis was carried out by SPSS 19. Result: The typically developing group consisted of 50 children with the mean age of 27.14 months, and the ASD group included50 children with the mean age of 29.62 months. The mean of the total score for the typically developing group was 22.4 (SD=6.26) on Q-CHAT and it was 50.94 (SD=12.35) for the ASD group, which was significantly different (p=0.00).The Cronbach's alpha coefficient of the checklist was 0.886, and test-retest reliability was calculated as 0.997 (p<0.01). The estimated area under the curve (AUC) was 0.971. It seems that the total score equal to 30 can be a good cut point to identify toddlers who are at risk of autism (sensitivity= 0.96 and specificity= 0.90). Conclusion: The Persian translation of Q-CHAT has good reliability and predictive validity and can be used as a screening tool todetect18 to 24 months old children who are at risk of autism

Availability analysis of predictive hybrid M-out-of-N systems

In m-out-of-n system, if m-out-of-n modules agree, system can report consensus; otherwise, the system fails. On the other hand, in predictive hybrid system if there is no agreement, a history record of previous successful result(s) is used to predict the output. In order to analyze the availability of predictive hybrid redundancy system, Markov modeling is utilized. By using Markov model of the system in steady state, the availability is derived and compared with m-out-of-n system. The results of simulation demonstrated that the availability of predictive hybrid system is higher than m-out-of-n system especially for large m

Identification and ranking of effective factors of marketing (controllable) to receive the services from free zone with MADM approach

This study applies the fuzzy MCDM (multicriteria decision making) to evaluate the services Performance in free trade zone. Performance evaluation is an important issue for managers, since it can be used as a reference in decision making with regard to performance improvement, specially teaching performance improvement. For this purpose, in this study, we use fuzzy set theory for the measurement of performance and apply AHP in obtaining criteria weight and TOPSIS in ranking. A fuzzy MCDM is an approach for evaluating decision alternatives involving subjective judgments made by a group of decision makers. A pairwise comparison process is used to help individual decision makers make comparative judgments, and a linguistic rating method is used for making absolute judgments

Identification and ranking of effective factors of marketing (controllable) to receive the services from free zone with MADM approach

This study applies the fuzzy MCDM (multicriteria decision making) to evaluate the services Performance in free trade zone. Performance evaluation is an important issue for managers, since it can be used as a reference in decision making with regard to performance improvement, specially teaching performance improvement. For this purpose, in this study, we use fuzzy set theory for the measurement of performance and apply AHP in obtaining criteria weight and TOPSIS in ranking. A fuzzy MCDM is an approach for evaluating decision alternatives involving subjective judgments made by a group of decision makers. A pairwise comparison process is used to help individual decision makers make comparative judgments, and a linguistic rating method is used for making absolute judgments

Identification and ranking of effective factors of marketing (controllable) to receive the services from free zone with MADM approach

This study applies the fuzzy MCDM (multicriteria decision making) to evaluate the services Performance in free trade zone. Performance evaluation is an important issue for managers, since it can be used as a reference in decision making with regard to performance improvement, specially teaching performance improvement. For this purpose, in this study, we use fuzzy set theory for the measurement of performance and apply AHP in obtaining criteria weight and TOPSIS in ranking. A fuzzy MCDM is an approach for evaluating decision alternatives involving subjective judgments made by a group of decision makers. A pairwise comparison process is used to help individual decision makers make comparative judgments, and a linguistic rating method is used for making absolute judgments