On the Communication Cost of MDS Erasure Codes in Distributed Storage Systems

Distributed storage systems store some redundant data to keep the degree of availability of the stored data constant and also to increase the system's resistance against failures. This type of systems usually use pure replication or methods based on RAID systems as redundancy schemes. In this paper, we study the communication cost of a distributed data storage system using Maximum Distance Separable (MDS) erasure codes. Our focus is reduction of the cost of one-to-many communication used in data reconstruction/repair initialization and update operations. We propose the use of two different communication approaches on the area of distributed storage systems for the above operations; Steiner tree approach and multi-shortest path approach. We also analyse these two communication approaches empirically and theoretically. Our theoretical results indicate that Steiner tree approach has lower message usage, whereas, multi-shortest path approach has lower time usage for data reconstruction/repair initialization operations. On the other hand, Steiner tree approach has better message and time metrics for the data update process. Furthermore, our experimental results support these theoretical results. Thus, users can choose between the two approaches depending on their needs and priorities

LDPC kodlarında artık veri kullanımı

In distributed storage systems/coded caching systems, padding operations should be performed when the encoded data cannot be divided by the number of storage nodes evenly. Thus, extra zero values are stored in one of the nodes to balance each node’s storage content. In this study, distribution of data to storage nodes with no padding was investigated for distributed caching context in which a base station and devices both store the coded data. In other words, no redundancy (no-padding) is included into the encoded data. This approach is named as residual data distribution. LDPC codes are selected as the erasure code due to their low complexity encode/decode operations. Moreover, performance comparisons were conducted between using traditional data distribution approach (with padding) and using residual data (use of no-padding) (standard) in terms of repair time. In our work, the effect of no-padding data usage on the repair time and the ratios of storage savings have been also demonstrated.Dağıtık sistemlerde ve dağıtık ön-bellekleme sistemlerinde, kodlanmış veri boyutu depolama düğümü sayısına tam olarak bölünemediğinde genel olarak fazladan veri depolama işlemi gerçekleştirilmektedir. Bu çalışmada, baz istasyonunun ve düğümlerin kodlanmış veriyi depoladığı bir ön-bellekleme sistemi için, fazladan veri eklenmeden kodlanmış sembollerin depolama düğümlerine dağıtılması konusu incelenmiştir. Silinti kodları olarak zaman açısından yüksek kodlama verimliliğine sahip LDPC kodları kullanılmış olup düğüm tamir zamanı açısından fazladan verinin kaydedildiği kodlanmış veri paylaştırımı yaklaşımı ile fazladan verinin kullanılmadığı (artık veri paylaştırımı) kodlanmış veri paylaştırımı yaklaşımlarının performansı karşılaştırılmıştır. Bu kapsamda düğüm tamiri zamanı ile toplamda depolanması gereken verinin miktarı ile ilgili sonuçlar elde edilmiştir.Scopus - Affiliation ID: 6010507

Managing TCP Connections of File Reconstruction Process in Erasure Codes

23nd Signal Processing and Communications Applications Conference (SIU) -- MAY 16-19, 2015 -- Inonu Univ, Malatya, TURKEYWOS: 000380500900455In this paper, we propose a new method for reducing the elapsed time and the number of messages used in the data reconstruction process of distributed storage systems based on erasure codes through managing TCP connections in case of congestion. The data reconstruction process using the new method and one not using such management of TCP connections are both implemented in the network simulation environment. According to the simulation results, the new method requires less time and fewer messages for data reconstruction in case of congestion as compared to the data reconstruction process without such control frame.Dept Comp Engn & Elect & Elect Engn, Elect & Elect Engn, Bilkent Uni

Homomorphic Minimum Bandwidth Repairing Codes

28th International Symposium on Computer and Information Sciences (ISCIS) -- OCT 28-29, 2013 -- Inst Henri Poincare, Paris, FRANCEWOS: 000333692000033To store data reliably, a number of coding schemes including Exact-Minimum Bandwidth Regenerating codes (exact-MBR) and Homomorphic Self Repairing Codes (HSRC) exist. Exact-MBR offers minimum bandwidth usage whereas HSRC has low computational overhead in node repair. We propose a new hybrid scheme, Homomorphic Minimum Bandwidth Repairing Codes, derived from the above coding schemes. Our coding scheme provides two options for node repair operation. The first option offers to repair a node using minimum bandwidth and higher computational complexity while the second one repairs a node using fewer nodes, lower computational complexity and higher bandwidth. In addition, our scheme introduces a basic integrity checking mechanism

A new reconstructable distributed connected dominating set algorithm for extending the lifetime of wireless sensor networks including energy harvester nodes

Wireless sensor networks are utilized in many different areas such as health, agriculture, security, and entertainment. Since the nodes that constitute wireless sensor networks have limited energy resources, many studies have been carried out on use of their resources in an energy efficient manner. These studies generally focused on duty cycle techniques or constructing energy efficient communication backbones. In wireless sensor systems, the connected dominating sets are generally considered to be used as a backbone. In addition, the deployment of the nodes that harvest their own energy in wireless sensor networks has also been considered in recent studies. In this study, a new distributed algorithm is proposed to construct reusable connected dominating set for wireless networks that possess energy harvester nodes and ordinary nodes which could not harvest its energy. Whenever an energy depletion problem in a node or in more than one node occurs, after a specific interval, the proposed algorithm is re-employed on the alive nodes unless wireless sensor network is disconnected. The proposed algorithm was implemented on SensEH simulation environment based on Cooja which is one of the most commonly used tools in the wireless sensor network area. The new algorithm and the rival algorithm in the area are analyzed with respect to the lifetime of the systems together with the time and the energy consumptions required by the algorithms. According to the results, it is observed that the proposed algorithm can double the total lifetime compared to the rival algorithm

Data repair-efficient fault tolerance for cellular networks using LDPC codes

The base station-mobile device communication traffic has dramatically increased recently due to mobile data, which in turn heavily overloaded the underlying infrastructure. To decrease Base Station (BS) interaction, intra-cell communication between local devices, known as Device-to-Device, is utilized for distributed data caching. Nevertheless, due to the continuous departure of existing nodes and the arrival of newcomers, the missing cached data may lead to permanent data loss. In this study, we propose and analyze a class of LDPC codes for distributed data caching in cellular networks. Contrary to traditional distributed storage, a novel repair algorithm for LDPC codes is proposed which is designed to exploit the minimal direct BS communication. To assess the versatility of LDPC codes and establish performance comparisons to classic coding techniques, novel theoretical and experimental evaluations are derived. Essentially, the theoretical/numerical results for repair bandwidth cost in presence of BS are presented in a distributed caching setting. Accordingly, when the gap between the cost of downloading a symbol from BS and from other local network nodes is not dramatically high, we demonstrate that LDPC codes can be considered as a viable fault-tolerance alternative in cellular systems with caching capabilities for both low and high code rates.WOS:000742731500006Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ1ArticleUluslararası işbirliği ile yapılmayan - HAYIRNisan2022YÖK - 2021-2

A Hybrid Distributed Mutual Exclusion Algorithm for Cluster-Based Systems

WOS: 000323038600001Distributed mutual exclusion is a fundamental problem which arises in various systems such as grid computing, mobile ad hoc networks (MANETs), and distributed databases. Reducing key metrics like message count per any critical section (CS) and delay between two CS entrances, which is known as synchronization delay, is a great challenge for this problem. Various algorithms use either permission-based or token-based protocols. Token-based algorithms offer better communication costs and synchronization delay. Raymond's and Suzuki-Kasami's algorithms are well-known token-based ones. Raymond's algorithm needs only O(log(2)(N)) messages per CS and Suzuki-Kasami's algorithm needs just one message delivery time between two CS entrances. Nevertheless, both algorithms are weak in the other metric, synchronization delay and message complexity correspondingly. In this work, a new hybrid algorithm is proposed which gains from powerful aspects of both algorithms. Raysuz's algorithm (the proposed algorithm) uses a clustered graph and executes Suzuki-Kasami's algorithm intraclusters and Raymond's algorithm interclusters. This leads to have better message complexity than that of pure Suzuki-Kasami's algorithm and better synchronization delay than that of pure Raymond's algorithm, resulting in an overall efficient DMX algorithm pure algorithm

Using Twitter as a Diagnostic Teaching and Learning Assessment Tool

25th Annual Conference of the European-Association-for-Education-in-Electrical-and-Information-Engineering (EAEEIE) -- MAY 30-JUN 01, 2014 -- Cesme, TURKEYWOS: 000345865400019Higher education students coming from different regions and schools have different interests and knowledge levels. These differences can be exploited by teachers to improve the course efficiency. Knowing beforehand the misconceptions and the prior knowledge of the students, the teacher can tune the content of the lecture accordingly. In traditional systems, short essay, multiple choice or true-false diagnostic quizzes that include several potential misconceptions related to the targeted learning, are often practiced for this purpose. This approach reveals the differences in prior knowledge, misconceptions and deficiencies in prerequisite skills amongst the students. The teacher armed with this information can organize both the content and the structure of his/her teaching more efficiently. In this paper, we propose using Twitter as a diagnostic teaching and learning assessment tool. In this scenario the teacher tweets hashtags related to key concepts or misconceptions. The comments of the students are retrieved using Twitter APIs and stored in a local database. The teacher views and analyzes the retrieved data to tune her/his instruction. After lecturing, the same hashtags are sent and responses are collected. Analysis of the data before and after will reveal how much learning is achieved. Besides, this tool will enable instructors to provide some hints to students about the topic of the lecture and engage students more through the use of social media.European Assoc Educ Elect & Informat Engn, IEEE, IGI