Abstract Synchronization is a promising approach to solve the consistency problems in replicated distributed file systems. The synchronization can be repeated periodically, with fixed time interval or a time interval which can be adjusted adaptively. In this paper, we propose a policy-based performance efficient distributed file synchronization approach, in which synchronization processes occur in varying time intervals and adjusted adaptively. The study is based on tracing network idle times by means of measuring and clustering Round Trip Time (RTT) values. K-means clustering is used to cluster RTT values as idle, normal, and busy. To estimate the most suitable synchronization time intervals, the measured RTT values are included into these classes with an algorithm similar to Transmission Control Protocol (TCP) Additive-Increase/Multiplicative- Decrease (AIMD) feedback control. The efficiency and feasibility of the proposed technique is examined on a distributed file synchronization application within the scope of Fatih project, which is one of the most important educational projects in Turkey.

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[24] Yang Y. and Lam S., General AIMD Congestion Control, in Proceedings of the IEEE International Conference on Network Protocols, Osaka, pp. 187-198, 2000. Idle Time Estimation for Bandwidth-Efficient Synchronization in Replicated ... 185 Fidan Kaya G la z has received her BEng. in Computer Engineering from Kocaeli University in 2010 and ME. in Computer Engineering from Kocaeli University in 2013. She is currently working towards Ph.D. degree in Computer Engineering from Kocaeli University, Turkey. Also, she is currently a Research Assistant of Computer Engineering Department at Kocaeli University in Turkey. Her main research interests include data synchronization, distributed file systems and data filtering methods. S leyman Eken has received his BEng. in Computer Engineering from Karadeniz Technical University in 2009 and ME. in Computer Engineering from Kocaeli University in 2012. He is currently working towards Ph.D. degree in Computer Engineering from Kocaeli University, Turkey. Also, he is currently a Research Assistant of Computer Engineering Department at Kocaeli University in Turkey. His current research interests include distributed file systems, data synchronization, satellite image processing, remote sensing, WEB-GIS applications and spatial databases. Adnan Kavak received the B.S. degree from the Electrical and Electronics Engineering Department, Middle East Technical University, Ankara, Turkey, in 1992. He received the M.S. and Ph.D. degrees from the Electrical and Computer Engineering Department, The University of Texas at Austin, TX, USA, in 1996 and 2000, respectively. He worked as a Satellite Control Engineer with Turksat Satellite Control Center, Ankara, Turkey, from December 1992 to May 1994. He worked as a Senior Research Engineer at Wireless Systems Laboratory, Samsung Telecommunications America in Richardson, TX, USA, from January 2000 to July 2001. He then joined Kocaeli University, Turkey, in August 2001 and worked as an Assistant Professor there until May 2005. Currently, he serves as the Director of Wireless Communications and Information Systems (WINS) Research Center and as an Associate Professor with the Computer Engineering Department, Kocaeli University, Turkey. He works also as an Adjunct Faculty at the Department of Electrical and Electronics Engineering at Yeditepe University, Turkey. His current research interests include 3G and beyond wireless networks, software and cognitive radios, smart antenna and MIMO systems, resource allocation in wireless networks, and wireless sensor networks. Ahmet Sayar received M.S. in Computer Science (2001) from Syracuse University and Ph.D. in Computer Science (2009) from Indiana University, USA. He has worked at Los Alamos National Laboratory (New Mexico, USA) and Community Grids Laboratory (Indiana, USA) as a researcher. Since 2010, he is a professor at Computer Engineering Department, Kocaeli University, Turkey. His current research interests include distributed systems, big data, data- Intensive computing, remote sensing, GIS, and spatial data-databases. He has co- authored 3 books and around 70 papers.