Nuallain, E. O., K. Lung Ng, H. Ying Pun, A. Sharma, and S. Weber. “The Impact of Controller Placement in an Open Flow Wide Area Network”. Journal of Information Sciences and Computing Technologies, Vol. 7, no. 2, May 2018, pp. 683-92, http://scitecresearch.com/journals/index.php/jisct/article/view/1410.