1. School of Information Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China
2. State Key Laboratory of Networking and Switching Technology, Beijing University of Posts and Telecommunications, Beijing 100088, China
3. Department of Computer, Mathematical and Physical Sciences, Sul Ross State University, Alpine, TX 79830, USA
4. Computer Department, Tianjin Ren’ai College, Tianjin 301636, China
5. School of Information Science and Technology, North China University of Technology, Beijing 100144, China