1. School of Computer Science, Guangzhou University, P.R. China
2. State Key Laboratory of Integrated Service Networks (ISN), Xidian University, P.R. China
3. Department of Computer Science, Virginia Polytechnic Institute and State University, USA
4. College of Computer and Control Engineering, Nankai University, P.R. China
5. School of Computer Science and Technology, Xidian University, P.R. China