[Hu, Xiaohua] Cent China Normal Univ, Dept Comp Sci, Wuhan 430079, Peoples R China.^[Liu, Junwan] Cent S Univ Forestry & Technol, Sch Comp & Informat Engn, Changsha 410004, Hunan, Peoples R China.^[Li, Zhoujun] Beihang Univ, State Key Lab Software Dev Environm, Beijing 100191, Peoples R China.^[Li, Zhoujun] Beihang Univ, Beijing Key Lab Network Technol, Beijing 100191, Peoples R China.^[Hu, Xiaohua] Drexel Univ, Coll Informat Sci, Philadelphia, PA 19104 USA.^[Chen, Yiming] Hunan Agr Univ, Sch Informat Sci & Technol, Changsha 410128, Hunan, Peoples R China.