1. Key Laboratory of Pervasive Computing, Ministry of Education, Department of Computer Science and Technology, Tsinghua University, China
2. Department of Computer Science and Technology, Tsinghua University, China
3. Paul G. Allen School of Computer Science and Engineering, University of Washington, United States
4. Xinya College, Tsinghua University, China
5. Institute for Network Sciences and Cyberspace, Tsinghua University, China
6. Department of Computer Science and Technology, Tsinghua University, China and Intelligent Computing and Application Laboratory of Qinghai Province, Qinghai University, China