1. Department of Computer Science and Technology, Tsinghua University, China
2. Institute for Network Sciences and Cyberspace, Tsinghua University, China
3. Institute for Network Sciences and Cyberspace, Tsinghua University and Zhongguancun Laboratory, China
4. University of Illinois at Urbana-Champaign, United States
5. Information School, University of University of Washington, United States
6. Tsinghua University and Zhongguancun Laboratory, China