Abstract: Today's microblogging services such as Twitter have long outgrown their initial designs as SMS-based social networks. Instead, a massive and steadily-growing user population of more than 100 million is using Twitter for everything from capturing the mood of the country to detecting earthquakes and Internet service failures. It is unsurprising that the traditional centralized client-server architecture has not scaled with user demand, leading to server overload and significant loss of availability. In this work, we argue that the divergence in usage models of microblogging services can best be addressed using complementary mechanisms, one that provides reliable messages between friends, and another that delivers events from popular celebrities and media outlets to their millions of followers. We present Cuckoo, a new microblogging system that offloads processing and bandwidth costs away from a small centralized server base while ensuring reliable message delivery. We use a 20-day Twitter availability measurement to guide our design, and trace-driven emulation of 30,000 Twitter users to evaluate our Cuckoo prototype. Compared to a centralized approach, Cuckoo achieves 30-50% server bandwidth savings and 50-60% CPU load reduction, while guaranteeing reliable message delivery. Short Bio: Xiaoming Fu obtained his Ph.D. degree in Computer Science from Tsinghua University in 2000. After that he moved to Germany, firstly at Technical University Berlin, then at the University of Goettingen, where he is currently a Chaired Professor and heading the Computer Networks Group. He also serves as Vice Chair of the IEEE Communications Society Technical Committee on Computer Communications. His research areas include architecture, protocols and applications of Internet-based communication systems.