1. Mirror Mirror on the Ceiling: Flexible Wireless Links for Data Centers Presenter: Lu Gong

2. About Authors

3. About Authors: Xia Zhou PhD candidate, UCSB Fields: Networks & Communications, Mathematics, Microbiology

4. About Authors: Zengbin Zhang PhD candidate, UCSB Fields: Wireless Systems and Networking, Mobile Computing and Distributed Systems

5. About Authors: Yibo Zhu PhD candidate, UCSB Fields: Data Center Networks, Mobile Networks and Online Social Networks

6. Problems with any wired network topology Any large-scale network consists of multiple stages → nr of fibers/wires are doubled/tripled Distribute fixed amount of fibers to every rack → fibers are over deployed for the worst case Once deployed, very hard to modify

7. Our goal Focus on a subset of applications – that do not require non-blocking all-to-all communication – exclude high-end datacenter computing We hope to create a new primitive – high-throughput, beamforming wireless links in the 60GHz band

8. Existing works Signal leakage → limits the concurrent active links Line-of-sight requirement → limits the effective range of links

9. Properties of 60GHz band wireless links 7GHz spectrum → multi-Gbps bandwidth High frequency → small interference Able to use beamforming to enhance link rate and further suppress interference 5mm wavelength → any object larger than 2.5mm can block/reflect signal

10. Beamforming A physical layer technique to concentrate transmission energy in a specific direction

11. Testbed of link blockage

12. Testbed of radio interference

13. 3D Beamforming Components: – Beamforming Radios – Ceiling Reflectors – Electromagnetic Absorbers Prevent local reflections and scattering

14. Testbed of 3D Beamforming

15. Microbenchmark: Validate Physical Properties

16. Microbenchmark: Radios per Rack

17. Microbenchmark: Sensitivity to Hardware

18. Scheduling: Goal & Challenges Goal – Maximize efficiency – Minimize wireless interference Challenges – Require accurate interference model (accumulate interference) – Handle short-lived traffic burst → must be online – Account for antenna rotation delay (0.01s~1s)

19. Scheduling: Design Conflict-Degree based Greedy Scheduling – Goal → Minimize job completion time – Graph coloring problem Color: 60GHz frequency channels & time slots – Link preemption or not? – Minimize antenna rotation overhead

20. Evaluation: Addressing Traffic Hotspots Does adding 3D beamforming links to existing wired networks significantly increase available bandwidth for hotspots? How significant are the benefits of 3D beamforming over 2D beamforming, and where are they most visible? Will antenna rotation delay of today’s rotators be a performance bottleneck for 3D beamforming?

21. Evaluation: Flow Completion Time

22. Future Work Routing Traffic management Priority-based scheduler Wired/wireless co-scheduling

23. Related Work Address traffic congestion – Network architecture design & traffic scheduling – Modeling network traffic characteristics 60GHz wireless technology Optical circuit switching