Mirror Mirror on the Ceiling:
Flexible Wireless Links for Data Centers
Presenter: Lu Gong
About Authors
About Authors: Xia Zhou
• PhD candidate, UCSB
• Fields:
Networks & Communications,
Mathematics, Microbiology
About Authors: Zengbin Zhang
• PhD candidate, UCSB
• Fields: Wireless Systems and Networking, Mobile
Computing and Distributed Systems
About Authors: Yibo Zhu
• PhD candidate, UCSB
• Fields: Data Center Networks, Mobile
Networks and Online Social Networks
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
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
Existing works
• Signal leakage
→ limits the concurrent active links
• Line-of-sight requirement
→ limits the effective range of links
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
Beamforming
• A physical layer technique to concentrate
transmission energy in a specific direction
Testbed of link blockage
Testbed of radio interference
3D Beamforming
• Components:
– Beamforming Radios
– Ceiling Reflectors
– Electromagnetic Absorbers
• Prevent local reflections and scattering
Testbed of 3D Beamforming
Microbenchmark: Validate Physical Properties
Microbenchmark: Radios per Rack
Microbenchmark: Sensitivity to Hardware
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)
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
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?
Evaluation: Flow Completion Time
Future Work
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Routing
Traffic management
Priority-based scheduler
Wired/wireless co-scheduling
Related Work
• Address traffic congestion
– Network architecture design & traffic scheduling
– Modeling network traffic characteristics
• 60GHz wireless technology
• Optical circuit switching