Patch Panels in the Sky: A Case for Free-Space Optics in Data Centers Navid Hamed Azimi, Himanshu Gupta Vyas Sekar, Samir Das

Datacenter network design is hard! Cost Performance CablingExpandability Energy CoolingAdaptability 2

Over subscribed (tree, leaf spine,…) 3 Performance Existing Choices Cost … Core Top of Rack (ToR)

Over subscribed (tree, leaf spine,…) Existing Choices … 4 Over provisioned (Fattree, Jellyfish,…) Performance Cost Top of Rack (ToR) Core

Existing Choices … 5 Core Over subscribed (tree, leaf spine,…) Performance Cost Augmented (c-Through, 3D Beam) Top of Rack (ToR) Over provisioned (Fattree, Jellyfish,…)

Existing Choices 6 Over subscribed (tree, leaf spine,…) Performance Cost Augmented (c-Through, 3D Beam) Over provisioned (Fattree, Jellyfish,…) Can we get here?

Our Vision 7 … Core  Coreless Wired  Wireless Static  Flexible

Potential Benefits of This Vision Cost Performance Cabling Expandability Energy Cooling Adaptability 8 Wireless Coreless Flexible

Challenges in Realizing the Vision 9 Flexible wireless links Network management

Outline 10 Flexible wireless links Network management Feasibility & cost

Traditional RF is not Sufficient 11 … Wide beam High interference

Traditional RF is not Sufficient 12 … Wide beam Difficult to narrow High interference

Solution: Free Space Optical Links (FSOs) 13 No interference High throughput over long range … Easy to narrow beam

14 Concerns with FSOs Cost : $30K Size : 3 ft³ Power: 60w Flexibility

Why Size, Cost, Power Can be Reduced? 15 Traditional use : outdoor, long haul ‒ High power ‒ Weatherproof Data centers: indoor, short haul ‒ Low power Feasible roadmap via commodity fiber optics ‒ E.g. Small form transceivers (Optical SFP)

Proof of Concept (1 Gbps) 16 Fiber connected to SFP (TX) Lens Mirror SFP (RX) SFP : 2x$40 Lens : 2x$30

FSO Link Throughput 17 PDF Throughput FSO link is the same as optical cable

FSO Link Misalignment Tolerance Effect of vibrations, etc. Movement tolerance – 0.7mm at destination – 3mm at source 3 mm 0.7 mm 18 FSO link is stable TX RXRX

Cost : $30K Size : 3 ft³ Power: 60w Flexibility 19 FSOs (1Gbps) Cost : $140 Size : 1x4 in Power: 0.3w Flexibility

Flexibility via Switchable Mirror 20 Sender Ceiling Mirror Receiver 1 Reciever2 Switchable Mirror: glass mirror Electronic control, low latency SM in “mirror” mode

Flexibility via Switchable Mirror 21 Sender Ceiling Mirror Receiver 1Reciever2 SM in “mirror” mode Receiver 1 Reciever2 Switchable Mirror: glass mirror Electronic control, low latency

Outline 22 Flexible wireless links Network management Feasibility & cost

Management: Pre-Configuration I nput: FSO#, SM#,… 23 Sender Receiver 1 Reciever2 Output: Candidate links (Alignment of each SM)

Management: Reconfiguration Input: Traffic 24 Sender Receiver 1 Reciever2 Output: Run-time topology

Current Solutions: Simple Heuristics Pre-Configuration : Regular Random Graph Reconfiguration Only reconfigure for large flows Only delete a link if network remains connected 25

Outline 26 Flexible laser link Management Feasibility & cost

Throughput racks, 48 server/rack, hotspots traffic, flow level simulations FSO based 2-4x improvement

Cost Comparison 28 ArchitectureCostEffective Bisection Bandwidth Fattree 1 Gbps$ 13 M1 Gbps FSO based$ 38 M8.5 Gbps Fattree 10 Gbps$ 57 M10 Gbps FSO based: Near 10G performance with 65% of cost

Conclusions Data center network is challenging Our vision: Fully flexible, coreless, wireless network Key enablers : FSO + switchable mirrors Early promise: ~ 10Gbps 65% cost Future work: Improve FSO, better management 29