Patch Panels in the Sky: A Case for Free-Space Optics in Data Centers

Patch Panels in the Sky:A Case for Free-Space Optics

in Data Centers

Navid Hamed Azimi, Himanshu GuptaVyas Sekar, Samir Das

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Datacenter network design is hard!

Cost

Performance

Cabling Expandability

Energy

Cooling Adaptability

Over subscribed(tree, leaf spine,…)

3

Performance

Existing ChoicesCost

…

Core

Top of Rack (ToR)


Existing Choices

…

4

Over provisioned(Fattree, Jellyfish,…)

Performance

Cost

Top of Rack (ToR)

Core

Existing Choices

…

5

Core


Performance

Cost

Augmented (c-Through , 3D Beam)

Top of Rack (ToR)


Existing Choices

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Performance

Cost

Augmented (c-Through , 3D Beam)


Can we get here?

Our Vision

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…

• Core Coreless

• Wired Wireless

• Static Flexible

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Potential Benefits of This Vision

CostPerformance

Cabling

ExpandabilityEnergyCooling

Adaptability

WirelessCoreless

Flexible

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Challenges in Realizing the Vision

• Flexible wireless links

• Network management

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Outline



• Feasibility & cost

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Traditional RF is not Sufficient

…

• Wide beam High interference

Traditional RF is not Sufficient

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…

• Wide beam• Difficult to narrow

High interference

Solution: Free Space Optical Links (FSOs)

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• No interference• High throughput over long range

…

• Easy to narrow beam

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Concerns with FSOs

• Cost : $30K• Size : 3 ft³• Power: 60w• Flexibility

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Why Size, Cost, Power Can be Reduced?

• 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)

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Proof of Concept (1 Gbps)

Fiber connectedto SFP (TX)

Lens LensMirror Mirror

SFP (RX)

SFP : 2x$40Lens : 2x$30

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<924 924- 928 928- 932 >932 Mbps

0

0.2

0.4

0.6

0.8

1Optical fiberFSO

FSO Link ThroughputPDF

Throughput

FSO link is the same as optical cable

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FSO Link Misalignment Tolerance• Effect of vibrations, etc.

Movement tolerance– 0.7mm at destination– 3mm at source

3 mm 0.7 mm

FSO link is stableTX RX

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• Cost : $30K• Size : 3 ft³• Power: 60w• Flexibility

FSOs (1Gbps)

• Cost : $140• Size : 1x4 in• Power: 0.3w• Flexibility

Flexibility via Switchable Mirror

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Sender

Ceiling Mirror

Receiver 1 Reciever2

• Switchable Mirror: glass mirror• Electronic control, low latency

SM in “mirror” mode

Flexibility via Switchable Mirror

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Sender

Ceiling Mirror


SM in “mirror” mode


• Switchable Mirror: glass mirror• Electronic control, low latency

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Outline




Management: Pre-ConfigurationInput: FSO#, SM#,…

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Sender


Output: Candidate links (Alignment of each SM)

Management: Reconfiguration

Input: Traffic

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Sender


Output: Run-time topology

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Current Solutions: Simple Heuristics

• Pre-Configuration : Regular Random Graph

• Reconfiguration

Only reconfigure for large flows Only delete a link if network remains connected

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Outline

• Flexible laser link

• Management


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Throughput• 512 racks, 48 server/rack, hotspots traffic, flow level simulations

(4,5) (4,10) (8,5) (12,5) (8,10) (16,5) (12,10) (16,10)0

0.5

1

1.5

2Fattree 2G 3D-Beamforming

c-through FSO

(Hot Spots %, Average Load per Hot spot (Gbps))

Ave

rage

Thr

ough

put

Per S

erve

r (G

bps)

FSO based 2-4x improvement

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Cost ComparisonArchitecture Cost Effective Bisection

BandwidthFattree 1 Gbps $ 13 M 1 GbpsFSO based $ 38 M 8.5 GbpsFattree 10 Gbps $ 57 M 10 Gbps

FSO based: Near 10G performance with 65% of cost

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Conclusions• Data center network is challenging

• Our vision: Fully flexible, coreless, wireless network

• Key enablers : FSO + switchable mirrors

• Early promise: ~ 10Gbps performance @ 65% cost

• Future work: Improve FSO, better management

Patch Panels in the Sky: A Case for Free-Space Optics in Data Centers

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