A Survey on Optical Interconnects for Data Centers

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A Survey on Optical Interconnects for Data Centers

• Speaker Shih-Chieh Chien
• Adviser Prof Dr. Ho-Ting Wu

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Outline

• Introduction
• Current Data Center
• Network traffic characteristics
• Optical technology
• Architectures
• Comparison
• Conclusion
• Reference

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Introduction

• Internet traffic
• Emerging application
• e.g. Stream video, Social network, Cloud
  computing
• Data-intensive
• e.g. cloud computing, search engines, etc.
• High interaction(servers in the data center)
• Power consumption(inside the rack)
• each rack must the same ? thermal constraints

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Rack mount
Blade server
????wikipedia
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Introduction (cont.)
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Introduction (cont.)

• IT power percentage
• Server 40, Storage 37, Network devices 23
• Include HVAC (Heating-Ventilation and
  Air-Conditioning)
• ICT GHG from 14 to 18(2007 2020)
• Goal
• High throughput, reduced latency, low power
  consumption
• ? Using optical network

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Introduction (cont.)

• Optical network
• Opaque networks (older telecom. network)
• OEO(optical-electrical-optical)
• Main draw back is power hungry
• all-optical networks (currently)
• Device
• Optical cross-connects (OXC)
• Reconfigurable optical add/drop
  multiplexers(ROADM)
• Point-to-point links( based on multi-mode fibers)
• Provide 75 energe saving

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Current DC with commodity switches

• Data center
• 3 tiers
• Core switches, Aggregate switches, and ToR
• Advantage
• Scaled easily
• Fault tolerant
• DrawBack
• High power consumption
• High number of links required

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Current DC with commodity switches

• Data center
• 3 tiers
• Core switches, Aggregate switches, and ToR
  switches
• Advantage
• Scaled easily
• Fault tolerant
• DrawBack
• High power consumption
• High number of links required

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Fat-tree
Core level
Aggregate level
Access level
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ToR switch

1Gbps links
????IBM
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Current DC with commodity switches

• Data center
• 3 tiers
• Core switches, Aggregate switches, and ToR
• Advantage
• Scaled easily
• Fault tolerant
• DrawBack
• High power consumption
• High number of links required

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Current DC with commodity switches

• Data center
• 3 tiers
• Core switches, Aggregate switches, and ToR
• Advantage
• Scaled easily
• Fault tolerant
• DrawBack
• High power consumption
• High number of links required

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Network traffic characteristics

• Three classes (categorized by Microsoft research)
• University campus DC
• private enterprise DC
• cloud-computing DC
• Model traffic
• Interarrival rate distribution of the packet
• Lognormal distribution (in the private DC)
• Weibull distribution (in the campus DC)

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Network traffic characteristics

• Three classes (categorized by Microsoft research)
• University campus DC
• private enterprise DC
• cloud-computing DC
• Model traffic
• Interarrival rate distribution of the packet
• Lognormal distribution (in the private DC)
• Weibull distribution (in the campus DC)

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Network traffic characteristics (cont.)

• Main empirical findings
• Applications
• e.g. HTTP, HTTPS, LDAP, Database?
• Traffic flow locality
• Inter rack traffic 1080
• Intra rack traffic
• Traffic flow size and duration
• Concurrent traffic flows
• Packet size
• Link utilization

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Optical Technology

• Splitter and combiner
• Coupler
• Arrayed-Waveguid Grating(AWG)
• Wavelength Selective Switch(WSS)

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Optical Technology (cont.)

• Micro-Electro-Mechanical Systems
  Switches(MEMS-swtch)
• Semiconductor Optical Amplifier(SOA)
• Tunable Wavelength Converters(TWC)

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Architectures (C-Through)
Electrical network
Optical network
Rack servers
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Architectures (C-Through (cont.))

• Hybrid electrical-optical network
• Traffic monitoring system
• Optical configuration manager
• Traffic in the ToR switch
• Demutiplexed by VLAN-based routing
• Packet based and circuit based network
• Evaluation
• Reduce completion time of the application
• Reduce latency between two nodes

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Comparison

• Technology
• All optical interconnection
• Hybrid interconnection
• Connectivity
• Circuit based switching
• Based on MEMS switch
• Packet based switching
• Array fixed lasers
• Fast tunable transmitters

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Comparison Hybrid all-optical
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Comparison

• Technology
• All optical interconnection
• Hybrid interconnection
• Connectivity
• Circuit based switching
• Based on MEMS switch
• Packet based switching
• Array fixed lasers
• Fast tunable transmitters

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Comparison(connectivity)
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Comparison(cont.)

• Scalability
• Constrained by what?
• Number of switch optical port
• Number of wavelength channels
• Capacity
• Routing
• Prototypes

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Comparison(scalability)
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Comparison(cont.)

• Scalability
• Constrained by what?
• Number of switch optical port
• Number of wavelength channels
• Capacity
• Routing
• Prototypes

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Comparison(capacity)
Capacity limitation technology
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Comparison(cont.)

• Scalability
• Constrained by what?
• Number of switch optical port
• Number of wavelength channels
• Capacity
• Routing
• Prototypes

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Comparison(cont.)

• Scalability
• Constrained by what?
• Number of switch optical port
• Number of wavelength channels
• Capacity
• Routing
• Prototypes

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Comparison(prototype)
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Cost and power consumption

• Commercially available (lower price)
• c-Through, Helios, and Proteus (optical modules)
• Data-vortex, and DOS (SOA modules)
• Intresting thing
• OPEX (operation cost)
• CAPEX(equipment's cost)

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Cost and power consumption(cont.)

• Simulation
• Replacement of current switches
• Data center with 1536 servers
• Two-tier topology
• 512 ToR switches
• 16 aggregate switches (32x10 Gbps ports) ?each
  arround 5k
• Power consumption will be 77kW

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Cost OPEXCDCN - (CAPEXOI OPEXOI)where,CDCN
CurrentDataCenterNetworkOI
OpticalInterconnects
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Conclusion

• Optical interconnets (promising solution for DC)
• High BW, low latency , and reduced energy
  consumption
• Hybrid proposed as an upgrade to current networks
• Schemes based on SOA for switching
• Faster reconfiguration time than MEMS switches
• Proteus shows high performance optical networks
  with readily available optical componetnts
• Schemes based on SOA and TWC
• Provide higher capacites and better scalability

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Reference

• http//www.hirose.co.jp/cataloge_hp/e83001002.pdf
• http//www.answers.com/topic/optical-switch
• G. Wang, D. G. Andersen, M. Kaminsky, K.
  Papagiannaki, T. E. Ng, M. Kozuch, and M. Ryan,
  c-Through Part-time Optics in Data Centers, in
  Proc. ACM SIGCOMM 2010 conference on SIGCOMM,
  ser. SIGCOMM 10, 2010, pp. 327338.
• Kachris, Christoforos Tomkos, Ioannis , "A
  Survey on Optical Interconnects for Data
  Centers," Communications Surveys Tutorials,
  IEEE , vol.14, no.4, pp.1021-1036, Fourth Quarter
  2012