A Survey on Optical Interconnects for Data Centers
Speaker: Shih-Chieh ChienAdviser: 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 mountBlade server
資料來源 :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
資料來源 :wikipedia
Core level
Aggregate level
Access level
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ToR switch
1Gbps links
…
資料來源 :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 10%~80% 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)
Rack servers
Electrical network
Optical network
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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. 327–338.
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