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