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A Survey on Optical Interconnects for Data Centers

Speaker: Shih-Chieh Chien Adviser: Prof Dr. Ho-Ting Wu. A Survey on Optical Interconnects for Data Centers. Outline. Introduction Current Data Center Network traffic characteristics Optical technology Architectures Comparison Conclusion Reference. Introduction. Internet traffic

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A Survey on Optical Interconnects for Data Centers

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  1. Speaker: Shih-Chieh Chien Adviser: Prof Dr. Ho-Ting Wu A Survey on Optical Interconnects for Data Centers

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

  3. 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

  4. Rack mount Blade server 資料來源:wikipedia

  5. Introduction (cont.)

  6. Introduction (cont.) • IT power percentage • Server 40%, Storage 37%, Network devices23% • 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

  7. 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

  8. 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

  9. 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

  10. Fat-tree Core level Aggregate level Access level 資料來源:wikipedia

  11. ToR switch … 1Gbps links 資料來源:IBM

  12. 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

  13. 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

  14. 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)

  15. 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)

  16. 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

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

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

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

  20. 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

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

  22. Comparison Hybrid & all-optical

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

  24. Comparison(connectivity)

  25. Comparison(cont.) • Scalability • Constrained by what? • Number of switch optical port • Number of wavelength channels • Capacity • Routing • Prototypes

  26. Comparison(scalability)

  27. Comparison(cont.) • Scalability • Constrained by what? • Number of switch optical port • Number of wavelength channels • Capacity • Routing • Prototypes

  28. Comparison(capacity) Capacity limitation technology

  29. Comparison(cont.) • Scalability • Constrained by what? • Number of switch optical port • Number of wavelength channels • Capacity • Routing • Prototypes

  30. Comparison(cont.) • Scalability • Constrained by what? • Number of switch optical port • Number of wavelength channels • Capacity • Routing • Prototypes

  31. Comparison(prototype)

  32. 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)

  33. 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

  34. Cost = OPEXCDCN − (CAPEXOI + OPEXOI)where,CDCN : CurrentDataCenterNetworkOI : OpticalInterconnects

  35. 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

  36. 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

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