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Optical Interconnects for Efficient Data Centers: A Comprehensive Survey

This survey covers optical technology, architectures, traffic characteristics, and comparisons for data centers to improve efficiency, reduce power consumption, and enhance connectivity. It discusses current challenges and future trends in optical interconnects for data centers.

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Optical Interconnects for Efficient Data Centers: A Comprehensive Survey

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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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