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

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

3. 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. 4 Rack mount Blade server 資料來源 :wikipedia

5. 5 Introduction (cont.)

6. 6 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

7. 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. 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. 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. 10 Fat-tree 資料來源 :wikipedia Core level Aggregate level Access level

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

12. 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. 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. 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. 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. 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. 17 Optical Technology Splitter and combiner Coupler Arrayed-Waveguid Grating(AWG) Wavelength Selective Switch(WSS)

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

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

20. 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. 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. 22 Comparison Hybrid & all-optical

23. 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. 24 Comparison(connectivity)

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

26. 26 Comparison(scalability)

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

28. 28 Comparison(capacity) Capacity limitation technology

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

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

31. 31 Comparison(prototype)

32. 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. 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. 34 Cost = OPEX CDCN − (CAPEX OI + OPEX OI ) where, CDCN : CurrentDataCenterNetwork OI : OpticalInterconnects

35. 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. 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