1. TCOM 513 Optical Communications Networks Spring, 2007 Thomas B. Fowler, Sc.D. Senior Principal Engineer Mitretek Systems

2. 2ControlNumber Topics for TCOM 513 Week 1: Wave Division Multiplexing Week 2: Opto-electronic networks Week 3: Fiber optic system design Week 4: MPLS and Quality of Service Week 5: Optical control planes Week 6: The business of optical networking: economics and finance Week 7: Future directions in optical networking

3. 3ControlNumber Fiber optic system design Project development review Steps in system design –Requirements analysis –Engineering of system Selection of values for system components/factors Design trade-offs –Calculation of system power, loss, error values Estimating performance System design tools

4. 4ControlNumber Project development phases Initiation Requirements Concept development Detailed analysis Development Deployment Operation and maintenance

5. 5ControlNumber Initiation phase Identify and validate opportunity to improve business –Current accomplishments –Deficiency related to a business need Identify significant assumptions and constraints For data systems, determine at what OSI levels design will concentrate Recommend alternative concepts and methods to satisfy the need

6. 6ControlNumber Requirements analysis Determine functional requirements that system must satisfy –Locations –Data rates –Error rates –Availability –Security

7. 7ControlNumber Concept development Identify system interfaces, Establish system boundaries Identify goals, objectives, critical success factors, and performance measures Evaluate costs and benefits of alternative approaches Assess project risks, Identify and initiate risk mitigation actions Develop major solution components at high level –High level architecture –Process models –Data models –Concept of operations.

8. 8ControlNumber Detailed analysis Further define and refine the functional and data requirements Complete business process reengineering of the functions to be supported (if appropriate) Develop detailed data and process models, Define functional and system requirements not easily expressed in data and process models Develop high level architecture and logical design in more detail to support functional and technical requirements Continue to identify and mitigate risks

9. 9ControlNumber Development Design, develop, integrate, and test the system Update and finalize plans to deploy system Complete business transition planning and initiate business transition activities

10. 10ControlNumber Deployment Installation of hardware (fiber, switches, other components) Installation of software Testing User notification and training Integration of the system into daily work processes

11. 11ControlNumber Operation and maintenance Operate, maintain, and enhance system Conduct periodic assessments of system to ensure functional requirements are being satisfied Determine when the AIS needs to be modernized, replaced, or retired

12. 12ControlNumber System development schematic

13. 13ControlNumber Characteristics of good functional requirements Necessary –Essential capability, physical characteristic, or quality factor of product or process Concise –Only one requirement stating what must be done and only what must be done Attainable (feasible) –Can be achieved by one or more developed system concepts at a definable cost Complete Consistent Unambiguous Verifiable

14. 14ControlNumber Functional requirements flowchart

15. 15ControlNumber Design of optical networks Design proceeds at several levels (rough classification) –Physical: fiber, amplifiers, ADMs (hardware) –Data link: Ethernet, SONET (encoding, access control) –Network: ATM, IP (addressing, routing) There is interaction among these layers –SONET may require particular physical layer configuration, e.g., rings –Ethernet, especially GigE or 10GigE will require switches

16. 16ControlNumber Optical networking and OSI protocol stack Application Presentation Session Transport Network Data Link Physical TCP IP Applications: Telnet FTP SMTP HTTP Ethernet (802.3) Or SONET LLC Sublayer MAC Sublayer Physical signaling Media attachment TCP/IP Application Protocols OSI Reference Model TCP/IP Implementation Ethernet or SONET

17. 17ControlNumber Steps for physical layer design Determine topology needed –Point-point –Star –Ring Determine key functional requirments –Data rates –Error rates Make initial design Use manufacturer data to complete/modify design –Satisfy budgets –Meet performance goals

18. 18ControlNumber System factors for designing from scratch FactorAvailable choices Type of fiberSingle mode, multimode, plastic DispersionRepeaters, compensation Fiber nonlinearitiesFiber characteristics, wavelengths used, transmitter power Operating wavelength (band) 780, 850, 1310, 1550, 1625 nm typical Transmitter power~0.1 to 20 mw typical; usually expressed in dBm Light sourceLED, laser Receiver characteristicsSensitivity, overload Multiplexing schemeNone, CWDM, DWDM

19. 19ControlNumber System factors (continued) FactorAvailable choices Detector typePIN diode, APD, IDP Modulation schemeOOK, multilevel, coherent End-end bit error rate<10 -9 typical; may be much lower Signal-to-noise ratioSpecified in dB for major stages Max number of connectors Loss increases with number of connectors Max number of splicesLoss increases with number of splices EnvironmentalHumidity, temperature, sunlight exposure MechanicalFlammability, strength, indoor/outdoor/submarine Source: Goff

20. 20ControlNumber System factors (continued) FactorAvailable choices AmplifiersType, spacing SwitchesOEO, all optical Add/drop multiplexersNumber, location

21. 21ControlNumber System budgets Optical link loss (attenuation) Dispersion Signal-to-noise ratio

22. 22ControlNumber Optical link loss budget Key calculations in designing a simple fiber optic link Objective is to determine launch power and receiver sensitivity Variables –Environmental and aging –Connector losses –Cable losses –Splices –Amplfier –Other components

23. 23ControlNumber Optical link loss budget 0 -5 -40 -10 -15 -30 -20 -35 -45 Optical power (dBm) Launch Temperature Fiber coupling Aging Source variables Con- nector Fiber Con- nector Receiver Insertion loss Attenuation Temperature Insertion loss Other allowances (repair, splice, safety margin Receiver Sensitivity Range +2 db 0-3 db0-2 db -4 db +1 db 0-2 db0-3 db

24. 24ControlNumber Optical link loss budget (continued) Transmitter -10 dBm Receiver -10 to –25 dBm Splice -0.1 dB Splice -0.1 dB Connector -0.5 dB Connector -0.5 dB 15.5 km @ 0.35 dB/km

25. 25ControlNumber Optical link loss budget (continued)

26. 26ControlNumber Optical link loss budget—example Point-to-point fiber optic link between 2 computers –Path length measured as 1.2 km Multimode fiber to be used Patch panel at each end to facilitate connections 3 fusion splices required Transmitter power: -10 dBm Receiver sensitivity: -20 dBm Problem: choose type of fiber to be used

27. 27ControlNumber Example (continued) Transmitter -10 dBm Receiver -10 to –25 dBm Splice -0.1 dB Splice -0.1 dB Patch panel -1.0 dB 1.2 km Patch panel -1.0 dB Splice -0.1 dB

28. 28ControlNumber Available fiber

29. 29ControlNumber Example (continued) Using 62.5/125 with 3.0 db/km loss:

30. 30ControlNumber Example (continued) Using 100/140 with 4.0 db/km loss:

31. 31ControlNumber Example (continued) Power at receiver: -10 dBm – 9.1 dBm = -19.1 dBm – OK, since receiver sensitivity –25 dBm

32. 32ControlNumber Dispersion budget Dispersion sources –Fiber –Amplifiers –Other components Types –Chromatic –PMD

33. 33ControlNumber Dispersion budget: point-point example Length of link: 500 km –SMF –PMD: 0.1 ps/nm/km –Chromatic dispersion: 0.5 ps/nm/km Speed of link: OC192 ~ 10 Gbps –Pulse width: 100 ps –Allowable dispersion with 20% rule: 20 ps Amplifiers every 50 km –PMD: 1.0 ps Spectral width: 0.3 nm

34. 34ControlNumber Dispersion budget (example) Transmitter Receiver 500 km … Amp 50 km Amp 50 km

35. 35ControlNumber Dispersion budget (continued) PMD calculation: 50 km x 0.3 nm x 0.1 ps/nm/km = 1.5 ps Material calculation: 50 km x 0.3 nm x 0.5 ps/nm/km = 7.5 ps

36. 36ControlNumber Dispersion budget (continued) Every third link requires repeater

37. 37ControlNumber Dispersion budget (continued) Transmitter Receiver 500 km … Amp 50 km Amp 50 km Rptr 50 km Rptr 50 km

38. 38ControlNumber Dispersion budget—same example but at OC48 Length of link: 500 km –SMF –PMD: 0.1 ps/nm/km –Chromatic dispersion: 0.5 ps/nm/km Speed of link: OC48 ~ 2.5 Gbps –Pulse width: 400 ps –Allowable dispersion with 20% rule: 80 ps Amplifiers every 50 km –PMD: 1.0 ps Spectral width: 0.3 nm

39. 39ControlNumber Dispersion budget—same example but at OC48 (continued) Every eighth link requires repeater

40. 40ControlNumber Dispersion budget—same example but at OC12 (continued) Transmitter Receiver 500 km Amp 50 km Amp 50 km Rptr 50 km Amp 50 km

41. 41ControlNumber Multimode fiber dispersion Rather than quoting dispersion in ps/nm/km, manufacturers often give figure of merit called bandwidth-length product –Units: megahertz-km –Example: 400 MHz-km means 400 MHz signal can be transmitted 1 km, or 200 MHz signal for 2 km

42. 42ControlNumber Signal-to-noise ratio budget SNR goes down due to attenuation and dispersion in fiber –Effect is generally small Amplifiers cause further loss –Major source of SNR deterioration –Generally about 3 dB per amplifier reduction Some passive components also cause losses –Usually affects signal and noise equally, so no deterioration of SNR Type of signal encoding also affects SNR –Multilevel encoding has inherently lower SNR than OOK

43. 43ControlNumber Signal-to-noise ratio budget (continued) If extinction ratio > 0 (normal), SNR effectively reduced –Power of logic 0 if not exactly 0 –Extinction ratio: 10 log logic 1 power/logic 0 power –10 dB ~ effective 1 dB SNR reduction –3 dB ~ effective 5-7 dB SNR reduction Receiver error rate goes up as SNR goes down –No simple relationship –Depends on receiver design, coding scheme –Examples SNR of 22 dB ~ BER 10 -9 ; SNR of 17 dB ~ BER 10 -6 SNR of 18 dB ~ BER 10 -9 ; SNR of 15 dB ~ BER 10 -6

44. 44ControlNumber Typical relationship of SNR and BER Bit error rate 10 -6 10 -8 10 -7 10 -10 10 -9 10 -11 10 -12 SNR at receiver 15 20 18 22 24 26 28 OC3 OC12 OC48 OC192

45. 45ControlNumber Signal-to-noise ratio budget Transmitter Receiver 250 km Amp 50 km Amp 50 km Amp SNR: 30 dB at launch, extinction ratio 10 dB BER 10 -9 for SNR 21 dB

46. 46ControlNumber Signal-to-noise ratio budget (continued) 5 amplifiers with noise figure 3 dB SNR at launch: 30 dB Extinction ratio: 10 dB => 1 dB SNR reduction (see Dutton, p. 404) Receiver characteristics –SNR of 20 dB ~ BER 10 -9 ; SNR of 17 dB ~ BER 10 -6 System won’t work: SNR at receiver = 30 dB – 1 dB - 5x3 dB = 14 dB Need one repeater after 2 amplifiers –Assume output of repeater is SNR of 30 dB –Extinction ratio 10 dB –SNR at receiver now 30 dB – 1 dB - 2x3 dB = 23 dB Gives margin of 3 dB

47. 47ControlNumber Signal-to-noise ratio budget (continued) Transmitter Receiver 250 km Amp 50 km Amp 50 km SNR: 29 dB at launch BER 10 -9 for SNR 20 dB Rptr SNR: 24 dB SNR: 29 dB SNR: 23 dB

48. 48ControlNumber Design summary: 250 km OC48 link OK

49. 49ControlNumber Practical design Use modern interactive, graphics-based software tools –Calculate all relevant design data after component specs entered –Also will give OSA graphs, eye diagrams

50. 50ControlNumber Fiber optic design software Physical layout and verification software: http://www.designw.com/PDA-Overview.php For demo version (30 day license) of full-scale optical network design software, go to this page and download OptiSystem 2.0: http://www.optiwave.com Rsoft demo: http://www.rsoftdesign.com/products/system_simulation/OptS im/

51. 51ControlNumber Rsoft demos

52. 52ControlNumber RSoft Screen Shot

53. 53ControlNumber RSoft Screen Shot