1. Kayukov Valeriy Optical System Engineer Step Logic April 15, 2016 Cisco Optical Networking – Chromatic Dispersion calculation. Cisco Support Community Expert Series Webcast

2. 2 © 2015 Cisco and/or its affiliates. All rights reserved. Question1 Have you ever had deal with DWDM Cisco ONS devices? 1. Yes 2. No 3. Cisco have such platforms?

3. 3 © 2015 Cisco and/or its affiliates. All rights reserved. Chromatic Dispersion Measurement of CD in real Fiber Sample of calculation in CTP Polarization Mode Dispersion Content of presentation

4. 4 © 2015 Cisco and/or its affiliates. All rights reserved. Chromatic Dispersion

5. 5 © 2015 Cisco and/or its affiliates. All rights reserved. Chromatic Dispersion (CD) – is based on effect of impulse broadening during passing through optical fiber. Polarization Mode Dispersion - a temporary difference between the polarization components of the same signal. Optical Dispersion types:

6. 6 © 2015 Cisco and/or its affiliates. All rights reserved. Optical pulse time-expanded by passing through the optical fiber. This process triggers limitation of bandwidth throughput or maximum transition distance with constant bandwidth. Chromatic Dispersion is fiber characteristic with is measured in ps/km*nm and depends on wavelength. To compensate dispersion used pre-compensation and post-compensation techniques. Dispersion compensators is based on negative dispersion fiber. Chromatic Dispersion (CD)

7. 7 © 2015 Cisco and/or its affiliates. All rights reserved. Different cables have different CD depending on internal construction Typical CD values of different fibers Fiber typeNormal dispersion at 1550 nm measured in ps/km-nm Single Mode Fiber (SMF)17 E-Large Effective area fiber (ELEAF) 4 TrueWave RS (TW-RS)4.2 Dispersion shifted fiber (DSF)-0.33

8. 8 © 2015 Cisco and/or its affiliates. All rights reserved. Cisco DCU compensators uses fiber loops with negative dispersion fiber. Attenuation of DCU varieties from 2.1db to 8.8 db. Compensation Level (ps/nm) varieties from 100ps/nm to 1950 ps/nm Cisco ONS 15216 DCU modules DCU chassis PN: 15216-DCU-SA= DCU module PN: 15216-DCU-XXXX=

9. 9 © 2015 Cisco and/or its affiliates. All rights reserved. Optical spool produced and measured in Thailand, completed in in hard case in Denmark. For Sample this DCU has 1950 ps\nm nominal, but in real how we see in report it has 1957,33 ps/nm. Insertion loss 6.97db vs 8.8db in data sheet. What is inside DCU module?

10. 10 © 2015 Cisco and/or its affiliates. All rights reserved. Disadvantage of use DCU in network is that DC add significant attenuation\loss. This is due to difference of coupling transition and fiber and fiber used in DCU. Advantage of use compensators is that DCU limit nonlinear effects. Different dispersion profile result in a phase mismatch, witch prevent from FWM happening. Pluses and minuses of use DCU

11. 11 © 2015 Cisco and/or its affiliates. All rights reserved. Values of CD Tolerance XFP: Fixed Wavelength XFP -500 to +1100 ps/nm Tunable Wavelenght XFP -400 to +1300 ps/nm CD Tolerance of different XFP 10G modules

12. 12 © 2015 Cisco and/or its affiliates. All rights reserved. Values of CD Tolerance SFP+: Fixed Wavelength XFP -500 to +1100 ps/nm Tunable Wavelenght XFP -400 to +1300 ps/nm CD Tolerance of different SFP+ 10G modules

13. 13 © 2015 Cisco and/or its affiliates. All rights reserved. Use of fixed wavelength SFP+\XFP has disadvantages in case failure. Fixed wavelength could be replaced by tunable module or the SAME wavelength module. GLP Price Discount could be higher for tunable modules that for fixed. Contact to your Cisco CAM. In future line DWDM network could be upgraded to colorless or directionless. Comparison of SFP+ vs XFP modules

14. 14 © 2015 Cisco and/or its affiliates. All rights reserved. Single-Shelf DCU Application East-to-West and West-to-East Samples of use DCU modules Cascaded DCU Shelf per Direction DCU Placed Between Wavelength Selective Switch (WSS) and Amplifier

15. 15 © 2015 Cisco and/or its affiliates. All rights reserved. CD Tolerance of different SFP+ 10G modules

16. 16 © 2015 Cisco and/or its affiliates. All rights reserved. DWDM network based on 10G services called coherent networks and networks based on 100G and higher services called non-coherent networks. Design coherent networks depends on compensation systems. Non-coherent networks in most (but not in all) cases doesn’t depends on compensation systems because tolerance of recoveries around 94 000 ps/nm for 200G. For example 94 000ps/nm is equivalent to 5200 km with 18ps/nm-km. CD Tolerance of 10G, 200G, 400G modules

17. 17 © 2015 Cisco and/or its affiliates. All rights reserved. Measurement of CD of real fiber

18. 18 © 2015 Cisco and/or its affiliates. All rights reserved. What parameters are measured: dispersion coefficient values measured at specified wavelength dispersion maximum over specified range of wavelengths zero dispersion wavelength and dispersion slope at this wavelength CD measurement, Introduction

19. 19 © 2015 Cisco and/or its affiliates. All rights reserved. Both methods measure propagation delay (or group delay) at selected wavelength and, from the measured delay versus wavelength data, interpolate the delay for other wavelength not directly measured by using numerical fitting algorithms. Phase Shift – method of comparison of test signal and reference signal used to modulate the input signal. The phase difference is performed versus wavelength over the entire wavelength range of source. Pulse Delay - Measurement methods (Phase Shift vs Pulse Delay )

20. 20 © 2015 Cisco and/or its affiliates. All rights reserved. Phase Shift advantages:  high accuracy measurement  high dynamic range (40 db+) (>15 db higher than the Pulse Delay method)  high measurement reliability  compatible with non-biderectional components (such EDFA amplifiers) Phase Shift Method Phase Shift disentangles:  measurement time can depend on number of data ponts  requires two units  dispersion versus length info not provided  Fiber length must be known to calculate the average CD coefficient

21. 21 © 2015 Cisco and/or its affiliates. All rights reserved. Group Delay advantages:  require access to only one end of link  detects regions of different dispersion within a link? As it can analyze reflections at intermediate points (only if reflectance are present mid-span)  Combines an OTDR allowing a simultaneous distance and loss measurement Group Delay Method Group Delay disentangles:  distance range is limited by the end reflection: higher reflectance? The longer distance. Not suitable for APC connections installed.  Not suitable for long-haul or high-loss fiber link (>30db)  not compatible with non-biderectional components (EDFA amplifiers)

22. 22 © 2015 Cisco and/or its affiliates. All rights reserved. 100G/100G/400G Cards now have advanced measurement method build in. 100G/100G/400G Cards CD measurement

23. 23 © 2015 Cisco and/or its affiliates. All rights reserved. Sample of calculation in CTP, XLS

24. 24 © 2015 Cisco and/or its affiliates. All rights reserved. Need to design network with requirements: 5 sites 4 channel 10GE fiber used is SMF G652 In this example we will not consider design of multiplexing, add\drop and amplification systems. Real Sample of Calculation. Planning of DCU Scheme of compensation in DWDM network

25. 25 © 2015 Cisco and/or its affiliates. All rights reserved. In this step we will make: Start – “Project Creation Wizard” Start – “Run the Network Wizard Now” Create circuit – “Create Net Point-to-Point Demand” Start – “Network Analyze” Go to – “Summary” –> “Optical Reports” Lets start to work in CTP. Step 1 – Preparation.

26. 26 © 2015 Cisco and/or its affiliates. All rights reserved. Project Creation Wizard

27. 27 © 2015 Cisco and/or its affiliates. All rights reserved. Run the Network Wizard Now

28. 28 © 2015 Cisco and/or its affiliates. All rights reserved. In this section we will not cover types of transponders and so on, just create circuit. Create Circuits

29. 29 © 2015 Cisco and/or its affiliates. All rights reserved. DWDM trunk type we are changing to Tunable SFP+. It is not matter what type of coding (FEC\EFEC\NO-FEC), it doesn’t add any price for total BOM. Coding (FEC\EFEC\NO-FEC) in 10G networks no licensable by Cisco. After this choice we exactly know CD tolerance of trunk ports. Edit trunk SFP manually to SFP+ Tunable C band

30. 30 © 2015 Cisco and/or its affiliates. All rights reserved.  Report shows per channel CD calculation at the end of circuit in BOTH directions. Chromatic Dispersion compensation systems is separate per each direction.  Cisco Transport Planner (CTP) use value 1100ps/nm for Tunable SFP+, but in data sheet 1300ps/nm. Advantage of use CTP is that it has fund\margin in reports.  CTP doesn’t use any fiber characteristic\function of DC depending on wavelength.  If Residual CD cross CD Robustness (CD tolerance) value than CTP triggers Single-Channel NLE Status RED. Later will discus situation with Single-Channel NLE Status RED.  CTP maximum optimally calculates DCU unites. In case of alarms power EOL, EOS you can manually change DCU to lower values, in most cases it helps to improve power SOL value. Analyze “Optical Report”

31. 31 © 2015 Cisco and/or its affiliates. All rights reserved. Click on Site 1-5, choose “Layout” Click on Site 1-5, choose “Functional view” Lets do that for every Site and draw big topology per each direction Lets understand what CTP calculated

32. 32 © 2015 Cisco and/or its affiliates. All rights reserved. Site-1 Functional view

33. 33 © 2015 Cisco and/or its affiliates. All rights reserved. Site-1 Functional view

34. 34 © 2015 Cisco and/or its affiliates. All rights reserved. Site-3 Functional view

35. 35 © 2015 Cisco and/or its affiliates. All rights reserved. Site-4 Functional view

36. 36 © 2015 Cisco and/or its affiliates. All rights reserved. Site-5 Functional view

37. 37 © 2015 Cisco and/or its affiliates. All rights reserved.  In attach XLS based calculation of DC of Channel between Site-1 and Site-5 XLS based DC Calculation

38. 38 © 2015 Cisco and/or its affiliates. All rights reserved. As result we can see some errors and make some conclutions:  CTP show in layout or doesn’t show correct DCU values on which based DC results in “Optical Results” report  Be care with CTP, use manual calculation to check, also use Forcing Manager to unlock and clear CD cache calculation.  Use “Forcing Manager” when you add new circuits in design  Do not make “Over-Compensation” and “Under-Compensation”, try to have CD of signal all the time in tolerance window. For example tolerance window for SFP+ Tunable from - 100 to 1100 ps/nm XLS based DC Calculation

39. 39 © 2015 Cisco and/or its affiliates. All rights reserved. Force to clear CD calculation

40. 40 © 2015 Cisco and/or its affiliates. All rights reserved. Polarization Mode Dispersion

41. 41 © 2015 Cisco and/or its affiliates. All rights reserved. Polarization Mode Dispersion - a temporary difference between the polarization components of the same signal. Example A - optic cable has ideal dimensions of the X-axis and Y -> the same velocity of propagation. Example B - optic cable has different dimensions to the X-axis and Y -> propagation speed is different. Polarization Mode Dispersion (PMD)

42. 42 © 2015 Cisco and/or its affiliates. All rights reserved. Causes of PMD: The asymmetry of the core or the internal stress caused by the core during production Internal stress caused by the core during the installation of optical cable Polarization Mode Dispersion (PMD)