Evaluatio ion of Ela lasti tic Modulation Gain ins in in Microsoft’s Optical Backbone in North Americ ica Monia Ghobadi Jamie Gaudette, Ratul Mahajan, Amar Phanishayee, Buddy Klinkers ( Microsoft ), Daniel Kilper ( University of Arizona)
Demand is increasing Conventional wisdom to increase capacity • add more wavelengths • light more fiber To support the exploding demand in the cloud, we need to efficiently use the deployed fiber. 2
Data • All fiber paths in Microsoft’s North America backbone • Three-months (Feb-April 2015) • Poll signal quality (Q-factor) for 100Gbps PM- QPSK line cards • 1000s of line cards • Segments length range: 5km - 2600km • Fiber type: LEAF, SSMF • 15-min bin samples: min, max, average Is there ability to carry more bits? 3
Higher order modulation 1.0 • Performance of each channel 100Gbps QPSK 150Gbps 8-QAM 200Gbps 16-QAM Cumulative Distribution Function 0.9 • Margins for higher order 0.8 0.7 modulations 0.6 • Convert Q-factor to SNR 0.5 0.4 0.3 0.2 0.1 0.0 5 6 7 8 9 10 11 12 13 14 15 16 17 Signal-to-Noise Ratio (dB) 4
Higher order modulation 1.0 100Gbps 150Gbps 200Gbps Cumulative Distribution Function 0.9 0.8 0.7 43% 0.6 0.5 0.4 0.3 200G 150G Gain: 70% 0.2 0.1 99% 0.0 5 6 7 8 9 10 11 12 13 14 15 16 17 100G Signal-to-Noise Ratio (dB) Using the same fiber paths, we get more bits 5
Higher order modulation 1.0 100Gbps 150Gbps 200Gbps 12% Cumulative Distribution Function 0.9 0.8 penalty 1.5 dB Propagation 0.7 0.6 penalty 2.2 dB Propagation 0.5 0.4 200G 100 0.3 G Gain: 45-70% 0.2 78% 150G 0.1 0.0 5 6 7 8 9 10 11 12 13 14 15 16 17 100G Signal-to-Noise Ratio (dB) 6
Higher order modulation 1.0 125Gbps 175Gbps 225Gbps 250Gbps 100Gbps 150Gbps 200Gbps Cumulative Distribution Function 0.9 0.8 150G 225G 0.7 0.6 200G Gain: 86% 175G 0.5 0.4 200G 100 0.3 G Gain: 45-70% 0.2 150G 0.1 0.0 5 6 7 8 9 10 11 12 13 14 15 16 17 100G Signal-to-Noise Ratio (dB) 7
Higher order modulation 1.0 1.0 125Gbps 175Gbps 225Gbps 250Gbps 100Gbps 150Gbps 200Gbps Gain: 99% Cumulative Distribution Function Cumulative Distribution Function 0.9 0.9 0.8 0.8 150G 225G 0.7 0.7 0.6 0.6 200G Gain: 86% 175G 0.5 0.5 0.4 0.4 200G 100G 0.3 0.3 Gain: 45-70% 0.2 0.2 150G 0.1 0.1 0.0 0.0 5 5 6 6 7 7 8 8 9 9 10 11 12 13 14 15 16 17 10 11 12 13 14 15 16 17 100G Signal-to-Noise Ratio (dB) Signal-to-Noise Ratio (dB) 8
How to deploy higher order modulations • Should we use the same modulation for all segments? • Different segments have different SNRs. • Should we use the same modulation for all wavelengths in a segment? • Different wavelengths have different SNRs. • Should the modulation for a wavelength be static? • SNR varies over time. 9
How to deploy higher order modulations • Should we use the same modulation for all segments? • Different segments have different SNRs. • Should we use the same modulation for all wavelengths in a segment? • Different wavelengths have different SNRs. • Should the modulation for a wavelength be static? • SNR varies over time. 10
SNR variation across wavelengths 14.0 1 3.8 dB 0.9 13.5 Signal-to-Noise Ratio (dB) 0.8 CDF over all segments 13.0 0.7 0.6 12.5 0.5 0.8 dB 12.0 0.4 0.9 dB 11.5 0.3 0.2 11.0 0.1 10.5 0 1545 1550 1555 1560 1565 0 1 2 3 4 5 6 Different wavelengths need different modulation formats even Wavelength (nm) (max – min) SNR (dB) though the path is shared 11
How to deploy higher order modulations • Should we use the same modulation for all segments? • Different segments have different SNRs. • Should we use the same modulation for all wavelengths in a segment? • Different wavelengths have different SNRs. • Should the modulation for a wavelength be static? • SNR varies over time. 12
SNR variation over time 14.5 Signal-to-Noise Ratio (dB) 14 13.5 Jumps are due to: • Occasional network changes 13 • Removal of legacy 10G OOK 12.5 • Removal of old optical gear 12 • Maintenance 11.5 11 10.5 Time 13
SNR variation over time Per channel max - min 14.5 1 0.9 Signal-to-Noise Ratio (dB) 14 CDF over channels 0.8 5.8 dB 13.5 0.7 0.6 13 0.5 12.5 0.4 0.3 12 0.2 11.5 0.1 0 11 0 1 2 3 4 5 6 7 8 9 10 10.5 Time SNR (dB) SNR changes over time, depending on changes in infrastructure 14
How to deploy higher order modulations • Should we use the same modulation for all segments? • Different segments have different SNRs. • Should we use the same modulation for all wavelengths in a segment? • Different wavelengths have different SNRs. • Should the modulation for a wavelength be static? • SNR varies over time. Bandwidth Variable Transponders 15
Conclusions • Existing fiber can support higher order modulation • Deployment should be realized using bandwidth variable transponders 16
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