In DWDM :
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We use single mode fiber for long distance traffic transport.
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We use C band and L band because the lowest attenuation level.
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We use ROADMs for channels adding, dropping & pass through via WSS.
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We use coherent detection systems in case of long distance, High capacity and no need for DCM.
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We could achieve ultra high capacity on single channel like 100, 200, 400 Gbps or even higher in special cases.
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We use Qpsk & 16 Qam modulation for coherent detection systems.
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We use optical amplifiers for distance extending like EDFA & RAMAN , meanwhile EDFA add noise ASE.
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We use optical line protection and SNCP , MSP & MSP ring.
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We use OTN frame for data Transportation in L1 and mangment , the frame contains 3 layers (OPU , ODU , OTU).
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We use CDC Roadms in case of higher traffic routing flexibility needed (colourless , directionless , contentionless).
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We use flexgrid and fixed grid channels, for fixegrid the frequency spacing is fixed and predetermined like 50 & 100 Ghz.
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In flexgrid we could use variable spacing allows dynamic adjustment of channel spacing, making it much more efficient and scalable, especially in high-capacity optical networks.
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