Traditional ROADM networks strictly follow the coarse ITU-T standard wavelength grids and channel spacings, which would result in low optical spectrum utilizations under dynamic traffic requests of variable spectrum lightpaths. This paper presents a spectrum-efficient optical drop-add-drop network with a centralized multi-carrier light source (C-MCLS). The C-MCLS generates thousands of optical carriers with uniform and narrow channel spacings. The optical carriers are distributed to each network node as light sources on demand through ROADMs designed with the carrier-drop function. Spectrum-aware optical carrier allocation is studied first in the proposed network. This paper proposes a Minimum Fragmentation Request First (MinFragRF) optical carrier allocation algorithm compared with the Maximum Spectrum Request First (MaxSRF) and Minimum Spectrum Request First (MinSRF) allocation algorithms. This paper also studies how channel spacings of optical carriers impact on the network performance under variable traffic demands. We perform both network analysis and simulations to evaluate the network performance in terms of the lightpath blocking probability (LP_BP) and the effective spectrum efficiency. We analytically derive the formulas of LP_BP and average effective spectrum efficiency in the proposed network. Simulation results show that the proposed network with more narrow channel spacings greatly reduces the lightpath blocking probability compared with the traditional ROADM network. The average effective spectrum efficiency of the proposed network can be improved about 100 % compared with that of the traditional ROADM network by choosing appropriate network design parameters. The MinFragRF allocation algorithm has a better LP_BP performance than that of the MaxSRF and has a better spectrum utilization efficiency than that of the MinSRF. The optimal channel spacing evaluations show that narrow channel spacings such as 6.25 and 12.5 GHz greatly improve LP_BP performance when low bit-rate traffic requests dominate in the traffic model. However, as the high bit-rate traffic requests increase, the performance advantage of narrow channel spacings is gradually disappearing.
Photonic Network Communications – Springer Journals
Published: Feb 21, 2014
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