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SOLUTIONS FOR L-BAND NODE node (N2) and the tributary node E, but node E
ARCHITECTURES can not extract this wavelength, which is only
extracted from the network at the other hub
Two node architectures based on the FD&W node (the dashed pink line represents this path
architecture will be described: the amplified in Figure 2). So, this solution wastes the
and the unamplified solutions. The C+L band spectrum.
node amplified solution described in Figure 1
Nevertheless, this solution limits the L-band
relies on a single EDFA for each optical band signal transmission distance to adjacent
and two C/L filters at the node input/output. As nodes or near adjacent nodes (Source 1).
already referred to, a capacity penalty Figure 3 shows a possible wavelength
associated with this architecture is related to planning for the unamplified solution, where
the bandwidth waste caused by the guard there are no EDFAs inside the nodes. As shown
band between C and L band imposed by the C/L in Figure 3, λ is reused in the next hop, and λ is
1
2
filters before and after the EDFAs. reused after one hop. As in this unamplified
Two additional solutions exist for optical solution, the signal is not amplified, it arrives at
amplification at C+L band nodes to avoid this the next node with very low power, and so a
waste of bandwidth: one relies on using single new signal with the same wavelength can be
wide-band amplifiers based on semiconductor used.
OA, and the other uses a typical hybrid Raman-
EDFA amplifier configuration.
L-BAND AMPLIFIED SOLUTION
In the amplified solution, amplifiers are
inside the node before and after the FD&W
block, whereas in the unamplified solution,
these amplifiers are not present, as depicted in
Figure 1. These amplifiers will introduce ASE
noise that will contribute to degrading the
system performance. Figure 2: Amplified filterless solution with no
frequency reuse for the horseshoe topology.
Figure 2 presents a possible wavelength
planning for the amplified solution in the L- However, this weak signal contributes to
band in a horseshoe topology. This solution impair the main signal and so this unamplified
does not allow the reuse of frequencies inside solution is impaired by in-band crosstalk. So,
the horseshoe network since the hub node can with this solution it is possible to reuse the
only extract each wavelength assigned in the same wavelength, providing a simple and very
network. The tributary nodes have no such low-cost capacity upgrade for MANs with
capacity since they are based on S/Cs (FD&W dedicated capacity for short lightpaths
architecture). An example of this scenario can between tributary nodes, albeit with a more
be seen in Figure 2: the pink wavelength is c h a l l e n g i n g o p t i c a l p e r f o r m a n c e
assigned to the connection between the hub management.
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