## 5 Evaluation Results and Discussion  
The analysis of the Flex-O network deployment scenario is performed in mesh network topologies MESH-9, MESH-20, and MESH-38, also studied in [20,35], which are presented in Figure 3. In the networks, the link lengths are distributed uniformly between 1 and 3 km. A \(k\)-shortest path algorithm was used to generate candidate TPs and the paths of the length exceeding 10 km were excluded (according to the assumption in Section 3.4).  
Two scenarios with the WDM capacity being equal to 4 and 8 wavelengths (channels) are studied. These capacities reflect the limited number of wavelengths available in the passive WDM solutions considered for low-cost 5G xHaul networks [9] and correspond to the number of wavelengths supported by system xWave 400G [18]. The fiber loss coefficient accounts on both the value of 0.40 dB/km reported in [40] and additional margin of 0.10 dB/km due to splices losses and environmental factors. The connector loss and the maintenance margin are 0.3 dB and 2.0 dB, respectively. The values of \(P_{\text{TX}}\) and \(P_{\text{RX}}\) are based on the specification [18]. The system parameters are summarized in Table 2.  
The attenuation of OADMs [23] and MUXs [41,42], presented in Table 3, corresponds to typical values of commercial products. In scenario Fix-O, the OADM is composed of a pair of MUX modules, similar to [19,20], where one MUX operates as a de-multiplexer and the ports of bypassed channels are connected directly by means of patchcords. Accordingly, the OADM attenuation in Fix-O is 3.0 dB and 3.8 dB for OADM-4 and OADM-8, respectively, and it includes the losses of a patchcord.  
\begin{table}
\begin{tabular}{l r} \hline WDM capacity (\(W\)) & \(\{4,8\}\) \\ Fiber loss coefficient (\(a\)) [dB/km] & 0.5 \\ Connector loss (\(A_{\text{C}}\)) [dB] & 0.3 \\ Maintenance margin (\(A_{\text{MM}}\)) [dB] & 2.0 \\ Minimal transmitter outer optical modulation amplitude (\(P_{\text{TXoma}}\)) [dBm] & 3.0 \\ Sensitivity of receiver (\(P_{\text{RXoma}}\)) [dBm] & \(-14.0\) \\ Power budget (\(P=P_{\text{TXoma}}-P_{\text{RXoma}}\)) [dBm] & 17.0 \\ \hline \end{tabular}
\end{table}
Table 2: Assumed values of the transmission system parameters.  
Figure 3: Network topologies studied, where MESH-9 and MESH-20 are the subgraphs of MESH-38.  
The lease price of a km of dark fiber (\(\kappa^{\text{F}}\)) is assumed to be equal to $250 [(43; 44)]. A linear cost model is considered for the optical devices, where one channel is estimated at the cost of $15 for a MUX and $30 for an OADM [(45)].  
For each remote site, the number of requested wavelengths was generated randomly between \(W^{\text{min}}\) and \(W^{\text{max}}\) such that \(1\leq W^{\text{min}}\leq W^{\text{max}}\leq 4\). The traffic load (denoted as \(\rho\)) represents the average number of wavelengths requested by a remote site; in particular, \(\rho=(W^{\text{min}}+W^{\text{max}})/2\). In the analysis, we consider \(1.0\leq\rho\leq 4.0\), where \(\rho=1\) corresponds to \(W^{\text{min}}=W^{\text{max}}=1,\rho=2.0\) to \(W^{\text{min}}=1,W^{\text{max}}=3\), etc.  
Solver CPLEX v.12.9 [(46)] was used to solve the MILP model. The solver was run in a parallel mode and with default settings on a dual-processor 2.2 GHz 10-core Xeon workstation (40 logical cores in total) with 128 GB RAM. We report that all the results obtained were optimal.