# Earthquake-Tolerant Energy-Aware Algorithm for WDM Backbone Network
## 2 Materials and Methods
### Operation of the Proposed Algorithm  
Analysis reveals that the primary source of energy consumption is the IP routing ports, necessitating a reduction in their usage for significant energy savings. The total number of IP routing ports depends on the total number of paths, which, in turn, relies on the number of areas with a high seismic probability, the fibers they pass through, and the total number of new bypass paths. Based on these data, we conclude that reducing fibers passing through these areas would result in reduced energy consumption. Removing all these fibers would significantly reduce energy consumption but could also create a disconnected network, resulting in lost communication between nodes. Therefore, fiber removal from the network must be selective. Leveraging this knowledge, the proposed algorithm selectively removes specific fiber connections from the topology to reduce energy consumption while considering the seismic risk of the areas. Energy reduction will be calculated using the EAFFB algorithm [6]. The proposed algorithm aims to identify critical fibers, passing through seismically active areas, that can be removed without causing network disconnection. It selects combinations of links for removal, creating a new network that achieves two goals: prevents network disconnection and minimizes total energy consumption. The algorithm emphasizes complete links, assuming identical WDM channel sets. Link removal or deactivation is treated as a unified entity without considering the WDM level. For example, when two neighboring regions are potential candidates for catastrophic earthquakes, and the only way to access a node in the network is through links passing through these regions, none of these links can be categorized as critical. Removing any of these links would render the node unreachable. This can be seen in Figure 4, where there are three affected regions: 35, 34, and 1, and the affected links are 270 and 341. Neither of them can be characterized as critical because removing any of those links immediately sets the RHO node as inaccessible. The algorithm first identifies critical fibers in the physical topology and then determines the best combination of these fibers to exclude from the final topology. This ensures both full connectivity of the backbone network and significantly reduced energy consumption. Below is a concise description of the proposed algorithmic approach, with the corresponding pseudocode in Algorithm 1. The input parameters in line 1 are a physical topology \(G\) (\(N,L\)), comprising a set of nodes \(N\) and a set of links \(L\). In line 2, nodes (\(N\)) represent the network nodes, and in line 3, links (\(L\)) denote the physical fibers connecting pairs of nodes. In line 4, a traffic matrix [\(\lambda\)] specifies the precise traffic demand between two nodes. The [\(\lambda\)] is generated by a random function uniformly distributed within the range [\(10,\,2X-10\)] Gb/s, where \(X\in\)[\(20,\,40,\,60,\,80,\,100,\,120\)]. A maximum of 80 wavelengths are multiplexed in each fiber, with a restriction on the total number of fibers on each physical link set at 48. The modulation format can be changed, as the presented algorithm is modulation-agnostic. Moreover, the presented algorithm can operate with varying link capacities, requiring minimal adjustments to its implementation. The link capacity of 40 Gbps was chosen in order to have a fairer comparison of the presented algorithm result with the results of the previous work presented in [6,37]. Additionally, the chosen modulation format is the Non-Return-to-Zero (NRZ). In optical communication, NRZ is a simple modulation format, where each bit is represented by a single pulse and the transmission capacity of each wavelength is 40 Gbps. There are no digital signal processing activities conducted in the channels in our WDM network that are being considered in the simulation. In line 5, the matrix [\(R\)] includes all 36 regions of the network map.