gy environments. Fig. 1.1 illustrates the evolution stages of 4G to 5G networks, where the distributed archi- tectures evolved to centralized architectures, NFs have been virtualized, and later the Wavelength division multiplexing allows different data streams to be sent simultaneously over a single optical fiber network. There are two main types of wavelength division multiplexing technologies in use: Coarse wavelength division multiplexing and dense wavelength division multiplexing. Coarse wavelength division multiplexing allows up to 18 channels to be transported over a single dark fiber, while dense wavelength divi- sion multiplexing supports up to 88 channels. Both technologies are independent of transport protocol. The main difference between coarse wavelength division multiplexing and dense wavelength division multiplexing technologies lies in how the transmission channels are spaced along the electromagnetic spectrum. Wavelength division multiplexing technology uses infrared light, which lies beyond the spectrum of visible light. It can use wavelengths between 1260 and 1670 nm. Most fibers are optimized for the two regions 1310 and 1550 nm, which allow effective channels for optical networking. Coarse wavelength division multiplexing is a convenient and low-cost solution for distances up to 70 km. But between 40 and its maximum distance of 70 km, coarse wavelength division multiplexing tends to be limited to eight channels due to a phenomenon called the water peak of the fiber. Coarse wavelength division multiplexing signals cannot be amplified, mak- ing the 70 km estimate an absolute maximum. Dense wavelength division multiplexing works on the same principle as coarse wavelength division multiplexing, but in addition to the increased channel capacity, it can also be amplified to support much longer distances. The following figure shows how the dense wavelength division multiplexing channels fit into the wavelength spectrum compared to coarse wavelength division mul- tiplexing channels. Each coarse wavele