# A Vision of 6 th Generation of Fixed Networks (F6G): Challenges and Proposed Directions
## 2 Services and Requirements for F6G
### The Indispensable Network Transformation in Order to Realize the F6G Vision  
In order to elaborate on the requirements of each of the six categories of services presented in Figure 2, we illustrate how F6G extends the key quantities when it is compared with F5G (Figure 3). Of course, there are additional critical requirements that need to be satisfied and are usually service-dependent, such as security, operational efficiency, spectral utilization, cost/power efficiency [7], jitter, etc. However, in this work, we are focusing on the three key metrics, which are latency, bit rate, and fiber density, as at least one of them is critical for any F6G service. Figure 3 highlights that, first, the introduction of a fresh Passive Optical Network (PON) standard is required in order to reach data rates of 100 Gb/s and beyond in the access domain and support bandwidth-critical services. Further, a new densification strategy needs to be adopted in order to realize Fiber to the Everything (FTTE), which aims to integrate all \"Fiber to the X\" concepts that are expected to be introduced during F5G into a single network entity (such as Fiber to the Home (FTTH), Fiber to the Office (FTTO), Fiber to the Room (FTTR), Fiber to the Desk (FTTD), and Fiber to the Machine (FTTM) [9]). At the same time, this densification will aid in integrating fixed and wireless networks, leading to a major network transformation through which the network will be able to concretely support the demands of both wireless-based and wired-based services. Regarding latency, the F6G infrastructure is expected to advance significantly compared with F5G in order to support services with very low latency requirements, especially those of the industrial sector, which can be down at the order of some tens of \(\mu\)s [10; 11; 12; 13]. In order to attain all these very strict requirements, there is a strong need for network/service providers to upgrade their current network infrastructure both at the component and network levels, as well as to make their network fully automated in order to perform fast and accurate decisions at a \(\mu\)s timescale. Towards this target, in the next three sections, this work proposes various directions and solutions that can aid in underpinning F6G services in a cost- and energy-efficient way. Indicatively, a significantly larger spectrum needs to be allocated, which can be realized either by exploiting all five low attenuation bands of the optical fiber or by performing SDM, which in essence means data transmission through bundles of fibers, multi-core fibers, multi-mode fibers, few-mode fibers, and/or their combination [14; 15; 16]. At the same time, very high-capacity switches need to be installed and operate at very high bit rates (per channel) [17; 18; 19; 20]. Further, ultra-fast optical switching will be a must in order to attain as low an end-to-end delay as possible by eliminating delay [10; 13]. In order to reduce the overall cost and power consumption, novel all-optical transceivers need to be deployed, e.g., without the need for cumbersome modules such as electronic Digital to Analog Converters (eDACs) while the introduction of wavelength band converters and comb generators will assist in removing the electronic conversion, which can lead to a lower end-to-end delay. Finally, convergence between various technologies and methods such as those in 6G and F6G, as well as an all-encompassing integration, is required. This conversion will transform the network into a sensor, communicator, and super-computer, enabling it to automatically make AI-based decisions.