# A Vision of 6 th Generation of Fixed Networks (F6G): Challenges and Proposed Directions
## 5 Optical Switching: Key Challenges and Proposed Directions
### Ultra-Fast Switching
One of the main advantages of this flexible solution is that services can be migrated seamlessly to micro-DC located in a different location, increasing the reliability and availability of the services and allowing for the smooth growth and upgrade of the processing capabilities. The key element of this network is the Flexible Optical Add/Drop Multiplexing (FOADM) node. This new design will incorporate software-programmable photonically integrated-circuit-based subsystems, controlled by an intelligent software management system, capable of simplifying and optimizing network operations. More specifically, novel photonic switching schemes (optical switches), which are fast-reconfigurable (sub-ms) and optimize the utilization of resources across different kinds of traffic (non/-time-sensitive) using an intelligent control plane, need to be implemented. These optical switches allow for fast routing of traffic on individual wavelengths that can be dynamically added, forwarded, or dropped at any network point. While the optical switch itself is going to operate at high speeds in the order of 10 ns, a key element of this network is the scheduling of the traffic in the FOADM nodes. The scheduling with the assistance of an intelligent software management system will ensure the ultra-low latency and jitter required for traffic delivery in Industry 4.0 use cases. In the intra-factory network, the candidate architecture aims to provide a solution that will replace the current options for Industrial Ethernet and several other proprietary communications buses. These options are almost entirely based on electrical interconnects, using expensive copper cables and electronic switches for the aggregation of the non-time sensitive traffic and point-to-point links for the time-sensitive traffic. The most advanced demonstration of time-sensitive networks over packet-switched networks can achieve a latency of <100 us with <100 ns jitter, making use of proprietary hardware that essentially creates a point-to-point link between the switches, with a very inefficient use of the network resources [150]. This will aid in developing a solution using a low-cost P2 MP fiber network that will replace the copper-based electrical interconnects with an optical fiber and passive splitters/combiners. The proposed network aims to support both time-sensitive and time-insensitive connectivity. While the time-insensitive traffic can be easily supported by terminating and aggregating the connections from the end points at the input of the optical switch, the time-sensitive traffic and connections will be forwarded directly to the network by the FOADM node. The Intra-factory solution can support the optical aggregation of up to 64 end-points with data rates up to around 1 Gb/s per end-point and distances of a few kilometers. The solutions will use PON interfaces and technologies developed for residential optical access networks, such as XGS-PON and NG-PON2. In order to interface with the proposed optically switched network and meet the required latency and reliability performances, scheduling of the traffic in the PON systems will need to be integrated with new designs of the overall architecture. The design of the PON scheduler can be based on the work performed in utilizing TDM-PON for fronthaul applications [151]. The proposed solution can effectively address all the KPIs in Table 7 set for ultra-fast switches, whilst, in addition, it will allow one to: (i) reduce the congestion since optical networks can support high capacity; (ii) reduce the power consumption, due to the lower consumption of optical components in comparison with electronic ones; and (iii) reduce the cost of transmission interfaces thanks to the use of end-to-end optics, avoiding intermediate conversions to the electrical domain, thus collectively improving performance while, at the same time, minimizing the environmental impact. The fact that control can only be performed at the edges of the network makes the above solution an ideal candidate for the F6G ecosystem.