# 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  
Switches that are able to provide very low latency are indispensable components within an Industrial 4.0 and or/a Data Center (DC) environment. In particular, these switches need to:  
* Ensure low congestion, latency, and jitter when routing the traffic flows in the optical domain from the various end-points of the industrial network. * Provide high scalability and cascadeability, allowing the seamless operation of a highly densified industrial environment, consisting of a large number of inter-connected \"things\" such as robots, machines, etc. * Provide a sufficient physical layer performance even for demanding industrial environments, which comprise a large number of inter-connected buildings and \"things\", such as robots, machines, etc., ensuring a very low BER even after a large number of traversed nodes in a densified environment. * Provide a cost- and energy-efficient switching solution, which comprises low-cost and zero/low-power consumption components (e.g., power splitters, combiners, arrayed waveguide gratings, and wavelength blockers). The switches with these characteristics need to be able to satisfy various KPIs concurrently, as the Industrial services are both latency- and jitter-critical, while a high connectivity along with a very low packet loss ratio is required. The main KPIs for both intra and inter-factory connectivity are illustrated in Table 7.  
Currently available solutions are not able to support TSN as they cannot provide the required levels of flexibility (e.g., traffic dynamics) and determinism (e.g., jitter) concurrently [11]. In particular, Ethernet can effectively support the traffic dynamics; however, it cannot offer the required determinism. This is a result of multiple flows, which contend for the same output port experiencing random latency, and hence, jitter. To solve this issue, synchronous arrivals of packets and regular interleaving are needed, which would require client synchronization to the network. Another potential available solution is Industrial Ethernet, which provides determinism through its protocols (with sub-\(\upmu\)s jitter); however, static scheduling hinders the dynamics and flexibility. The next solution according to [11] is an Optical Transport Network (OTN), which is deterministic but inflexible. In general, an OTN or its variation (FlexE) can meet the current fronthaul requirement; however, they lack standardization to carry CPRI traffic and limited dynamics, and the relatively high cost makes them unsuitable for local networks, such as the ones on factory floors. Next, various PON standards can be potential solutions; however, they can address either flexibility or determinism but not both at the same time. For example, TWDM-PON, through the use of a Fixed Bandwidth Assignment (FBA) scheduler, can counterbalance jitter; however, it removes the benefits of statistical multiplexing while reducing the network dynamics, which is static in essence. Finally, the introduction of TSN maintains the trade-off between flexibility and determinism; however, it is a very