# A Vision of 6 th Generation of Fixed Networks (F6G): Challenges and Proposed Directions
## 5 Optical Switching: Key Challenges and Proposed Directions
### Ultra-High Capacity Switching
As such, optical channel bandwidths are increasing and, concurrently, the number of wavelength multiplexed channels over a given spectral window is decreasing. This trend suggests that full-band transceivers (having integrated frequency comb sources with dedicated modulators and detectors per spectral line) may become commoditized by the decade's end and optical bandwidth will be resourced by full fiber bandwidth and routed throughout the network using space switches, i.e., OXC. This optical networking scenario lacks the efficiencies associated with resource sharing (of fibers, optical amplifiers, switches, etc.) and flexibility to adapt the optical bandwidth utilization to the per-connection capacity needs. Furthermore, the optical fiber infrastructure for full fiber allocation per connection will necessarily be massively fiber-parallel and require very large OXC to be deployed at network nodes from the onset to support full connectivity [140]. The proposed novel switching paradigm, which can address the aforementioned challenges posed by optical switching, is pictorially described in Figure 37. This node can cross-connect communication channels among spatially parallel links that support UWB/WDM operation (covering, e.g., at first three distinct bands: S, C, and L) and can serve as a part of a MG switch, which will be able to switch traffic from single channels, super-channels, bands, and entire fibers concurrently. Fundamentally, there is a strong need for a new WBSS module, such as the one pictorially described in Figure 38, that has the following characteristics: (a) It is efficiently implemented in a PIC platform, (b) it can be adaptively tuned in wavelength and optical bandwidth, (c) it can be scalable to large port counts, and  
Figure 37: Generalized architecture of a node with SDM/UWB functionality. crosecond switching rates. Network nodes utilizing the WBSS can be structured in a route-and-select topology, with individual switches placed on each I/O fiber port and expressing band-spanning fiber traffic towards its ultimate destination. The network node architecture supports legacy traffic by conventional WSS at a hierarchy below the WBSS, offering routing to DWDM traffic channels, before being re-multiplexed to the multi-band network (Figure 38). Connectivity between the network hierarchy elements is implemented by an OXC that further assists in transceiver sharing for handling add/drop channels in a colorless/directionless/contentionless (C/D/C) manner. The node can be reconfigured per accepted request in a centralized fashion, as done in today's networks, which lack significant dynamicity, yet accelerated due to a combination of faster processing power for requests and faster response times of the WBSS. An alternative operation mode of cycling through predetermined time-slotted connectivity patterns can allow direct connections between communicating pairs at target switch epochs, with data buffering at the transmitter, thereby guaranteeing time-of-flight latencies across the network and no loss of information due to buffer overflows.