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With the emergence of IoT applications, 5G, and edge computing, network resource allocation has shifted toward the edge, bringing services closer to the end users. These applications often require communication with the core network for purposes that include cloud storage, compute offloading, 5G-and-Beyond transport communication between centralized unit (CU), distributed unit (DU) and core network, centralized network monitoring and management, etc. As the number of these services increases, efficient and reliable connectivity between the edge and core networks is of the essence. Wavelength Division Multiplexing (WDM) is a well-suited technology for transferring large amounts of data by simultaneously transmitting several wavelength-multiplexed data streams over each single fiber optics link. WDM is the technology of choice in mid-haul and long-haul transmission networks, including edge-to-core networks, to offer increased transport capacity. Optical networks are prone to failures of components such as network fiber links, sites, and transmission ports. A single network element failure alone can cause significant traffic loss due to the disruption of many active data flows. Thus, fault-tolerant and reliable network designs remain a priority. The architecture called “dual-hub and dual-spoke” is often used in metro area networks (MANs). A dual-hub, or in general a multi-hub network, consists of a set of designated destination nodes (hubs) in which the data traffic from all other nodes (the peripherals) should be directed to the hubs. Multiple hubs offer redundant connectivity to and from the core or wide area network (WAN) through geographical diversity. The routing of the connections (also known as lightpaths) between the peripheral node and the hubs has to be carefully computed to maximize path diversity across the edge-to-core network. This means that whenever possible the established redundant lightpaths must not contain a common Shared Risk Link Group (SRLG). An algorithm is proposed to compute the most reliable set of SRLG disjoint shortest paths from any peripheral to all hubs. The proposed algorithm can also be used to evaluate the overall edge-to-core network reliability quantified through a newly introduced figure of merit. 

Optical network technology is one of the leading candidates for meeting the required backhaul transport layer latency and capacity requirements of 5G services. In addition, its physical layer programmability supports the execution of advanced methods that can improve 5G service reliability and SLA compliance in the face of equipment failure. While a number of such methods is addressed in the literature, including Virtual Network Function (VNF) fault-tolerant methods, a full proof of concept is yet to be reported.The study in this paper describes a testbed — along with its Software Defined Networking (SDN) and Network Function Virtualization (NFV) capabilities — which is used to experimentally showcase the key functionalities that are required by VNF fault-tolerant methods. The testbed makes use of OpenROADM compliant Dense Wavelength Division Multiplexing (DWDM) equipment to implement the programmable backhaul of a Next Generation Radio Access Network (NG-RAN) Non-standalone (NSA) architecture running 4G Evolved Packet Core (EPC) with the 5G next-generation NodeB (gNB). Specifically, the testbed is used to showcase the live migration of virtualized EPC components that is required to restore pre-failure VNF.