## 1 Introduction
### Review of Related Works
#### 1.1.2 Enabling Technologies  
A review of the emerging optical access network schemes for supporting 5G wireless applications was given in [24]. The work focused on the achievement of a low-latency, high-capacity, low-cost, as well as low-power per bit network. To achieve this, advanced modulation and detection schemes were considered along with the tailored digital signal processing (DSP). Furthermore, means of improving the network performance with efficient fronthaul schemes were deliberated. Moreover, the envisioned massive broadband connections and the associated traffic will not only result in stringent demands on the transport networks regarding an end-to-end latency and bandwidth, but will also cause considerable complexity in the radio access network (RAN). To address these, some research efforts on disruptive scheme concerning RAN functional split have been reported in the literature. In [5; 8; 11; 23; 25; 27; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48], RAN split options were studied along with the associated transport requirements, and some recommendations regarding a cost-effective solution for lower-layer and higher-layer RAN split options were given. Furthermore, to enable the MNOs networks to offer advantages such as high flexibility, scalability, reliability, efficiency, and low complexity, there is utmost need for a transition from the vendor-specific, hardware-based to the software-based network functionalities. Furthermore, when software-defined network functions are exploited, the underlining network will be able to meet the growing increase in on-demand services efficiently and cost-effectively. In this perspective, the architectural challenges and viable solutions like software-defined networking (SDN), network function virtualization (NFV), and SDN-enabled NFV solutions were discussed in [49]. The advantages of SDN in addressing the traditional space-based network architecture performance limitations were analyzed in [50]. Besides, in [51], a setup that combines SDN and NFV technologies was presented to address the realization of network slices. This was due to the observation that a specific SDN architecture lacks certain key capabilities that can be offered by the NFV. Furthermore, for effective fulfillment of the requirements, an orchestration system conceived to choose and assign virtual resources in distributed data centers (DCs) that are interconnected through multi-layer networks was presented in [52]. In the work, to support the ingress demands, orchestration algorithms were considered. This is an effort to satisfy different requirements regarding the bandwidth, computing, and end-to-end latency constraints. Likewise, a multi-objective technique to realize an optimized resource orchestration among cloud-based slices was presented in [53]. Moreover, in [54], a comprehensive survey on software-defined optical networks (SDONs) was presented. A major consideration was given to studies on network virtualization and orchestration of multilayer as well as multi-domain networking. Besides, optical performance monitoring frameworks and flexible SDN-controlled switching paradigms were investigated. Similarly, to optimally minimize the monitoring cost in the optical network, a traffic trail that employs traffic lightpaths rather than dedicated supervisory lightpaths (monitoring trail) was presented in [55] to localize a single link failure in an SDON. Furthermore, in SDONs, network services are offered based on virtual optical networks (VONs) that impose further constraints compared with the electrical domain virtual networks provisioning. In [56], a mapping-based VON provisioning technique for distance-adaptive flexible-grid optical networks was presented. Likewise, to maximize the spectrum utilization efficiency, the impact of flexible virtual nodes-to-physical-node mapping on network resource utilization was investigated.