ronments by predicting the routing paths. Furthermore, it presented and compared different routing pro- tocols such as SDN-enabled connectivity-aware geographic-aware routing protocol (SCGRP). In [128], SDN-based multi-hop device-to-device (D2D) routing protocol has been proposed that offers high scalability and reduces the energy consumption for mobile nodes. Minimizing the energy consumption has been discussed in [129] by proposing an energy-efficient and secured routing protocol for software-defined Internet of vehicles. Meanwhile, Anjum et al. [130] proposed a real-time multipath transmission protocol to improve the best path selection in data center networks. On the other hand, secure and efficient topology discovery protocol (sOFTDP) has been proposed in [132] that offers a high level of security and reduces the topology discovery time in several orders of magnitude compared to the OFDP. Several discovery algorithms have been addressed in [133] such as fuzzy topology discovery protocol (FTDP) that improves the efficiency of software-defined wireless sensor network (SDWN). 1.4.2 Network Functions Virtualization (NFV) The NFV standardization has been launched in 2012 by ETSI and ISG. It has been initiated by seven leading telecom network operators and became the most relevant standard for NFV. The NFV and the SDN technology are the key enablers for network softwarization. The NFV facilitates decoupling the NFs from dedicated hardware by implementing the NFs as software components running on VMs [134]. NFV promises to optimize the network resources, offer portability and design flexibility, reduce the CAPEX/OPEX, and fulfill the fast-varying user service requirements [135, 136]. In cellular networks, the virtualization is not only limited to the infrastructure and computing resources, but it includes also the spectrum, air interface, and multiple radio access virtualization [3, 60]. In this context, 3GPP deployed a virtual-EPC (vEPC) [137]. Moreover, ETSI NFV ISG discussed a zero-touch network concept in order