# Leveraging Blockchain Technology for Secure 5G Offloading Processes +
## 2 State-of-the-Art  
Offloading refers to transferring data from cellular networks to alternative networks to reduce congestion and improve user experience. These alternative networks refer to other technologies, usually Wi-Fi [16], but they could also refer to other existing cellular networks which are not so congested at a given time [9]. In this way, the amount of data transmitted over cellular networks is reduced, thereby freeing up capacity for other users. It is also employed in situations where the coverage is insufficient, enabling users to connect to more reliable services. The implementation of 5G technology relies on Software-Defined Networking (SDN) and Network Functions Virtualization (NFV), which provide network virtualization and automation [17; 18]. On the one hand, SDN enables centralized and programmable management of network traffic, facilitating decision making on how and when to divert traffic from the cellular network to other networks, thus reducing the load on the core cellular network. With SDN, it is also possible to implement advanced load balancing algorithms that distribute traffic evenly among available resources, avoiding overloads and improving the quality of service. On the other hand, NFV enables the virtualization of network functions that traditionally ran on dedicated hardware, increasing flexibility and efficiency as required by the offloading processes. Therefore, the use of these two technologies allows for the implementation of dynamic policies that divide data in real-time sending a part to other available networks based on the current state of the network. In this sense, resources available in the network must be managed and the load must be balanced. There are already several studies in the literature discussing data offloading solutions in 5G [19]. Some of them are related to user-initiated offloading techniques in which the user equipment automatically switches from the cellular network to another one, such as Wi-Fi, without having a lot of knowledge of the state of the network. This switching is done without the user noticing, thus improving the connectivity experience [20; 21]. However, thanks to the use of SDN and NFV in 5G, it is the network itself that orchestrates the offloading process so as to reduce network congestion or improve the quality of the coverage [22; 23]. In this case, the state of the network is known and the decisions are better taken. In both cases, it is necessary to know the available resources at each moment in order to manage the offloading process in a suitable way. In this sense, there are already some proposals in the literature of marketplaces for bandwidth trading [24; 25]. Marketplaces can be implemented through centralized databases, which offer high transaction speed and efficiency but are less secure and transparent than decentralized solutions [26]. Decentralized databases are similar to centralized ones, but data are distributed among several nodes, improving redundancy and availability as well as complexity to manage. However, other options such as Blockchain-based marketplaces [27; 28] have started to be considered as they address some of the main disadvantages of marketplaces based on databases. In addition, during an offloading process, private data are transferred between different networks. Although different cryptographic techniques have already been analyzed in the literature [29], it is still essential to ensure that only authorized devices and users can access these networks to protect data integrity and privacy as well as the security of the network by preventing malicious actors from introducing malware or conducting cyberattacks. Authentication ensures that only legitimate devices can connect to the alternative network, preventing unauthorized access that could compromize the security of the network and the data transferred.