# Practical Implementation of a Blockchain-Enabled SDN for Large-Scale Infrastructure Networks
## 2 Related Work  
This section addresses related research to blockchain, ISP networks, SDNs used in the WAN with blockchain enhancements and simulator utilization in the aforementioned domains. In recent years, blockchain technology has garnered substantial attention. In the following section, we highlight articles that discuss applications of blockchain, focusing on scenarios that are of particular relevance to the current research. The study presented in [2] proposes a system for cross-blockchain smart contract synchronization. The system creates a client contract on another blockchain that mirrors the logic and state of the original contract. The client contract is synchronized in a verifiable manner using Merkle proofs without the need for trusted intermediaries. The system also supports lightweight synchronization due to transition confirmations without the need for transaction re-execution. The system requires that the targeted blockchains support the same execution environment (i.e., Ethereum Virtual Machine-compatible blockchains). The study showcased in [3] proposes a solution that combines federated learning (FL), blockchain technology and multi-agent systems in order to obtain an architecture that enables the training of a neural network to solve a specific problem. The proposed solution is inspired by the smart contract concept and uses smart agents that have both the role of a peer in the blockchain network and the role of being a participant in the FL task. The study obtains a distributed solution that avoids being vulnerable to the information leakage attacks of the central server. The study in [4] researches the means of obtaining a solution that provides secure storage and access to the task-scheduling scheme on a consortium blockchain and interplanetary file system (IPFS). The study compares different versions of Hyperledger Fabric in order to evaluate their functionality and features. Also, they select a blockchain as a service provider that supports Hyperledger Fabric in order to use and validate the proposed solution. The study presented in [5] proposes a new consensus algorithm for a lightweight blockchain. This type of implementation targets distributed systems with resource constraints such as IoT architectures. This solution aims to introduce decentralization in these systems by using blockchain technology with minimal impact on the associated devices. Also, with the proposed solution, the blockchain becomes application-specific. Next, articles are presented that address ISPs' integration or ISP activity over network traffic. Paper [6] presents the ISPs' interactions and the types of ISPs. Inter-ISP communication is presented in regard to traffic control, and the need for new dynamic control protocols related to this is discussed. Inter-ISP cooperation techniques, such as caching and content-peering, are presented. In this context, the authors propose a cooperation scheme for inter-ISP traffic control that uses game theory (cooperative game). The interactions between ISPs are formulated as a two-step bargaining game model in which the steps contain the main issues: the service price and the limited bandwidth. The proposed cooperation scheme has the goal of reaching a consensus between ISP interactions while maintaining fairness for every participant. The study presented in [7] has a similar focus. The interactions between ISPs of identical and diverse tiers are explored, along with the interaction involving content providers. The study advocates for a solution that implies cache sharing between the different entities and also between different tier ISPs. Using aspects derived from game theory, a solution for optimizing pricing negotiations in collaborative settings, which takes into consideration QoS (Quality of Service) and OPEX (operational costs), is investigated and proposed. In [8], the effect of the zero-rating method is analyzed as a differential pricing scheme.