## 7 Final Thoughts, Propositions, and Prospects for the Future  
This review article first provides overviews of blockchain technology and the concept of Knowledge-Defined Networking. Blockchain, being a distributed, immutable, and transparent ledger, has been integrated with artificial intelligence in knowledge-based networks to improve diverse high-level networking functions such as network administration, traffic optimization, service provisioning, security and privacy, etc. These existing blockchain-based applications in knowledge-based networks were reviewed, and this survey proves that blockchain has been successfully applied in diverse network applications. Finally, we critically discussed the benefits and challenges of implementing blockchain systems in knowledge-based networks. This research adds a thorough analysis to the body of knowledge already available on the deployment of the blockchain system in Knowledge-Defined Networking. As we have identified generic and specific blockchain applications, it will be very helpful for future researchers to readily identify blockchain applications in KDN with reference to existing literature. This can open avenues for academicians to further investigate blockchain applications in new areas by obtaining insight into fields where blockchain has already been applied. Furthermore, researchers can formulate innovative ideas to overcome the challenges of applying blockchain to intelligent networks. The following propositions can be recommended when applying blockchain to Knowledge-Defined Networking:  
* In blockchain systems integrated with KDN, as the handling and processing of big data were identified as challenges, alternative techniques for improving the handling and processing of big data in blockchain are recommended. These include sharding [394], compression, fragmentation of data, parallel processing [4], and using off-chain storage of data while storing metadata in the blockchain for verification [397];
* Blockchain systems consume excess energy, causing an additional burden on knowledge-based networking systems. Therefore, it is recommended to use an energy-efficient consensus approach such as PoS [97], DPoS [107], PBFT [103], etc. ;
* As resource management is challenging in blockchain systems, it is recommended to use appropriate optimization [398] techniques to optimize resource management for efficient performance of tasks such as consensus;
* To promote interoperability between KDN systems that may utilize different blockchain frameworks, blockchain interoperability frameworks such as PIEChain [399], Interchain [400], etc. are recommended;
* It is advised to use a directed acyclic network to build blockchain with the aim of increasing its capacity for a growth-based approach having parallel processing capability [4]. Furthermore, lightweight and low-energy-consuming blockchain frameworks such as Sensor-Chain [393] can be utilized in KDN systems to improve scalability. Not only that, but off-chain storage [397] is also recommended to improve scalability;
* With the goal of reducing the extra latency imposed by blockchains, which makes the operation of the KDN system challenging, sharding and pruning [394] techniques are recommended;
* As conventional linear blockchains are well known for low transaction throughput, if such blockchains are employed in a KDN, it can limit the performance of the KDN system. Therefore, to obtain maximum performance from the KDN, high-throughput blockchain frameworks such as Conflux [396], which are based on the DAG blockchain, are recommended;
* To overcome the known security vulnerabilities of blockchain, different techniques can be recommended. First, in order to mitigate security attacks such as DDoS attack detection, ML algorithms can be utilized [401].