# Blockchain Interoperability for Future Telecoms
## 3 Literature Review
### Comparison of Interoperability Projects  
This review covered design issues and an analysis of well-known projects. As a result, an ideal telecom solution was proposed. This solution and approach can serve as a foundation for ensuring the interoperability of existing and future telecom projects. As previously demonstrated, permissioned blockchains include must-have features for future telecom and 6G deployment. Therefore, permissioned blockchains are a critical requirement in telecom use cases. In [70], the proposed initial design principles were presented with respect to supporting research papers, and details of these projects and design approaches were provided. If required, the readers of this paper can view the design architectures in [71], in which six design principles were covered: decentralization, homogeneous networks, smart contracts, wide range of contributors, SPoF, and side-by-side architecture. Here, these design principles are combined with the additional topics covered in this review, such as access management, the safety of policies, and core blockchain process isolation. Furthermore, in [71], heterogeneous blockchain interoperation was considered crucial for the enterprise processes formed by blockchain frameworks and telecom use cases. This review's results established eight distinct comparison categories for an ideal blockchain interoperability solution, offering a forward-looking approach to the final design. These categories are defined as follows:  
* Interoperability Type: Interoperability in blockchain solutions is characterized by various types, such as permissioned, permissionless, or hybrid. Each type of blockchain has its own feature set, which affects its security and access policies. These features are crucial in ensuring private blockchain interoperability in the telecom industry. The hybrid type involves a combination of private and public blockchains within a solution. * Decentralization: Existing project designs include intermediaries, notaries, and side-by-side modules that facilitate interactions between blockchains. However, these patterns are sometimes decentralized. In the telecommunications field, intermediaries causing centralization should be removed. * Multi-Network Support: Many solutions are tailored to connect two blockchains. Assessing whether a solution is scalable for future research and enterprise endeavors--such as multi-network integration--is crucial. These solutions should facilitate the interoperability of three or more blockchains, which is becoming increasingly important with the emergence of 6G technology. * Chain Isolation: Isolating the mainchain provides a strict access policy and minimizes external effects. Most solutions offer direct access to a relay or an intermediary. This approach renders the solution vulnerable to attackers, particularly in the case of regulated telecoms. A thin interoperability layer with multiple layers has a minimal effect on the operation of the mainchain. It protects the solution from external attacks and provides high-level user privacy and security. * Sovereignty: Numerous solutions presented in existing research projects provide integrated and synchronized access policies between interconnected blockchains. However, synchronizing access policies can create security vulnerabilities that hackers can exploit. The mainchain is expected to remain autonomous and enforce restricted minimal access policies for interoperability solutions without unifying the access policy with interconnected chains. This approach aims to safeguard user privacy and establish self-sovereignty in telecommunication. * Storage Efficiency: In a traditional independent blockchain network, the mainchain is expected to be the central storage for status updates in DLTs. For interoperated blockchains, especially in the 6G context, the storage requirement is expected to be much higher due to the additional storage required for interoperability. According to [PERSON] et al.