# Blockchain Interoperability for Future Telecoms
## 3 Literature Review
### Interoperability Techniques
Consequently, the sidechain transfers the assets to the final chain. If this intermediary chain is responsible for the interoperability of two independent blockchains, the challenge lies in who owns the sidechain and how it is managed. Therefore, sidechains cannot act as a decentralized interoperability approach when deployed as intermediaries between interoperating blockchains. In the final solution, a sidechain can still be used if it is deployed as a side component of that chain and does not act as an intermediary. As previously discussed, the five schemes presented primarily concentrate on the interoperability between two blockchain networks. However, when the interoperability extends to encompass three or more blockchain systems, the complexity of the process significantly increases. This complexity is particularly relevant in scenarios such as end-to-end enterprise processes that traverse multiple blockchain environments. [PERSON] et al. called this scenario type a blockchain of blockchains (BoB) [46]. Figure 7 illustrates an international roaming use case where a decentralized, intermediary-free process is developed with blockchain interoperability. As seen on the left side of Figure 7, most telecom operators use clearing houses to facilitate the reconciliation of roaming records for their users in the visiting country. By implementing a direct interoperability architecture, clearing houses can be eliminated, as illustrated on the right side of Figure 7. This scenario can be viewed as a unified process between two or more operators. Once the blockchain networks are established for direct interoperation among multiple telecom operators, the process can be described as a BoB. Figure 7 illustrates how future telecoms can form interoperable processes with other telecom operators. Blockchain interoperability cases are also applicable to 6G. Figure 8 illustrates how different parties are integrated with the 3D 6G space for future telecom interoperation landscapes. Figure 9 illustrates the mobile number portability process for three mobile operators. Once the MNP provider shown in Figure 5 is eliminated and handled as a decentralized process with no intermediary, the blockchain layers form a process between the three mobile operators. For 5G and 6G networks, a decentralized MNP process can be established using interoperability layers. When a user triggers a porting request, the blockchain network sends the request to the target mobile subscriber. Suppose a user ports from Network 1 to Network 2, and their unique subscriber code (USC) is transferred to the target operator. Once the porting request is completed, asset exchange occurs from the blockchain perspective. Consequently, the new owner of the USC is shared with Operator 3. This is considered data sharing from a blockchain perspective, and an update is reflected in the blockchain's distributed ledger. Figure 8: Blockchain interoperability service architecture for 6G Mobile Networks. Figure 7: New international roaming process with blockchain interoperability. BC, blockchain. In 6G, more enhanced interoperability use cases can be deployed for network slicing and spectrum sharing. Unlike the use cases presented in the literature that rely on a single blockchain or intermediary, a blockchain interoperability architecture can be established for each service provider. This allows for much faster deployment of network slices by external service providers. As shown in Figure 10, the intermediary is replaced by standalone blockchains for each service provider, as illustrated in Figure 10.  
The architecture in Figure 10 employs an O-RAN architecture, providing a flexible virtual resource allocation environment that permits the dynamic use of the available spectrum in constructing dedicated network slices requested by external parties. Utilizing smart contracts, spectrum allocation and network slicing rules can be established and executed in real time for each external service provider.