# Blockchain Interoperability for Future Telecoms
### Problem Statement and Motivation  
Most research into blockchain use cases in future telecom technologies focuses on deploying a single blockchain and its interoperability with internal applications through decentralized applications (dApps). According to [PERSON] et al. [6], blockchain interoperability operates at three distinct levels:  
* A: among blockchain and other systems;
* B: among dApps on the same blockchain;
* C: among different blockchains. In Figure 1, the three levels of blockchain interoperability are illustrated according to the description of [PERSON] et al. [6]. Levels A and B are integral to research projects focused on existing and future telecom technologies. Studies such as [7] exemplify research projects that demonstrate interest in using blockchain in telecoms. In [7], the authors proposed dynamic spectrum allocation in 6G using a Level A oracle [8; 9], which they call an intermediary. Additionally, they covered a use case for the interoperability of Level B using dApps [10; 11] in the same research project. However, there is limited research and almost no studies on the interoperability of independent blockchains (Level C) operating across different telecom networks. This lack of research motivated this literature review to explore the Level C type of blockchain interoperability and its use cases in the context of telecommunications. With the introduction of 6G, a significant number of edge devices are anticipated to be deployed in mobile networks, which raises issues relating to security, privacy, and scalability. The deployment of multi-access edge computing (MEC) nodes allows for the processing of sensitive data at the network edge (e.g., federated learning), thereby increasing vulnerability to data tampering, DDoS attacks, Sybil attacks, and insider threats. Traditional centralized identity management systems are prone to single points of failure (SPoFs), data breaches, and identity spoofing in large-scale IoT and MEC deployments. Self-sovereign identity (SSI) deployed with blockchain allows devices, users, and network components to be authenticated using decentralized identity (DID) mechanisms stored on a blockchain, thereby preventing unauthorized access. Along with significant improvements in latency and reliability, 6G introduces AI-driven network optimization, seamless interconnection, and ubiquitous connectivity through the space-air-ground integrated network (SAGIN) concept. The novel features  
Figure 1: Three levels of blockchain interoperability in telecom. dApp, decentralized application. and their challenges can be effectively addressed by leveraging blockchain technology and its interoperability capabilities. The primary aim of this literature review is to emphasize the critical aspects of this research area and propose future directions, particularly for Level C-type interoperability use cases. Through the use of a blockchain interoperability architecture--particularly for Level C use cases--telecommunications providers can tackle the challenges of security, privacy, fragmented data, and interoperability issues with their external partners, including roaming, interconnection, and ecosystem partners. In current telecom practices, employing trusted third parties (TTPs) is a common method whenever data exchange between two or more telecom operators is required. On the other hand, TTPs are vulnerable to security issues, censorship, and privacy concerns. Blockchain technology can facilitate reliable peer-to-peer transactions without compromising security or privacy by removing the need for trusted intermediaries. Utilizing a blockchain interoperability architecture allows telecommunications providers to unlock new opportunities for securely and efficiently connecting and exchanging information between diverse networks and systems. Another emerging area of interoperability research is [12; 13], which is becoming a vital part of decentralized organizations and is increasingly recognized as an essential component of the Metaverse [14].