Relevance and description of the problem Roaming allows you to provide services to a subscriber outside the service area of ​​the "home" network using the resources of another network. At the same time, the subscriber doesn’t need to conclude a contract with the operator of a foreign network, and the fee for using the service is deducted from his account. An appropriate roaming agreement is concluded between the operators of the "home" and foreign networks. This Roaming Agreement covers the technical and commercial components that are necessary for providing the roaming service to the customer. In the development phase of the roaming agreement, the parties, i.e. the mobile network operators, go through a negotiation process that currently still uses tools such as e-mail or even regular mail to exchange information. This process is manual, slow and unreliable and leads to incorrect perception by the parties of information received from each other, so as unorganised and non-confidential storage of it. Incorrect understanding and unreliable storage of this information leads to the problem of non-transparent conclusion of the agreement, loss of confidential information and, as a result, financial losses for both parties. To solve the described problems, blockchain technologies are used and smart contracts are created on their basis. This makes it possible to conclude contracts in the form of a computer algorithm that is signed and stored on the basis of the blockchain with automated fulfilment of obligations under the agreement.

You can highlight the following elements that are worth paying attention to when researching smart contracts: ● Subject of the contract. This is an object that resides inside the environment of the smart contract itself. For example, cryptocurrencies. ● Digital signatures. The parties certify the contract with their own secret digital keys generated using a single technology. In Ukraine, the possibility of using an electronic signature is practised. ● Terms of the contract. They are laid out in the exact sequence of operations, that is, in the form of an algorithm, and agreed upon by the parties. The terms of the smart contract must be specific (clear, unambiguous), implemented (objective), valid. The terms of a smart contract can be formulated according to the formula "if …, then …". ● Decentralized platform. Recording, storage and enforcement of the smart contract takes place on a resource independent of the parties. But smart contracts also have their own characteristics. An understanding of programming is necessary to implement smart contracts. To create a reliable smart contract that reflects the needs of the company, you need to engage an experienced developer.

Blockchain and smart contracts in roaming Blockchain ensures transparent relations between mobile operators in the field of roaming. And the cryptographically protected and immutable joint register acts as a single source of up-to-date and reliable data for operators, allowing direct exchange of information. Authorization and settlement occurs through transactions performed on the basis of a consensus model and automatically implemented using smart contracts. Roaming agreements are encoded in smart contracts in the blockchain network. Smart contracts are computer programs that are deployed on the blockchain network and execute exactly as programmed, with no downtime. The activity of the subscriber in the roaming network is registered in the blockchain network with the help of transactions, and the contract between the home operator and the roaming operator is executed based on the roaming smart contract, instantly eliminating accusations and avoiding the involvement of third parties such as clearing houses.