# Addressing ZSM Security Issues with Blockchain Technology
## 5 Criteria for the Selection of the Blockchain/DLT Platform to Build the ZSM-Tailored Solution  
The selection of the most suitable DLT solution for the development of a blockchain-based ZSM scenario should be based on specific criteria which should be clearly defined. The following section of this paper aims to present the characteristics that a DLT solution should present in order to satisfy the needs of the ZSM use case. Furthermore, we proceed to the identification of the most suitable blockchain and DAG solutions, and we analyze their main functionalities and characteristics. Then we evaluate their suitability for the particular use case and we propose modifications to fulfill the requirements of our scenario. The performance of the blockchain network directly affects the performance of the overall system which means that characteristics of the network such as latency and throughput affect the end user's QoE. Furthermore, other characteristics such as the accessibility of the network, the resiliency, the scalability and the network's ability to easily accept new features, are vital for the systems' successful operation and future growth. To this end, we define certain characteristics that a DLT solution should present in order to build a secure, scalable and high-performance environment ready to be integrated with the ZSM framework. The DLT solution integrated with the ZSM framework must be:  
* Access controlled: the access and the ability to perform actions in the network should be allowed only to permitted members and should be restricted to anyone else. * Scalable: the nodes of the network are hosted by the NPs only. Every provider who wishes to join the network should be able to easily deploy a node and become an active member of the solution. * Resilient: the proper functionality of the network should not be affected if a node or a number of nodes become unavailable for a period of time. The network should be resilient to network failures in order to present high availability which is one of the main requirements of NGNs. Figure 3: Lifecycle of a blockchain-enabled ZSM scenario. Very fast: the network should be able to perform multiple actions in a short period of time (in the unit of seconds or even milliseconds), to meet the dynamicity and resource management agility target by NGNs. Programmable: the DLT adopted in this particular use case should be able to support the development of code to implement the necessary functions which proliferate over time. Extensible: the DLT chosen for the implementation of this scenario should be able to accept new features that will upgrade its functionality and cover needs that may occur in the future. Interoperable: the DLT should be able to support interaction with services outside the network in order to successfully communicate with ZSM services. This characteristic increases the ability of the network to interact with the outside world and use services that may leverage the functionality of the whole solution. The above characteristics are translated in blockchain terms as follows:  
Permissioned network: only the permitted entities can access the network and perform actions in the form of transactions. This feature increases the security of the system since every entity is known to others, and therefore, it is less possible to act maliciously. It should be noted that the government entity does not control the operation of the network and its role is restricted only to the authorization of the NPs. Private/Consortium network: the network is supported by the NPs only, which means that the nodes of the network are created, managed and maintained by the participants. Although this feature seems to question the sentiment of decentralization in the network, it increases the security of the system since only the NPs are responsible for the proper operation of the network. In this particular use case, an NP who wishes to become an active member of the network should be able to easily deploy a node that will automatically become part of the network.