Network Digital Twin is a use case for the Digital Twin application layer. Among the different Digital Twin use cases, it is an important use case in IOWN Global Forum for the automation and the efficiency of the management of IOWN-based network infrastructures. This document aims to provide Network Digital Twin technical requirements to ensure they will be fulfilled in the Digital Twin application layer. The requirements cover the following topics: Data models, Interfaces with IOWN infrastructure (APN-C, IDH, DCI), Interfaces for application developers (External APIs) and Data Security.