  The open radio access network (O-RAN), with its disaggregated and open
architecture, is poised to meet the demands of the next generation of wireless
communication. However, to unlock the full potentials of O-RAN, real-time
network modeling and optimization are essential. A promising solution for such
requirement is the use of network digital twin (NDT). NDT provides a
comprehensive view of a network, covering both physical and logical components,
including infrastructure, protocols, and algorithms. NDT, as a real-time
virtual representation of O-RAN facilitates a variety of operations, such as
emulations, test, optimization, monitoring, and analysis of a new configuration
in a risk-free environment, without requiring them to be implemented in real
network. Such capability enables the vendors and network operators for a faster
adoption of new solutions with frequent updates, while ensuring the resiliency
of the existing services via planning ahead under various "what-if" scenarios.
In this paper, we first describe what exactly NDT means in the context of
O-RAN, as well as its key enablers. We then describe the NDT application within
the O-RAN in both prior and post-deployment. Finally, we provide two practical
uses cases, namely network energy efficiency and traffic steering, where the
NDT can be leveraged effectively.
