# [UOM - Free5 gc]
### Digital Maps: Preparing the Way towards an NDT-Ready Architecture  
In order to tackle specific problems in the NDT scenario without requiring planning, designing, and implementing a complete NDT system from scratch, which would be very costly and time-consuming, the research community has begun to consider the possibility of building NDTs in a modular fashion. In this context, we propose to adopt the term Digital Map (emerged in recent IETF discussions) to describe a DMap as a subset of an NDT that focuses on a single specific dimension of the NDT functionality exposing its services through an API that other DMaps can easily consume to interact with it. The scope of application of a DMap is purposedly limited in nature; hence, it targets a narrow set of tasks, such as fault test simulation or energy optimization of the real network. The bidirectional flow of information between the virtual network and the physical system, formatted in JSON or another similar data exchange format, can synchronize the state of both networks. In this way, DMap can be incrementally developed, and the interconnection of several DMaps can lead to a complete NDT system. In our proposal for a DMap-based NDT solution, which is illustrated in Figure 6, the following elements can be identified: (1) the physical network, (2) the Digital Twins (DTs) of the physical components of the network, (3) the NDT that represents the interconnection of DTs and comprises the virtualization of the network, the data flows between DTs and the DTs that conform it, and (4) several Digital Maps (DMap) that represent a set of functionalities build upon one or more DT, thus serving as a concrete view or dimension of the NDT. The rationale behind the Digital Map concept, which we propose as a novelty, is justified on the need to build a complete NDT in a modular manner and thus avoid the cost of planning, designing, and implementing a complete NDT system from scratch. In this way, DMaps considerably reduces the complexity of building a fully featured NDT system that completely replicates the physical system. In particular, we propose a minimal NDT architecture that allows the connection of new DMap modules to an existing network to incrementally build an NDT system. The minimal architecture consists of an NDT connector, which is responsible for the communication between the NDT and the physical network, and an NDT orchestrator, which is responsible for managing and coordinating the orchestration of the different network elements that compose the NDT. In particular, the NDT connector serves as a bridge that enables data exchange between the virtual and physical networks. In this way, the data flow between the network components of the physical system and the corresponding replicas of these components (DTs) in the NDT are constantly synchronized. On the other hand, the NDT orchestrator will be responsible for replicating and provisioning the required network configuration of the physical system (network elements, interconnections, traffic routing, etc.). Based on this minimal NDT architecture, new DMaps can be developed and included in the NDT at any time to enrich it with new functionalities. It should be noted that multiple DMaps can share some of the underlaying components that conform the minimal NDT architecture (e.g., a subset of replicated network elements, the NDT connector, and the NDT orchestrator). In addition, the deployment of a DMap-based NDT allows for selectively limiting the scope and visibility of the network according to the operator needs. Thus, a DMap can be deployed to cover a specific set of network components, or a specific range of IP addresses based on the specific service provider requirements. In contrast, a monolithic approach to  
Figure 6: Diagram architecture of the DMap-based NDT. the development of a DMap does not allow such flexibility and the NDT will always have full network visibility in all situations.