## 3 System Architecture  
### General System Architecture  
As discussed in the previous paragraphs, the scope of this research work is focused on the design and development of a real-time, remote maintenance assistance framework based on AR by enabling the creation of new communication channels between the expert engineers and the shop-floor technicians. Concretely, there is an opportunity to eliminate the need for preparing AR scenes, which considerably decreases the time and effort needed for creating such content. Moreover, certain limitations can be overcome as expert engineers, through the use of the proposed framework, are able to guide shop-floor technicians in less likely MRO scenarios. In order to meet the above-mentioned technical requirements, the methodology adopted by aiming at addressing the identified scientific gaps will be presented in detail in the following paragraphs. The general architecture flowchart is depicted in Figure 1.  
Figure 1: Flowchart of the proposed system. The sequence of actions begins as long as a malfunctioning machine tool has been noticed. Then, the shop-floor technician who is carrying a device, a Head Mounted Display (HMD), contacts the expert engineer for assistance. It is stressed out that the coexistence of the two involved parties under the same premises is not required. More specifically, through the use of dedicated communication protocols, the shop-floor technicians can be remotely connected to the technical support department of the machine tool manufacturer. As long as the connection between the two parties has been established, a live video stream from the shop-floor technicians' device is broadcast to the expert engineer. This process can be realized as a live teleconference between the two parties. Therefore, while the video stream is broadcast to the expert engineer, the shop-floor technician is capable of making annotations so as to ease the engineer to get a better understanding of the machine tool malfunction. As soon as the engineer is fully aware of the malfunction, they can create on-demand AR content, which will be projected in the shop-floor technician's FOV (Field Of View). It is stressed out that, during the live-video casting from the technician, the device is also capable to 3D scan the space around the technician. As such, the algorithm running in the background is fully aware of the user's surroundings. Therefore, the expert engineer can register 3D content in the technician's FOV more easily and more successfully. The framework architecture can be realized through a platform, where the shop-floor technicians can connect and request assistance from expert engineers in real-time. From the expert engineer point-of-view, the platform serves as a tool enabling the expert to guide the shop-floor technician with the use of simple 3D tools. Therefore, it is of great importance to initially present the platform architecture. In Figure 2, the architecture of the proposed framework is depicted. From the figure, the structure of the Cloud Platform is visible and consists of services and the toolbox. The most important component of the platform architecture is the online connection and user interconnection framework. More specifically, the platform acts as a cloud platform, where users, either expert engineers or field/shop-floor technicians, can connect to and, most importantly, they can exchange digital information. It is stressed out that there are no limitations in the type and volume of the exchanged information. Additionally, the user experience can be further improved by the support of live teleconference of the involved actors. In order to enhance the communication experience between the involved parties, the framework supports a teleconference feature. When this feature is enabled, then the user is capable of having a live video feed from the expert engineer, projected in his FoV. As such, it is expected that the communication between the two parties is facilitated, as the technician can perform MRO simultaneously.