## 3 ATON Framework
### Deployment Node  
We first define the _Deployment Node_ (DN) as the virtual or physical machine where one instance of the ATON framework is deployed. Thanks to Node.js portability and network scalability, a wide range of hardware solutions can be employed as DN (see Figure 3, top). These range from low-cost single board computers (like a Raspberry Pi ([[https://www.raspberrypi.org/](https://www.raspberrypi.org/)]([https://www.raspberrypi.org/](https://www.raspberrypi.org/)), accessed on 22 November 2021)), up to laptops/PCs in local networks (e.g., classrooms), up to small servers or large infrastructures available over internet connection, with world-wide reachability. Depending on requirements and specific demands, this also allows the entire framework to be deployed on all existing cloud services that support Node.js like Google Cloud ([[https://cloud.google.com/](https://cloud.google.com/)]([https://cloud.google.com/](https://cloud.google.com/)), accessed on 22 November 2021), Amazon Web Services (AWS) ([[https://aws.amazon.com/](https://aws.amazon.com/)]([https://aws.amazon.com/](https://aws.amazon.com/)), accessed on 22 November 2021), Heroku ([[https://www.heroku.com/](https://www.heroku.com/)]([https://www.heroku.com/](https://www.heroku.com/)), accessed on 22 November 2021) and many more.  
The default setup consists of a DN delivering content (e.g., 3D models) and web-applications to remote consumers (users) using a multitude of different devices, through local or internet network connection. There are also scenarios where a DN is used also as presentation device (e.g., museums kiosks) thus deploying and consuming the web-app on the same hardware (see Figure 3A), without any local network or internet connection required from the institution side. There are different services operating on a DN when the framework is up and running. They are designed to scale automatically with the DN hardware, adopting--where available--clustering and load balancing capabilities are used to improve the performance of the network.  
Figure 3: Deployment hardware (**top**) and (**A–C**) three different deployment scenarios (**bottom**).  
Figure 2: Overview of the ATON Framework architecture.  
offered by process managers like PM2 [51]. Such services have different roles and tasks including content streaming, user authentication, collaborative sessions (discussed in the next sections), and much more. Since a _microservice_ model is adopted, they can be easily configured or independently disabled to fulfill a wide range of requirement scenarios (see Figure 3, bottom). A documented REST API ([[https://aton.ispc.cnr.it/apidoc/server/](https://aton.ispc.cnr.it/apidoc/server/)]([https://aton.ispc.cnr.it/apidoc/server/](https://aton.ispc.cnr.it/apidoc/server/)), accessed on 22 November 2021) allows local (or external) web-apps to perform different operations on the current DN: this is also specifically designed to facilitate integration and communication with external CH tools or services within federated infrastructures or projects. Describing in detail each service is out of scope for the paper, thus for more technical details we suggest official documentation.