## 2 What Is IoNT?
### Architecture of IoNT
Owing to the portability of such IoNT-based healthcare solutions, the connection to the Internet is always provided through the data connection of mobile devices. In general, in the healthcare context, medical nanodevices can be deployed inside the human body or external environment and can also be used as wearable garments [11]. Depending on the deployed location, IoNT-enabled medical systems can be apportioned into three types: off-body systems (deployed anywhere based on the user preferences, such as in the home, vehicle, etc. ), on-body systems (deployed on the person's body), and intrabody systems (deployed inside the human body). Even though deployed location can vary, the architecture of a IoNT solution is always the same for all contexts [11]. Irrespective of the context wherein the IoNT solution is employed, the network architecture of a typical IoNT solution can be categorized into four layers, as shown in Figure 3.  
Figure 1: The IoNT network architecture for a smart home. Figure 2: The IoNT network architecture of intrabody network in healthcare. According to the generic network architecture of a typical IoNT solution as depicted in Figure 3, the topmost layer comprises the application layer, which interacts mainly with the end user. The transport layer is responsible for the transmission of data back and forth between the application and the network layer. The network layer holds the responsibility for establishing nano-communication between nanodevices and the transport layer. The physical layer ensures guaranteed information delivery to the destination. Since the transmission range for nanodevices is limited, a thick arrangement of nanodevices is required at the physical layer [7; 11]. As depicted in Figures 1 and 2, to keep the connection alive and provide necessary services, the following described components in the network architecture hold greater responsibility:  
* Nano-nodes  
Nano-nodes are the smallest and most basic type of nanomachine; they are capable of performing very basic processing, storing a small amount of data in memory, and transmitting data over extremely short distances due to their low power and bandwidth [1; 7]. Examples of nano-nodes include biological nanosensor nodes within the human body and nanomachines with communication capabilities integrated into a wide variety of objects in a smart home [1; 17];
* Nano-routers  
Nano-routers have comparatively larger computational resources than nano-nodes and are suitable for aggregating information coming from limited nanomachines [4]. Their functionality is very similar to that of the typical router in a computer network. In addition, nano-routers can also control the behavior of nano-nodes by exchanging very simple control commands (e.g., changing the on/off state). However, this increase in capabilities involves an increase in their size, and this makes their deployment more invasive;  
* Nano-micro-interface devices  
Interface devices aggregate information coming from nano-routers to convey it at the microscale and vice versa. On the other hand, these nano-micro interfaces act as hybrid devices and can communicate on the nanoscale using the aforementioned nano-communication techniques and use classical communication paradigms in conventional communication networks [1; 4; 5; 6; 7]. * Gateway  
The gateway device enables the remote control of the entire IoNT system over the Internet. For example, as shown in Figure 2, in an intrabody network, a smart mobile device can forward the information it receives from a nano-micro interface to the healthcare provider over the Internet [1; 4; 5; 6; 7; 15; 16; 17; 18; 19]. In addition, for IoNT networks to be completely operational, there has to be good integration and communication between nanodevices and macroscale components. Because of this, the construction of network topologies incorporating several communication paradigms, such as electromagnetic, acoustic, mechanical, and molecular communication,  
Figure 3: Layered network architecture of a generic IoNT solution.