## 5 Architecture of an IoT-Based Solution  
Internet of Things infrastructures allow data and services integration among smart objects (e.g., mobile robots), sensing devices and human beings, using different but interoperable communication protocols [34]. Following this definition, Figure 6 shows the architecture proposed for systems that support first responders in medium-sized or large urban incidents. The architecture involves four layers that implement the separation of concerns: _sensing_, _communication_, _information persistence and application_ (_i.e._, usage). The _sensing layer_ is responsible for capturing information from the field, which will be then used to support the decision making and coordination activities. Two types of components contribute to performing this activity: _regular sensors_ (RS) and _human-based sensors_ (HBS). The first ones (e.g., weather and motion sensors, or video-camera) capture information from the environment and transmit it through a component of the communication layer. The HBS (typically firefighters, police officers or government personnel) perform the same activity; however these people use their senses (hearing, sight, touch, smell and taste) to capture additional information from the environment. Using such information, and eventually the data given by regular sensors, the HBS produce knowledge that represents the current value of a certain context variable (e.g., the emergency type or size). Although the HBS are not accurate, they represent our best choice when the observed variable is not measurable by a regular sensor. The HBS uses a mobile device that allows him/her to share that knowledge with others and also to sense context variables (see the sensing layer in Figure 6), e.g., the presence of other responders in the area by using an opportunistic network (oppnet). As explained before, it is assumed that every component participating in this solution has a network interface that allows it to communicate with others through a digital network interface. The _communication layer_ is responsible for providing interaction capability to components participating in the first response process. Because there is no universal network interface, this layer is  
Figure 6: Hierarchy of architectural components. implemented as a set of heterogeneous solutions, hopefully linked through communication bridges (Figure 7a). Typically two types of communication solutions are used in these scenarios: _infrastructure-based_ and _ad hoc_ networks. The first one uses the regular communication infrastructure (_i.e._, satellites, cellular towers and wired networks) and also mobile antennas (e.g., deployed in vehicles) to communicate the resources in the affected area, with remote components (e.g., emergency offices, data centers, remote experts, government agencies). We call these _communication units_ (CU); components that link resources within the affected area with those that are outside the emergency area (see Figure 6). Thus, these CUs allow the remote gathering and analysis of information (e.g., through Internet) that comes from sensors deployed in the emergency area (Figure 7b). The reliability of the links provided by these networks can be estimated at the design time; therefore, the capability of a HWSN to disseminate information can be determined before implementing it. The same occurs when ad hoc networks are used as communication support. The role of these networks is to provide and enhance the communication links in the field, increasing thus the information availability in that area and reducing the improvisation during the response process [4,14,15]. The use of opportunistic networks (_oppnet_) is highly recommended because they can work although the regular communication infrastructure is not available. An oppnet is a peer-to-peer application-oriented mesh, able to support ad hoc interactions among stationary and mobile units that are physically close; e.g., sensors, human-based sensors and communication units deployed in the affected area.