## 5 IoT Systems in the Post-Disaster Stage
### Communication Technologies and Protocols  
Normal communication technologies and protocols are also suitable for communication in the post-disaster stage, such as Wi-Fi [38; 80; 93; 98], Bluetooth [98], Internet [98], MQTT [47; 80; 92; 100], LoRa/LoraWAN [92], WPAN [93], 3G/4G [80], and COAP [100]. However, disasters may destroy the infrastructure in the cities [94]. We may address this issue by maintaining the efficiency of existing communication infrastructure and using additional mobile communication tools. To maintain communication efficiency in the face of a reduced number of communication facilities, we should develop resilient communication networks and reduce contention during data communication. [PERSON] et al. [101] suggested using the Bluetooth Mesh emergency network to utilize the remaining sensors to mediate device-to-device communication in the post-disaster stage. Regarding energy-constrained IoT sensors, [PERSON] [102] suggested using the Cognitive Energy-Efficient Algorithm (CEEA). The CEEA was a topology-independent protocol that can handle randomness in IoT networks. The CEEA determined the path from routing nodes to sensors based on the remaining energy of each node. To be specific, the CEEA would control the remaining energy of neighbors of recent routing nodes each time before sending data from the recent routing nodes. If the energy of one of the neighboring routing nodes was less than half of its initial value, the CEEA might determine a new path to transmit the data. If the residual energy of all neighboring routing nodes are found to be below 50% of the beginning energy, the CEEA uses the same strategy. However, it was noted that multitier IoT networks and cluster- or tier-wide synchronization were the two assumptions for the effective use of the CEEA. [PERSON] and [PERSON] [77] introduced a multi-path resilient routing system based on software-defined networking (SDN), which combined aided-multipath routing with the capabilities of SDN. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [100] developed a multi-domain Asynchronous Gateway of Things to enable discovery across different communication protocols and administrative domains in post-disaster relief. In addition, epidemic protocols can solve the contention caused by the reduced numbers of communication infrastructure in the post-disaster stage. [PERSON] et al. [103] proposed an adaptive probabilistic epidemic protocol that can effectively suppresses redundant messages and reduces contention/collision levels. This protocol allowed a node to decide whether to respond to a broadcast based on information such as the number of neighbors of the broadcasting node. [PERSON] and [PERSON] [15] suggested using epidemic routing algorithms and spray and wait routing algorithms to support the dissemination of shared information among personal devices. In addition, we can use additional mobile communication tools in post-disaster relief, such as drones [90; 94; 103] and vehicles participating in relief [10; 22]. [PERSON] et al. [22] proposed an opportunistic data dissemination protocol. They proposed facilitating the transmission of information from victims to rescue agencies by using the existing vehicles, including ambulances, police cars, and fire trucks, as well as the sensors inside the network. We can store the data from drones in the cloud [90]. The vehicles participating in relief include dynamic vehicles (e.g., fire trucks, ambulances) and stationary vehicles [15]. Dynamic vehicles aim to transmit data from sensors to stationary vehicles, while stationary vehicles (e.g., the base vehicles) focus on the transmission between different teams or companies in post-disaster relief [15]. Further, [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [92] suggested using the base vehicle as a central server that utilizes Wi-Fi to receive data from sensors deployed on mobile unmanned vehicles and in cities.