## 3 Network Structure and Link Characterization
### Link Characterization  
It is difficult to gather and utilize the real-time information in emergency situations without DAWNs. In this context, a predeployed network infrastructure may be completely destroyed. People both in and out of disaster areas need a rapidly deployable replacement network to communicate with each other. Intermittent connectivity, abrupt changes in network topology, and a low reception rate are the most important properties that distinguish DAWN from other types of self-organized networks. In order to meet the requirements of DAWN's frequently changing topology, appropriate routing protocols should be considered. They become more significant in the emergency-affected network due to the time-critical nature of the service and information requirements. The nodes in DAWNs are limited in radio coverage and communicational ability because of limitations of power supply, thus influencing the lifetime of the whole DAWNs. It is essential to calculate the residual energy of each node in DAWNs so as to balance the energy consumption. When one node is sending or receiving messages, it may be connected to its neighbors as an intermediate forwarding node. The more nodes that are connected, the higher possibility of congestion in the link. In order to improve the performance of DAWNs, we should choose a next-hop node that is connected by less neighbors. A low hop count means low latency from source to destination, so we usually choose next-hop node with the lowest hop counts to deliver data. Each node in a DAWN is equipped with Global Position System (GPS) for localization, so the distance between nodes can be calculated. Generally speaking, a node near a destination is chosen as next-hop, since it may connect to the destination through the lowest hop counts. We take three different kinds of disasters--earthquake, fire, and typhoon--as examples to elaborate the universality of the four selected criteria: energy consumed (EC), number of connected nodes (CN), hop counts to ECVs (HC), and distance to the nearest ECVs (DIS). We assume that predeployed network infrastructures are totally destroyed during the three disasters, so rapidly deployed DAWNs are helping affected people communicate with each other. EC determines the lifetime of DAWNs, regardless of hazard types. The more energy consumed, the shorter DAWNs last. In strong earthquakes, the victims may be buried in the ruins, waiting for rescue. It takes hours or more to complete the rescue mission before predeployed network communication recovery, so low-energy consumption nodes are essential for first responders. However, situations are contrary in a fire disaster. Firemen need to implement rapid rescue before trapped people get burned, so the lifetime of DAWNs may be not as essential as other criteria. As for CN, the more nodes that are connected, the higher possibility of congestion in the link. In order to improve the performance of DAWNs, we should choose the next-hop node, which is connected by less neighbors, regardless of hazard type. A low hop count means low latency from source to destination, so we usually choose the next-hop node with the lowest hop counts to deliver data, no matter the kind of disaster. As for DIS, each node in DAWNs is equipped with GPS for localization, so the distance between nodes can be calculated. Generally speaking, a node that is near the destination is chosen as next-hop, since it may connect to the destination through the lowest hop counts. In earthquakes or typhoons, ECVs cannot enter the epicenter because roads are blocked, so they cannot provide communication \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Destination**} & \multirow{2}{*}{**Hop**} & \multicolumn{2}{c}{**Energy**} & **Connected** & **Hop Counts to** & **Distance to the** \\  & & **Consumed (EC)** & **Nodes (CN)** & **ECVs (HC)** & **Nearest ECVs (DIS)** \\ \hline B & 1 & 30\% & 3 & 2 & 100 \\ C & 2 & 60\% & 5 & 1 & 40 \\ ⋮ & ⋮ & ⋮ & ⋮ & ⋮ & ⋮ \\ X & 1 & 40\% & 4 & 3 & 80 \\ \hline \hline \end{tabular}
\end{table}