## 2 Existing Routing Methods for the DTN
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Routing** & **Item** & \begin{tabular}{c} **Restriction on the Number of Copies** \\ **Sending Node** \\ \end{tabular} & **Relay Node** & **Role Division** & \begin{tabular}{c} **Special Information** \\ **Used for Routing** \\ \end{tabular} \\ \hline Epidemic routing & None & None & None & None \\ \hline Spray and wait routing & Restricted (\({}^{\text{(1)}}\)) & Restricted (\({}^{\text{(1)}}\)) & None & None \\ \hline Location-based routing & None & - (\({}^{\text{(2)}}\)) & None & Location information \\ \hline Motion vector routing (MoVe) & None & - (\({}^{\text{(2)}}\)) & None & \
\begin{tabular}{c} Moving speed, \\ moving direction \\ \end{tabular} \\ \hline Message ferry routing & Restricted (\({}^{\text{(1)}}\)) & - (\({}^{\text{(2)}}\)) &
\begin{tabular}{c} Yes (dedicated relay \\ node is defined) \\ \end{tabular} & None \\ \hline \hline \end{tabular} \({}^{\text{(1)}}\) The upper limit to the number of copies is determined at the time of network design based on the required characteristics. (\({}^{\text{(2)}}\)) Message copies are not retained; they are discarded after having been relayed.  
\end{table} 
Table 1: Characteristics of the existing routing methods. Figure 1: Classification of existing and proposed delay/disruption tolerant networking (DTN) routing methods. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Routing** & **Item** & \begin{tabular}{c} **Arrival Rate** \\ \end{tabular} & \
\begin{tabular}{c} **Network load factors** \\ **Number of Copies** \\ \end{tabular} &
\begin{tabular}{c} **Required Buffer Size** \\ \end{tabular} \\ \hline Epidemic routing & High & Large & Large & Large \\ Spray and wait routing & Medium (\({}^{\text{(1)}}\)) & Medium (\({}^{\text{(1)}}\)) & Medium (\({}^{\text{(1)}}\)) & Medium (\({}^{\text{(1)}}\)) \\ Location-based routing & Low & Small & Large & Small \\ Motion vector routing (MoVe) & Low & Small & Large & Small (\({}^{\text{(2)}}\)) & Small (\({}^{\text{(2)}}\)) \\ Message ferry routing & High (\({}^{\text{(2)}}\)) & Small (\({}^{\text{(2)}}\)) & Small (\({}^{\text{(2)}}\)) & Small (\({}^{\text{(2)}}\)) \\ \hline \hline \end{tabular} \({}^{\text{(1)}}\) This depends on the upper limit that is set for the number of copies. It is difficult to determine the number of copies that is sufficient to enable the network to achieve the required performance. (\({}^{\text{(2)}}\)) This assumes an ideal situation that the traveling node can visit all of the clusters.  
\end{table} 
Table 2: Comparison of the existing routing methods in terms of network characteristics. Routing Based on Information about the Routes of Traveling Nodes and the Concept of the Destination Node  
This paper proposes a routing that is based on information about the routes of traveling nodes and the concept of \"destination area\". This routing is hereinafter referred to as \"traveling route information-based routing\". As shown in Figure 2, this routing uses three types of node: mobile terminals, traveling nodes and storage points. Mobile terminals are terminals owned by pedestrians. Traveling nodes are buses or trains that travel on fixed routes and are equipped with capabilities to store, transport and relay data. The idea is to use public transportation vehicles as dedicated relay nodes, thereby removing routing restrictions imposed by the message ferry routing, which requires dedicated relay nodes to visit all of the clusters. Storage points are fixed devices located at places where multiple traveling nodes come and stop temporarily. They relay a bundle from one relay node to another. Traveling nodes and storage points are together referred to as \"relay nodes\". Receiving nodes are mobile terminals. A destination area, which is identified by its location information, contains a cluster of receiving nodes. Within a destination area, bundles are relayed by receiving nodes using epidemic routing.