# An Efficient Routing Protocol with Overload Control for Group Mobility in Delay-Tolerant Networking
###### Abstract  
In delay-tolerant networking (DTN), messages are delivered to destination nodes by using opportunistic contacts between contact nodes, even if stable routing paths from source nodes to destination nodes do not exist. In some DTN network environments, such as military networks, nodes movement follows a group movement model, and an efficient DTN routing protocol is required to use the characteristics of group mobility. In this paper, we consider a network environment, where both intra- and intergroup routing are carried out by using DTN protocols. Then, we propose an efficient routing protocol with overload control for group mobility, where delivery predictability for group mobility is defined and proactive overload control is applied. Performance evaluation results show that the proposed protocol had better delivery ratios and overhead ratios than compared protocols, although the delivery latency was increased. delay tolerant network; routing protocol; group mobility; overload control +
Footnote †: journal:  
0000-0002-111-1111  
generated message. When a message is generated at a source node originally, it forwards \(L-1\) copies of messages to \(L-1\) contact nodes in the Spray phase until \(L\) nodes including the source node has exactly one copy of the message. In the Wait phase, the message is forwarded to a destination node only. Although the Spray and Wait routing protocol can alleviate the high overload problem of an Epidemic protocol, it is a blinded forwarding protocol basically, since messages are forwarded to \(L-1\) contact nodes blindly without any efficient forwarding criteria. In a PRoPHET protocol [8], delivery predictability (DP) between any two nodes is calculated based on the contact history between nodes. If the delivery predictability between two nodes is higher, it is more probable to deliver messages between them. Therefore, if two nodes contact, they compare delivery predictability for the destination nodes of stored messages, and a message is forwarded to a contact node if a contact node has a higher delivery predictability to a destination node for the considered message. The PRoPHET protocol was standardized as an Internet Research Task Force (IRTF) request for comments (RFC) [8] by the DTN research group [9]. In [10], the authors define quality of node, which is a weighted sum of message handling capacity and the improved delivery predictability. Then, they proposed an adaptive Spray and Wait routing protocol based on quality node by adaptively allocating the number of message copies based on the quality of the node in the Spray phase. In the Wait phase, a message is forwarded only if the contact node has a higher improved delivery predictability. In [11], the authors proposed a vehicular DTN routing protocol, where the message forwarding decision is based on the encounter probability comparison in the PRoPHET protocol, and the number of message replications at forwarding is controlled based on the Spray and Wait protocol in the vehicular DTN networks. In some network environments, such as military networks, nodes movement follows a group mobility model [12; 13; 14]. A group consists of a number of member nodes, and they move together based on an assumed group mobility model. In [12], a reference point group mobility model (RPGM) was proposed. In an RPGM, there is a logical center in each group and the mobility of group members follows the movement of the logical center, which includes location, speed, direction, acceleration, etc. Group members are distributed uniformly within the geographic scope of a group. A reference point is assigned to each group member by following the group movement, and a group member is located in the neighborhood of its assigned reference point randomly at each movement. In [13], an RPGM was extended by considering the velocity of groups and group members, and it was called as a reference velocity group mobility model (RVGM).