# An Efficient Routing Protocol with Overload Control for Group Mobility in Delay-Tolerant Networking
## 3 A Proposed Routing Protocol with Overload Control for Group Mobility
Then, this delivery information is shared with future contact nodes, and the already delivered message is removed from the buffer of the contact nodes in order to reduce unnecessary forwarding of already delivered \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Case**} & **Group of** & **Group of** & **Group of** & **Forwarding Condition** \\  & **Node**\(\mathbf{x}\) & **Node**\(\mathbf{y}\) & **Node**\(\mathbf{z}\) & \\ \hline
1 & \(A\) & \(A\) & \(A\) & \(P(y,z)>P(x,z)\) \\
2 & \(A\) & \(A\) & \(B\) & \(P(y,z)>P(x,z)\) AND \(P_{g}(y,\mathbf{G}_{B})>P_{g}(x,\mathbf{G}_{B})\) \\
3 & \(A\) & \(B\) & \(B\) & \(P(y,z)>T_{p}\) OR \(P_{g}(y,\mathbf{G}_{B})>T_{p}\) \\
4 & \(A\) & \(B\) & \(A\) & \(P(y,z)>T_{r}\) AND \(P_{g}(y,\mathbf{G}_{A})>T_{r}\) \\
5 & \(A\) & \(B\) & \(C\) & \(P(y,z)>P(x,z)\) AND \(P_{g}(y,\mathbf{G}_{C})>P_{g}(x,\mathbf{G}_{C})\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Forwarding conditions of the proposed protocol. messages, which is similar to the vaccine scheme [24]. This protocol is called reactive overload control (OC) in this paper. The concept of reducing unnecessary forwarding of already delivered messages to a destination node in reactive overload control is similar to the work in our previous work [25], where the concept of the anti-packet [24] was also applied for multiple requesters and multiple caching nodes environment in DTN for information-centric networking (ICN) by defining a satisfaction flag for a pair of delivered data and requester. Secondly, in order to carry out the overload control more proactively, we propose a proactive overload control. In the proactive overload control, if a message is delivered to a node that belongs to the same group as the destination node of the message, the \"delivery state of the message to a node in the same group as the destination node\" is recorded as \"delivered\" at the overload control table of the forwarding node additionally. Then, the message that is delivered to any node in the same group as the destination node can be delivered to a destination node only, i.e., direct delivery, without forwarding to any other nodes to reduce overload. The rationale of the proposed proactive protocol is to use the direct delivery by the receiving node within the same group as the destination node for intragroup delivery, which may have higher delivery probability. The delivery state information is shared with future contact nodes, and a contact node with the already delivered message to a node in the same group as a destination node does not forward the message to any other nodes, except the destination node, too. We note that the message delivered to a node in the same group as a destination node is not removed from the buffer of contact nodes, although it is not permitted to forward the message any further since it is not still guaranteed that the message is delivered to a destination node yet, and thus, it is safe not to remove the message at the buffer of future contact nodes. In the proactive overload control, if a message is delivered to a destination node of the message, the \"delivery state of the message to a destination node\" is recorded as \"delivered\" at the overload control table of the forwarding node, too, as in reactive overload control. Then, this information is shared with contact nodes to reduce unnecessary forwarding of already delivered messages to destinations, and the delivered message is removed from the buffer of the contact node. Reducing message forwarding for delivered a message to a node that belongs to the same group as the destination node of the message in proactive overload control is different from that in [24; 25], since message forwarding is restricted proactively; although, a message is not delivered to a destination node but is only delivered to a node that belongs to the same group as the destination node of the message for more active overload control.