# Enhanced Message Replication Technique for DTN Routing Protocols
## 2 Related Works  
### Flooding Protocols  
A common DTN flooding protocol is the Epidemic routing protocol that was proposed by [PERSON] and [PERSON] [23]. The Epidemic protocol transmits the messages between the nodes in the network without any restriction. Due to the limited DTN network resources and unlimited message replicas disseminated through the network, the Epidemic routing protocol has proven less sufficient in the congested traffic network, leading to dropped messages and high overhead. To address the issues associated with the Epidemic routing protocol, [PERSON] and [PERSON] [24] proposed the (\(p\)-\(q\)) Epidemic algorithm with a vaccination routing protocol (PQERPV). The \(q\) probability indicates the probability of receiving a message from the source, while the \(p\) probability indicates the probability of receiving a message from other nodes. The performance of the PQERPV protocol is influenced by the value of \(q\) and the \(p\)-values, which can impact the protocol's performance. Lower \(p\)-values can lead to a low rate of message dissemination. In [25], the two-hop forwarding protocol was proposed by [PERSON]. In this routing protocol, the sender nodes exchange bundles with arbitrarily encountered nodes that will forward these messages only to the destination node. The overhead of this protocol is lower than the overhead of pure Epidemic since the message is sent across two hops only. However, if the destination node is not reachable via two hops, the messages may fail to be delivered to the destination node. Furthermore, due to the low dissemination rate, the message may suffer from a large delay. Additionally, various DTN protocols that select the next hop node based on encounter history have been proposed to decrease the network overhead issue of flooding protocols. One example of these protocols is PROPHET, which was presented by [PERSON] et al. [13]. PROPHET utilizes the delivery predictability parameter to estimate the probability of delivering the messages to their destination. In PROPHET, the delivery predictability parameter is updated after each node's encounter. However, when a node encounters a neighboring node with low delivery predictability, there is no guarantee that it will encounter another node with a higher delivery predictability value during the message lifetime; therefore, the messages may never leave the source node. On the other hand, if the source encounters many nodes with high delivery probability, the overhead will be high because the messages are flooded through the network. MaxProp is another example of a flooding-based routing protocol, which achieves better performance in terms of high delivery rates and low average latency [9]. However, MaxProp may produce a high overhead on restricted-resource networks [6]. Moreover, in the RAPID protocol [8], the messages are ordered using a utility function. Each message is assigned a utility by the RAPID protocol. RAPID replicates messages that lead to an increase in utility [8]. One major drawback of RAPID is that replica information must be flooded throughout the network to derive the utility of messages, leading to high overhead and high delivery delays. Additionally, the information disseminated may be outdated when it reaches the nodes because of delays. PREP is a prioritized Epidemic routing protocol where the messages are assigned with priority based on both the cost to the destination and the expiration time. This assigned priority is used to determine which messages should be sent or dropped when the buffer or bandwidth is limited. [PERSON] and [PERSON] [10] proposed techniques to utilize the properties of nodes to make forwarding decisions by selecting the optimal node to forward messages based on utility value. However, this technique causes flooding when many encountered nodes have high utility values. Moreover, the messages may never leave the source nodes when many of the encountered nodes have low utility values.