# Enhanced Message Replication Technique for DTN Routing Protocols
## 1 Introduction  
Delay-tolerant networks (DTNs) are intermittently connected (wireless) networks, wherein there is no guaranteed end-to-end connectivity between the source and destination nodes [1, 2, 3, 4]. These networks can be disrupted by factors such as node mobility, density, and limited radio range, leading to frequent disconnections. As a result, traditional Transmission Control Protocols/Internet Protocols (TCPs/IPs) cannot be used, and instead, a store-carry-forward approach is employed to allow data transmission to continue despite the lack of a continuous path [4, 5]. However, this routing approach can cause issues such as buffer congestion and inefficient use of network resources due to the dissemination of multiple copies of a message across the network. [6, 7, 4]  
There are several routing techniques [8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18] available for addressing the routing problem in delay-tolerant networks (DTNs), which can be divided into two categories: flooding-based and quota-based [19, 20]. Flooding-based protocols allow nodes to replicate messages indefinitely, which can lead to good network performance when resources are not limited. However, they may have a low delivery ratio, high overhead, and high delay when resources are limited [21, 22]. Quota-based protocols, on the other hand, set a maximum number of replicas for each message--unlike flooding-based protocols, where the number of copies is determined by the number of encounters [20]. These protocols are resource-efficient and perform well when resources are limited but may experience low deliveryrates and long delays when resources are insufficient. Additionally, the number of replicas is fixed for all messages and is not affected by network capacity, such as node buffer size, energy, time-to-live (TTL) values, and encounter rate [21; 22].  
The limitations of both flooding-based and quota-based routing protocols in DTNs have led us to propose the Enhanced Message Replication Technique (EMRT). The EMRT dynamically adjusts the number of message replicas based on a node's ability to quickly disseminate the message, taking into consideration various parameters, such as existing connections, encounter history, buffer size history, energy, and TTL values. This can improve the delivery ratio and enhance the network resource utilization. The main contributions of this paper are as follows:  
* This is the first study to focus on optimizing the parameters of quota-based routing protocols in delay-tolerant networks (DTNs). Our focus is on the initial number of replicas, which can be increased or decreased. It is worth noting that existing quota-based protocols assume a fixed maximum initial number of replicas for each generated message.
* We propose a heuristic called the Enhanced Message Replication Technique (EMRT) to improve the performance of existing quota-based routing protocols in delay-tolerant networks (DTNs) by adaptively adjusting the maximum initial number of replicas for each generated message based on network circumstances such as density, buffer availability, energy, and TTL values.
* Simulation results show that applying the EMRT over well-known quota-based routing protocols improves the network performance in terms of delivery ratio, overhead, and latency average compared to the original forms of existing protocols.  
The remainder of this paper is organized as follows: Section 2 describes the related works. Section 3 proposes the Enhanced Message Replication Technique (EMRT). The simulation studies and their results are presented in Section 4. Finally, Section 5 concludes the paper.