Copyright © 2018 Md. Sharif Hossen et. al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. International Journal of Engineering & Technology, 7 (3) (2018) 1735-1739 International Journal of Engineering & Technology Website: www.sciencepubco.com/index.php/IJET doi: 10.14419/ijet.v7i3.14122 Research paper Impact of buffer size and TTL on DTN routing protocols in intermittently connected mobile networks Md. Sharif Hossen 1 *, Md. Masum Billah 2 , Suraiya Yasmin 2 1 Department of Information and Communication Technology, Comilla University, Bangladesh 2 Dept. of Computer Science and Information Technology, Bangabandhu Sheikh Minibar Rahman Agricultural University, Bangladesh *Corresponding author E-mail:mshossen@cou.ac.bd Abstract Delay-Tolerant Networks (DTNs) are kinds of networks where there does not exist any complete end-to-end route from source to desti- nation. Such networks can also be referred to as Intermittently Connected Mobile Networks (ICMNs), which are featured by asymmetric data rates, large delay, limited resources and high error rates. In this network, size of buffer and Time-to-Live (TTL) for fixed number of nodes and message generation rates contribute to the network performance because of limited resources and short life span of a packet in the net-work. Therefore, investigating efficient routing for altering TTL and size of buffer is very important for overall network perfor- mance. This paper presents a performance analysis based on simulation of the impact of buffer size and TTL for several DTN routing protocols in ICMNs scenario. ONE, i.e., Opportunistic Network Environment is used to simulate the routing protocols considering three performance metrics: delivery ratio, mean latency and overhead ratio. Investigated results mention that Spray-and-Focus (SNF) routing exhibits the best performance for altering TTL and size of buffer than other DTN routing protocols, i.e., Epidemic, PRoPHET, PRoPHETv2, MaxProp, RAPID, and Binary-SNW in the considered performance metrics and simulation scenario. Keywords:Delay-Tolerant Networks; Intermittently Connected Mobile Networks; Routing; Routing Protocols; Message Replication; Simulation; Delivery Probability; Average Latency; Overhead Ratio; Opportunistic Network Environment Simulator 1. Introduction Delay-Tolerant Networks (DTNs) are kinds of mobile ad-hoc networks, where there is no persistent route from source to desti- nation. It is an intermittent and sparsely connected mobile ad-hoc network due to fixed transmission range and mobility model. Hence, the network exists in an abrupt change of delay and mes- sage errors [1−2]. In such challenging network, popular ad-hoc routing protocols like ad-hoc on-demand distance vector [3] and dynamic source routing [4] cannot be implied for selecting a route to send data properly, as they require an uninterrupted way of communication between two nodes. DTNs are named as Intermit- tently Connected Mobile Networks (ICMNs) [5] where there ex- ists an intermittent gateway and physically burst connections [6]. It takes benefits using “store and carry” technique to easily reach the messages between two nodes in the network [7−9] as illustrat- ed in Figure 1. DTNs are mainly seen in the areas of interplanetary networks [10], underwater networks [11], wildlife tracking sensor networks [8], satellite communication [12], vehicular ad-hoc networks [13], and military networks, etc. In this paper, the several replication-based DTN routing protocols have been analyzed as applied to intermittently connected mobile networks, with focus on Epidemic [14], PRoPHET [15], PRoPHETv2 [16], MaxProp [7], RAPID [17], Binary-Spray-and- Wait (B-SNW) [18] and Spray-and-Focus (SNF) [19] for varying buffer size and TTL, respectively [20−21]. Fig. 1: Store and Forward Strategy. Although the simulation of these DTN routing protocols is not novel, obtained result in the context is new (added SNF routing) and provides an efficient comparision seen in the simulation. For example, SNF, with specific metrics in a given network scenario could be the best due to the mechanism of the protocol. Studying the results of simulation helps to understand the working comparision of routings to determine what can be achieved in the networks. The remaining part of the paper is maintained as following: The brief discussion of DTN routings are shown in Section II. The simulation setting and discussion of the simulator is included in Section III. Section IV discusses the obtained results. Overall