Routing Protocols for Delay Tolerant Networks: a Quantitative Evaluation * Khalil Massri Dipartimento di Informatica e Sistemistica Università degli Studi di Roma Via Ariosto 25 - 00185 Roma, Italy massri@dis.uniroma1.it Alessandro Vernata Dipartimento di Informatica e Sistemistica Università degli Studi di Roma Via Ariosto 25 - 00185 Roma, Italy alex.vernata@gmail.com Andrea Vitaletti Dipartimento di Informatica e Sistemistica Università degli Studi di Roma Via Ariosto 25 - 00185 Roma, Italy vitale@dis.uniroma1.it ABSTRACT In this paper we propose a new taxonomy for Delay Tol- erant Networks (DTNs) routing protocols and a thorough quantitative evaluation of many protocols proposed in the literature. We categorize DTN protocols, according to their use of three main techniques: queue management, forwarding and replication. Queue management orders and manages the messages in the node’s buffer, forwarding selects the mes- sages to be delivered when there is a contact and finally replication bounds the number of replicas in the network. Contrary to most previous papers, where either only qual- itative comparisons have been presented or only a single category of protocols have been analysed, in our work we discuss the results of our experimental activity on many of the DTN protocols in the literature. Our results show that, an effective combination of the proposed techniques, can sig- nificantly improve the performance of the protocols in terms of delivery ratio, overhead and delay. Categories and Subject Descriptors C.2.2 [Computer-Communication Networks]: Network Protocols—Routing protocols General Terms Experimentation, Performance Keywords Delay Tolerant Network * Partially supported by VITRO EU Project No 257245 Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. PM2HW2N’12, October 21–22, 2012, Paphos, Cyprus. Copyright 2012 ACM 978-1-4503-1626-2/12/10 ...$15.00. 1. INTRODUCTION Delay tolerant networks [10] (DTNs) are made of wireless nodes characterised by high end-to-end latency, frequent dis- connections, limited resources (e.g., battery, computational power, bandwidth), and unreliable wireless transmission. However, nodes in a DTN are able to communicate even if a route connecting them never exists. To this purpose, beyond wireless transmission, DTNs also use nodes’ mobil- ity in order to carry the message to the intended destination. DTNs are often disconnected, and thus nodes are not sup- posed to possess or acquire any knowledge about the network topology, which is instead necessary in traditional MANET routing protocols. As possible examples of contexts in which DTNs might operate we mention: Inter-planetary networks [5], DFT-MSN for pervasive information gathering [33], So- cial DTN [13][6] and Ferry Boats [34]. Due to the wide diversity in contexts in which DTN rout- ing is applicable, many different protocols have been pro- posed in the literature. Contribution of the paper The first contribution of this paper, is the clear identification of the main techniques characterising DTN routing protocols in order to better un- derstand and classify the solutions proposed in the litera- ture. In particular, we consider forwarding, replication and queue management as the main techniques for DTN proto- cols and we show how each protocol can be classified ac- cording to the techniques it adopts. We observe that those technique has been already considered in the literature, but we propose a unifying approach which in our opinion better clarify their role and interaction (see Figure 1) The second contribution is the first quantitative compar- ison of many DTN routing protocols proposed in the litera- ture based on extensive simulations with the ONE simulator [15]. To achieve this goal, we extended the ONE simulator, which is considered one of the reference simulator for DTN [19], implementing new mobility models and DTN protocols. We stress again, that to the best of our knowledge, this is the first paper that tries to provide a quantitative comparison. Structure of the paper The paper is organised as fol- lows: in section 2 we briefly present previous works survey- ing DTN routing protocols and we clarify our contribution with respect to the state of the art. In our approach, we abstract the most relevant techniques adopted by DTN pro- tocols in the literature, namely forwarding, queue manage- ment and replication and in section 3 we use such techniques to define a taxonomy for the classification of DTN routing