# Routing Protocols for Delay Tolerant Networks:
## 1 Introduction
### The Need for a Quantitative Evaluation  
A second reason for the limited uptake of DTN protocols in industrial ICT systems is the approach followed by the majority of the DTN research community in terms of evaluating the performance of the protocol designs proposed. As real-world deployments of DTN or the creation of large-scale test-beds are costly and hard to control, the majority of the proposed protocols are evaluated using simulated environments. It is well known that simulated environments lack the necessary realism and provide results that could lead to great surprises when deployed in real-world environments. As an attempt to improve the accuracy of simulation studies, one part of the research community increased the complexity of the simulated environments in order to make them more realistic, while in parallel, another part focused on the development of complex synthetic mobility models [16], as well as the collection of mobility and connectivity traces from real-world networks [17; 18]. All efforts so far have led to a wide spectrum of scenarios and tools, spanning from completely synthetic scenarios (like random way-point) to very realistic (based on trace data), from generic network simulators to very complex and specific to a particular networking technology. Since the research community did not converge to a specific range of benchmarking scenarios and simulation tools, it is very hard (if not impossible) to make a comparative evaluation of different DTN designs based on a literature review. Evaluations performed in very realistic settings are very specific to that particular scenario, and any conclusions drawn cannot be expected to be valid in other scenarios. This is also evident by examining the existing surveys that only provide a qualitative comparison of the protocols; as an example, see Table 2 in [12] and Tables 1-3 in [19]. It is therefore important to provide an evaluation framework that will produce comparable quantitative evidence. In this paper, we attempt to provide a detailed quantitative comparison framework that establishes a repeatable set of benchmarking scenarios. The scenarios proposed are based on realistic technical assumptions that are derived from existing real-world applications and address both indoor and outdoor deployments. Our evaluation is based both on the synthetic scenario, as well as traces collected from real-world deployments with varying mobility patterns and network area size. We work with the Opportunistic Network Environment (ONE) simulator [20], a JAVA-based simulator for evaluating protocols for opportunistic networking. We selected the ONE simulator as it is most commonly used in the relevant literature and for which existing implementations are available for most of the protocols considered. Although a recently-developed tool, it has gained wide acceptance in the DTN research community and is considered as the reference simulator for DTN [21]. We significantly extend ONE by implementing two new synthetic mobility models (Levy Walk [16] and Community [6; 22]) and a mechanism for reproducing the motion of nodes based on real traces of mobility (Infocom2006 [23], Rome Taxis [24]). Furthermore, we implement for the first time three DTN routing protocols (Fuzzy Spray [25], Fad [6] and Scar [26]). Our model and protocol implementations are open-source and available online for free. We believe that our implementation effort reinforces ONE and works towards making it a mature tool for the DTN research community [27]. Given this quantitative comparison framework, we conduct a detailed evaluation of 10 characteristic DTN routing protocols proposed in the relevant literature. Our results are based on extensive simulations with the ONE simulator [20], which is considered one of the reference simulator for DTN [21].