# Routing Protocols for Delay Tolerant Networks:
## 5 Conclusions and Future Work  
We identified forwarding, queue management and replication as the core components for designing efficient and effective DTN routing protocols. On the basis of these components, we proposed a _reference architecture_ and discussed how a large group of existing and well-established DTN routing protocols presented in the relevant literature can be used to implement it. Contrary to most previous papers, where either only qualitative comparisons have been presented or only a single category of protocols have been analyzed, in this work, we conduct an extensive comparative study of the performance of 10 DTN routing protocols. To the best of our knowledge, this is the first time that such a large set of protocols has been examined. The key criterion for selecting these protocols is the techniques employed given the three core components of our reference architecture. We suitably selected protocols such that we can understand the effect of each component in stand-alone and in combination with the others. Therefore, the performance evaluation conducted goes beyond pair-wise comparison of protocols that either follow similar techniques or are completely different, since it can provide insights on the prevailing design choices and crucial protocol properties. Our results show \begin{table}
\begin{tabular}{p{113.8 pt} p{284.5 pt}} \hline \hline
**System Property** & **Recommendation** \\ \hline Predictable Movement Patterns & Prioritization of messages in terms of age, hops and number of replicas. \\ \hline Correlated Movement Patterns & Combination of forwarding techniques and queue management (e.g., FAD) improves overall network performance. \\ \hline Uncorrelated Movement Patterns & Direct-Delivery keeps network overhead at minimum levels. \\ \hline Sparse Contacting & Increased message replication increases reliability. If there is large availability of message storage, Epidemic-based techniques achieve high performance. \\ \hline High Node Mobility & Limited message replication improves bandwidth utilization. Forwarding techniques (e.g., PRoPHET) reduce latency. Queue management techniques (e.g., Fuzzy-Spray) do not affect performance. \\ \hline Low Message Generation Rate & Setting high values of message TTL improves performance. \\ \hline Low Message Storage Capacity & Forwarding techniques (e.g., PRoPHET) hinder performance due to increased message drop rates. Queue management techniques (e.g., Fuzzy-Spray) maximize performance. \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Synopsis of technical recommendations. that an effective combination of the proposed techniques can significantly improve the performance of the protocols in terms of delivery ratio, overhead and delivery delay. In our extensive study, we used a combination of synthetic mobility models and models based on traces acquired from monitoring the actual motion patterns of nodes when executing real-world application. Our evaluation was done based on the broadly-accepted ONE simulator. We have extended the tool to include two additional synthetic mobility patterns and a generic mechanism to replay traces from real-world experiments. Based on the results of the synthetic and realistic traces, we provide a comparison between the two approaches and identify how and when each model should be employed during the evaluation process of a DTN routing protocol. Our implemented models and extensions along with the protocols' implementations are open-source and freely available on-line for researchers to use. We believe that the evaluation of the DTN protocol should continue given traces from other real-world applications. We are currently working towards providing a tool for acquiring such traces using OpenBeacon tags [49] as test-beds. Such a tool will help reduce the cost of collecting such traces and curating them into datasets that can be used by the research community for benchmarking DTN protocols and their applicability in real-world application scenarios.