# On the Potential of Enhancing Delay-Tolerant Routing Protocols via Age of Information
###### Abstract  
In this paper, we study the potential of using the metric of Age of Information (AoI) for enhancing delay-tolerant routing protocols. The latter have been proposed for alleviating the impact of long roundtrip time in networks operating in harsh environments, e.g., in distributed applications deployed in a desert/sparsely populated area without infrastructure, a space network, etc. Delay-tolerant routing protocols can prevent excessive packet timer expiration, but do not provide any packet delivery time guarantee. Thus, they are unsuitable for time-sensitive applications that are more intensely desired nowadays in the next generation networking applications. By incorporating AoI into the operation of delay-tolerant routing protocols, we aim at devising routing protocols that can cope with both long propagation times and challenges related to time-sensitivity in packet delivery. More specifically, in this work, we modify the operation of a well-known delay-tolerant routing protocol, namely FRESH, to make AoI-based packet forwarding decisions, aiming at achieving specific delay guarantees regarding the end-to-end delivery time. We investigate the advantages and disadvantages of such an approach compared to the traditional FRESH protocol. This work serves as a cornerstone for successfully demonstrating the potential of exploiting AoI in delay-tolerant routing and its applications.  
age of information; delay-tolerant networks; distributed routing protocols; packet delivery time +
Footnote †: journal:  
are trying to take advantage of the social link awareness [12], while others are focused mainly on Vehicular Delay-Tolerant Networks (VDTNs), being concentrated on the field of Messages' Delivery Time [13]. However, none of the aforementioned works focuses on providing packet delivery time guarantees for delay-tolerant routing protocols, which is the main novelty of the current work.  
In this paper, we take a different approach. We capitalize on the metric of the Age of Information [14; 15], a time-based metric proposed in the last decade to measure the \"freshness\" of a piece of information, e.g., a sensor reading, a packet, etc. We suggest using this metric to enhance the operation of DT routing protocols, by bounding the end-to-end (e2e) packet delivery delay, and eventually the average end-to-end packet delivery delay. This feature can potentially enhance the operation of traditional DT routing protocols, allowing them to be applied even in time-sensitive applications.  
We demonstrate the above approach utilizing a specific DT routing protocol, namely FRESH [16]. We utilize AoI in the traditional operation of the above routing protocol, but also in two variations proposed in this work. We compare the results of the operation of all protocols with respect to several metrics and identify an emerging tradeoff: the enhanced protocols can achieve a notably bounded average packet delivery delay, at a very small cost of increased packet drop rate, compared to the zero packet drop rate and unbounded packet delivery delay of FRESH. Thus, the proposed enhancement demonstrates the efficacy of utilizing AoI for such routing protocols and paves the way for a broader spectrum of delay-tolerant protocol enhancements.  
The rest of this paper is organized as follows. Section 2 reviews relevant literature, while Section 3 presents the protocols of interest and their enhancement. Section 4 presents evaluation results and discusses their impact, while Section 5 provides an overall discussion of the outcomes from this work. Finally, Section 6 concludes the paper.