A Novel Congestion Control Technique in Delay Tolerant Networks

A Novel Congestion Control Technique in Delay Tolerant Networks

Saeid Iranmanesh (Department of Computer, Islamic Azad University-Robatkarim Branch, Robatkarim, Iran) and Maryam Saadati (Department of ITS, Technikum Wien, University of Applied Science, Vienna, Austria)
DOI: 10.4018/IJITN.2018010102


Delay Tolerant Networks (DTNs) are characterized by the lack of contemporaneous paths between any source and destination node. As a basic forwarding strategy, nodes may flood their bundles to every encountered node. This results in congestion and unnecessarily consumes precious network resources. Another strategy is to take advantage of quota based protocols in which only a limited number of copies or replicas are disseminated throughout the network in order to reduce resource usage. However, they suffer from low delivery ratios as their dissemination rate is low. In this paper, the authors propose an Adaptive Message Replication Technique (AMRT) that is fit onto quota protocols to intelligently limit the number of replicas for each generated message. In other words, a source node under AMRT considers the congestion exist amongst the neighbours in order to generate a proper number of replicas for the generated messages. The simulation studies show that when AMRT is applied onto the quota protocols namely, SprayAndWait, EBR, and DBRP, the network performance such as delivery ratio and delay is improved.
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1. Introduction

Delay Tolerant Networks (DTN) (DTN Research Group, www.dtnrg.org) provides communications between source and destination nodes where there is no direct path between any source and destination at a same time. In such environment, intermediate nodes are involved in order to receive messages from sources and carry them for a while until forwarding opportunities arise. Hence, messages are routed based on store-carry-forward manner. However, as the network may have limited resources such as buffer size, energy, and bandwidth, the network performance, namely delivery ratio, delivery delay and, overhead is affected by the following problems (Balasubramanian, Levine & Venkataramani, 2007). Firstly, if messages are flooded throughout the network, congestion may happen in the network which results in the network with high network overhead, low delivery ratio and large delays (Elwhishi, Ho, Naik & Shihada, 2013; Krifa, Barakat & Spyropoulos, 2012; Krifa, Barakat & Spyropoulos, 2008). On the other hand, in order to reduce the signaling overhead, number of replicas may be limited that in turn, due to low dissemination rate, decreases delivery ratio and increases delay.

Many routing protocols are proposed to address the issue of routing in DTNs (Elwhishi, Ho, Naik & Shihada, 2013). These routing protocols are categorized into two groups (Iranmanesh, Raad & Chin, 2014; Nelson, Bakh & Kravets, 2009) (1) Flooding-based and (2) Quota-based. In the first group, although nodes are able to replicate messages infinitely, these protocols may reduce the number of replications such that the network overhead decreases. It should be noted that when the network resources are not limited, despite of high energy usage (Juang, Wang & Martonosi, 2002), these protocols provide a high network performance such as high delivery ratio and low delivery delay. However, the overhead of these protocols is high and they suffer from low delivery ratio when the network resources are limited. Contrary to flooding based routing protocols where the number of replicas is dependent on the number of encounters, quota protocols limit the number of replicas for each generated message. These protocols reduce the network overhead and consume less energy compared to flooding based protocols. However, these protocols suffer from low delivery ratio and large delays due to low messages dissemination. In addition, without respect to the network’s capacity i.e., nodes’ buffer size and nodes’ service rate, the number of replicas for all messages is fixed. This means if a quota protocol generates a large number of replicas for each message when congestion happens in the network, the protocol similar to flooding protocols will suffer from high ratio of dropped messages. On the other hand, if the number of generated replicas is small and traffic is low in the network, the protocol suffers from low delivery ratio.

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