A novel congestion control framework for delay and disruption tolerant networks

Delay and Disruption Tolerant Networks (DTNs) are networks that experience frequent and long-lived connectivity disruptions. Unlike traditional networks, such as TCP/IP Internet, DTNs are often subject to high latency caused by very long propagation delays (e.g. interplanetary communication) and/or intermittent connectivity. Another feature that sets DTNs apart from conventional networks is that there is no guarantee of end-to-end connectivity between source and destination. Such distinct features pose a number of technical challenges in designing core network functions such as routing and congestion control mechanisms. Dectecting and dealing with congestion in DTNs is an important and challenging problem. Currently end-toend congestion control is handled by the TCP (Transmission Control Protocol) that prevents the network from collapsing, but network degradation does occur when the network becomes congested. TCP/IP works well when there is no disruption to end-to-end communication. DTN addresses weaknesses in TCP such as implementing congestion control mechanisms where each router can make decisions based on local information such as accepting a bundle of data from another router. This local information may include storage availability and the risk of accepting the data bundle based on previous experience which may have had adverse effects on the networking resulting in loss of data. Existing DTN congestion control mechanisms typically try to use some network global information or they are designed to operate in a particular scenario and they depend on forwarding strategy, for example, replication forwarding. As a result, existing DTN congestion control mechanisms do not have good performance when they are applied in different scenarios with different routing protocols. In this thesis, we first review important challenges of DTNs and survey the existing congestion control mechanism of this domain. Furthermore, we provide a taxonomy of existing DTN congestion control mechanisms and discusses their strengths and weaknesses in the context of their assumptions and applicability in DTN applications. We also present a quantitative analysis of some DTN congestion control mechanisms to evaluate how they behave in deep space communication scenario since they were designed to operate at terrestrial DTN. We extensively evaluated these mechanisms using two different applications and three different routing protocols and mobility patterns. The evaluation results show that the selected mechanisms poorly perform in deep space scenario. Therefore, in view of DTN characteristics, to study new congestion controls and better undersand the impact of congestion in DTN we modeled DTN con-