DTN Bundle Layer over TCP: Retransmission Algorithms in the Presence of Channel Disruptions

“Challenged networks” often violate the TCP design key assumption of continuous path availability from the source to the sink node. These networks are the preferred target of Delay/Disruption Tolerant Networking (DTN), which aims at providing a more robust network architecture. Against disruptions, however, even standard TCP offers a certain level of robustness, through its many retransmission algorithms. This intrinsic TCP resilience against disruptions is retained and enhanced if TCP is inserted in a DTN architecture. Focusing on this, the aim of the paper is to present an in-depth analysis of TCP and DTN bundle protocol retransmission algorithms that are triggered by channel disruptions, thus providing the reader with a comprehensive view of the many mechanisms involved and their complex interactions. The first sections, devoted to the description of TCP and DTN algorithms, are completed by the presentation of some numerical evaluations obtained by means of a Linux testbed. They refer to a GEO satellite environment and clarify the previous algorithm descriptions. Moreover, they also offer the reader some useful insights on both TCP and DTN resilience to disruptions, considering some performance metrics, like the “maximum tolerable disruption length” and the “restart delay”, introduced and explained in the paper.