Every mission into deep space has a communications system to carry commands and other information from Earth to a spacecraft or to a remote planet and to return scientific data to Earth [1]. Communications systems are central to the success of space missions. Large amounts of data need to be transferred (for example, nearly 25 TB in 2013 concerning the Mars Reconnaissance Orbiter (MRO)), and the demand will grow in the future [1] because of the employment of more sophisticated instruments that will generate more data. This will require the availability of high network transfer rates. Satellite systems already have to cope with difficult communication challenges: long round trip times (RTTs); the likelihood of data loss due to errors on the communication link; possible channel disruptions; and coverage issues at high latitudes and in challenging terrain. These problems are magnified in space communications characterized by huge distances among network nodes, which imply extremely long delays and intermittent connectivity. At the same time, a space communications system must be reliable over time due to the long duration of space missions. Moreover, the importance of enabling Internet-like communications with space vehicles is increasing, realizing the concept of extended Future Internet, an IP (Internet Protocol) pervasive network of networks including interplanetary communication [2], where a wide variety of science information values are acquired through sensors and transmitted.The Delay-and Disruption Tolerant Network (DTN) architecture [3] introduces an overlay protocol that interfaces with either the transport layer or lower layers. Each node of the DTN architecture can store information for a long time before forwarding it. Thanks to these features, a DTN is particularly suited to cope with the challenges imposed by space communication. As summarized in [4], the origin of the DTN concept lies in a generalization of requirements identified for interplanetary networking (IPN), where latencies that may reach the order of tens of minutes, as well as limited and highly asymmetric bandwidth, must be faced.However, other scenarios in planetary networking, called "challenged networks," such as military tactical networking, sparse sensor networks, and networking in developing or otherwise communications-challenged regions, can also benefit from the DTN solution. Delays and disruptions can be handled at each DTN hop in a path between a sender and a destination. Nodes on the path can provide the storage necessary for data in transit before forwarding it to the next node on the path. In consequence, the contemporaneous end-to-end connectivity that Transmission Control Protocol (TCP) and other standard Internet transport protocols require in order to reliably transfer application data is not required.In practice, in standard TCP/IP networks, ABSTRACTDelay-and Disruption Tolerant Networks (DTNs) are based on an overlay protocol and on the store-carry-forward paradigm. In practice, each DTN node can store information for a...
AlthoughInterplanetary Telecommunications rely on preconfigured contact schedules to make routing decisions, there is a lack of appropriate mechanisms to notify the network about contact plan changes. In order to fill this gap, we propose and evaluate a framework for disseminating information about queueing delays and link disruptions. In this context, we present such a mechanism, focusing not only on its functional properties, but rather on its impact objectives: to improve accuracy and routing performance. Supportively, we couple this mechanism with a DTN-compatible protocol, namely Contact Plan Update Protocol (CPUP), which implements our dissemination policy. Through simulation of space scenarios we show that accuracy can be significantly improved in all cases while routing performance can achieve a wide range, from minor through to significant gains, conditionally.
SUMMARYIn this paper, we analyze the performance of two contact graph routing (CGR) enhancements, namely, CGR with earliest transmission opportunity (CGR-ETO) and overbooking management. CGR-ETO aims to improve the accuracy of predicted bundle delivery time by exploiting existing information on queueing delay, in routing decisions. Overbooking management aims to proactively handle contact oversubscription, which occurs when high-priority bundles are forwarded to a contact that is already fully subscribed by lower-priority bundles. These two enhancements have been recently included in the official CGR version as part of the Interplanetary Overlay Network delay-tolerant/disruption-tolerant networking implementation maintained by the National Aeronautics and Space Administration. In parallel to the comparative evaluation of the enhancements against the original CGR, we introduce an experimental version of CGR-ETO that exploits information on locally routed data to calculate queueing delays in all hops through the path to destination, rather than in the first hop only. We evaluate the aforementioned enhancements in a set of emulation experiments conducted on a GNU/Linux testbed and compare official and experimental versions of CGR. Results show that the two enhancements are complementary and can significantly improve routing decisions compared with older versions of CGR, particularly in the presence of parallel routes and traffic of different priorities. These advantages are further extended when the experimental version of ETO is considered.
In this paper we present two enhancements to Contact Graph Routing (CGR), a Delay-/ Disruption-Tolerant Networking routing algorithm developed by NASA JPL for space environments with predetermined connectivity schedules, such as Interplanetary communications and LEO satellite systems. The first enhancement, CGR-ETO, aims to improve the accuracy of predicted bundle delivery time by considering the available information on queueing delay. The second, the Overbooking Management, aims to proactively handle contact oversubscription, which occurs when high priority bundles are forwarded for transmission on a contact that is already fully subscribed by lower priority bundles. Both enhancements have been inserted as optional features in the Interplanetary Overlay Network CGR implementation in order to comparatively evaluate their performance on a GNU/Linux testbed running the full protocol stack. The results show that the two enhancements are complementary and can significantly improve routing decisions compared to standard CGR.
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