Routing in delay-tolerant networking concerns itself with the ability to transport, or route, data from a source to a destination, which is a essential ability all communication networks must have. Delay tolerant networks (DTNs) are categorized by their absence of connectivity, causing in a absence of sudden end-to-end paths. In these challenging environments, popular ad hoc routing protocols such as AODV and DSR fail to establish routes. This is due to these protocols trying to first create a complete route and then, after the route has been established, forward the real data. However, when instantaneous end-to-end paths are difficult or difficult to establish, routing protocols must take to a "store and forward" approach, where data is incrementally moved and stored throughout the network in hopes that it will ultimately reach its destination. A common procedure used to make best use of the chance of a message being successfully transferred is to duplicate many copies of the message in hopes that one will succeed in reaching its destination. In this paper I have surveyed some of the useful routing protocol in delay tolerant network.

A mong the broad set of top-down Millennium Development Goals that the United Nations established in 2000 (http://www.un. org/millenniumgoals), one stands out: "Make available the benefits of new technologies-especially information and communications technologies." Alongside good governance, technology is considered among the greatest enablers for improved quality of life. However, the majority of its benefits have been concentrated in industrialized nations and therefore limited to a fraction of the world's population. We believe that technology has a large role to play in developing regions, that "First World" technology to date has been a poor fit in these areas, and that there is thus a need for technology research for developing regions.Despite the relative infancy of technology studies in developing regions, anecdotal evidence suggests that access to technology has a beneficial economic impact. Cellular telephony is probably the most visible application, but there are many others, some of which we cover in this article.The World Bank's infoDev site catalogs hundreds of information and communications technologies (ICT) projects (http://www.infodev.org), albeit not all successful. Most of these projects use existing off-the-shelf technology designed for the industrialized world.Although it is clear that there are large differences in assumptions related to cost, power, and usage, there has been little work on how technology needs in developing regions differ from those of industrialized nations. We argue that Western market forces will continue to meet the needs of developing regions accidentally at best. ICT RESEARCH FOR UNDERSERVED REGIONSEvidence from the development of other technologies, such as water pumps and cooking stoves, demonstrates widespread impact from research.1, 2 Novel ICT has the potential for great impact in a variety of fields ranging from healthcare to education to economic efficiency. However, we do not propose that ICT offers a panacea for the complex problems facing nations on the path to economic development. On the contrary, at best, ICT can enable new solutions only when applied with a broad understanding and a multidisciplinary approach.I hope the industry will broaden its horizon and bring more of its remarkable dynamism and innovation to the developing world.

We consider the problem of routing in a delay tolerant network (DTN) in the presence of path failures. Previous work on DTN routing has focused on using precisely known network dynamics, which does not account for message losses due to link failures, buffer overruns, path selection errors, unscheduled delays, or other problems. We show how to split, replicate, and erasure code message fragments over multiple delivery paths to optimize the probability of successful message delivery. We provide a formulation of this problem and solve it for two cases: a 0/1 (Bernoulli) path delivery model where messages are either fully lost or delivered, and a Gaussian path delivery model where only a fraction of a message may be delivered. Ideas from the modern portfolio theory literature are borrowed to solve the underlying optimization problem. Our approach is directly relevant to solving similar problems that arise in replica placement in distributed file systems and virtual node placement in DHTs. In three different simulated DTN scenarios covering a wide range of applications, we show the effectiveness of our approach in handling failures.

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We consider the problem of efficient MAC design for long-distance WiFi-based mesh networks. In such networks it is common to see long propagation delays, the use of directional antennas, and the presence of inter-link interference. Prior work has shown that these characteristics make traditional CSMA-based MACs a poor choice for long-distance mesh networks, prompting several recent research efforts exploring the use of TDMA-based approaches to media access. In this paper we first identify, and then address, several shortcomings of current TDMA-based proposals, which exhibit inefficienct throughput and delay charactersistics as they use fixedlength transmission slots that cannot adapt to dynamic variations in traffic load. We show that throughput achieved by existing solutions falls far short of the optimal achievable network throughput. Current TDMA-based solutions also only apply to bipartitie network topologies due to interference scheduling contraints.In this paper, we present JazzyMac, a simple, practical and efficient MAC protocol that addresses the above limitations. JazzyMac achieves efficiency by enabling variable-length link transmissions slots; each node can adapt the length of their transmission slots in accordance with changing traffic demands. JazzyMac is practical as it can be applied to arbitrary network topologies, and each node can use purely local information for slot adaptation. Finally, the use of dynamic slot lengths allows JazzyMac to achieve better tradeoffs between throughput and delay.We evaluate JazzyMac using detailed simulation over a range of traffic patterns and realistic topologies. Our results show that JazzyMac improves throughput in all considered scenarios. This improvement is often substantial (e.g.,in 50% of our scenarios, throughput improves by over 40%) and is particularly pronounced for the common case of asymmetric traffic (e.g.,leading to almost 100% improvements). Furthermore, JazzyMac can achieve much better average delay for the same throughput.