Cooperation in Delay Tolerant Networks
The delay tolerant networking architecture was proposed for the networks where the typical assumptions made for the Internet fails. One of the primary characteristics of such networks is the intermittent connectivity among the nodes, resulting in the lack
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Cooperation in Delay Tolerant Networks Sudip Misra, Sujata Pal, and Barun Kumar Saha
3.1 Introduction The ubiquitous Internet, based on the TCP/IP stack, fails to work in environments that exhibit one or more of the following characteristics [1]: • Intermittent connectivity among the nodes in the network, which turns the assumption of the existence of end-to-end paths false. Such connectivity could be scheduled, for example, a satellite in the Mars’ orbit communicating with the Earth station only at certain times, or could be opportunistic, for example, two smart phones carried by human beings in an urban scenario communicate when they come in each other’s transmission range. • High or variable latencies in the message deliveries as an effect of intermittent connectivity among the nodes. • Asymmetric connections or link bandwidths—such constraints make an interactive protocol like TCP fail. • High error rates along the transmission media call for multiple retransmissions, which may not be feasible given the limited availability of communication opportunities. To contrast the so characterized challenged networks with the Internet, consider some quantitative examples. While the round-trip time (RTT) in the Internet is about few hundred milliseconds [2], the speed of light pushes the propagation delay between Earth and Mars in the range of 3–20 minutes [3] depending on the positions of S. Misra (B) · S. Pal · B.K. Saha School of Information Technology, Indian Institute of Technology, Kharagpur, West Bengal, India e-mail: [email protected] S. Pal e-mail: [email protected] B.K. Saha e-mail: [email protected] N. Chilamkurti et al. (eds.), Next-Generation Wireless Technologies, Computer Communications and Networks, DOI 10.1007/978-1-4471-5164-7_3, © Springer-Verlag London 2013
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the planets. Moreover, the speed of transmission directly between Earth and Mars is only about 500 bps–32 Kbps, whereas a typical dial-up modem provides a data rate of about 56 Kbps [4]. In case of underwater acoustic networks, too, the transmission speeds are limited to around 38 Kbps [5]. To cope with such characteristics, and provide interoperability among heterogeneous networks, the DTN architecture was proposed [6]. DTN acts as an “overlay” to make the diverse networking architectures inter-operate. Thus, DTN enables to connect the terrestrial Internet with the deep-space network. While traditional Internet uses a store-and-forward strategy, DTNs provide a paradigm shift by using the store-carry-and-forward strategy. Typical examples of DTNs include, but are not limited to, Interplanetary Internet (IPN) [3, 7] and underwater acoustic sensor networks [8].
3.1.1 Evolution The evolution of DTN began with the efforts of Cerf et al. [7] to define an IPN architecture. The choice of extending the terrestrial Internet for interplanetary communications was evident, given its tremendous success. However, several environmental challenges, as mentioned previously, prevented the direct ad
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