Abstract
Opportunistic networks are one of the emerging evolutions of the network system. In opportunistic networks, nodes are able to communicate with each other even if the route between source to destination does not already exist. Opportunistic networks have to be delay tolerant in nature (i.e., able to tolerate larger delays). Delay tolerant network (DTNs) uses the concept of “store-carry-forward” of data packets. DTNs are able to transfer data or establish communication in remote area or crisis environment where there is no network established. DTNs have many applications like to provide low-cost internet provision in remote areas, in vehicular networks, noise monitoring, extreme terrestrial environments, etc. It is therefore very promising to identify aspects for integration and inculcation of opportunistic network methodologies and technologies into delay tolerant networking. In this chapter, the authors emphasize delay tolerant networks by considering its architectural, routing, congestion, and security issues.
TopIntroduction
Delay Tolerant Networking (DTNs) is a new way of communication that facilitates the data transfer between source and destination even if a fully connected path may not exist between two end nodes. The Delay Tolerant Network (DTN)(Cerf et al., 2007) is an emerging area that has attracted keen research efforts from both academia and industry. DTNs consider an extreme network condition that is different from the traditional communication networks. There may not exist a complete end-to-end path between the data source and destination, and thus network is subject to dynamic node connections and unstable topologies. The communication in DTN is done by exploiting the characteristic of nodes i.e. mobility, available connections, and provided buffer space etc. DTNs find broad applications in the situations where legacy networks cannot work effectively, such as data communications in rural areas where stable communications infrastructure is not available or is costly. DTN is useful for extreme environments like battlefields, volcanic regions, deep oceans, deep space, developing regions etc., where they suffer challenging conditions as military wars and conflicts, terrorist attacks, earthquakes, volcanic eruptions, floods, storms, hurricanes, severe electromagnetic interferences, congested usage, etc. These challenging conditions result in excessive delays, severe bandwidth restrictions, remarkable node mobility, frequent power outages and recurring communication obstructions (Khabbaz et al., 2011). Vehicular networking is a wide and growing field of DTNs, where many applications are being explored (Benamar et al., 2014). One of these applications is to provide Internet access to vehicles by connecting to roadside wireless base stations (Ott and Kutscher, 2004). Non-commercial applications include monitoring and tracking wildlife animals (Juang et al., 2002), and environmental monitoring, such as lake water quality monitoring and roadside noise monitoring. DTNs can be applied in a variety of other fields ranging from healthcare to education to economic efficiency (Abdelkader et al., 2016).
The idea of Delay Tolerant Network (DTN) (Warthman, 2012) was taken from Inter Planetary Networks (IPN) (Burleigh et al., 2003), this was started in 1970s. The IPN was invented to communicate between earth and mars. The DTN is a type of wireless ad-hoc network which tolerates the intermittent connectivity. The intermittent connectivity can be defined as the sudden change of state (up/down) of any communication link between the nodes. The DTN can also be defined as intermittently connected wireless ad-hoc network (“Mobile Ad-Hoc and”, n. d.) that can tolerate longer delays, intermittent connectivity and prevent data from being lost by using store-carry-forward approach. The Store-carry-forward approach enables the nodes to take the message, store it in the buffer provided at each node and forward the same whenever new node comes in its communication range. DTN technology has become a new research focus in many fields including deep space communications, military tactical communications, and disaster rescue and internet access in remote areas. Internet Research Task Force (IRTF) has organized Delay-Tolerant Research Group (DTNRG) to research OTN technology, and as an important research theme, DTN technology has been accepted by the guidelines in MobiCom 2008 and Milcom 2009(Lu et al., 2010).
With the advent of the Internet of Things (IoT) a number of new devices will become part of our day today life. Constrained Application Protocol (CoAP), and its extensions, are specially designed to address the integration of these constrained devices in IoT environment. However, due to their limited resources, they are often unable to be fully connected and instead form intermittently connected and sparse networks in which Delay Tolerant Networking (DTN) is more appropriate, in particular through the Bundle Protocol (BP).
The chapter is organized as follows. In next section, the characteristics of DTNs, types of DTNs and applications of DTNs are mentioned in different sub-sections. The architectural structure of DTNs is described in further section. Then Routing and buffer management of DTNs are explained. Security aspects of DTNs are mentioned further. Some case studies of DTNs are given in last section.
Key Terms in this Chapter
Opportunistic Networks: An opportunistic network is a network of wirelessly connected nodes. Communication range between two connected nodes is not further than walking distance. Nodes are connected only temporarily, and the network topology may change due to node mobility or node activation and node deactivation respectively. The network provides at least the following functionalities: Node discovery. A network node is able to discover other network nodes in direct communication range. One-hop message exchange. A node is able to send and receive arbitrary data to or from any other node in direct communication range.
DTN Architecture: The DTN architecture provides a common method for interconnecting heterogeneous gateways or proxies that employ store- and-forward message routing to overcome communication disruptions. It provides services similar to electronic mail, but with enhanced naming, routing, and security capabilities. The architecture embraces the concepts of occasionally-connected networks that may suffer from frequent partitions and that may be comprised of more than one divergent set of protocols or protocol families. The basis for this architecture lies with that of the interplanetary internet, which focused primarily on the issue of deep space communication in high-delay environments.
Buffer Management: The buffers available in routers are valuable resources. A router uses them for storing incoming packets to forward them later. Due to the large number of packets that arrive in a router and limited buffer size, not all packets can be saved at the router. The quality of buffer management can define the quality of service provided to the customers. The buffer management module takes care of managing buffers shared by a number of modules and interfaces within the network layer. The default “best-effort” packet-forwarding service of IP is typically implemented in routers by a single, fixed-size, FIFO queue shared by all incoming packets.
Security: Network security is the security provided to a network from unauthorized access and risks. It is the duty of network administrators to adopt preventive measures to protect their networks from potential security threats. Computer networks that are involved in regular transactions and communication within the government, individuals, or business require security. The most common and simple way of protecting a network resource is by assigning it a unique name and a corresponding password.
Delay-Tolerant Networks: Delay-tolerant networking (DTN) is an approach to computer network architecture that seeks to address the technical issues in heterogeneous networks that may lack continuous network connectivity. DTN is the key internet engineering technology needed for interplanetary networking. DTN is actually a suite of experimental protocols developed by members of the Delay & Disruption Tolerant Networking Research Group. Examples of such networks are those operating in mobile or extreme terrestrial environments, or planned networks in space.