Good Definition’s on ad-hoc network:-
There is no unique definition what an ad-hoc network is, but one which describes the subject very well was formulated by the IETF work group on Mobile Ad-hoc Networks (MANET): “A mobile ad hoc network is an autonomous system of mobile routers … connected by wireless links – the union of which form an arbitrary graph. The routers are free to move randomly and organize themselves arbitrarily; thus, the network’s wireless topology may change rapidly and unpredictably. Such a network may operate in a standalone fashion, or may be connected to the larger Internet.”
Perhaps the most widespread notion of a mobile ad hoc network is a network formed without any central administration which consists of mobile nodes that use a wireless interface to send packet data. Since the nodes in a network of this kind can serve as routers and hosts, they can forward packets on behalf of other nodes and run user applications. ((IEEE) replaced the term packet-radio network
With ad hoc network.)
How Ad hoc networks work:-
To give a very simple example, let us assume that there is already a small ad-hoc network in place. When a new node – in this example it can be the PDA of Tom – joins the ad-hoc network, there are a number of things to do: The device needs to set up contact to other nodes in range, telling them: “I am here”. By this, the new node teaches who the neighbor nodes are, and vice versa. Another point is that the new node, in this example the PDA, needs a unique identifier to make it addressable – an IP address in IP networks. For all this, the new node is on its own, as there is neither a central controlling entity nor a pre-existing fixed infrastructure in ad-hoc networks. When Tom wants to send a message from his PDA to that of Maria, other nodes serve as a relay station in a process called multi-hop routing, if the PDA of Maria is not in direct reach, using one of the routing protocols designed for ad-hoc networks.
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This small example shows a few imminent advantages of ad-hoc networks: They can extend the range of the wireless technology in use, e.g. WLAN or Bluetooth, they can reduce the node’s power consumption due to a lower transmission power required, and they increase the node’s mobility. To make this work, though, ad-hoc networks require a critical mass of well-behaving nodes, willing to forward other’s traffic.
There are a number of application areas for ad-hoc networks. The cover theme articles in this issue will provide insights into a few selected application areas and research activities. The following overview should give you an idea of the wide range of application areas:
• Personal Area Networks:- (PANs) are formed between various mobile (and immobile) devices mainly in an ad-hoc manner, e.g. for creating a home network. They can remain an autonomous network, interconnecting various devices, at home, for example, but PANs will become more meaningful when connected to a larger network. In this case, PANs can be seen as an extension of the telecom network or Internet. Closely related to this is the concept of ubiquitous / pervasive computing where people, noticeable or transparently will be in close and dynamic interaction with devices in their surrounding.
• Sensor networks:- can be used for environmental monitoring. They can be used to collect various types of data, e.g. temperature, humidity, and vibration. Applications are the measurement of ground humidity for agriculture, forecast of earthquakes, or monitoring the progress of bushfires.
• Ad-hoc networks formed by users near a hotspot could extend that hotspot’s coverage. Hotspot coverage is often limited in densely built areas. Their extension would enable other users to get access even if they are not in direct reach. Going a step further, also other systems, for instance UMTS cells, could be extended beyond their range. This idea is not that absurd if one remembers the numerous white spots (small areas with no reception) on the GSM coverage maps still existing today. A crucial prerequisite for this, however, is the availability of suitable authentication, accounting, and charging mechanisms to ensure revenues for operators.
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• Automotive networks:- are widely discussed currently. Cars should be enabled to talk to the road, to traffic lights, and to each other, forming ad-hoc networks of various sizes. The network will provide the drivers with information about road conditions, congestions, and accident-ahead warnings, helping to optimize traffic flow.
• Last but not least, military applications should be mentioned. They exploit the ability of ad-hoc networks to work in situations where there is no pre-installed infrastructure available, as in combat areas. Rescue operations in remote areas would also be facilitated.
Mobile ad hoc networks have been the focus of many recent research and development efforts. So far, ad hoc packet-radio networks have mainly been considered for military applications, where a decentralized network configuration is an operative advantage or even a necessity. In the commercial sector, equipment for wireless, mobile computing has not been available at a price attractive to large markets. However, as the capacity of mobile computers increases steadily, the need for unlimited networking is also expected to rise. Commercial ad hoc networks could be used in situations where no infrastructure
(fixed or cellular) is available. Examples include rescue operations in remote areas, or when local coverage must be deployed quickly at a remote construction site. Ad hoc networking could also serve as wireless public access in urban areas, providing quick deployment and extended coverage. The access points in networks of this kind could serve as stationary radio relay stations that perform
ad hoc routing among themselves and between user nodes. Some of the access
points would also provide gateways via which users might connect to a fixed backbone network.5 At the local level, ad hoc networks that link notebook or palmtop computers could be used to spread and share information among participants at a conference. They might also be appropriate for application in home networks where devices can communicate directly to exchange information, such as audio/video, alarms, and configuration updates. Perhaps the most far-reaching applications in this context are more or less autonomous networks of interconnected home robots that clean, do dishes, mow the
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lawn, perform security surveillance, and so on. Some people have even proposed ad hoc multi-hop networks (denoted sensor networks)
Example, for environmental monitoring, where the networks could be used to forecast water pollution or to provide early warning of an approaching tsunami.
6 Short-range ad hoc networks can simplify intercommunication between various mobile devices (such as a cellular phone and a PDA) by forming a PAN, and thereby eliminate the tedious need for cables. This could also extend the mobility provided by the fixed network (that is, mobile IP) to nodes further out in an ad hoc network domain. The Bluetooth system is perhaps the most promising technology in the context of personal area networking.