Ad-Hoc Network

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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