09-07-2011, 03:08 PM
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ABSTRACT:
Secure communication, an important aspect of any networking environment, is an especially signicant challenge in ad hoc networks. The MANET paradism seeks to enable communication across networks whose topology and membership can change frequently. Its distinctive feature is that network nodes need to collaborate with their peers in supporting the network functionality. In such an environment, malicious or selfish nodes can disrupt or even deny the communications of potentially any node within the ad hoc networking domain. This is so, exactly because every node in the network is not only entitled, but is in fact required, to assist in the network establishment, the network maintenance, and the network operation.
Ad-Hoc Networks consist of peer-to-peer communicating nodes that are highly mobile. As such, an ad-hoc network lacks infrastructure and topology of the network changes dynamically. The task of routing data from a source to a destination in such a network is challenging. Several routing protocols have been proposed for wireless ad-hoc networks. Most of these protocols, however, presuppose the presence of bi-directional links between the nodes in the network. In reality the ad-hoc network may consist of heterogeneous nodes with different power capabilities and hence, different transmission ranges. When this is the case, a given node might be able to receive the transmission of another given node but might not be able to successfully transmit to the latter. Thus, unidirectional links are formed. Most of the current routing protocols are unsuitable for deployment when such unidirectional links are present. We consider a routing protocol called the zone routing protocol (ZRP) that has been proposed for wireless ad-hoc networks with bi-directional links. The zone routing protocol employs a hybrid proactive (table driven) and reactive (on- demand) methodology to provide scalable routing in the ad-hoc network. However, in the presence of unidirectional links some routes remain undiscovered if ZRP is used. We propose extensions to ZRP to support its deployment when unidirectional links are present. In particular, we propose a query enhancement mechanism that recursively builds partial routes to a destination.
Introduction:
WHAT IS AD-HOC NETWORKS?
A wireless network that transmits from computer to computer. Instead of using a central base station (access point) to which all computers must communicate,
This peer-to-peer mode of operation can greatly extend the distance of the wireless network. To gain access to the Internet, one of the computers can be connected via wire or wireless to an ISP routing from one node to another on such a "mesh" network typically uses an on-demand routing protocol, such as PROACTIVE and REACTIVE, which generates routing Information only when a station initiates a transmission.
In the past, much research effort has been devoted on Service Discovery in static networks, like the Internet. The emergence of wireless communications and small mobile computing devices has created the need for developing service discovery protocols and architectures targeted to mobile environments. Especially, the proliferation of Mobile Ad Hoc Networks (MANETs) has introduced new requirements to service discovery due to the inherent characteristics of these networks.
It is a collection of mobile computing devices equipped with wireless network interfaces which can connect together dynamically to create a multi-hop wireless network, without the requirement for any pre-existing infrastructure. The mobility of the nodes makes the topology of the network time-variant. The rate of change of the network topology depends upon the velocity of the nodes. The wireless network is characterized by low bandwidth links that are subject to harsh conditions of fading and interference. Thus, routing in such a network is difficult and challenging. A plethora of routing protocols has been proposed for wireless ad-hoc networks. These protocols may be mainly classified as either proactive or reactive
PROACTIVE:
When proactive routing protocols are employed a node would possess routing information to a destination before it would actually need to route data to that destination.
