Routing protocols in mobile and wireless networks

Mobile and wireless networks allow the users to access information and services electronically, regardless of their geographic location. There are infrastructured networks and infrastructureless (ad hoc) networks. Infrastructured network consists of a network with fixed and wired gateways. A mobile host communicates with a Base Station (BS) within its communication radius. The mobile unit can move geographically while it is communicating. When it goes out of range of one BS, it connects with a new BS and starts communicating through it by using a handoff. In this approach, the BSs are fixed.

In contrast to infrastructure-based networks, in ad hoc networks all nodes are mobile and can be connected dynamically in an arbitrary manner. All nodes of these networks behave as routers and take part in discovery and maintenance of routes to other nodes in the network. Ad hoc networks are very useful in emergency search-and-rescue operations, meetings, or conventions in which persons wish to quickly share information and data acquisition operations in inhospitable terrain.

An ad hoc network is a collection of mobile nodes forming a temporary network without the aid of any centralized administration or standard support services regularly available in conventional networks. We assume that the mobile hosts use wireless radio frequency transceivers as their network interface, although many of the same principles will apply to infrared and wire-based networks. Some form of routing protocol is necessary in these ad hoc networks since two hosts wishing to exchange packets may not be able to communicate directly.

Wireless network interfaces usually operate at significantly slower bit rates than their wire-based counterparts. Frequent flooding of packets throughout the network, a mechanism many protocols require, can consume significant portions of the available network bandwidth. Ad hoc routing protocols must minimize bandwidth overhead at the same time as they enable routing.

Ad hoc networks must deal with frequent changes in topology. Mobile nodes change their network location and link status on a regular basis. New nodes may unexpectedly join the network or existing nodes may leave or be turned off. Ad hoc routing protocols must minimize the time required to converge after the topology changes. A low convergence time is more critical in ad hoc networks because temporary routing loops can result in packets being transmitted in circles, further consuming valuable bandwidth.

The routing protocols meant for wired networks cannot be used for mobile ad hoc networks because of the mobility of networks. The ad hoc routing protocols can be divided into two classes: table-driven and on-demand routing, on the basis of when and how the routes are discovered. In table-driven routing protocols, consistent and up-to-date routing information to all nodes is maintained at each node, whereas in on-demand routing the routes are created only when desired by the source host. We discuss current table-driven protocols as well as on-demand protocols.

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