.FLYINGHEAD WIRELESS INFRASTRUCTURE
.TITLE Data communication in mobile ad-hoc networks
.AUTHOR Humayun Bakht
.SUMMARY What are some of the communications and resource management issues involved in mobile ad-hoc networks? In this article, Contributing Editor Humayun Bakht gives you an idea.
.OTHER
Wireless networks allow a more flexible communication structure than traditional networks. Unlike cellular wireless networks, a mobile ad-hoc network does not have any fixed communication infrastructure. A mobile ad-hoc, or peer-to-peer network, is one of the latest additions in the wireless networks family. Fast and easy deployment along with reduction in installation and maintenance cost makes mobile ad-hoc networks a suitable choice to advance current wireless technology.
In the existing wireless technology, routing support for mobile hosts is presently being understood as "Mobile IP" technology. Mobile IP is used to support mobile host roaming, where a mobile host connects to the network through various means other than its fixed-address domain space. On the other hand, the aim of a mobile ad-hoc network is to advance mobility into the chain of autonomous wireless domains, where a set of nodes themselves establishes the network routing structure in an ad-hoc manner.
A mobile ad-hoc network is defined as a collection of mobile nodes each combining the functionality of a router and a host. These mobile hosts are attached to a number of wireless mediums and are free to organize themselves. These hosts are equipped with wireless transmitters and receivers. Designing routing protocols for mobile ad-hoc networks has taken approaches similar to routing protocols used for conventional wired networks. Most of these protocols are based on table-driven or on-demand routing techniques.
The main task of any routing protocol is to aid communication within the network. The primary objective of a routing protocol is to establish correct routing between a source and a destination node to deliver messages in a timely fashion. In a mobile ad-hoc network environment, it may be necessary for one mobile host to assist other hosts in forwarding a packet to its destination. In a mobile ad-hoc network, to establish an active connection, the end node as well as the intermediate nodes can be mobile.
A node’s mobility poses several scalability problems for mobile ad-hoc network protocols. When network topology changes, control messages are broadcast frequently between nodes, so that new routes can be formed and propagated throughout the network. It’s expected that when nodes change topology there might be a short period where lots of control messages will propagate the network to broadcast the new destination paths. Minimizing control messages is necessary because of the additional load they place on the wireless links. Therefore, the techniques to reduce control messages must create a balance between, on the one hand, minimum amounts of messages by keeping network state information in each node, and on the other hand, flooding the network each time the topology changes. This could also lead to very slow network convergence where nodes contain either incomplete or expiry views of the network topology.
Mobile nodes in mobile ad-hoc networks usually depend on an exhaustible means for providing energy, such as batteries. This makes energy conservation an important design decision for mobile ad-hoc network protocols. Nodes with low battery power may decide to enter a power saving or sleep mode when they having nothing to send or to receive, until another high priority event is generated. This may disturb the entire operation of the mobile ad-hoc network, as each node acts as a router, forwarding packets for other nodes.
In conclusion, mobile ad-hoc networks are expected to play an important role in future wireless generations. In a mobile ad-hoc network, a distributed set of performance issues requires new protocols for network operations. This makes the design of a routing protocol for mobile ad-hoc networks a challenging issue. The presence of so many protocols for routing in a mobile ad-hoc network is an indication that the problem of routing is not very well understood. To invent an efficient routing strategy in a mobile ad-hoc network, the routing approach should show a high degree of adaptivity toward the dynamics of the mobile ad-hoc network.
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