.FLYINGHEAD WIRELESS INFRASTRUCTURE
.TITLE Network wide broadcasting, handling data loss in mobile ad-hoc networks
.AUTHOR Humayun Bakht
.SUMMARY As great as mobile ad-hoc technology can be, it can still be a source of frustration as mobile ad-hoc networks are subject to transmission errors and data loss. In this article, Contributing Editor Humayun Bakht looks at why data loss happens and what could be done about it.
.DEPT
Mobile ad-hoc networks offer a unique art of network formation where mobile devices can communicate with each other without a pre-existing infrastructure. Ad-hoc networks have been considered to be the foundation for new technologies. The first and second generation mainly focused on military applications while the third generation, from 1992 onwards, is geared towards commercial applications such as Bluetooth and ad-hoc sensors networks.
One important issue is to try to reduce the packet or the data loss during an active transmission. In mobile ad-hoc networks, mobile link transmission errors, mobility, and network congestion are some of the major causes of data loss. Data loss due to transmission errors is mainly affected by the physical condition of the channel and the region where networks are deployed. These losses can’t be reduced with the improvement in ad-hoc routing protocols.
Each mobile device in an ad-hoc network has to rely on others for forwarding data packets to other nodes in the network. Routing protocols of a mobile ad-hoc network is another way to transmit data from one device to another. NWB (Network-wide Broadcast) is considered to be one of the routing or data exchange related operations and it’s used to discover routes for both unicast (one-to-one) and multi-cast (one-to-many) data exchange operations.
NWB can also be defined as a process through which one mobile device sends a packet to all other devices in the network. NWB in mobile ad-hoc networks provides important control and route establishment functionality to different protocols of mobile ad-hoc networks. It’s especially important for paging, alarming, location updates, route discoveries or even routing in highly mobile ad-hoc environments. Network-wide broadcasting is normally achieved via flooding.
In a flooding or broadcasting task, a source mobile device floods or broadcasts the same message to all the devices in the network. Therefore, it becomes crucial for routing protocols to have some sort of scalable flooding mechanism that can help each device decide between an active or passive state, so that network can remain connected and its lifetime could be maximized. Some of the desirable properties of a scalable flooding scheme are reliability and power and bandwidth efficiency, which can be measured by savings in rebroadcasts.
Until recently, NWB was limited to blind flooding schemes, where each mobile device receiving the message for the first time will re-transmit it. This solution is considered to be less efficient due to collision, contention, and several redundancy problems. Some of the existing methods for flooding a wireless network intelligently are using omni-directional or directional antennas, with equal or adjusted transmission radius and for scheduling node activities and selective rebroadcast approach. These can play an important role in enhancing NWB.
Recent research in this area reported that a selective broadcast approach for NWB could possibly lead to a considerable improvement in network-wide broadcast coverage with a small increase in network overhead. Moreover, this approach does not require proactive neighbor discovery and is resilient to mobility. Finally, the solution can be added to virtually all NWB approaches to improve their reliability.
.BEGIN_KEEP
Mobile ad-hoc networks suffer with packet or data loss more than the fixed mobile network systems. The problem is much more complicated as in ad-hoc networks, mobile links are subject to transmission errors and the network topology changes frequently and unpredictably. A packet gets lost due to several transmission errors such as no route to the destination, broken links and network congestions. Network-wide broadcasting is one of main approach used in routing protocols to assist data transfer from one to the other location in ad-hoc networks.
There are different types of flooding or broadcasting techniques which are used by network-wide broadcasting. Each of these flooding or broadcasting techniques has certain benefits and drawbacks in them. As NWB is one fundamental routing operation, it requires more discrete and accurate guidelines to be drawn for routing protocols to decide which flooding mechanism could be best suited in a particular situation. I have little doubt in stating that resolution in an exact form could help us in improving the network efficiency by reducing the packet loss in an active transmission.
.BIO
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