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WIRELESS INFRASTRUCTURE
Handling distributed applications in an ad-hoc environment
By Humayun Bakht
A mobile ad-hoc network is a dynamic multi-hop network that's formed by a group of mobile nodes on a shared wireless channel. In an ad-hoc environment, wireless transmissions are locally broadcast in the region of the transmitting host; hosts that are in close proximity can hear each other and are considered to be neighbors. The transitive closure of the neighborhood of all the hosts in the set of mobile hosts forms an ad-hoc network.
In an ad-hoc environment, the participating nodes route communication traffic from sender to receiver. Every participating host in these networks executes a routing protocol to allow messages to be sent to the other nodes along a route to the receiver. Routing protocols in ad-hoc networks have to consider the mobility of the participating nodes and the variation in the network topology.
Distributed applications are programs designed to run on multiple computers. To run business management, you may need to communicate with different programs that run on multiple computers on the network. If the application is divided into tiers, it's a distributed application. Supporting distributing applications, as shown in Figure A, is one of the main issues of mobile ad-hoc networks.
FIGURE A
 
Here's a typical diagram showing distributed applications in a network. Roll over picture for a larger image.
Distributed applications in an ad-hoc network have different requirements than those in wired networks. Capacity could be seen as one of the main constraints to support distributed communication. If a distributed application operates on an ad-hoc network, it must limit its use of all-to-all communication, as the capacity of the ad-hoc network is limited. Moreover, limited bandwidth and low-power devices are some of the other factors which limit the use of an ad-hoc network on a distributed platform.
Consider the scenario of a factory environment. The domain here is the management of a large-scale fertilizer site. At some point, the factory staff might want to download documents or leave messages and notes. The data may be stored within a system in the field office or in an otherwise reachable place.
After taking into account the nature of the site, establishing a network by laying down cables or installing a few access points will be a problem. An ad-hoc network under this scenario could minimize the need to set up a separate infrastructure for routine network operations. One of the advantages of an ad-hoc network is that no or very little on-site management is required.
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