Some of these other factors are low power, bandwidth constraints, security, and frequent topology changes. A good number of papers have proposed various solutions to the routing problems of mobile ad-hoc networks. These protocols can be broadly classified into link state and on-demand.

Link state
Link state protocols maintain routing tables filled with the whereabouts of the other nodes in the network. These protocols adopt various techniques to periodically receive the link information of the other nodes. Using this method does offer some benefits, but there are some shortcomings as well, leaving a good number of sub-issues unanswered.

Studies have shown that large numbers of routing tables and continued updates seriously affect the overall bandwidth of the system. This, in turn, causes unnecessary waste of the bandwidth and the battery life of the nodes. Reliability is another issue. Just how secure is the transmission? To date, the security issue has yet to be resolved.

On-demand
With on-demand protocols, the routes between the nodes are formed when needed, on demand. This is a completely new strategy. Is it really suitable for the mobile ad-hoc network environment? As mentioned before, the mobile ad-hoc network suffers with frequent changes in the topology. Therefore, it isn't always possible that the route established via the route discovery process will still be available when the transmission actually starts. Apart from the standard route discovery mechanism of on-demand protocols, several different sub-processes have been adopted.

Too many packets result in the unnecessary consumption of the system bandwidth. However, these types of protocols are easy on the battery life of the network nodes as they aren't required to maintain a constant overview of the network.

Security
Security is a core issue with mobile ad-hoc networks because all network services are configured on the fly. For security in fixed networks, the mechanism of maintaining a list of authenticated users is followed. The server checks the available list and authenticated password whenever a network access attempt is made. If the user information matches, access is granted.

This client-server structure isn't applicable with the mobile ad-hoc network, as it operates without a fixed infrastructure. Neither of the proposed routing techniques discussed above provide a security scheme.

Mobile ad-hoc networks are highly dynamic. Topology changes and link breakage happen quite frequently. Therefore, a dynamic security solution is needed. In other words, any proposed solution should be able to cope with the ad-hoc network environment.

Malicious or misbehaving nodes can create hostile attacks. These kinds of attacks can seriously damage basic security aspects, such as integrity, confidentiality, and privacy of the node. It's also necessary for the entire routing solution to be secure enough, as the routing protocols in ad-hoc networks are more vulnerable to attack.

Conclusion
In this article, I highlighted different aspects related to mobile ad-hoc networks. The issues discussed here present obstacles to the successful deployment of the ad-hoc network. Therefore, it isn't possible to fully utilize this technology until these issues are resolved. That said, there's a lot of promise here and we'll discuss some of the possibilities in future articles.

Eng. Humayun Bakht is pursing his Ph.D at the School of Computing and Mathematics in Liverpool at John Moores University. Prior to his current course of studies, he has successfully completed his MSc Software Engineering and BSc Electronics Engineering from University of Liverpool UK and Sir Syed University of Engineering and Technology in Karachi, Pakistan. Humayun's research interest is mobile ad-hoc networks, in particular, the development of a new routing algorithm for this type of networking.