In stage one, servers register their services with the centralized controller, and clients make contact with the centralized system for the offer services. In stage two, servers announce their services to the others, and in stage three, clients send their queries to the server in order to get replies from them.

This client server model is not applicable for mobile ad-hoc networks. Mobile ad-hoc networks are a recent addition to the family of wireless networks. Also known as peer-to-peer or short live network, this type of network makes network deployment possible in the absence of any centralized controller. Absence of fixed infrastructure in mobile ad-hoc networks makes service discovery a challenging issue. Thus, development of efficient service discovery mechanisms are required for mobile ad-hoc networks.

Mobile ad-hoc networks are a unique art of network formation, as each participating node in these networks can function both as a client and as a router, eliminating the need of any centralized supporting system.

Unlike a fixed wireless network, the central registry cannot be found in advance in mobile ad-hoc networks; therefore, finding the location of the central registry becomes the primary concern in the service discovery mechanism. In mobile ad-hoc networks, mechanisms like service advertisement and service query have been used as solutions to this problem.

Mobile ad-hoc networks are highly dynamic and suffer from frequent and unpredictable changes in the network topology. This makes service advertisement and service query process extremely difficult. Moreover, nodes in mobile ad-hoc networks operate on low battery power. Any node providing services usually spends more time then the others and can only provide services on a temporary basis, not on a permanent basis. Therefore, in mobile ad-hoc networks, clients are required to update information about the server at regular intervals of time.

Service discovery mechanisms in a network are one of the interesting aspects yet to be seen. If the adopted approach is efficient enough, it will ease the job of both the client and the servers. In mobile ad-hoc networks, all clients' services are provided through the mutual agreement among the participating nodes. By keeping specific characteristics of mobile ad-hoc networks in mind, we will be successful in delivering suitable services discovery procedure. No doubt, mobile ad-hoc networks can play an important role in wireless communication networks.

Dr. Humayun Bakht completed 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. He can be reached at humayunbakht@yahoo.co.uk and you can visit his Web site at http://www.geocities.com/humayunbakht/.