In a layered approach, Pastry's node joining process has been reformed to allow the use of expanding ring search for locating a node wants to rejoin the network. Another important factor is the network delay, since it's affected by many factors and has a high variability in ad-hoc networks. A modified Pastry is needed to use a hop count metric for proximity.

Finally, to reduce the cost of proximity probing, certain modifications need to be made to the basic structure of DSR. DSR can then use its cache to reply to pings from Pastry if there's a cached path to the node that's pinged. In the absence of such a cached path, DSR can initiate the route request process.

In the integrated approach, a DHT is supported by integrating Pastry and DSR at the network layer of mobile ad-hoc networks via one-to-one mapping between the IP addresses of the mobile nodes and their respective node IDs in the namespace. Through this type of integration, a routing structure could be developed between a DHT and an ad-hoc routing protocol. Among the above two discussed approaches, the layered design adopted the same procedure as it's in use for the Internet. This scheme explores the existing routing infrastructure for mobile ad-hoc networks to the full extent.

DHTs were designed to support larger networks, but they could also benefit mobile ad-hoc networks. The above two discussed schemes could possibly be extended further to support implementation of DHTs at a better scale in mobile ad-hoc networks.

James Booth is Editor-at-Large at ZATZ Publishing. In addition to writing for Computing Unplugged and Connected Photographer, he's the author of Do-It-Yourself Wedding Photography. A self-taught photographer, James also dabbles in digital graphics and has learned to be a PC and handheld specialist through personal trial and error. James can be reached at jbooth@zatz.com.