Routing and Addressing in Ad-Hoc Networks

 
During the past few years the research efforts in the area of communications have been increased. And more recently an important part of these efforts have been fo-cused on the Mobile Ad-hoc Networking (MANET). A MANET is mainly a wire-less network without infrastructure, in which the nodes must behave simultaneously as a host and as a router.
 
Figure 1. Example of a MANET. If node S wants to Tx data to node D (outside of its coverage area), it must Tx the data through the intermediate nodes, and they mus colaborate forwarding the data until it reachs its destination (node D).
 
One of the main research issues has been the routing. Routing in MANETs can be classified in topology based routing, and Position based routing approaches. The latter determines relative or absolute positions (e.g. GPS) of the nodes in the network. On the other hand, the former approach determines the routes according to topological in-formation to achieve connectivity. Two of the main protocols obtained in the routing area are the well-known AODV (reactive) and the OLSR (proactive) topology based protocols.
 
One of the main drawbacks of the topological based approaches is the scalability in reaction to the number of nodes (limiting factor). In MANET every node in the net-work requires to participate as a router and the topological protocols rely on flooding of the control packets through the entire network to create and maintain routes. If the number of nodes grows largely, the number of control packets will increase drasti-cally, increasing the overhead in the network, consuming the scarce bandwidth in the network, and therefore reducing the throughput. Without taking into account the mo-bility of the nodes, this scenario is something similar to what happened to the ARPA-net at the beginning.
 
Figure 2. MANET using subnetting structure.
 
We are currently working on solutions to improve the scalibility of the routing protocols in MANETs . One of our proposals is to use a structure like the used in Internet, in which the nodes are aggregated into subnets to be handled as a single entity for routing purposes. Unfortunately, the difficulty to apply this sub-netting structure in MANETs is high, due to their dynamic and distributed nature. However, there are scenarios in MANETS in which the nodes can be grouped follow-ing physical or environmental constraints to apply the aforementioned structure. These formed groups can be considered subnets of a MANET, giving the chance of repre-senting multiple routes of a large number of nodes by a single route. Since the routing information is cutting down, a reduction in the overhead may be obtained. We have demonstrated that using analytical models, figure 3 shows resumes that results:
 
 
Figure 3. Overhead comparison between a reactive protocol and the same protocol with subnets
 
Some examples of the mentioned scenarios are the Wireless Mesh Networks and the wireless emergency networks.
 
The main challenges in which are working for applying this subnetting structure are: the address allocation under mobility scenarios, the dynamic creation and removal of subnets, and finally the maintenance of the already established sessions when a node moves from one subnet to other (mobility between subnets).
 

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