Cooperation in Ad Hoc Networks

zyso-2026-03-21_10_29_58-lec04.pdf

The next topic is cooperation in ad hoc networks. Cooperation as we have seen in the introduction is a very important issue, a very important topic when it concerns ad hoc networks. Without cooperation, without successful cooperation between the different nodes in the network, the networks are not going to survive at all. So, let us look at the different ways in which cooperation is ensured in ad hoc networks.

So, before we do so let us first review some of the characteristics of ad hoc networks. So, this is what we have already seen, we know that ad hoc networks operate the nodes in the networks. They operate in the wireless environment, wireless medium, they are mobile, the nodes are mobile, there is no definite structure of these networks. So, basically a collection of nodes, they are going to talk to one another and there is no one topology that governs these networks. The nodes could be heterogeneous having different specifications. They have, you know the ad hoc networks they basically exhibit autonomous behavior; that means, they should be able to, you know, to survive on their own. They should be able to operate on their own and whenever there is some kind of abnormality, they would be able to survive through such kind of situations. Multi hop radio relaying is another that we have already seen, distributed operation for security routing and host configuration is another property. So, I do not need to elaborate this we have already understood this particular aspect. Dynamic network topology is another, energy constrained behavior, mobile and spontaneous behavior, intermittent connectivity and the different nodes in the networks are prone to different types of abuse, different kinds of attacks and so on, these are some of the typical characteristics of mobile ad hoc networks.

Let us look at some of the challenges in enabling these networks. So, all these things we have already gone through. So, let us just review them quickly. So, the first is the limited bandwidth of the environment, dynamic changes in the topology. So, the nodes are supposed to be very mobile in a MANET particularly. So, there the topology is all also going to be made and broken quite fast and reformed faster. So, routing overhead is another, because you know whenever the nodes move, the topology changes and there is going to be overhead in you know in discovering the routes once again and maintaining the route information at the different nodes. So, all these things basically bring in a lot of routing overhead.

Hidden terminal problem this is something that we will look at when we you know when we look at a medium access control, hidden terminal problem and exposed terminal problems, packet losses due to transmission errors, mobility induced route changes, battery constraints we have seen already in the introduction. So, there are different, you know, severe constraints on energy consumption in these different nodes because the batteries have very small amount of energy that comes with them, security threats and uncooperative behavior of the selfish nodes.

Now, in this particular backdrop; that means, that we have looked at the characteristics of MANETs, we have looked at the different challenges in implementing MANETs. So, in this backdrop we have to understand the issue of cooperation. So, before we do that we need to understand that the nodes in MANETs they they may operate ideally, they may operate properly or they may not. So, based on the behavior of the different nodes, these nodes in MANETs they can be classified into two categories, unintentional and intentional. In the unintentional category we have the failed nodes and the badly failed nodes whereas; in the intentional category we have selfish nodes and malicious nodes. So, let us look at each of these different types of node behaviors each of these different types of nodes and what they mean in more detail.

Misbehaved nodes

· Failed nodes are simply those unable to perform an operation; this could be because of power failure and environmental events.

· Badly failed nodes exhibit features of failed nodes but they can also send false routing messages which are a threat to the integrity of the network.

· Selfish nodes are typified by their unwillingness to cooperate, as the protocol requires whenever there is a personal cost involved. Packet dropping is the main attack by selfish nodes.

· Malicious nodes aim to deliberately disrupt the correct operation of the routing protocol, denying network service if possible.

So, failed nodes are simply those, which are unable to perform an operation maybe due to different reasons such as power failure or maybe there is some kind of an environmental condition, an environmental event that has made a particular node to fail the way it is supposed to do. The second is the badly failed nodes which basically exhibit features of failed nodes, but they also send false routing messages which can be a threat to the overall integrity of the network. The selfish nodes are typically those which basically are willing to cooperate initially, but later on they are unwilling to cooperate.

So, initially they are willing to cooperate, but later on due to their different constraints such as, you know they have very limited energy in them they have very limited computational power and so on. So, initially they agree to cooperate, but later on they do not cooperate right. So, they are unwilling to cooperate because they want to be miser, they want to save their own limited resources and they do not want to help the other nodes in routing their messages through them. So, packet dropping is the main attack and that is done by the selfish node.

So, what it means is a selfish node, when it receives a packet because initially it agreed to forward the packets, so, when it receives the packet then instead of forwarding it to the next hop neighbor or it is going to do is it is going to silently it is going to drop the packet and that is the selfish node. So, the other nodes are not going to know that it has, in fact, dropped the packet right and malicious nodes basically, what they do is unlike the selfish nodes these nodes do it silently, what they do is they deliberately they disrupt the correct operation of the routing protocol or other protocols that are running in these different nodes, thereby denying network service if it is possible.