# MPH-M, AODV-M and DSR-M Performance Evaluation under Jamming Attacks
## 2 Reactive Jamming Attack  
In this section, we will explain the jamming attack model, which in general produces a Denial of Service (DoS) effect in the target nodes [6].  
A jammer is defined in [7] as \"... an entity who is purposefully trying to interfere with the physical transmission and reception of wireless communications\".  
Jamming models can be stationary or mobile whether or not the attacker stays in the same position during the attack. The detection of jammer that moves through the network is more difficult, because the detector needs to consider the dynamic behavior of the channels in each node [8].  
Jamming models can be also classified as constant or deceptive. A constant jammer continuously sends a radio signal or random bits to the channel without following any MAC-layer protocol; a deceptive jammer constantly injects regular packets to the channel without any gap between subsequent packet transmissions.  
In the random jamming model, the jammer switches between active and sleeping modes; when the attacker is in the active mode, it behaves as either a constant or deceptive jammer. In contrast, in the reactive jamming model, the attacker remains quiet while the channel is idle; when it detects a packet, then it sends an interference signal in order to corrupt the ongoing transmission [9].  
In reactive jamming, for MAC-layer protocols using Backward Error Correction, such as go-back-n or repetitive select, the attack would be successful if at least one bit of the packet is altered. Reactive jammer is energy efficient, because only transmits when it detects a packet, and therefore it is harder to detect since it could mimic packet collisions that are caused by normal traffic activity in the network [9; 10].  
In a previous work, we have shown that some performance metrics, such as the number of packet retransmissions, the number of retrials in the inner loop of the CSMA/CA algorithm, and the energy consumption are all affected by a jamming attack [11].  
In this work, we will evaluate the performance of a number of WSNs for MPH-M, AODV-M, DSR-M respectively) with an attacker that uses a reactive jammer model.  
Figure 1 shows how the mechanism of reactive jamming behaves; the shaded area represents the coverage area of a given node. In this example, we depict two coverage radii. One for the jammer node and another for an arbitrary node of the network. We can observe that there are two cases for the resultant behavior due to the mechanism of reactivity. One is when a packet is directed to any node that is within the coverage area of the jammer node. The second case is when a packet is directed to a node that is outside the coverage area of the jammer node. In the latter case, the jammer still tries to make packets collide, but since the receiver is far beyond its coverage area then the packet can correctly reach its destination without interference. This last alternative is shown in the figure by means of the packets marked with the number 1, which is actually the same packet. Nodes marked with an \(X\) are nodes that are within the coverage area of the jammer node and their packets can be intercepted. Nodes marked with \(\checkmark\) are nodes that are beyond the coverage area of the jammer node.  
Figure 1: Reactive mechanism for packet collision.