**3.2 Targets of attacks**

The system is exposed to different types of attacks; some of these attacks are presented in the following subsections. Generally, expected attacks are divided into three groups: attacks against availability, authenticity, and confidentiality :

	- a.Message suppression attack: packets are dropped by the attackers from the network, they exploit these packets in other time. This type of attack causes a lot of problems in the network.
	- b.Drop the package**:** black hole attack is a dropping attack where the existence of this type of attack is the reason of package losing.
