A WSN is a network of devices, denoted as nodes which are termed as \"Heart of WSN\". That node can sense the environment and communicate the information collected through the wireless links from the monitored field. Existing security work in this area has focused primarily on denial of communication at medium access control levels. Denial of service attack and distributed denial of attacks made the network unavailable to the users. There are some of the schemes are introduced to prevent short - term availability attacks, that methods do not address attacks that affect long-term availability.