In this section, we briefly introduce the basic building blocks of communication security. We describe how these building blocks are applied in existing wireless networks like IEEE 802.11 wireless LAN and discuss their importance in cognitive networks.
One of the fundamental requirements for any type of a network is availability. If the network is down and not usable, the purpose of its existence is defeated. Most of the attacks that we hear about these days like the denial of service (DoS) attacks, jamming attacks, buffer overflow attacks on network queues are all targeted towards rendering the network unavailable either temporarily or permanently . An issue that is closely related to network availability is data availability. This is the availability of data (user information, routing tables, etc.) to the users in the network.
In wireless networks, availability usually refers to the availability of the wireless transmission medium. Several techniques are used to ensure that the wireless communication medium is available for transmission. For example, random back-off mechanism  is used to prevent collision (jamming) between multiple users at the medium access control (MAC) sublayer of the IEEE 802.11 link layer.
In the context of cognitive networks, availability refers to the ability of primary and secondary users to access the spectrum. For primary (licensed) users, availability refers to being able to ...