Availability denotes that the information is available to authorized users. If it isn't available to authorized users, again it will incur a loss. Information has value if the right people can access it at the right time. Almost every week you can find news about high profile websites being taken down by distributed denial of service (DDoS) attacks. The main aim of a DDoS attack is not to allow users with any website access to the resources of the website. Such downtime can be very costly.
Now coming onto the next model, the AAA model focuses on Authentication, Authorization, and Auditing.