Availability describes the redundancy that has been applied to Lync Server 2013 to keep the service up and running for users. The secondary focus of high-availability is to reduce the end-user impact in the event of a system failure. To make a Lync Server system highly available, it often means deploying redundant quantities of every component. The simplest example of this is to deploy at least two of each server type; in theory, this provides the system with high-availability. However, that simple concept is much more complicated. Lync Server 2013 has many components, as well as shared systems, that must be accounted for.