To deploy Lync 2013 in our internal network, we will need Windows 2008 R2 or Windows 2012, the Lync 2013 installation media, and the Office Web Apps setup. An Active Directory infrastructure is mandatory to install Lync, and it is useful to have an internal certification authority available. If we want to grant access to the external users, a reverse proxy solution (IIS, Apache, or any hardware or software enabled for publishing) is required, along with an additional Lync server dedicated to the Edge role. Also, in the aforementioned scenario, we will usually prefer to have an SSL certificate from a third-party authority.