In a previous post we setup and deployed a Lync2013 environmemt for hybrid split domain with Office365. That environment was later upgraded to Skype for Business 2015 servers while retaining all the hybrid functionality such as users homed on-prem and on-line, as well as Exchange Online with UM. In preparation to deploy and move users to Office365 E5 Cloud PBX with On-Premise PSTN Connectivity, one of the first tasks is to upgrade the existing DirSync server to Azure AD Connect. The version of AAD Connect must be version 1.0.9125.0 or later. This blog posts walk through the steps required and follows the guidance provided in this Azure documentation.