Active Directory is Carnegie's authoritative direcotry service (i.e. Carnegie Accounts), providing user identity, authentication, and authorization services for integrated services and systems.  It is a geographically distributed across the United States, with master servers at nearly all Carnegie sties and integrations to provide authentication and identity services to Carnegie's cloud services.  This enables Carnegie to maintain a highly-available directory service both locally and across all organizational services while being managed from multiple locations and by personnel at multiple administrative levels.