Windows Server 2008 R2 requires that at least one Remote Desktop Licensing (RD Licensing) server be installed and running on any network that has an RD Session Host. If a license server is not installed within 120 days, all RD Session Host connections will be disabled. Remote Desktop Services requires a separate Windows Server 2008 R2 Remote Desktop Services CAL or Windows Server 2008 Terminal Service CAL for each user or device in addition to any Windows Server CALs you might need. The RD Licensing server does not enforce per-user licensing, but it does track usage in Active Directory against the installed per-user licenses. Per-device licenses are enforced by the RD Licensing server.