Microsoft modifies its licensing periodically, and in 2007, in addition to the core CAL, which has existed for a while, the Enterprise CAL will also be of interest to organizations. The figure shows a diagram of the CAL model. Other "additive" CALs exist, which are not part of any suites. For example, for Windows Server 2003 both Terminal Server and Rights Management Services (RMS) CALs exist, and for Microsoft Exchange Server 2007 the Exchange 2007 Enterprise CAL. Additive CALs are also known as Premium CALs. As you can see from the figure, if you purchase the Enterprise CAL the Exchange Enterprise and Rights Management Services additive CALs are included, but not the Terminal Services CAL.