RDP, or Remote Desktop Protocol, is the protocol on which Windows Terminal Server is based. It is a very Windows-specific protocol, and takes great advantages of the Win32 / Win16 platforms. The protocol includes such enhancement as cutting and pasting between the two, port redirection, local printing through a remote session, and even such additions as sound and other plug-ins via a published SDK (in more recent versions). Citrix, the other Windows Terminal Server provider, does not use RDP, but rather their own proprietary (not as if the RDP protocol is published) software.