Originally, Terminal Services was available in remote administration mode or application server mode. Today, in Windows Server 2003, Terminal Services remote administration mode is no more as it has been replaced with the Remote Desktop feature.
Windows Server 2003 and XP Professional have built-in support for Remote Desktop Connections. The underlying protocol used to manage the connection is RDP. RDP is a low bandwidth protocol used to send mouse movements, keystrokes, and bitmap images of the screen on the server to the client computer. RDP does not actually send data over the connectiononly screenshots and client keystrokes.
Any discussion of remote access is sure to include security, and for a good reason: Remote access opens your network to remote users. Although you'd like to think that only authorized users would try to connect from remote locations, the reality is that an equal number of illegitimate users will probably attempt to connect. Because many of the methods used to establish remote access are over public networks, securing the data you send and the points at which you connect at an important consideration. A significant element of this security is encryption.
Encryption is the process of encoding data so that it can be securely sent over remote connections. As well as encrypting the data itself, the usernames and passwords used to gain access to the remote network are also typically encrypted. In practical terms, encryption is the process of encoding data using a mathematical algorithm that makes it difficult for unauthorized users to read the data if they are able to intercept it. The algorithm used in the encryption is actually a mathematical value known as a key. The key is required in order to read the encrypted data. Encryption techniques use public and private keys; public keys can be shared, and private keys cannot.