The Remote Desktop Protocol (RDP) is a protocol developed by Microsoft® to enable remote desktop connections in which a user on one computer can see and control the screen on another. RDP powers Microsoft®’s Remote Desktop Services, a series of remote desktop applications. The protocol allows communication between a client and server on nearly any type of network, and features encryption, bandwidth restriction, and load balancing capabilities. Remote desktop software that uses RDP is available for several platforms and is used behind the scenes in some other Microsoft® products.
A protocol is a set of rules and standard behaviors that govern communication between different computers. In the case of the remote desktop protocol, these rules specify how the image on the screen of one computer is encoded and sent over a network connection to be displayed on another computer. RDP forms the basis for Microsoft®’s remote desktop software, currently known as Remote Desktop Services. Once a client system, also known as a terminal, is logged into the host computer, it displays the host’s screen and allow users to access files, applications, and other resources on the host machine.
Protocols are commonly thought of in terms of layers, with the lowest layers acting as a foundation for higher ones. The remote desktop protocol is an application layer protocol, meaning it relies upon several layers underneath it. This also means that RDP can be used over many different types of network connections because application layer protocols rely upon the lower level network and link protocols for networking functionality.
To prevent eavesdropping, the remote desktop protocol encrypts data before sending it across the network. Varying levels of encryption are available depending on the version of the protocol. Some versions of RDP included with Windows® 2000 and XP are vulnerable to an attack that can bypass this encryption; users with these operating systems may wish to update their software.
The remote desktop protocol also offers several features to increase performance on a slow or unreliable connection. New data is only sent when something on the screen changes, which means few packets of information are needed to interpret a change. Using less colors can speed up a connection, and RDP can compress data as well. On the sever side, load balancing features are supported to equally distribute resources on servers accepting many simultaneous connections.
Client software that supports the remote desktop protocol is included in every version of Windows® from XP forward; Microsoft® also offers an RDP client for the Mac®. Server software is included in most server operating systems offered by Microsoft®, as well as some professional level flavors of Windows®. Although RDP is a proprietary protocol, several client applications, such as tsclient, are available for Linux and other Unix®-like operating systems. Some other Microsoft® products, such as the software that powers media streaming from a computer to an Xbox 360®, also use the remote desktop protocol behind the scenes.