Architecture
The server component of Remote Desktop Services is Terminal Server (termdd.sys), which listens on TCP port 3389. When an RDP client connects to this port, it is tagged with a unique SessionID and associated with a freshly spawned console session (Session 0, keyboard, mouse and character mode UI only). The login subsystem (winlogon.exe) and the GDI graphics subsystem is then initiated, which handles the job of authenticating the user and presenting the GUI. These executables are loaded in a new session, rather than the console session. When creating the new session, the graphics and keyboard/mouse device drivers are replaced with RDP-specific drivers: RdpDD.sys and RdpWD.sys. The RdpDD.sys is the device driver and it captures the UI rendering calls into a format that is transmittable over RDP. RdpWD.sys acts as keyboard and mouse driver; it receives keyboard and mouse input over the TCP connection and presents them as keyboard or mouse inputs. It also allows creation of virtual channels, which allow other devices, such as disc, audio, printers, and COM ports to be redirected, i.e., the channels act as replacement for these devices. The channels connect to the client over the TCP connection; as the channels are accessed for data, the client is informed of the request, which is then transferred over the TCP connection to the application. This entire procedure is done by the terminal server and the client, with the RDP protocol mediating the correct transfer, and is entirely transparent to the applications. RDP communications are encrypted using 128-bit RC4 encryption. Windows Server 2003 onwards, it can use a FIPS 140 compliant encryption schemes.
Once a client initiates a connection and is informed of a successful invocation of the terminal services stack at the server, it loads up the device as well as the keyboard/mouse drivers. The UI data received over RDP is decoded and rendered as UI, whereas the keyboard and mouse inputs to the Window hosting the UI is intercepted by the drivers, and transmitted over RDP to the server. It also creates the other virtual channels and sets up the redirection. RDP communication can be encrypted; using either low, medium or high encryption. With low encryption, user input (outgoing data) is encrypted using a weak (40-bit RC4) cipher. With medium encryption, UI packets (incoming data) are encrypted using this weak cipher as well. The setting "High encryption (Non-export)" uses 128-bit RC4 encryption and "High encryption (Export)" uses 40-bit RC4 encryption.
Read more about this topic: Remote Desktop Services
Famous quotes containing the word architecture:
“They can do without architecture who have no olives nor wines in the cellar.”
—Henry David Thoreau (1817–1862)
“I don’t think of form as a kind of architecture. The architecture is the result of the forming. It is the kinesthetic and visual sense of position and wholeness that puts the thing into the realm of art.”
—Roy Lichtenstein (b. 1923)
“Poetry is not only dream and vision; it is the skeleton architecture of our lives. It lays the foundations for a future of change, a bridge across our fears of what has never been before.”
—Audre Lorde (1934–1992)