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  • Microsoft Remote Desktop Protocol (RDP)
  • posted on 2013-12-20 10:41:43
  • Remote Desktop Protocol (RDP) is Microsoft's distributed presentation services protocol, which controls the transmission of display and user input between the client and the Terminal Server. RDP has been adapted from the T.120 set of standards to meet the specific needs of the Terminal Server environment and continues to be updated with new features to improve the user's server-based computing experience. The following sections discuss the features available with RDP 5.0, which ships with Windows 2000 Terminal Services, and RDP 5.2, which ships with Windows Server 2003 Terminal Services. I begin by outlining the overall behavior of the RDP protocol.

     

    RDP Basics

    The transfer of RDP information between the server and the client can be broken down into two main components:

    • Graphical data transmission
    • Mouse/keyboard data transmission
    Graphical Data Transmission

    All graphical information that would normally be displayed on the console needs to be encoded and transmitted to the Terminal Server client so it can be displayed on the user's local desktop. As described in the earlier section "Virtual Memory Management," each user session has its own session address space that contains its own Win32 kernel and display and printer drivers. Each of these sessions uses a special RDP display driver that's responsible for receiving display commands from the GDI (just as a normal driver would) and passing this information to the kernel-mode Terminal Server device driver (termdd.sys). This driver encodes the input as RDP data and passes it on to the transport layer to be sent to the client. On reception, at the client, the RDP data is decoded and the display updated accordingly. Figure 1.7 illustrates the flow of graphical data between the server and the client.

    Mouse/Keyboard Transmission

    Every time a user generates an input message (keyboard or mouse), the information is captured by the RDP client, encoded as RDP data, and sent to the server. When input data is received by the Terminal Server device driver on the server, it's decoded and the actual mouse and keyboard input is sent to the Win32 kernel in the user's session address space, where it's processed as normal input. Figure 1.8 shows the flow of input data between the client and the server.

     

    Remote Desktop Protocol (RDP)远程桌面协议(RDP) - 浪上飞郑 - 小型企业信息化

     

     

    RDP Encryption

    To ensure that data is transmitted securely between the client and the server, three encryption levels are available, from which you can choose based on your security requirements. All levels are encrypted using the RC4 encryption algorithm.

    • Low security Only data sent from the client to the server is encrypted; data from the server to the client is not encrypted. The encryption key is 56-bit for both Windows 2003 and 2000.

    • Medium security Uses the same encryption level as the low-security option, except that data is now encrypted in both directions, from the server to the client and from the client to the server.

    • High security The high-security  option encrypts data in both directions, using a 128-bit encryption key.


       

    RDP Client Integration Features

    As mentioned, each new Windows Terminal Server release has introduced new client integration features that enhance the user's computing experience. Table 1.3 summarizes the features supported by the RDP 5.xclients, and what version of Windows Terminal Server is required to enable the feature. The latest RDP client (5.2) can be used to connect to older Terminal Servers (Windows NT 4.0, Terminal Server Edition; or Windows 2000 Terminal Server).

    Table 1.3. RDP 5.x Features and Required Server Version
     

    Feature

    RDP Version

    Terminal Server Version

    Description

     

    5.0

    5.1

    5.2

    Local/remote clipboard integration

    X

    X

    X

    Both

    Allows clipboard contents to be cut and pasted seamlessly back and forth between the active Terminal Server session and the user's local desktop.

    Local/remote file copy and paste integration

     

    X

    X

    Windows 2003 only

    Allows the cut and pasting of entire file objects back and forth between the active session and the local desktop.

    Local client printer redirection

    X

    X

    X

    Both

    Printers that are configured on a local client can be made available automatically from within the user's Terminal Server session.

    Network client printer redirection

       

    X

    Both

    This allows for access to locally mapped network printers on the client desktop.

    Session remote control

    X

    X

    X

    Both

    Session remote control is the capacity for one person to remotely view and even control another user's active session.

    Persistent bitmap cache

    X

    X

    X

    Both

    The persistent bitmap cache is stored on disk so that it can be reused the next time a session is started. Version 4.0 allowed only in-memory caching.

    Connection bar

     

    X

    X

    Both

    This allows you to still easily minimize a full-screen session without having to toggle the session between full screen and windowed using the Ctrl+Alt+Break key combination.

    Automatic session reconnect

       

    X

    Both

    If a network disruption causes your connection to a Terminal Server to be lost, the Remote Desktop Connection client will automatically attempt to reestablish that connection. If the connection cannot be reestablished, then after about one minute the client will give up and an error message will appear saying the connection has been lost.

    Client drive redirection

       

    X

    Windows 2003 only

    The automatic redirection of a client's local and network drives so they are accessible from within the Terminal Server session.

    Client serial port redirection

       

    X

    Windows 2003 only

    Redirection of the local serial ports.

    Client audio redirection

       

    X

    Windows 2003 only

    Audio is redirected from the Terminal Server session to the local client for output.

    Smart card sign-on

       

    X

    Windows 2003 only

    The user is able to provide their smart card to a local reader attached to their PC and have those credentials transmitted and authenticated on the Terminal Server.

    Windows shortcut key support

     

    X

     

    Both Client must be running WinNT, 2000, XP, or 2003. Windows 98 or 95 operating systems don't support this feature.

    Introduces support for the Alt+Tab and other Windows key combinations within the Terminal Server session.

    Client time zone support

     

    X

     

    Windows 2003 only

    Client time zone support lets the RDP client provide its own local time zone information to a Windows 2003 Terminal Server so that the server can automatically configure the user's session to reflect the same time zone information. A Terminal Server can support any number of users located in different time zones, and this feature lets the user maintain proper time and date information within his or her own session.

    Direct Terminal Server console access

     

    X

     

    Windows 2003 only

    This feature allows for the creation of a direct connection to the console and not a Terminal Server session. Applications that require direct console access will function within this special remote session. This feature is dependent on having a Windows 2003 Terminal Server.

     

     

     

    Microsoft RDP Clients

    Table 1.4 summarizes the native Microsoft RDP client versions and the operating systems they support.

    Table 1.4. RDP Client Versions and Their Supported Operating Systems
     

    Operating System

    RDP Client Version Supported

    Notes

    Windows 2003, XP, 2000, client are ME, 98, and NT 4.0

    RDP 5.0 and higher

    All versions of the RDP supported on all 32-bit versions of Windows, NT 4.0 or higher.

    Windows 95

    RDP 5.0 or 5.1 only

    Microsoft does not officially support the RDP 5.2 (or newer) client on Windows 95.

    Windows for Workgroups 3.11

    RDP 5.0 only

    Microsoft no longer supports this version of Windows with the new RDP client. Only the client that originally ships with Windows 2000 is available for the 16-bit version of Windows.

    Macintosh OS X

    Mac OS X RDP Client 1.0.2

    This is currently the only RDP client that Microsoft produces for a non-Windows operating system.

    Pocket PC 2002

    PPC 2002 client

    This special RDP client is designed specifically to run on Pocket PC 2002. It will not run on older versions of Pocket PC.

    Windows CE

    Handheld and CE-based terminals running CE 3.0 and CE.NET

    Special versions of the RDP client can either be installed on a Windows CE client or come embedded with the CE operating system.