Tuesday, June 17, 2008

Terminal Services Virtual Channels (used by MMR)

Virtual channels are software extensions that can be used to add functional enhancements to a Terminal Services application. Examples of functional enhancements might include: support for special types of hardware, audio, or other additions to the core functionality provided by the Terminal Services Remote Desktop Protocol (RDP). The RDP protocol provides multiplexed management of multiple virtual channels.

A virtual channel application has two parts, a client-side component and a server-side component. The server-side component is an executable program running on the terminal server. The client-side component is a DLL that must be loaded into memory on the client computer when the Terminal Services client program runs.

Virtual channels can add functional enhancements to a Terminal Services client, independent of the RDP protocol. With virtual channel support, new features can be added without having to update the client or server software, or the RDP protocol.

Four major classes of users of virtual channels have been identified:

  • General kernel-mode drivers, such as serial or printer drivers.
  • File system redirection (this is just a special case of a general kernel-mode driver).
  • User mode applications, for example remote cut-and-paste.
  • Audio devices.

For more information, see Using Terminal Services Virtual Channels.

If you have enabled a virtual channels application in your Terminal Services deployment, you can make the application available to client computers that access the terminal server by means of the Remote Desktop Microsoft ActiveX control. For more information, see Scriptable Virtual Channels and Using the Remote Desktop ActiveX Control with Virtual Channels.

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