How Terminal Services Works

Terminal Services provides a client/server session that creates a virtual desktop within a single client window that emulates a true local desktop environment. Using primarily keyboard and mouse redirects, Terminal Services clients run applications on the Terminal Server, so almost no processing power is needed on the client system.

The Terminal Services client software communicates with the Terminal Services server by redirecting the local workstation's keyboard and mouse signals to the Terminal Server. These commands are sent to the Terminal Server via a single TCP port (3389), and only minimal network bandwidth per user is needed. In fact, so little network bandwidth is needed that Terminal Server clients can connect to Terminal Servers using 28.8Kbps modem connections. For richer terminal sessions utilizing advanced features such as port redirection, color settings higher than 256 colors, file transfer, and 128-bit encryption, increased line speed is recommended.

Modes of Operation

Windows Server 2003 Terminal Services can be run in two different modes of operation. One is called the Remote Desktop for Administration mode and the other is called Terminal Server mode.

Remote Desktop for Administration Mode

Terminal Services Remote Desktop for Administration mode is included and installed with the Windows Server 2003 operating system and only needs to be enabled. This eases automated and unattended server deployment by allowing an administrator to deploy servers that can be managed remotely after the operating systems have completed installation. This mode can also be used to manage a headless server, which reduces the amount of space needed in any server rack. More space can be dedicated to servers instead of switch boxes, monitors, keyboards, and mouse devices.

The Remote Desktop for Administration mode limits the number of terminal sessions to two, and only local administrators can connect to these sessions by default. No additional licenses are needed to run a server in this Terminal Services mode, which allows an administrator to perform almost all the server management duties remotely.

Even though Remote Desktop for Administration is installed by default, this mode does not have to be enabled. Some organizations may see this as an unneeded security risk and choose to keep it disabled. This function can easily be disabled throughout the entire Active Directory forest by using a Group Policy setting to disable users and groups from connecting to Terminal Servers located in the containers that the policy applies to. This mode of Terminal Services is available in every Windows Server 2003 version as well as in Windows XP Professional.

Terminal Server Mode

Terminal Server mode allows any authorized user to connect to the server and run a single application or a complete desktop session from the client workstation.

Running Terminal Services in this mode requires the purchase of a Terminal Server client access license (CAL) for each simultaneous connection. To manage these CALs, a Terminal Services License server is needed to allocate and track the licenses for the Terminal Server. The Terminal Services License server service can be installed on any Windows Server 2003 Enterprise or DataCenter server. The License server does not need to have Terminal Services enabled in any mode to run this service.

Note

To quickly obtain client license information on a client computer, use the Windows Server 2003 Resource Kit tool called Terminal Server Client License Dump (TscTst.exe).

Installing applications for Terminal Server mode requires that a strict process be followed to ensure that each application runs as it should in multiple user sessions. Some applications may not be properly suited to run on a Terminal Server; in such cases, special Terminal Server application compatibility scripts need to be run against the programs for these applications to run correctly. Thorough testing of each Terminal Server application is highly recommended before it is released into the production Terminal Server environment.

Note

Terminal Server mode is not available in Windows Server 2003 Web edition.

Client-Side Terminal Services

Windows XP Professional includes a scaled-down version of Terminal Services called Remote Desktop. Remote Desktop allows a user to connect to the XP workstation and remotely take over the workstation to run applications that he would normally run from his desk locally. This feature allows a user who works from home part time to connect to the company workstation to complete work or check email from a workstation that is already configured for him.

As an administration tool, this client-side Terminal Services can be used to install software on an end user's workstation from a remote machine. Also, it can be used to log in to a user's desktop environment to remotely configure a user's profile settings.

Remote Assistance

Remote Assistance is a feature new to Windows Server 2003 and Windows XP Professional. This feature allows a user to request assistance from a trusted friend or administrator to help deal with desktop issues and configurations. This feature gives the end user the power to control what level of participation the remote assistant can have. The remote assistant can be granted the ability to chat with the end user, view the desktop, or remotely control the desktop. During remote assistance sessions, both the end user and remote assistant can hand off control of the keyboard and mouse. Remote assistance uses the underlying Remote Desktop Protocol (RDP) used by Terminal Services.

Remote Desktop Connection

Remote Desktop Connection is the newly improved and renamed Terminal Server client. This full-featured client now enables the end user to control Terminal Server session settings such as local disk, audio, and port redirection, plus additional settings such as running only a single program or logging on automatically. Remote Desktop Connection information can be saved and reused to connect to Terminal Servers with previously defined session specifications.