A Terminal Server, also known as a communication server, is a crucial hardware device or specialized server that acts as a central connection hub. It enables various terminals—ranging from personal computers and printers to diverse network devices—to establish a shared connection point to a local area network (LAN) or wide area network (WAN). These terminals interface with the terminal server through their RS-232C or RS-423 serial ports. Conversely, the terminal server connects to networks via network interface cards (NICs) to a LAN, commonly Ethernet, through modems for dial-in/out WAN access, or to networks like X.25 or a 3270 gateway. The specific interconnection options can vary depending on the terminal server’s make and model, with some even offering customizable configurations to meet specific customer needs.
The primary advantage of deploying a terminal server is the elimination of the need for individual NICs or modems for each terminal. Instead, the connection resources within the terminal server are dynamically allocated and shared among all connected terminals, optimizing resource utilization and reducing hardware costs.
Certain advanced terminal servers are engineered to support connections from hundreds of terminals concurrently. These terminals can encompass a broad spectrum of devices, including PCs, terminals designed to emulate 3270 mainframes, printers, and other devices equipped with an RS-232/423 interface. For network communication, terminals can leverage TCP/IP for Telnet connections to a host system, LAT for connecting to a Digital Equipment Corporation (DEC) host, or TN3270 for Telnet sessions with IBM hosts running 3270 applications. Furthermore, sophisticated terminal servers can facilitate a single user terminal to maintain simultaneous connections to multiple host operating systems, such as UNIX, IBM, and DEC environments, enhancing user flexibility and productivity.
While the concept of terminal servers originated in mainframe computing environments, modern operating systems like Windows Server have evolved to incorporate terminal server functionalities. This integration allows Windows Server to operate as a robust terminal server, extending the accessibility and applicability of terminal server technology to contemporary IT infrastructures.
Delving into the Functionality of a Terminal Server
The operational mechanics of a terminal server can differ based on the vendor and specific implementation. In the context of a Windows terminal server, the Windows Server operating system is specifically configured to accommodate multiple concurrent user sessions. This is a significant departure from standard multi-session environments like a Windows file server, as a terminal server uniquely renders a complete user interface for each active session.
Users establish connections to a terminal server using a Remote Desktop Protocol (RDP) client. This client, which can be a desktop application or a mobile app, is designed to connect to the terminal server and present the visual output of the user session. The RDP client communicates with the terminal server through a designated connection port. A session manager component within the terminal server plays a critical role in maintaining isolation between user sessions. It also manages essential session-related tasks, such as enabling users to seamlessly reconnect to their existing sessions even after inadvertently closing the RDP client, ensuring session persistence and continuity. Although the user sessions are executed as part of the terminal server utility, the session manager is the module responsible for their comprehensive management.
When a user interacts with a session through input devices like a keyboard, mouse, or touch interface, these inputs are captured within the RDP client environment. The RDP client then transmits these user inputs to the terminal server for processing. The terminal server undertakes the task of performing all graphical rendering operations. However, it is the RDP client that is ultimately responsible for displaying the session’s graphical output to the end user, creating a seamless interactive experience.
Terminal Server in Contrast to Remote Desktop
Although both terminal servers and remote desktops offer users the capability to interact with a remote computing session through an RDP client, they are fundamentally distinct in their underlying architecture and user experience. The primary differentiation lies in the operating system environment. Terminal servers operate on Windows Server, presenting users with a Windows Server desktop environment. Conversely, remote desktop environments typically utilize desktop operating systems, such as Windows 10, operating within virtual machines (VMs). Consequently, users in a remote desktop scenario are provided with a full-fledged desktop operating system experience, as opposed to a session that is hosted on a server operating system. This distinction impacts the user experience, performance characteristics, and the administrative overhead associated with each technology.
