Terminal server

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A terminal server connects devices with a serial port to a local area network (LAN). Products marketed as terminal servers can be very simple devices that do not offer any security functionality, such as data encryption and user authentication. The primary application scenario is to enable serial devices to access network server applications, or vice versa, where security of the data on the LAN is not generally an issue. There are also many terminal servers on the market that have highly advanced security functionality to ensure that only qualified personnel can access various servers and that any data that is transmitted across the LAN, or over the Internet, is encrypted. Usually, companies that need a terminal server with these advanced functions want to remotely control, monitor, diagnose and troubleshoot equipment over a telecommunications network.


A console server (also referred to as console access server, console management server, serial concentrator, or serial console server) is a device or service that provides access to the system console of a computing device via networking technologies.


Although primarily used as an Interface Message Processor starting in 1971, the Honeywell 316 could also be configured as a Terminal Interface Processor (TIP) AND PROVIDE terminal server support for up to 63 ASCII serial terminals through a multi-line controller in place of one of the hosts. [1]

Historically, a terminal server was a device that attached to serial RS-232 devices, such as "green screen" text terminals or serial printers, and transported traffic via TCP/IP, Telnet, SSH or other vendor-specific network protocols (e.g., LAT) via an Ethernet connection.

Digital Equipment Corporation's DECserver 100 (1985), 200 (1986) and 300 (1991) are early examples of this technology. (An earlier version of this product, known as the DECSA Terminal Server was actually a test-bed or proof-of-concept for using the proprietary LAT protocol in commercial production networks.) With the introduction of inexpensive flash memory components, Digital's later DECserver 700 (1991) and 900 (1995) no longer shared with their earlier units the need to download their software from a "load host" (usually a Digital VAX or Alpha) using Digital's proprietary Maintenance Operations Protocol (MOP). In fact, these later terminal server products also included much larger flash memory and full support for the Telnet part of the TCP/IP protocol suite. Many other companies entered the terminal-server market with devices pre-loaded with software fully compatible with LAT and Telnet.

Modern usage

A "terminal server" is used many ways but from a basic sense if a user has a serial device and they need to move data over the LAN, this is the product they need.

Console server

A Lantronix 32-port serial console server ConsoleServer.jpeg
A Lantronix 32-port serial console server

A console server (console access server, console management server, serial concentrator, or serial console server) is a device or service that provides access to the system console of a computing device via networking technologies.

Most commonly, a console server provides a number of serial ports, which are then connected to the serial ports of other equipment, such as servers, routers or switches. The consoles of the connected devices can then be accessed by connecting to the console server over a serial link such as a modem, or over a network with terminal emulator software such as telnet or ssh, maintaining survivable connectivity that allows remote users to log in the various consoles without being physically nearby.


A ZPE Systems 96-port serial console server. 96pTAB XL.jpg
A ZPE Systems 96-port serial console server.

Dedicated console server appliances are available from a number of manufacturers in many configurations, with the number of serial ports ranging from one to 96. These Console Servers are primarily used for secure remote access to Unix Servers, Linux Servers, switches, routers, firewalls, and any other device on the network with a console port. The purpose is to allow network operations center (NOC) personnel to perform secure remote data center management and out-of-band management of IT assets from anywhere in the world. Products marketed as Console Servers usually have highly advanced security functionality to ensure that only qualified personnel can access various servers and that any data that is transmitted across the LAN, or over the Internet, is encrypted. Marketing a product as a console server is very application specific because it really refers to what the user wants to do—remotely control, monitor, diagnose and troubleshoot equipment over a network or the Internet.

Some users have created their own console servers using off-the-shelf commodity computer hardware, usually with multiport serial cards typically running a slimmed-down Unix-like operating system such as Linux. Such "home-grown" console servers can be less expensive, especially if built from components that have been retired in upgrades and allow greater flexibility by putting full control of the software driving the device in the hands of the administrator. This includes full access to and configurability of a wide array of security protocols and encryption standards, making it possible to create a console server that is more secure. However, this solution may have a higher TCO, less reliability and higher rack-space requirements, since most industrial console servers have the physical dimension of one rack unit (1U), whereas a desktop computer with full-size PCI cards requires at least 3U, making the home-grown solution more costly in the case of a co-located infrastructure.

An alternative approach to a console server used in some cluster setups is to null-modem wire and daisy-chain consoles to otherwise unused serial ports on nodes with some other primary function.

See also

Related Research Articles

Telnet Network protocol for bidirectional communication using a virtual terminal connection

Telnet is an application protocol used on the Internet or local area network to provide a bidirectional interactive text-oriented communication facility using a virtual terminal connection. User data is interspersed in-band with Telnet control information in an 8-bit byte oriented data connection over the Transmission Control Protocol (TCP).

Terminal emulator Program that emulates a video terminal

A terminal emulator, or terminal application, is a computer program that emulates a video terminal within some other display architecture. Though typically synonymous with a shell or text terminal, the term terminal covers all remote terminals, including graphical interfaces. A terminal emulator inside a graphical user interface is often called a terminal window.

Serial port Communication interface transmitting information sequentially

In computing, a serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel. Throughout most of the history of personal computers, data has been transferred through serial ports to devices such as modems, terminals, various peripherals, and directly between computers.

DECnet is a suite of network protocols created by Digital Equipment Corporation. Originally released in 1975 in order to connect two PDP-11 minicomputers, it evolved into one of the first peer-to-peer network architectures, thus transforming DEC into a networking powerhouse in the 1980s. Initially built with three layers, it later (1982) evolved into a seven-layer OSI-compliant networking protocol.

Shell account User account on a remote server

A shell account is a user account on a remote server, traditionally running under the Unix operating system, which gives access to a shell via a command-line interface protocol such as telnet, SSH, or over a modem using a terminal emulator.

Null modem Serial cable connecting two computers

Null modem is a communication method to directly connect two DTEs using an RS-232 serial cable. The name stems from the historical use of RS-232 cables to connect two teleprinter devices or two modems in order to communicate with one another; null modem communication refers to using a crossed-over RS-232 cable to connect the teleprinters directly to one another without the modems. It is also used to serially connect a computer to a printer, since both are DTE, and is known as a Printer Cable.

Port forwarding Application of network address translation

In computer networking, port forwarding or port mapping is an application of network address translation (NAT) that redirects a communication request from one address and port number combination to another while the packets are traversing a network gateway, such as a router or firewall. This technique is most commonly used to make services on a host residing on a protected or masqueraded (internal) network available to hosts on the opposite side of the gateway, by remapping the destination IP address and port number of the communication to an internal host.

In computer networks, a tunneling protocol is a communication protocol which allows for the movement of data from one network to another, by exploiting encapsulation. It involves allowing private network communications to be sent across a public network through a process called encapsulation.

Remote administration refers to any method of controlling a computer from a remote location. Software that allows remote administration is becoming increasingly common and is often used when it is difficult or impractical to be physically near a system in order to use it. A remote location may refer to a computer in the next room or one on the other side of the world. It may also refer to both legal and illegal remote administration.

Local Area Transport (LAT) is a non-routable networking technology developed by Digital Equipment Corporation to provide connection between the DECserver terminal servers and Digital's VAX and Alpha and MIPS host computers via Ethernet, giving communication between those hosts and serial devices such as video terminals and printers. The protocol itself was designed in such a manner as to maximize packet efficiency over Ethernet by bundling multiple characters from multiple ports into a single packet for Ethernet transport.

Home network Type of computer network

A home network or home area network (HAN) is a type of computer network that facilitates communication among devices within the close vicinity of a home. Devices capable of participating in this network, for example, smart devices such as network printers and handheld mobile computers, often gain enhanced emergent capabilities through their ability to interact. These additional capabilities can be used to increase the quality of life inside the home in a variety of ways, such as automation of repetitive tasks, increased personal productivity, enhanced home security, and easier access to entertainment.

In computer networking, DECserver initially referred to a highly successful family of asynchronous console server / terminal server / print server products introduced by Digital Equipment Corporation (DEC) and later referred to a class of UNIX-variant application and file server products based upon the MIPS processor. In February 1998, DEC sold its Network Products Business to Cabletron, which then spun out as its own company, Digital Networks, in September 2000.

Perle Systems Serial to Ethernet, fiber to Ethernet and device networking hardware manufacturer

Perle Systems is a technology company that develops and manufactures serial to Ethernet, fiber to Ethernet, I/O connectivity, and device networking equipment. These types of products are commonly used to establish network connectivity across multiple locations, securely transmit sensitive information across a LAN, and remotely monitor and control networked devices via out-of-band management.

A network host is a computer or other device connected to a computer network. A host may work as a server offering information resources, services, and applications to users or other hosts on the network. Hosts are assigned at least one network address.

Reverse telnet is a specialized application of telnet, where the server side of the connection reads and writes data to a computer terminal line, rather than providing a command shell to the host device. Typically, reverse telnet is implemented on an embedded device, which has an Ethernet network interface and serial port(s). Through the use of reverse telnet on such a device, IP-networked users can use telnet to access serially-connected devices.

In systems management, out-of-band management involves the use of management interfaces for managing and networking equipment. Out-of-band (OOB) is a networking term which refers to having a separate channel of communication which does not travel over the usual data stream.

Conserver is a serial console management system that provides remote access to system consoles and logs to a central (master) host. It supports both local and network serial connections and allows replay of the server console history even if the server is down. Multiple users can connect to a single serial connection, with one having write-access.

ZOC (software)

ZOC is a popular computer-based terminal emulator and Telnet software client for the Microsoft Windows and Apple Macintosh macOS operating systems that supports telnet, modem, SSH 1 and 2, ISDN, serial, TAPI, Rlogin and other means of communication. Its terminal emulator supports Xterm emulation with full colors, meta-keys and local printing, VT102, VT220 and several types of ANSI as well as Wyse, TVI, TN3270, and Sun's CDE. It supports full keyboard remapping, scripting in REXX and other languages, and support for named pipes.

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  1. Kirstein, Peter T. (July–September 2009). "The Early Days of the Arpanet". IEEE Annals of the History of Computing. 31 (3): 67. doi:10.1109/mahc.2009.35. ISSN   1058-6180.