A terminal server connects devices with a
serial port
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. ...
to a
local area network
A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger ...
(LAN). Products marketed as terminal servers can be very simple devices that do not offer any security functionality, such as
data encryption
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decip ...
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
One meaning of system console, computer console, root console, computer operator, operator's console, or simply console is the text entry and display device for system administration messages, particularly those from the BIOS or boot loader, the ...
of a computing device via networking technologies.
History
Although primarily used as an
Interface Message Processor
The Interface Message Processor (IMP) was the packet switching node used to interconnect participant networks to the ARPANET from the late 1960s to 1989. It was the first generation of gateways, which are known today as routers. An IMP was a r ...
starting in 1971, the
Honeywell 316
The Honeywell 316 was a popular 16-bit minicomputer built by Honeywell starting in 1969. It is part of the Series 16, which includes the Models 116 (1965, discrete), 316 (1969), 416 (1966), 516 (1966) and DDP-716 (1969). They were commonly used f ...
could also be configured as a Terminal Interface Processor (TIP) AND PROVIDE terminal server support for up to 63
ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
serial terminals through a multi-line controller in place of one of the hosts.
Historically, a terminal server was a device that attached to serial
RS-232
In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such a ...
devices, such as "green screen"
text terminal
A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. The teletype was an example of an early-day hard-copy terminal and ...
s or serial printers, and transported traffic via
TCP/IP
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...
,
Telnet
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 i ...
,
SSH
The Secure Shell Protocol (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution.
SSH applications are based on a ...
or other vendor-specific network protocols (e.g.,
LAT
Lat or LAT may refer to:
Places
* Lat, Fuman, village in Gilan Province, Iran
* Lat, Rasht, village in Gilan Province, Iran
* Lat, Mazandaran, village in Iran
* Lat-e Disar, village in Mazandaran Province, Iran
* Lat, Qazvin, village in I ...
) via an
Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
connection.
Digital Equipment Corporation
Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president unt ...
'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
Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for the NOR and NAND logic gates. Both us ...
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
VAX (an acronym for Virtual Address eXtension) is a series of computers featuring a 32-bit instruction set architecture (ISA) and virtual memory that was developed and sold by Digital Equipment Corporation (DEC) in the late 20th century. The V ...
or Alpha) using Digital's proprietary
Maintenance Operations Protocol The Maintenance Operation Protocol (MOP) is used for utility services such as uploading and downloading system software, remote testing and problem diagnosis. It was a proprietary protocol of Digital Equipment Corporation
Digital Equipment Corp ...
(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.
* Raw TCP socket connection: A raw TCP socket connection which can be initiated from the terminal server or from the remote host/server. This can be point-to-point or shared, where serial devices (like card readers, scanners, bar code readers, weight scales, etc.) can be shared amongst multiple devices. TCP sessions can be initiated from the TCP server application or from the terminal server.
* Raw UDP socket connection: For use with UDP based applications, terminal servers can convert serial equipment data for transport across UDP packets on a point-to-point basis or shared across multiple devices.
* Console management - reverse Telnet, reverse SSH: In console management terminology, users can use
reverse Telnet or SSH to connect to a serial device. They run Telnet or SSH on their client (PC) and attach to the terminal server, then connect to the serial device. In this application, terminal servers are also called
console server
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. ...
s because they are used to connect to console ports which are found on products like routers, PBXes, switches and servers (Linux or Sun). The idea is to gain access to those devices via their console port.
* Connect serial-based applications with a COM/TTY port driver: Many software applications have been written to communicate with devices that are directly connected to a server's serial
COM
Com or COM may refer to:
Computing
* COM (hardware interface), a serial port interface on IBM PC-compatible computers
* COM file, or .com file, short for "command", a file extension for an executable file in MS-DOS
* .com, an Internet top-level d ...
ports (robotic assembly machines, scanners, card readers, sensors, blood analyzers, etc.). Companies may want to network these applications because the devices that were directly connected to the server's COM ports need to be moved to a location some distance away from the application server. Since the original application was designed to talk directly to a specific COM port, a solution seamless to both the application and device must be implemented to enable communication across an IP network. (i.e., a solution that makes the application think it is talking directly to a COM port.) In this application,
serial port
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. ...
s can be connected to network servers or workstations running
COM port redirector
A virtual serial port is a software representation of a serial port that either does not connect to a real serial port, or adds functionality to a real serial port through software extension.
Software virtual ports
A software-based virtual seri ...
software operating as a virtual COM port. Many terminal server vendors include COM port redirector software with their terminal servers. This application need is most common in Windows environments, but also exists in Linux and Unix environments.
* Serial tunneling between two serial devices: Serial tunneling enables users to establish a link across Ethernet to a serial port on another terminal server.
* Back to back: This application is designed to solve a wiring problem. For example, a user needs to replace RS-232, RS-422 or RS-485 wire and run their data over Ethernet without making any changes to the server or the ultimate serial device, a user wants to replace a parallel leased line modem network with their parallel Ethernet network, or someone has a pick and place machine that puts ICs on boards, and they want to move the server into a back room where the equipment will be safe from damage. This application is ideal where a device exists with an application written to gather information from that device (common with sensors). This application allows them to eliminate the wiring. It can also be used with industrial devices (Allen-Bradley, Siemens, Modbus) so that those devices can be run transparently across the network.
* Virtual modem: Virtual modem is another example of a back-to-back application. It may be used to replace modems but still use an AT command set. An IP address is typed into the AT command set instead of the phone number of a serial device.
Console server
![ConsoleServer](https://upload.wikimedia.org/wikipedia/commons/a/a3/ConsoleServer.jpeg)
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
One meaning of system console, computer console, root console, computer operator, operator's console, or simply console is the text entry and display device for system administration messages, particularly those from the BIOS or boot loader, the ...
of a computing device via networking technologies.
Most commonly, a console server provides a number of
serial port
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. ...
s, 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
A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulati ...
, or over a network with
terminal emulator
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 termin ...
software such as
telnet
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 i ...
or
ssh
The Secure Shell Protocol (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution.
SSH applications are based on a ...
, maintaining survivable connectivity that allows remote users to log in the various consoles without being physically nearby.
Description
![96pTAB XL](https://upload.wikimedia.org/wikipedia/commons/5/5f/96pTAB_XL.jpg)
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
In systems management, out-of-band management involves the use of management interfaces (or serial ports) for managing networking equipment. Out-of-band (''OOB'') management is a networking term which refers to accessing and managing network infras ...
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 Commodity computing (also known as commodity cluster computing) involves the use of large numbers of already-available computing components for parallel computing, to get the greatest amount of useful computation at low cost. It is computing done in ...
hardware, usually with multiport serial cards typically running a slimmed-down
Unix-like
A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
operating system such as
Linux
Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
. 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
A rack unit (abbreviated U or RU) is a unit of measure defined as . It is most frequently used as a measurement of the overall height of 19-inch and 23-inch rack frames, as well as the height of equipment that mounts in these frames, whereby th ...
(1U), whereas a desktop computer with full-size
PCI
PCI may refer to:
Business and economics
* Payment card industry, businesses associated with debit, credit, and other payment cards
** Payment Card Industry Data Security Standard, a set of security requirements for credit card processors
* Pro ...
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
may refer to:
Science and technology Astronomy
* Cluster (spacecraft), constellation of four European Space Agency spacecraft
* Asteroid cluster, a small asteroid family
* Cluster II (spacecraft), a European Space Agency mission to study t ...
setups is to
null-modem
Null modem is a communication method to directly connect two DTEs ( computer, terminal, printer, etc.) 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 ord ...
wire and
daisy-chain consoles to otherwise unused serial ports on nodes with some other primary function.
See also
*
Conserver
*
KVM switch
A KVM switch (with KVM being an abbreviation for "keyboard, video, and mouse") is a hardware device that allows a user to control multiple computers from one or more sets of keyboards, video monitors, and mice.
Name
Switches to connect mu ...
*
Linux Terminal Server Project
Linux Terminal Server Project (LTSP) is a free and open source terminal server for Linux that allows many people to simultaneously use the same computer. Applications run on the server with a terminal known as a thin client (also known as an X te ...
*
Modem sharing device
*
P4000
The P4000 is a low-cost, low-profile terminal server produced by Lantronix during the mid-1990s. As the industry's first compact design terminal server, it found it way to shops that were looking for low-cost access methods to a fast-growing base ...
*
Time-sharing
In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and multi-tasking.DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Number 1
Its emergence a ...
References
External links
*Tom Fine
Console Server*How to build your ow
console serverusing
FreeBSD
FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...
Remote Serial Console HOWTOLinux Serial Consoles for Servers and ClustersBy Matthew Hoskins 2004
Project Hydra: the USB Multiheaded Monsterby Poul Petersen 2004
{{DEFAULTSORT:Terminal Server
Telecommunications equipment
System administration
Out-of-band management
Server
Server may refer to:
Computing
*Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients
Role
* Waiting staff, those who work at a restaurant or a bar attending customers and su ...
Networking hardware
Telnet