Local Area Transport (LAT) is a non-routable (

data link layer The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer p ...

) networking technology developed by

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 ...

to provide connection between the DECserver

terminal 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 and Digital's

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 ...

and

Alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whic ...

and MIPS host computers via

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 ...

, giving communication between those hosts and serial devices such as

video terminal A computer terminal is an electronic or electromechanical computer hardware, hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. The Teleprinter, teletype was an example of an e ...

s 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. One ''LAT'' strength was efficiently handling time-sensitive data transmission. Over time, other host implementations of the LAT protocol appeared allowing communications to a wide range of

Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...

and other non-Digital operating systems using the LAT protocol.

History

In 1984, the first implementation of the LAT protocol connected a terminal server to a VMS VAX-Cluster in Spit Brook Road, Nashua, NH. By "virtualizing" the terminal port at the host end, a very large number of plug-and-play VT100-class terminals could connect to each host computer system. Additionally, a single physical terminal could connect via multiple sessions to multiple hosts simultaneously. Future generations of terminal servers included both LAT and

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 ...

protocols, one of the earliest protocols created to run on a burgeoning

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 ...

based Internet. Additionally, the ability to create reverse direction pathways from users to non-traditional RS232 devices (i.e. UNIX Host TTYS1 operator ports) created an entirely new market for Terminal Servers, now known as

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 in the mid to late 1990s, year 2000 and beyond through today. LAT and VMS drove the initial surge of adoption of "thick-wire"

by the computer industry. By 1986, terminal server networks accounted for 10% of Digital's $10 billion revenue. These early Ethernet LANs scaled using Ethernet bridges (another DEC invention) as well as

DECnet 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 ...

routers. Subsequently, Cisco routers, which implemented TCP-IP and DECnet, emerged as a global connection between these packet-based Ethernet LANs. Over time, when terminals became less popular,

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 ...

s had a built-in LAT client.

LAT features

If a computer communicating via ''LAT'' doesn't receive an acknowledgment within 80 milliseconds for a packet it transmitted, it resends that packet; this can clog a network. No data is sent if no data is offered and under heavy loads LAT limits the number of packets sent per second to twenty-four: twelve transmits and twelve receives. As more characters are sent, the packets get bigger but not more numerous. Above 80 milliseconds latency a touch typist will notice the sluggish character echo. The LAT 80 millisecond delay offloads both the network by sending fewer larger packets which also reduces interrupts at each system.

Early Terminal Server Vendors

- primarily via their DECserver systems. * Able Computer - An early provider of Terminal Server products. * Chase Research - A Europe-based early provider of Terminal Server products. *

Cisco Systems Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational corporation, multinational digital communications technology conglomerate (company), conglomerate corporation headquartered in San Jose, California. Cisco develo ...

- Provided LAT on Terminal Servers as early as 1990. *

Emulex Corporation Emulex Corporation is a provider of computer network connectivity, monitoring and management hardware and software. The company's I/O connectivity offerings, including its line of Ethernet and Fibre Channel-based connectivity products, are or ...

- A California-based early provider of Terminal Server products that included X.25 and 3270 features; they sold through Datability and other OEMs. * Hughes LAN Systems - Provided LAT capability in 1989.Breidenbach, Susan: "HLS unveils file servers, software", ''Network World'' 6.33 (1989): 21,24. *

Interlink Computer Sciences Interlink Computer Sciences, of Fremont, California, was a developer of hardware and software that allowed IBM mainframe computers running the MVS operating system to be connected to non-IBM networks. Interlink was founded in 1983 by Lambert O ...

, an early 1990 LAT vendor. * Xyplex Corporation - An early provider of Terminal Server products based in Massachusetts.

Open Source solutions

Most

Linux distributions A Linux distribution (often abbreviated as distro) is an operating system made from a software collection that includes the Linux kernel and, often, a package management system. Linux users usually obtain their operating system by downloading one ...

offer a client and server ''lat'' package, that can easily be installed via a

package manager A package manager or package-management system is a collection of software tools that automates the process of installing, upgrading, configuring, and removing computer programs for a computer in a consistent manner. A package manager deals wi ...

. This allows e.g. to access 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 ...

server while being connected to a corporate VPN network that would otherwise block local

traffic.

References

External links

* http://sourceforge.net/apps/mediawiki/linux-decnet/index.php?title=LAT -

Open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized sof ...

LAT project for

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 ...