 | This article needs additional citations for verification .(August 2010) |
Attached Resource Computer NETwork (ARCNET or ARCnet) is a communications protocol for local area networks. [1] ARCNET was the first widely available networking system for microcomputers and it became popular in the 1980s for office automation tasks. It was later applied to embedded systems where certain features of the protocol are especially useful.
ARCNET was developed by principal development engineer John Murphy, at Datapoint Corporation in 1976 under Victor Poor, and announced in 1977. [2] It was originally developed to connect groups of their Datapoint 2200 terminals to talk to a shared 8" floppy disk system. It was the first loosely coupled LAN-based clustering system, making no assumptions about the type of computers that would be connected. This was in contrast to contemporary larger and more expensive computer systems such as DECnet or SNA, where a homogeneous group of similar or proprietary computers were connected as a cluster.
The token-passing bus protocol of that I/O device-sharing network was subsequently applied to allowing processing nodes to communicate with each other for file-serving and computing scalability purposes. An application could be developed in DATABUS, Datapoint's proprietary COBOL-like language, and deployed on a single computer with dumb terminals. When the number of users outgrew the capacity of the original computer, additional 'compute' resource computers could be attached via ARCNET to run the same applications and access the same data. If more storage was needed, additional disk resource computers could also be attached. This incremental approach broke new ground and by the end of the 1970s (before the first IBM PC was announced in 1981), over ten thousand ARCNET LAN installations were in commercial use around the world while Datapoint had become a Fortune 500 company. As microcomputers took over the industry, well-proven and reliable ARCNET was also offered as an inexpensive LAN for these machines.
ARCNET remained proprietary until the early-to-mid 1980s. This did not cause concern at the time, as most network architectures were proprietary. The move to non-proprietary, open systems began as a response to the dominance of International Business Machines (IBM) and its Systems Network Architecture (SNA). In 1979, the Open Systems Interconnection Reference Model (OSI model) was published. Then, in 1980, Digital, Intel and Xerox (the DIX consortium) published an open standard for Ethernet that was soon adopted as the basis of standardization by the IEEE and the ISO. IBM responded by proposing Token Ring as an alternative to Ethernet but kept such tight control over standardization that competitors were wary of using it. ARCNET was less expensive than either of these, was more reliable, more flexible and, by the late 1980s, had a market share about equal to that of Ethernet. [ citation needed ] Tandy/Radio Shack offered ARCNET as an application and file sharing medium for their TRS-80 Model II, Model 12, Model 16, Tandy 6000, Tandy 2000, Tandy 1000 and Tandy 1200 computer models. There were also hooks in the Model 4P's ROM to boot from an ARCNET network. [3] [4] [5]
Ethernet became much more attractive when it moved from co-axial cable to twisted pair and an "interconnected stars" cabling topology based on active hubs. Easier cabling, combined with the greater raw speed of Ethernet (10 Mbit/s versus 2.5 Mbit/s for ARCnet) helped to increase Ethernet's demand. As more companies entered the market, the price of Ethernet started to fall while ARCNET and Token Ring volumes tapered off.
In response to greater bandwidth needs, and the challenge of Ethernet, a new standard called ARCnet Plus was developed by Datapoint and introduced in 1992. ARCnet Plus ran at 20 Mbit/s and was backward-compatible with original ARCnet equipment. However, by the time ARCnet Plus products were ready for the market, Ethernet had captured the majority of the network market and there was little incentive for users to move back to ARCnet. As a result, very few ARCnet Plus products were ever produced. Those that were built, mainly by Datapoint, were expensive and hard to find.
ARCNET was eventually standardized as ANSI ARCNET 878.1. It appears this was when the name changed from ARCnet to ARCNET. Other companies entered the market, notably Standard Microsystems who produced systems based on a single VLSI chip, originally developed as custom LSI for Datapoint, but later made available by Standard Microsystems to other customers. Datapoint eventually found itself in financial trouble and moved into video conferencing then and later to custom programming in the embedded market.
Even though ARCNET is now rarely used for new general networks, the diminishing installed base still requires support and it retains a niche in industrial control. [6]
Original ARCNET used RG-62/U coaxial cable of 93 Ω impedance and either passive or active hubs in a star-wired bus topology. At the time of its greatest popularity, this was a significant advantage of ARCNET over Ethernet. A star-wired bus was much easier to build, expand and maintain than the clumsy linear bus Ethernet of the time. The "interconnected stars" cabling topology made it easy to add and remove nodes without taking down the whole network, and much easier to diagnose and isolate failures within a complex LAN.
Another significant advantage ARCNET had over Ethernet was cable distance. ARCNET coax cable runs could extend 610 m (2,000 ft) between active hubs or between an active hub and an end node, while the RG-58 (50Ω) 'thin' Ethernet most widely used at that time was limited to a maximum run of 185 m (607 ft) from end to end. [7]
ARCNET had the disadvantage of requiring either an active or passive hub between nodes if there were more than two nodes in the network, while thin Ethernet allowed nodes to be spaced anywhere along the linear coax cable. However, ARCNET passive hubs were very inexpensive, being composed of a simple, small, unpowered box with four ports, wired together with nothing more than four discrete resistors, so the disadvantage was not significant. This disadvantage can also be seen as an advantage: often the cost of a 4 port ARCNET passive hub was less than the 4 BNC Tee connectors and 2 terminators that thin Ethernet requires to connect 4 computers. Unlike BNC Tee connectors that could sometimes be hard to obtain in the early days of Ethernet, an ARCNET passive hub could be easily manufactured in the field with 9 readily available parts: 4 connectors, 4 resistors and a box to put them in.
Passive hubs limited the distance between a node and an active hub to 30 m (100 ft). A passive hub could not be connected directly to another passive hub. Unused ports on both types of hubs had to be terminated with a special connector. This special connector, called a terminator, is just a BNC connector with a 93 ohm resistor in it. Thin Ethernet also requires nearly identical terminators at the two terminal ends, the only difference being Ethernet uses a 50 ohm resistor.
To reduce costs while still allowing wide area coverage, a common practice was to use one or more interconnected active hubs, each of which provided coverage for nodes no more than 60 m (200 ft) away. Cable was run from each port of the active hubs to a different location no more than 30 m (100 ft) away. A passive hub would then be attached to the end of the cable, and cables would be run locally from the passive hub, allowing connection of up to three nodes. In this way, a single 8-port active hub could be used to connect 24 networked devices over an area not exceeding 120 m (400 ft) in diameter.
ARCNET allowed only 255 nodes per network. Node IDs for LAN workstations were typically set by DIP switches on the network interface card. Larger networks would have to be split into smaller networks, and bridged. The small number of possible nodes and the need to manually configure IDs was a disadvantage compared with Ethernet, particularly as large enterprise networks became common.
To mediate access to the bus, ARCNET, like Token Ring, uses a token passing scheme, rather than the carrier sense multiple access approach of Ethernet. When peers are inactive, a single "token" message is passed around the network from machine to machine and no peer is allowed to use the bus unless it has the token. If a particular peer wishes to send a message, it waits to receive the token, sends its message then passes the token on to the next station. Because ARCNET is implemented as a distributed star, the token cannot be passed machine to machine around a ring. Instead, each node is assigned an 8 bit address (usually via DIP switches), and when a new node joins the network a "reconfig" occurs, wherein each node learns the address of the node immediately above it. The token is then passed directly from one node to the next.
Historically, each approach had its advantages: ARCNET added a small delay on an inactive network as a sending station waited to receive the token, but Ethernet's performance degraded drastically if too many peers attempted to broadcast at the same time, due to the time required for the slower processors of the day to process and recover from collisions.[ citation needed ] ARCNET had slightly lower best-case performance (viewed by a single stream), but was much more predictable. ARCNET also has the advantage that it achieved its best aggregate performance under the highest loading, approaching asymptotically its maximum throughput. While the best case performance was less than Ethernet, the general case was equivalent and the worst case was dramatically better. An Ethernet network could collapse when too busy due to excessive collisions. An ARCNET would keep on going at normal (or even better) throughput. Throughput on a multi-node collision-based Ethernet was limited to between 40% and 60% of bandwidth usage (depending on source). Although 2.5 Mbit/s ARCNET could at one time outperform a 10 Mbit/s Ethernet in a busy office on slow processors, ARCNET ultimately gave way to Ethernet as improved processor speeds reduced the impact of collisions on overall throughput, and Ethernet costs dropped. [ citation needed ]
In the early 1980s, ARCNET was much cheaper than Ethernet, in particular for PCs. For example, in 1985 SMC sold ARCNET cards for around US$300 whilst an Ungermann-Bass Ethernet card plus transceiver could cost US$500.
Another significant difference is that ARCNET provides the sender with a definite success/failure status of delivery at the receiver before the token passes on to the next node. This permits much faster fault recovery within the higher level protocols, rather than having to wait for a timeout on the expected replies. ARCNET also doesn't waste network time transmitting to a node not ready to receive the message, since the initial hardware-level inquiry establishes that the recipient is able and ready to receive the larger message before it is sent across the bus.
One further advantage that ARCNET enjoyed over collision-based Ethernet is that it guarantees equitable access to the bus by everyone on the network. Although it takes a time to get the token depending on the number of nodes and the size of the messages currently being sent, a node will always receive it within a predictable maximum time. It is therefore deterministic. This made ARCNET an ideal real-time networking system, which explains its use in the embedded systems and process control markets. Token Ring has similar qualities, but is much more expensive to implement than ARCNET.
In spite of ARCNET's deterministic operation and historic suitability for real-time environments such as process control, the general availability of switched gigabit Ethernet and Quality of service capabilities in Ethernet switches has all but eliminated ARCNET today.
At first the system was deployed using the RG-62/U coaxial cable commonly used in IBM mainframe environments to connect 3270 terminals and controllers, but later added support for twisted pair and fibre media. At ARCNET's lower speeds (2.5 Mbit/s), Cat-3 cable is good enough to run ARCNET. Some ARCNET twisted-pair products supported cable runs over 2,000 ft (610 m) on standard Cat-3 cable, far beyond anything Ethernet could do on any kind of copper cable.
In the early 1990s, Thomas-Conrad Corporation developed a 100 Mbit/s topology called TCNS based on the ARCNET protocol, which also supported RG-62, twisted-pair, and fiber optic media. [8] TCNS enjoyed some success until the availability of lower-cost 100 Mbit/s Ethernet put an end to the general deployment of ARCNET as a LAN protocol.
However, because of its simple and robust nature, ARCNET controllers are still sold and used in industrial, embedded, and automotive applications.
AppleTalk is a discontinued proprietary suite of networking protocols developed by Apple Computer for their Macintosh computers. AppleTalk includes a number of features that allow local area networks to be connected with no prior setup or the need for a centralized router or server of any sort. Connected AppleTalk-equipped systems automatically assign addresses, update the distributed namespace, and configure any required inter-networking routing.
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 1983 as IEEE 802.3. Ethernet has since been refined to support higher bit rates, a greater number of nodes, and longer link distances, but retains much backward compatibility. Over time, Ethernet has largely replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET.
A local area network (LAN) is a computer network that interconnects computers within a single physical location, which could range from a home network with one user to a large network at a school or office building. Ethernet and Wi-Fi are the two most common technologies in use for local area networks; historical network technologies include ARCNET, Token Ring and AppleTalk.
100BaseVG is a 100 Mbit/s Ethernet standard specified to run over four pairs of Category 3 cable. It is also called 100VG-AnyLAN because it was defined to carry both Ethernet and Token Ring frame types.
10BASE2 is a variant of Ethernet that uses thin coaxial cable terminated with BNC connectors to build a local area network. During the mid to late 1980s, this was the dominant 10 Mbit/s Ethernet standard.
10BASE5 was the first commercially available variant of Ethernet. The technology was standardized in 1982 as IEEE 802.3. 10BASE5 uses a thick and stiff coaxial cable up to 500 meters (1,600 ft) in length. Up to 100 stations can be connected to the cable using vampire taps and share a single collision domain with 10 Mbit/s of bandwidth shared among them. The system is difficult to install and maintain.
Ethernet over twisted-pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers.
Fiber Distributed Data Interface (FDDI) is a standard for data transmission in a local area network. It uses optical fiber as its standard underlying physical medium.
Network topology is the arrangement of the elements of a communication network. Network topology can be used to define or describe the arrangement of various types of telecommunication networks, including command and control radio networks, industrial fieldbusses and computer networks.
In computer networking, a token bus network is a network implementing a token-passing protocol over a virtual ring on a coaxial cable.
A controller area network (CAN) is a vehicle bus standard designed to enable efficient communication primarily between electronic control units (ECUs). Originally developed to reduce the complexity and cost of electrical wiring in automobiles through multiplexing, the CAN bus protocol has since been adopted in various other contexts. This broadcast-based, message-oriented protocol ensures data integrity and prioritization through a process called arbitration, allowing the highest priority device to continue transmitting if multiple devices attempt to send data simultaneously, while others back off. Its reliability is enhanced by differential signaling, which mitigates electrical noise. Common versions of the CAN protocol include CAN 2.0, CAN FD, and CAN XL which vary in their data rate capabilities and maximum data payload sizes.
Datapoint Corporation, originally known as Computer Terminal Corporation (CTC), was a computer company based in San Antonio, Texas, United States. Founded in July 1968 by Phil Ray and Gus Roche, its first products were, as the company's initial name suggests, computer terminals intended to replace Teletype machines connected to time sharing systems.
In telecommunications networks, a node is either a redistribution point or a communication endpoint.
An Ethernet hub, active hub, network hub, repeater hub, multiport repeater, or simply hub is a network hardware device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming. A hub works at the physical layer. A repeater hub also participates in collision detection, forwarding a jam signal to all ports if it detects a collision. In addition to standard 8P8C ("RJ45") ports, some hubs may also come with a BNC or an Attachment Unit Interface (AUI) connector to allow connection to legacy 10BASE2 or 10BASE5 network segments.
On a local area network, token passing is a channel access method where a packet called a token is passed between nodes to authorize that node to communicate. In contrast to polling access methods, there is no pre-defined "master" node. The most well-known examples are IBM Token Ring and ARCNET, but there were a range of others, including FDDI, which was popular in the early to mid 1990s.
Fiber to the x or fiber in the loop is a generic term for any broadband network architecture using optical fiber to provide all or part of the local loop used for last mile telecommunications. As fiber optic cables are able to carry much more data than copper cables, especially over long distances, copper telephone networks built in the 20th century are being replaced by fiber.
A computer network is a set of computers sharing resources located on or provided by network nodes. Computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are made up of telecommunication network technologies based on physically wired, optical, and wireless radio-frequency methods that may be arranged in a variety of network topologies.
Token Ring is a physical and data link layer computer networking technology used to build local area networks. It was introduced by IBM in 1984, and standardized in 1989 as IEEE 802.5. It uses a special three-byte frame called a token that is passed around a logical ring of workstations or servers. This token passing is a channel access method providing fair access for all stations, and eliminating the collisions of contention-based access methods.
HYPERchannel, sometimes rendered Hyperchannel, was a local area networking system for mainframe computers, especially supercomputers, introduced by Network Systems Corporation in the 1970s. It ran at the then-fast speed of 50 Mbits/second, performance that would not be matched by commodity hardware until the introduction of Fast Ethernet in 1995. HYPERchannel ran over very thick coax cable or fibre optic extensions and required adaptor hardware the size of a minicomputer. The networking protocol was entirely proprietary. Solutions for Control Data, IBM and Cray computers were their primary products, but a wide variety of support emerged in the 1980s, including DEC VAX and similar superminicomputers.
Classic Ethernet is a family of 10 Mbit/s Ethernet standards, which is the first generation of Ethernet standards. In 10BASE-X, the 10 represents its maximum throughput of 10 Mbit/s, BASE indicates its use of baseband transmission, and X indicates the type of medium used. Classic Ethernet includes coax, twisted pair and optical variants. The first Ethernet standard was published in 1983 and classic Ethernet operating at 10 Mbit/s was the dominant form of Ethernet until the first standard for Fast Ethernet was approved in 1995.