ARCNET

from Wikipedia, the free encyclopedia

ARCNET ( A ttached R esource C omputer Net work ) is a networking technology for local area networks ( LANs ). It defines cable types and signaling for the bit transmission layer ( physical layer ) and packet formats and protocols for media access control (MAC) / data link layer of the OSI model .

ARCNET was first introduced to the public on December 1, 1977, after the computer manufacturer Datapoint , who developed the technology, completed the installation at its first customer, the Chase Manhattan Bank in New York City , in the same year . ARCNET was developed at the same time as Ethernet , but held as a proprietary unique selling point for a few years until Standard Microsystems Corporation took over the production of the corresponding controller, achieved approval in 1982 and, in 1985 , won Novell as a further partner . In the meantime, for example, ARCNET has become one of the foundations of BACnet .

ARCNET is physically set up either like a classic 10BASE2 Ethernet as a bus or alternatively as a star or tree . In the case of the bus variant, the switching components are simple T-pieces , or in the case of the star, active or passive hubs , whereby active and passive hubs can be mixed as desired. In its original form, ARCNET was built with coaxial cables . In the course of development, UTP and fiber optics were also specified. The coaxial cables do not correspond to the type RG-58 (with a characteristic impedance of 50 Ohm ) known from 10BASE2 (Thin Ethernet) , but RG-62 with a characteristic impedance of 93 Ohm. This circumstance temporarily ensured that Arcnet spread more quickly than Ethernet, as the RG-62 cables corresponded to IBM's SNA cabling and therefore an existing infrastructure could already be used in many places.

The connection to the hub and computer is optionally made in star form directly via BNC connector without the T-piece known from 10BASE2 to the hub, whereby no terminating resistor is required, as the termination of the cables takes place directly in the hub or on the card. The bus variant is wired with T-pieces in the same way as 10BASE2 and also has terminating resistors (93 Ohm) at the end of the cable. The possible distances between nodes are 2.5 to 4 times that of 10BASE2.

The ARCNET access procedure is token passing on a token bus . Similar to the Token Ring access method , a token is sent on the journey, which is passed on in a defined order. With Token Ring this is specified by the ring cabling. With ARCNET, the token is always sent throughout the network, and the next station in a logical sequence receives the token. The order is to be given to the cards as node ID (consecutive numbering) on ​​an externally accessible DIP switch ; With current products, the ARCNET-ID is communicated via the software of the card.

At 2.5 Mbit / s (20 Mbit / s through the use of ARCNET-Plus cards), the transfer rate is lower than Ethernet and Token Ring. Since, however, as with Token Ring, no collision slows down the speed of the transmission, a higher speed can be achieved with 2.5 Mbit than with Ethernet networks that are 4 times faster - especially with the highest network load. In 1990, US network specialist Thomas Conrad also presented an (unspecified) 100 Mbit version of ARCNET with RG-62 and fiber optic cabling under the name “TCNS”, which had all the advantages of ARCNET via Ethernet and Token Ring. Compaq dropped this system after the takeover of Thomas Conrad in favor of Fast Ethernet, which had meanwhile become significantly cheaper. In the early years, however, ARCNET was much cheaper than Ethernet or Token Ring, both in terms of components, as well as cabling and maintenance costs.

The ARCNET cards were also a specialty. ARCNET was an open design and in particular also had a standardized card API so that cards from different manufacturers could also work with a uniform driver. Many manufacturers later made use of this practical simplification with the widespread NE2000 -compatible Ethernet cards. There, too, this reduced development costs and soon led to very inexpensive cards. However, today's ARCNET cards require manufacturer-specific drivers.

An ARCNET network with a hub in the middle was a good example for explaining network topologies : the cabling formed a star , the electrical network was a bus and logically a ring . With the further spread of Fast Ethernet in local networks, ARCNET has lost its importance, but is still used in areas such as industrial production, printing technology, wind energy technology, but also medical technology and logistics.

credentials

  1. ↑ a b ARCNETworks (PDF; 140 kB) ARCNET Trade Association. Fall 1998. Archived from the original on March 4, 2016. Retrieved March 10, 2013.
  2. ↑ Craig Zacker, Paul Doyle et al., Understanding and Repairing Networks, Macmillan Computer Publishing, USA, 1996, chapter 7

Web links