Digital communication networks have become a core technology in advanced building automation systems. Communication networks such as MS/TP, ARCNET, and Ethernet can be categorized as discrete-event dynamic systems (DEDS) (Casandras and Lafortune 1999).
The Attached Resource Computer Network (ARCNet) standard was created in 1977 at the Data Point Corporation by a scientist – John Murphy. ARCNet uses the token-passing protocol over a star and bus topology. The star and bus topology combines the flexibility of a star with the simplicity and throughput of a bus. Thus, ARCNet standard has a unique protocol/topology combination: token-passing protocol and Distributed star/bus topology.
Like Ethernet and Controller Area Network (CAN), ARCNET is a data-link layer technology with no defined application layer. ARCnet is an extremely easy-to-install LAN since it offers a flexible topology with few limitations. It can be configured as a simple Star or Bus topology network, or a Combined Star and Bus topology network. The ARCnet card is equipped with a standard BNC female connector for connection to RG-62 A/U coaxial cable.
ArcNet technology is described by the ANSI standard 878.1 and predates the IEEE Project 802 standards. ArcNet should not be confused with the IEEE Token Bus standard, IEEE 802.4. However, ArcNet does loosely comply to this token passing specification. ArcNet technology is described by the ANSI standard 878.1 and predates the IEEE Project 802 standards. ArcNet should not be confused with the IEEE Token Bus standard, IEEE 802.4. However, ArcNet does loosely comply to this token passing specification.
The token moves from one computer to another based on node addresses instead of the physical location of computers. This means that ArcNet passes the token to the next address regardless of whether the address is on a workstation in the same room or in a separate building.
Each computer in an ArcNet network is connected by a cable to a hub, which can be an active, a passive or a smart hub.
The standard cabling used for ArcNet is 93 ohm RG-62 A/U coaxial cable. ArcNet also supports twisted pair and fiber optic cables.
The use of star topology and cable filtering make ArcNet networks reliable. In a distributed star design, ArcNet uses passive and active hubs to control and route data tokens from one workstation to the next. Since token passing is done at a fixed rate and collisions do not occur, ArcNet is very stable.
Advantages of ARCNet.
Here are some of the ARCNet’s advantages:
1. It is extremely reliable.
2. ARCNet is easy to install and troubleshoot.
3. It has an excellent track record of interoperability for those using ARCNet components from various manufacturers.
4. ARCNet supports a variety of cable types including coaxial, UTP and Fiber Optics.
5. It is inexpensive and built to stay that way.
Disadvantages of ARCNet
Here are some disadvantages of ARCNet:
1. Standard ARCNet is very slow (2.5 Mb/s). It is almost seven times slower than Token Ring.
2. ARCNet was not designed with interconnectivity in mind. For many installations, it’s difficult to go beyond the confines of single LAN.
Dinesh Thakur holds an B.C.A, MCDBA, MCSD certifications. Dinesh authors the hugely popular