ARCNET
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
