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Most people who work in an office associate the term “Ethernet” with the physical cable behind their desk. This cable connects their office PC to the printers and Servers of the local network and the infinite web sites on the Internet. This cable is only the physical part of Ethernet, the media carrying Ethernet messages to your PC. On this wire are a whole series of communication protocols such as IP, the Internet Protocol; TCP, the Transport Control Protocol; and various Microsoft protocols such as NetBEUI. This suite of protocols works well for the office environment. It allows users to share files, access printers, send email, search the Internet and perform all the other communications used in the office environment.
The needs of the factory floor are much different with some very special requirements. Instead of accessing files and printers, factory floor controllers must access data embedded in drive systems, operator workstations and I/O devices. Instead of letting a user wait while a task is being performed, factory floor data communications needs are real-time or very close to real time. Terminating the fill operation on a bottle requires much more time-precise communications than accessing the next page of an Internet site.
Traditionally, Ethernet had only limited acceptance in Industrial Automation. Until recently the expense, lack of sophisticated switches and routers and the domination of large vendors with proprietary protocols prevented the wide acceptance of Ethernet on the factory floor. Now with prices falling, PCs with inherent Ethernet capability moving in droves onto the factory floor and intelligent switches and routers, Ethernet is gaining acceptance. Only the lack of a widely accepted, flexible application layer targeted to Industrial Automation has prevented its complete acceptance. |
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