工業(yè)網(wǎng)絡通信

　　工業(yè)應用中的聯(lián)網(wǎng)問題有著悠久而相當混亂的歷史。每一個行業(yè)都面臨著在單個設備上部署電子控制的任務，將這些控制連接到自動化的孤島上，最后將這些島嶼拉進一個工廠范圍內(nèi)的網(wǎng)絡。它們現(xiàn)在與企業(yè)網(wǎng)絡相連，并與銷售預測、庫存控制和管理信息系統(tǒng)等相關聯(lián)。然而，這超出了這一塊的范圍。這種方法的問題是，不同的行業(yè)開發(fā)了不同的實現(xiàn)網(wǎng)絡的方法。在20世紀80年代，有一種運動，用ISO來創(chuàng)建一個描述OSI（開放系統(tǒng)互連）模型的網(wǎng)絡的通用方法，并使用這種模型來發(fā)現(xiàn)不同網(wǎng)絡技術的交互方式。本文將通信視為七層模型。第1級是物理層，它定義了電線、連接器和信號穿越導線（或光纖）的方式。這些層變得越來越抽象，直到第7層，應用層，它是網(wǎng)絡和通信軟件之間的接口。

　　At the time there was a huge investment in OSI activities， with an important legacy consisting of the ability to describe current networking technologies in terms of the relevant OSI layers， even if they were not designed with that approach.

　　Today there are several networking technologies being deployed. Industrial Ethernet is making steady progress， particularly as it is seen as compatible with standard Ethernet. While it has significant plus points， it does have some disadvantages， particularly for hard real-time applications. Despite this， many earlier networking technologies， such as Modbus and Profibus， have been adapted as overlays on Ethernet.