| 詳細(xì)參數(shù) | |||
|---|---|---|---|
| 品牌 | MOTOROLA | 型號 | VMIVME-7750-746000 |
| 結(jié)構(gòu)形式 | 模塊式 | 安裝方式 | 控制室安裝 |
| LD指令處理器 | 硬PLC | 加工定制 | 否 |
VMIVME-7750-746000
說到控制系統(tǒng)很多人貌似說得頭頭是道，繼續(xù)深究下去，什么是控制器，什么是PLC，什么是DCS，什么是FCS？三兩句話介紹完基本概念后，頓時(shí)語塞，怎么聊都感覺枯燥生硬有朋友可能會問什么是組態(tài)？其實(shí)組態(tài)就是搭建系統(tǒng)軟件和硬件環(huán)境，再簡單地說，組態(tài)就是用已有的簡單功能組合出更復(fù)雜的功能。
那上下位機(jī)又是什么呢？舉個(gè)例子：設(shè)想自己開發(fā)一個(gè)控制系統(tǒng)。首先要做的是告訴計(jì)算機(jī)自己想干什么，然后由計(jì)算機(jī)通知控制器，最后控制器再告訴執(zhí)行器具體該怎么做。這里面我其實(shí)只跟計(jì)算機(jī)發(fā)生對話，這里的計(jì)算機(jī)就是上位機(jī)，接受計(jì)算機(jī)指令的控制器就是下位機(jī)。
其實(shí)計(jì)算機(jī)和控制器本質(zhì)上說都是計(jì)算機(jī)，只是外在表現(xiàn)形式，應(yīng)用環(huán)境和編程方式的差異，導(dǎo)致我們必須采取一些便于理解的命名方式。上位機(jī)要跟人互動，所以偏重GUI，有顯示器或觸摸屏、鼠標(biāo)和鍵盤燈外設(shè)等人機(jī)交互設(shè)備。下位機(jī)要跟執(zhí)行機(jī)構(gòu)互動，所以偏重算法，人們要把需求編寫成可執(zhí)行的程序下載到下位機(jī)，上位機(jī)給出的指令觸發(fā)下位機(jī)程序執(zhí)行，下位機(jī)更像是一個(gè)黑盒子，執(zhí)行過程中人們無法直觀的看到每一個(gè)過程和步驟，只能對結(jié)果進(jìn)行分析，對不對，準(zhǔn)不準(zhǔn)，好不好Distributed Control System-->DCS（分布式控制系統(tǒng)），因?yàn)镈CS也是控制系統(tǒng)，遵循控制系統(tǒng)的基本形態(tài)，也有上下位機(jī)，也要進(jìn)行軟件和硬件組態(tài)。Distributed分布式是講DCS這個(gè)控制系統(tǒng)的特點(diǎn)和差異化。因此我們要搞明白什么是DCS就要從分布式這個(gè)特點(diǎn)開始。
Repeater can be first a Supplicant and later Authenticator. A smaller difference is that the Access Protocol Packet may convey not only success or failure inbation but also indication of a failed dialog. The authentication dialog allowed by IEEE802.1X/EAP allows for the use of both shared secrets and certificates. This solves the problem of OPERA1 Phase1 of authenticating only on a MAC address basis.
The new specification of OPERA is quite similar to the IEEE 802.11i and it complies with the RSNA (Robust Secure Network Association) defined in it. Nevertheless, the multihop nature of PLC, as shown in Figure 1, is a major difference with respect to wireless. In fact IEEE802.11i does not take into account the possible existence of repeaters.
What the OPERA specification does, is to apply recursively the dialog between Supplicant and Authenticator.
A node is first Supplicant and, once admitted into the network, may become Authenticator for another Supplicant. This creates a chain of trust among devices onto which security relies upon. What happens is that the messages sent by the Authenticator to the AS are transmitted over the PLC network and, thus, should be protected with encryption and integrity mechanisms as well as the data messages.
In agreement with IEEE802.11i, OPERA Phase 2 uses the EAPOL 4-way handshake for key management. The bive of this handshake is to prove mutual knowledge of the PMK (Pairwise Master Key). But prior to this handshake, the PMK has to be transferred to the Authenticator and this again has to be done by means of the secure channel bed by the mentioned chain of trust.
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