快速以太網(wǎng) (100Base-T) 采用一對數(shù)據(jù)發(fā)送和一對數(shù)據(jù)接收，傳輸速率均為 100Mbps。帶 Dcoding 的 4 針 M12 連接器非常適合快速以太網(wǎng)傳輸。8 針連接器僅用于更高的傳輸速率，例如以 1000Mbps 傳輸?shù)那д滓蕴W(wǎng) (1000Base-T)。對于千兆以太網(wǎng)，所有四對線都用于在全雙工模式下發(fā)送和接收。IEC 11801:2002 Cat5 中規(guī)定的傳輸特性也涵蓋千兆以太網(wǎng)。

到目前為止，還沒有專門為以太網(wǎng)編碼的標準 8 針連接器封裝。帶有 8 針 M12 連接器的以太網(wǎng)電纜通常采用與傳感器-執(zhí)行器電纜相同的 A 編碼。這種方法消除了與為現(xiàn)場總線系統(tǒng)設計的 B 編碼 8 針連接器的任何混淆。

對于符合 IEEE 802.3af 的以太網(wǎng)供電應用，有兩種主要的傳輸類型：電源電壓和數(shù)據(jù)要么一起傳輸（類型 1），要么分別傳輸（類型 2）。4 針 M12 連接器僅適用于類型 1 傳輸；電源電壓必須疊加在兩個數(shù)據(jù)對上。在采用 8 針連接器構(gòu)建的快速以太網(wǎng)系統(tǒng)中，兩個備用線對可用于分別傳輸電源電壓。

 

工業(yè)控制和自動化網(wǎng)絡通常使用獨特的拓撲。與多端口交換機為其他節(jié)點提供點對點鏈路的典型辦公室以太網(wǎng)“星形”網(wǎng)絡不同，工業(yè)網(wǎng)絡的控制層通常基于環(huán)形布局。環(huán)形或菊花鏈簡化了布線，并且可以擴展以太網(wǎng)的覆蓋范圍，而無需支付基于光纖的系統(tǒng)的費用。Mike Jones 檢查了設計的含義。

 

與作為 IEEE 802.3 規(guī)范演變的基礎的令牌環(huán)網(wǎng)絡不同，實際上禁止將以太網(wǎng)配置為真正的環(huán)。以太網(wǎng)中的任何循環(huán)都將導致在無限循環(huán)中轉(zhuǎn)發(fā)的數(shù)據(jù)包重復，從而迅速降低網(wǎng)絡的帶寬和效率。沒有專門處理以太網(wǎng)環(huán)管理的可用通用標準。專有的網(wǎng)絡市場解決方案提供產(chǎn)品差異化和各種技術可用于網(wǎng)絡環(huán)管理的實施。然而，在尋找基于標準的環(huán)管理解決方案時，生成樹或快速生成樹協(xié)議可能符合要求。

生成樹協(xié)議 (STP) 在 IEEE 802.1d 中定義，通過阻止重復鏈接在任意兩個網(wǎng)絡節(jié)點之間形成單個活動路徑，在以太網(wǎng)交換機的網(wǎng)狀網(wǎng)絡中創(chuàng)建“生成樹”。如果任何活動鏈路發(fā)生故障，網(wǎng)絡中的冗余可以提供自動備份路徑。

冗余鏈路的這種管理對于減少工業(yè)網(wǎng)絡的停機時間是非常可取的。例如，圖 2 中所示的網(wǎng)絡包含鏈路 2、3、4 和 5 之間的環(huán)路。這里 STP 將強制這些鏈路之一進入阻塞狀態(tài)以中斷環(huán)路。在這種情況下，鏈路 4 被阻塞，然后可以充當備用鏈路。如果任何其他活動鏈路 2、3 或 5 隨后發(fā)生故障，協(xié)議將禁用阻塞狀態(tài)以啟用交換機之間的完全連接。請注意，在此示例中，鏈路 1 沒有冗余備份。

STP 由網(wǎng)絡中的每個交換機定期交換網(wǎng)絡狀態(tài)信息，每兩秒進行一次。此信息在稱為網(wǎng)橋協(xié)議數(shù)據(jù)單元 (BPDU) 的特殊數(shù)據(jù)包中承載，由以太網(wǎng)多播地址 01:80:C2:00:00:00 標識。協(xié)議的運行分為三個階段：

選舉根交換機；

查找到根交換機的所有路徑并確定“成本低”的路徑；

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Unlike a token-ring network, which has been the basis for much of the IEEE 802.3 specification evolution, it is in fact forbidden to configure Ethernet as a true ring. Any loops within an Ethernet network will result in the duplication of packets that are forwarded in endless loops, quickly degrading the bandwidth and efficiency of a network. There is no available common standard that specifically deals with the management of Ethernet rings. Proprietary network market solutions provide product differentiation and various techniques can be used for the implementation of network ring management. However, when looking for a standards-based solution for ring management, Spanning Tree or Rapid Spanning Tree Protocol may fit the bill.

Spanning Tree Protocol (STP) is defined in IEEE 802.1d and creates a ‘spanning tree’ within a mesh network of Ethernet switches by blocking duplicate links to form a single active path between any two network nodes. The redundancy in the network can provide automatic backup paths if any of the active links fail.

This management of the redundant links is very desirable to reduce the down time industrial networks. For example, the network shown in Fig. 2 contains a loop between links 2, 3, 4 and 5. Here STP will force one of these links into a blocked state to break the loop. In this case link 4 is blocked, which can then act as the backup link. If any of the other active links 2, 3 or 5 subsequently fail, the protocol will disable the blocked state to enable full connectivity between the switches. Note in this example there is no redundancy backup for link 1.

STP is conducted by each switch in the network regularly exchanging information on the status of network, every two seconds. This information is carried in special data packets called Bridge Protocol Data Units (BPDUs), identified by the Ethernet multicast address 01:80:C2:00:00:00. There are three stages of operation of the protocol:

Electing a root switch;

Finding all paths to the root switch and determining the ‘least cost’ paths;