IS200DSPXH2BBD工控调速器
MQTT允许您发送命令以控制输出、读取和发布传感器数据等。信息以主题层次结构组织。当发布者有一个新的数据项要分发时，它会向连接的代理发送一个带有数据的控制消息。然后，代理将信息分发给订阅了该主题的任何客户端。发布者不需要拥有关于订户数量或位置的任何数据，订户也不需要获得关于发布者的任何数据。因此，这使得在多个设备之间建立通信变得非常容易。EW200工业蜂窝网关205如果代理接收到当前订户的主题，它将丢弃该主题，除非发布者指示保留该主题。这允许主题的新订阅者接收当前值，而不是等待发布者的下一次更新。当发布客户端首次连接到代理时，如果代理检测到发布客户端已意外地与代理断开连接，则可以设置一条默认消息发送给订阅者。客户端仅与代理进行交互，但系统可能包含多个代理服务器，这些服务器基于其当前订户的主题交换数据。在MQTT中，有几个基本概念需要理解：MQTT-发布和订阅第一个概念是发布和订阅系统。在基于MQTT发布和订阅的系统中，客户端设备可以发布主题上的消息，也可以订阅特定主题以接收消息。MQTT代理代理主要负责接收所有消息、过滤消息、决定谁对它们感兴趣，然后将消息发布给所有订阅的客户端。EW200工业蜂窝网关206 MQTT-消息消息是您希望在设备之间交换的信息。无论是命令还是数据。最小的MQTT控制消息可以只有两个字节的数据。有十四种定义的消息类型用于连接和断开客户端与代理的连接、发布数据、确认数据接收以及监督客户端和服务器之间的连接。MQTT–主题主题是您注册对传入消息感兴趣的方式，或者是您指定要在哪里发布消息的方式。主题用以正斜杠“/”分隔的字符串表示。每个正斜杠表示主题级别。下面是一个示例，说明您如何为家庭办公室中的灯创建主题：EW200工业蜂窝网关
MQTT allows you to send commands to control outputs, read and publish data from sensor des, etc. Information is organized in a hierarchy of topics. When a publisher has a new item of data to distribute, it sends a control message with the data to the connected broker. The broker then distributes the information to any clients that have subscribed to that topic. The publisher does t need to have any data on the number or locations of subscribers, and subscribers in turn do t have to be cond with any data about the publishers. Therefore, it makes it really easy to establish a communication among multiple devices. EW200 Industrial Cellular Gateway 205 If a broker receives a topic for which there are current subscribers, it will discard the topic unless the publisher indicates that the topic is to be retained. This allows new subscribers to a topic to receive the current value rather than waiting for the next update from a publisher. When a publishing client first connects to the broker, it can set up a default message to be sent to subscribers if the broker detects that the publishing client has unexpectedly disconnected from the broker. Clients only interact with a broker, but a system may contain several broker servers that exchange data based on their current subscribers' topics. In MQTT there are a few basic concepts that need to be understood: MQTT - Publish and Subscribe The first concept is the Publish and Subscribe system. In a MQTT publish and subscribe based system, a client device can publish a message on a topic, or it can be subscribed to a particular topic to receive messages. MQTT - Broker The broker is primarily responsible for receiving all messages, filtering the messages, decide who is interested in them, and then publishing the message to all subscribed clients. EW200 Industrial Cellular Gateway 206 MQTT - Messages Messages are the information that you want to exchange among your devices. Whether it is a command or data. A minimal MQTT control message can be as little as two bytes of data. There are fourteen defined message types used to connect and disconnect a client from a broker, to publish data, to ackwledge receipt of data, and to supervise the connection between client and server. MQTT – Topics Topics are the way you register interest for incoming messages or how you specify where you want to publish the message. Topics are represented with strings separated be a forward slash ‘/’. Each forward slash indicates a topic level. Here is an example on how you would create a topic for a lamp in your home office: EW200 Industrial Cellular Gateway
