MQTT 作為MQ遙測的前身，是為了物聯網環境而設計的發佈/訂閱模式消息傳輸協定，它所需要的網路頻寬低也因此它能在受限的環境中，如機器與機器的通信（M2M），讓用戶端使用最少的硬體資源，達到傳送大量訊息的需求。
About MQTT
In IoT applications, devices often must communicate with each other (D2D). Device data is then must be collected and sent to the server infrastructure (D2S). That The server infrastructure has to share device data (S2S), possibly providing it back to devices, to analysis programs, or to people. The communication protocols can be described in this framework as:
• MQTT: a protocol for collecting device data and communicating it to servers (D2S)
• XMPP: a protocol best for connecting devices to people, a special case of the D2S pattern, since people are connected to the servers
• DDS: a fast bus for integrating intelligent machines (D2D)
• AMQP: a queuing system designed to connect servers to each other (S2S)
MQTT(MQTT (formerly MQ Telemetry Transport) is a publish-subscribe based "light weight" IoT communication protocol for use on top of the TCP/IP protocol. The publish-subscribe messaging pattern requires a message broker. The broker is responsible for distributing messages to interested clients based on the topic of a message.
MQTT has the following properties :properties:
1. Based on TCP/IP for basic network connection
2. Small code foot print
3. Three different message service qualities
a. “At most once”
b. “At least once”
c. “ExaclyExactly once”
4. 2- byte header to reduce package transfer loading
5. It has “LLast ast will and testament” to notifiesy client ifwhen connection is lost connection.
6. Provides Publishpublish/-Subscribe subscribe structure to provide one- to- many message sharing.
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Publisher is the source of the message, it which will passes data to Topic, and Subscriber will registers for in Topic to get Topic data form Topic.
So when , if some a Publisher sent sends a message to topicTopic, all registered Subscribers registered for that Topic will get this that message.
Based on these properties, especially “Small small code foot print” and “Publishpublish-/sSubscribe structure”, WISE-PaaS/RMM uses MQTT as the communication protocol to connect between agents(agents (gateway/devices device side) and servers(servers (back-end/cloud side). On the device side, the agent will collect data with different structures or protocols, and transfer it to MQTT. After this process, device data from devices will hasve the same form and be is kept in the WISE-PaaS/RMM server database of WISE-PaaS/RMM server. The IoT developer can create their applications based on WISE-PaaS server web-services(services (RESTful API).
