什麼是 MQTT

Nov 24, 2023 · 2 min read · mqtt  ·
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Evergreen Note

Question :: 這篇文章主要在說什麼?

Answer :: 初探 MQTT 的協議與使用目的，了解 MQTT 的特色。

Summary

MQTT 是設計給 IoT 作為訊息傳遞來使用的協定。通常 IoT 硬件通常會有資源上的限制，所以 MQTT 的特色就是輕量且高效。 下面列出了 MQTT 的特色：

  1. Lightweight and Efficient（輕量且高效）
  2. Bi-directional Communications（裝置跟服務可雙向溝通）
  3. Scale to Millions of Things（可平行擴充）
  4. Reliable Message Delivery（可靠的訊息傳遞）
  5. Support for Unreliable Networks（適用於網路不穩定的環境之下）
  6. Security Enabled （安全性，可使用 TLS 加密訊息）

下圖為 MQTT org 上的 Publish / Subscribe 架構，也繪出一份 flowchart 供紀錄。

MQTT pub/sub Flowchart

flowchart LR
   mc3[MQTT Client
Subscriber: Mobile device] --"Subscribe to topic:temperature"--> mb
   mc2[MQTT Client
Subscriber: Backend device] --"Subscribe to topic:temperature"--> mb
   mb --"Publish: 24°C"--> mc2
   mb --"Publish: 24°C"--> mc3
   subgraph MQtt Broker
     mb[MQTT Broker]
   end

   subgraph MQTT Client
     mc1[Publisher: Temperature Sensor] --"
     Publish to topic: temperature
Publish: 24°C"--> mb
   end

Note

原文 :: mqtt org

MQTT: The Standard for IoT Messaging

MQTT is an OASIS standard messaging protocol for the Internet of Things (IoT). It is designed as an extremely lightweight publish/subscribe messaging transport that is ideal for connecting remote devices with a small code footprint and minimal network bandwidth. MQTT today is used in a wide variety of industries, such as automotive, manufacturing, telecommunications, oil and gas, etc.

Why MQTT?

  • Lightweight and Efficient

    MQTT clients are very small, require minimal resources so can be used on small microcontrollers. MQTT message headers are small to optimize network bandwidth.

  • Bi-directional Communications

    MQTT allows for messaging between device to cloud and cloud to device. This makes for easy broadcasting messages to groups of things.

  • Scale to Millions of Things

    MQTT can scale to connect with millions of IoT devices.

  • Reliable Message Delivery

    Reliability of message delivery is important for many IoT use cases. This is why MQTT has 3 defined quality of service levels: 0 - at most once, 1- at least once, 2 - exactly once

  • Support for Unreliable Networks

    Many IoT devices connect over unreliable cellular networks. MQTT’s support for persistent sessions reduces the time to reconnect the client with the broker.

  • Security Enabled

    MQTT makes it easy to encrypt messages using TLS and authenticate clients using modern authentication protocols, such as OAuth.

MQTT Publish / Subscribe Architecture

MQTT publish subscribe image

參考 MQTT org

Is MQTT a standard?

v5.0 and v3.1.1 are now OASIS standards (v3.1.1 has also been ratified by ISO).

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