1. Communication Model and Real-Time Performance
MQTT
Advantages:
Utilizes a publish/subscribe model, enabling bidirectional communication and event-driven mechanisms. The server can actively push messages (e.g., real-time sensor data reporting) with latency as low as tens of milliseconds.
Disadvantages:
Relies on a centralized broker. If the broker fails, the entire system collapses.
HTTP
Advantages:
Based on the request/response model, simple to implement, and suitable for scenarios where clients actively fetch data (e.g., webpage loading).
Disadvantages:
Lacks native push capabilities. Real-time updates require polling, leading to high latency and bandwidth waste.
2. Transmission Efficiency and Resource Consumption
MQTT
Advantages:
Lightweight: Protocol headers are minimal (as small as 2 bytes), and binary encoding reduces redundancy. This results in 50 times less bandwidth consumption compared to HTTP.
Low Power Consumption: Maintains long connections to avoid frequent handshakes. In idle states, devices enter low-power modes, consuming only 1%-10% of HTTP’s energy.
High Efficiency: Faster transmission speeds (up to 20 times faster) under the same data volume.
Disadvantages:
Binary format requires specialized parsing libraries, increasing development complexity.
HTTP
Advantages:
Text-based format simplifies debugging. Supports compression (e.g., gzip) and caching mechanisms (e.g., ETag).
Disadvantages:
Redundant headers increase bandwidth usage. Frequent short-lived connections raise latency and resource costs (e.g., TCP three-way handshake).
3. Reliability and Scalability
MQTT
Advantages:
QoS Mechanisms: Three message reliability levels—QoS 0 (at most once), QoS 1 (at least once), and QoS 2 (exactly once)—ensure adaptability to diverse scenarios.
Offline Message Caching: Brokers store undelivered messages and automatically retransmit them upon device reconnection.
Dynamic Scalability: Topic wildcards (e.g., +, #) enable flexible subscription management, supporting large-scale device networks.
Disadvantages:
Limited standardization for advanced features (e.g., file transfer).
HTTP
Advantages:
Stateless Design: Simplifies server logic and suits distributed systems.
Broad Compatibility: Integrates seamlessly with web ecosystems (e.g., RESTful APIs, OAuth).
Disadvantages:
No built-in message reliability guarantees. Retries and persistence must be handled at the application layer.
4. Security
MQTT
Advantages:
Supports TLS encryption and topic-level access control (e.g., restricting device publish/subscribe permissions).
Disadvantages:
No default encryption; security relies on external configurations. Lacks standardized authentication schemes (e.g., OAuth).
HTTP
Advantages:
End-to-end encryption via HTTPS and mature authentication mechanisms (e.g., Basic Auth, JWT).
Disadvantages:
Historical versions (e.g., HTTP/1.1) transmit data in plaintext, vulnerable to man-in-the-middle attacks.
5. Application Scenarios
MQTT:
IoT devices (e.g., smart meters, sensors), real-time monitoring (industrial automation), and unstable networks.
HTTP:
Traditional web services (API calls), large file transfers (video streaming), and legacy system integration.
Summary
MQTT excels in real-time communication, low power consumption, and high concurrency, while HTTP remains dominant in web services due to its simplicity and universality. In practice, they complement each other: MQTT handles device-side data collection, and HTTP manages cloud-side processing and external interfaces.