Most Smart Home Devices can use both the HTTP and MQTT protocols to communicate with smart home control systems.
The HTTP protocol is generally used for initial device set up.
However when it comes to sending device data and for subsequent device control HTTP is not usually the best protocol, especially when dealing with lots of devices
Generally when you look for a comparison between the HTTP and MQTT protocols the main emphasis is on the fact that HTTP is a text based protocol, and not as efficient as MQTT which is a binary based protocol.
However when dealing with only a few devices that send data infrequently then it is not really a problem.
The main issues are the fact that MQTT is a real time protocol using the publish and subscribe model and therefore is excellent for working with a large number of devices, and for real time data.
As an example imagine you have 100 temperature sensors. How would you get the status of each sensor?
With HTTP you would need to poll each sensor frequently and you would require 100 client connections from the control dashboard.
With MQTT you would only require one connection to the broker from the control dashboard, and to subscribe to a single topic to receive status changes in real time.
This is what ChatGPT said about use cases
| Use Case | HTTP | MQTT |
|---|
| Device Control | OK for simple commands | Excellent for real-time control |
| Sensor Data Reporting | Less efficient | Highly efficient |
| Low Power/Resource Devices | Not ideal | Optimized |
| Scalability (many devices) | Harder to scale | Broker makes scaling easier |
Device IP Addresses
Another very important point that is usually not discussed is that when using HTTP for device control then the control dashboard needs to know the IP address of the device.
With many devices DHCP will be used, and so keeping track of device IP addresses isn’t always easy.
See Finding New Device IP addresses
However the task will become increasingly more difficult as networks move to IPV6, as the discovery methods used for IPv4 networks won’t work on IPv6.
Because MQTT doesn’t have a direct connection between devices then knowing the IP address of any device isn’t necessary for device control.
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MQTT Drawbacks
The main problem with MQTT in smart homes is the fact that your need an MQTT broker. This means that you have one more system to worry about.
Usually this isn’t a big problem as you can run an MQTT server on a raspberry PI or an old laptop/PC.
However for a small number of devices then it might just be too much trouble.
If you are using Zigbee devices then they will be controlled via MQTT anyway so an MQTT broker is required anyway.
Related Tutorials and Resources:
- Understanding HTTP Basics
- Using HTTP APIs For IOT -Beginners Guide
- IPv6 Explained for Beginners
- How MQTT Works