CoAP 和 LwM2M 有什么不同？

Question

I study about IoT protocol CoAP, MQTT, LwM2M.

I was able to know a little about CoAP and MQTT.

But I do not know what LwM2M is.

I do not know what's different from CoAP.

I just thought that LwM2M is not a protocol with some format but a system structure using CoAP.

Is that correct?

What is LwM2M and How Can I know more information about LwM2M?

Please someone teach me.

Answer 1

LwM2M (specified by OMA) is a is a protocol group largely built on top of CoAP (specified by the IETF).

LwM2M uses a subset of CoAP's capabilities that fit into an architecture of many small devices registering at a large LwM2M server that manages the devices. It prescribes particular path structures (that numbers are used in paths, and what they mean) that represent the LwM2M object model to allow that unified management.

Compared to "plain CoAP", this limits the scope of what devices can do. Devices can still provide other CoAP functionality on the same server that is not covered by LwM2M. Those limitations allow different vendors to build devices that can interoperate with a different management servers, and LwM2M provides additional specifications for easy deployment (eg based on smart cards) that are out of scope for CoAP.

Answer 2

The direct answer can be obtained from the official sites:

• CoAP "is a specialized web transfer protocol for use with constrained nodes and constrained networks in the Internet of Things. The protocol is designed for machine-to-machine (M2M) applications such as smart energy and building automation."
• LwM2M "is a device management protocol designed for sensor networks and the demands of a machine-to-machine (M2M) environment. With LwM2M, OMA SpecWorks has responded to demand in the market for a common standard for managing lightweight and low power devices on a variety of networks necessary to realize the potential of IoT."

Basically, we can simplify saying that CoAP was designed to communications between constrained IoT devices and it is very similar to HTTP protocol, which facilitates the developers work, while the LwM2M was designed mainly to manage constrained devices remotely, providing service enablement, for instance. Both protocols are commonly used together.

More information you can find in the following links:
- What is LwM2M? A device management solution for low power M2M
- CoAP functionality expected in a LwM2M system