Hello, good day.
I am currently pursuing my master’s degree and working on building a smart home model. I have decided to rely on Samsung SmartThings for this project.
However, before proceeding, I need to understand how it works and which protocol it uses, as this greatly impacts my research.
If you have any official documents or textual references that specify the protocol used, it would be extremely helpful for me.
Thank you very much 
This is the architecture of ST. Controllers like the ST app use the ST REST API to interact with hubs and cloud connected devices. Depending on the hub model, hubs interact with smart home devices using Z-Wave, Zigbee, Matter over Wi-Fi, Matter over Thread, or Matter over Bridge. The ST app can interact locally with some Samsung devices like TVs and appliances using the OCF protocol.
You’ll find developer documentation here. https://developer.smartthings.com/
In addition to the helpful information that @h0ckeysk8er already gave you, it is very important to understand that SmartThings is a black box system, and we as users are not allowed to upload code that runs on the hub itself with the very limited exception of “edge drivers”. And those have limited functionality.
SmartThings was designed as a “plug and play” mass market product for people who were not programmers. And the assumption was that most of them would have fewer than 15 devices or so. So it just has a lot of “guardrails“ which end up removing functionality from a SmartThings account that the protocols that it uses would otherwise provide.
Sometimes there are workarounds, sometimes there are not, but people who are trying to design sophisticated systems almost always move on to a different platform like home assistant or Hubitat or Homeseer.
Obviously, you can try it if you want to, and the cost of SmartThings is pretty low compared to some other systems, but it is possible that you will run into functionality barriers pretty quickly unless you are looking for a system that does not require any understanding of programming.
On the other hand, if your model is intended to be a simple Smart home system that will be used without any custom code, and that has limited functionality, it might be exactly what you need. So it comes down to the details.
Thank you for your response and for providing the information. I would like to know the primary protocol that SmartThings sensors operate on. Do they mainly use Zigbee, Z-Wave, Wi-Fi, or another protocol? Thanks again for your help!
Thank you for your response! I don’t want to get into the details of specific devices, but I would like to know which protocol SmartThings sensors primarily rely on. This information is very important for my research. I really appreciate your help!
Samsung itself no longer makes SmartThings branded sensors. It is a platform that works with sensors from many different companies. For customers in many different countries. So there’s just no one answer to your question: different things will work for different people. 
Some people have almost all Zwave devices.
Some people have only Zigbee devices.
Many people have a mix.
Wi-Fi typically is not used for battery powered sensors because it requires much more battery power than an identical sensor that utilizes a Zigbee or thread or even Z wave radio.
A sensor using one of those first three protocols will have a battery life typically of one and a half to two years, regardless of the platform it’s being used with and regardless of the company that manufactured it.
A Wi-Fi sensor with identical features will probably have a battery life of about three months. So they just aren’t very popular because people don’t want to change batteries that often.
BUT SOME PEOPLE DO USE WIFI BATTERY POWERED SENSORS
There is one company, Shelly, which has been working with the Wi-Fi standards group to try to improve battery life for its battery powered Wi-Fi sensors, but even those typically get about eight months. Really good for Wi-Fi, but not really good for this device class.
Still, people who don’t want to get a hub might use Shelly Wi-Fi sensors because those are the ones that will work without a hub.
AND MATTER ADDS EVEN MORE POSSIBLE FREQUENCIES AND PROTOCOLS
Yet another option is to use sensors That work with their own company’s “matter bridge”. In that case, the connection to SmartThings will probably be via Wi-Fi, but the individual sensors might use Bluetooth, Zigbee, or a proprietary frequency, or a proprietary protocol via 433 MHz. Or really anything else. SmartThings will talk to the bridge and the bridge will talk to the individual sensors, so SmartThings doesn’t care what protocol those use. That option is becoming much more popular.
SUMMARY: DIFFERENT PEOPLE USE DIFFERENT PROTOCOLS
So there just isn’t any “mainly” about it. One of the reasons that SmartThings became as popular as it did is because it worked with so many different third-party products and people could choose the ones that worked best for them.
