IoT Protocol Stack Layers : IoT Stack Layer 1 to Layer 7

This article breaks down the IoT (Internet of Things) protocol stack into its seven layers, detailing the function of each, from Layer 1 to Layer 7. Similar to wired and wireless technologies, IoT utilizes a layered approach, reminiscent of the OSI model.

We’re familiar with the OSI (Open System Interconnection) model, which defines a 7-layer networking framework. OSI specifies the functions and interfaces of each layer. Let’s explore the functional description of these 7 layers within the context of the IoT protocol stack, as illustrated below.

The IoT stack comprises the following seven layers:

• Sensor layer
• Processing/control layer
• Hardware interface layer
• RF layer
• Session/message layer
• User experience layer
• Application layer

IoT Stack Layer 1: Physical or Sensor Layer

This layer, analogous to the OSI physical layer, interfaces directly with physical components. These components are primarily sensors, such as:

• Humidity sensors
• Temperature sensors
• Pressure sensors
• Heart rate sensors
• pH sensors
• Odor sensors

These sensors are used to detect various parameters, depending on the specific application. A wide variety of sensors exist for the same functionalities; therefore, sensor selection hinges on both cost and quality considerations. This Layer 1 delivers the sensed data to the IoT stack for subsequent processing.

IoT Stack Layer 2: Processing and Control Layer

Here, the data received from Layer 1 (the sensors) undergoes processing. Microcontrollers/Processors and operating systems are critical components at this layer.

Various development kits are available, including:

• Arduino
• NodeMCU (based on ESP32 or ESP8266)
• ARM
• PIC

Typical operating systems utilized are Android, Linux, and iOS.

IoT Stack Layer 3: Hardware Interface Layer

This layer encompasses the components and interfaces that facilitate communication, such as:

• RS232
• RS485
• SPI
• I2C
• CAN
• SCI

These interfaces enable serial or parallel communication at various baud rates, in both synchronous and asynchronous modes. The protocols mentioned above ensure robust and reliable data transfer.

IoT Stack Layer 4: RF Layer

The Radio Frequency (RF) layer incorporates RF technologies that are selected based on range (short or long) and the desired data rate for the specific application. Common indoor RF/wireless technologies include:

• Wi-Fi
• Bluetooth
• Zigbee
• Z-Wave
• NFC
• RFID

Common outdoor RF cellular technologies include:

• GSM/GPRS
• CDMA
• LTE-M
• NB-IoT
• 5G

The RF layer facilitates data communication through radio frequency-based electromagnetic waves. Furthermore, light waves can also be used for data transmission; this technology is known as Li-Fi.

IoT Stack Layer 5: Session/Message Layer

This layer focuses on message protocols such as MQTT, CoAP, HTTP, and FTP (or Secure FTP), and SSH. It defines how messages are transmitted to the cloud.

IoT Stack Layer 6: User Experience Layer

This layer is dedicated to providing the best possible experience for end-users of IoT products. It achieves this through rich UI designs with extensive features.

A variety of languages and tools are employed for GUI interface software design. These include object-oriented and procedure-oriented technologies, as well as database languages (DBMS, SQL), and analytics tools.

IoT Stack Layer 7: Application Layer

This layer leverages the capabilities of the previous six layers to develop the intended application. Typical IoT applications and case studies include:

• Smart Home
• Smart Parking System (based on Zigbee, LoRaWAN, and other wireless technologies)
• Smart Energy System
• Smart City
• Smart Lighting System (based on the Zigbee standard)
• Smart Retail
• Smart Agriculture Farming
• Smart Waste Management

Conclusion

​The IoT protocol stack, structured into seven layers analogous to the OSI model, provides a comprehensive framework for facilitating seamless communication and interoperability among diverse IoT devices and systems. Each layer; from the Physical Layer, responsible for the tangible connection of devices, to the Application Layer, which interfaces directly with end user applications; plays a pivotal role in ensuring efficient data transmission, processing and utilization. A thorough understanding of these layers enables developers and engineers to design robust, scalable and secure IoT solutions, effectively addressing challenges related to connectivity, data management and user interaction. The selection of appropriate layers and protocols/technologies within the IoT protocol stack’s seven layers is determined by the specific IoT application.