Physical Design of IoT: Things and Network Protocols Stack

What is the Physical Design of IoT? (In Simple Words)

The Physical Design of an IoT System describes the actual hardware components you can touch and the communication rules they use to talk to each other:

1. The Physical “Things” (Hardware Devices): What hardware goes inside an IoT device (microcontroller, memory, sensors, actuators, and power supply).
2. The IoT Protocols (Network Stack): The wired and wireless networking protocols used to transfer data between the device, local routers, and cloud servers.

1. Anatomy of “Things” in IoT

In simple terms, a “Thing” is any real-world object fitted with an electronic board, a unique ID, and sensors/actuators so it can collect data and communicate.

Hardware Interfaces on an IoT Device:

An IoT microcontroller connects with external sensors and parts using standard pins and communication buses:

• I/O Interfaces for Sensors:
  • GPIO (General Purpose Input/Output): Digital pins that can be set as INPUT (reading a button or motion sensor as HIGH/LOW) or OUTPUT (turning an LED or relay ON/OFF).
  • ADC (Analog-to-Digital Converter): Most real-world sensors (like LDR light sensors or analog moisture probes) output varying voltage. The ADC converts this analog voltage into digital numbers (e.g. 0 to 1023) for the microcontroller.
• Serial Communication Buses:
  • I2C (Inter-Integrated Circuit): A simple 2-wire serial bus (SDA for data, SCL for clock) that allows connecting multiple sensors to the same pins.
  • SPI (Serial Peripheral Interface): A fast 4-wire bus used for high-speed components like SD card readers, small OLED displays, and radio modules.
  • UART (Universal Asynchronous Receiver-Transmitter): A common 2-pin serial interface (TX transmit, RX receive) used for GPS modules, Bluetooth modules (like HC-05), and computer serial monitors.

2. The IoT Protocols Stack (4-Layer Network Architecture)

Because IoT devices have limited battery power, small memory, and slow processors, they use a streamlined 4-layer protocol stack:

Layer-by-Layer Protocol Breakdown:

1. Link Layer Protocols:

Handles how data bits are sent over radio waves or wires in the immediate physical area:

• IEEE 802.15.4: A low-power wireless standard designed specifically for battery-operated sensor nodes (speed: 250 kbps, 2.4 GHz band). It is the base layer for Zigbee and 6LoWPAN.
• Bluetooth Low Energy (BLE): Designed for very short-range, ultra-low power devices like fitness bands, smart tags, and medical monitors. A single coin battery can run it for months or years!
• LoRaWAN (Long Range WAN): Sends small data packets across huge distances (up to 10 to 15 km in open areas) with very low battery consumption. Ideal for smart water meters and agricultural soil sensors.

2. Network Layer Protocols:

Handles addressing and routing packets from the device to the wider Internet:

• IPv4 vs IPv6: IPv4 uses 32-bit addresses (giving ~4.3 billion addresses), which has run out. IPv6 uses 128-bit addresses (giving 3.4 × 10³⁸ addresses) — enough for every smart gadget on the planet to have its own permanent IP address!
• 6LoWPAN (IPv6 over Low-Power Wireless PAN): Normal IPv6 headers are 40 bytes long — too heavy for tiny 127-byte sensor packets! 6LoWPAN compresses headers and fragments packets so small battery-powered sensors can talk directly on the global IPv6 Internet.

3. Transport Layer Protocols:

Ensures data packets travel properly between the device and cloud servers:

• TCP (Transmission Control Protocol): Connection-oriented. It ensures every packet arrives safely using acknowledgments (handshakes). It is reliable, but slightly heavier. Used by HTTP and MQTT.
• UDP (User Datagram Protocol): Connectionless and super fast. It sends packets immediately without waiting for acknowledgments. It is very lightweight and used by CoAP.

4. Application Layer Protocols:

The actual communication format used by IoT applications:

• MQTT (Message Queuing Telemetry Transport): A lightweight Publish-Subscribe protocol designed for low-bandwidth, unreliable networks. Perfect for mobile apps and telemetry data. Runs on top of TCP.
• CoAP (Constrained Application Protocol): A lightweight RESTful protocol (GET, POST, PUT, DELETE) designed specifically for small microcontrollers. Runs on top of UDP.
• WebSockets: Provides full-duplex (simultaneous two-way) live communication over a single TCP connection, ideal for real-time web dashboards.

💡 DAVV Exam Preparation Tips

5-Mark Question: “What are ‘Things’ in IoT? Draw and explain the internal hardware block diagram of an IoT device.”

• Definition: A ‘Thing’ in IoT is any physical object embedded with an MCU, sensors, actuators, and communication hardware that has a unique identity.
• Draw the 4 Hardware Blocks:
  1. Processing Unit (MCU / SoC)
  2. Sensors & Actuators
  3. Communication Module (Wi-Fi, BLE, LoRa)
  4. Memory & Power Supply
• Mention Interfaces: Explain GPIO (digital pins), ADC (analog sensor reading), I2C, SPI, and UART.

10-Mark Question: “Explain the Physical Design of IoT. Detail the 4-layer IoT protocol stack with protocols at each layer (Link, Network, Transport, Application). Why is 6LoWPAN required in IoT?”

• Explain the hardware components of an IoT node.
• Draw the 4-layer protocol stack diagram clearly (Link → Network → Transport → Application).
• Describe key protocols at each layer:
  • Link: IEEE 802.15.4, BLE, LoRaWAN
  • Network: IPv6 and 6LoWPAN
  • Transport: TCP vs UDP
  • Application: MQTT vs CoAP
• Explain why 6LoWPAN is needed: Standard IPv6 headers (40 bytes) are too big for small wireless packets (127 bytes). 6LoWPAN compresses headers and handles fragmentation so low-power sensors can connect to the Internet.