Communication Model in IOT

M4-R5.1 · Chapter 2: Things and Connections · 6 min read

1. Introduction to Communication Models

In IoT systems, devices from diverse manufacturers need to talk to each other and to cloud platforms reliably. Communication models provide a standardised framework that defines how data is transmitted, encoded, routed, and presented between devices. The two most fundamental models are the OSI (Open Systems Interconnection) model and the TCP/IP model.

IoT devices use these models to ensure interoperability across different hardware, operating systems, and network technologies — from Zigbee sensors to MQTT brokers to cloud APIs.

1. OSI Model — 7 Layers

Developed by ISO in 1984, the OSI model is a conceptual framework dividing communication into 7 distinct layers. Each layer serves the layer above it and is served by the layer below it.

WHAT IS OSI MODEL 7 LAYERS EXPLAINED

Layer 7 — Application

The topmost layer providing network services directly to end-user applications.

In IoT, this layer hosts lightweight protocols designed for constrained devices.

  • Provides interfaces between the application and the network
  • Handles message formatting, device management, and data semantics
  • IoT examples: MQTT (publish/subscribe), CoAP (RESTful for constrained devices), HTTP/HTTPS, AMQP

Layer 6 — Presentation

Presentation layer is Responsible for

  • Data translation
  • Encryption,
  • Compression.

It Ensures data sent by one system can be read by another

Layer 5 — Session

Manages and controls connections (sessions) between applications. Establishes, maintains, and terminates sessions.

  • Authentication and reconnection after interruption

Layer 4 — Transport

Provides end-to-end communication services. Segments large messages, manages flow control and error recovery.

  • TCP — reliable, ordered, connection-oriented (used when data integrity is critical)
  • UDP — unreliable, connectionless, fast (preferred in IoT for low-overhead sensors)
  • Port numbers identify applications (e.g., MQTT → port 1883, CoAP → port 5683)

Layer 3 — Network

Handles logical addressing and routing of packets across different networks. Routers operate at this layer.

  • IP addressing (IPv4 / IPv6 — IoT heavily relies on IPv6 due to address space)

Layer 2 — Data Link

Handles node-to-node data transfer and error detection within a single network segment. Divided into LLC and MAC sub-layers.

  • MAC addressing for device identification within a local network
  • IoT examples: IEEE 802.15.4 (Zigbee, Z-Wave), Bluetooth MAC, Wi-Fi MAC

Layer 1 — Physical

Transmits raw bit streams over the physical medium. Defines hardware specifications like voltage, frequency, and connector types.

  • Defines modulation schemes (FSK, OFDM, LoRa chirp spread spectrum)
  • IoT physical mediums: Wi-Fi (2.4/5 GHz), LoRaWAN (868/915 MHz), Zigbee, Z-Wave, NB-IoT, BLE
  • Wired: Ethernet, RS-232, RS-485 for industrial IoT

2. TCP/IP Model — 4 Layers

The TCP/IP model (also called the Internet Model) was developed by DARPA and is the practical model that underpins the modern internet and most IoT deployments.

It consolidates the OSI's 7 layers into 4.

Layer 1 — Network Access (Link Layer)

Handles data exchange between a device and the physical network. Combines the functions of OSI's Physical and Data Link layers.

  • Defines how data is physically sent over the medium (cables, radio)
  • MAC addressing, frame formatting and error detection
  • IoT protocols at this layer: IEEE 802.11 (Wi-Fi), IEEE 802.15.4, Ethernet, BLE, LoRa PHY

Layer 2 — Internet Layer

Provides logical addressing and routing of packets across interconnected networks.

  • IPv4 (32-bit) and IPv6 (128-bit) — IoT needs IPv6 for billions of device addresses
  • ICMP for error messaging and diagnostics (ping)
  • 6LoWPAN: adapts IPv6 for IEEE 802.15.4 low-power networks
  • RPL (Routing Protocol for Low-power and Lossy Networks) used in IoT mesh

Layer 3 — Transport Layer

Provides end-to-end communication between processes on different hosts.

  • TCP: reliable, ordered delivery with flow control — used for critical IoT data
  • UDP: fast, lightweight — used for real-time sensor data, video streams
  • DTLS (Datagram TLS) secures UDP connections in IoT (e.g., CoAP uses DTLS)

Layer 4 — Application Layer

Provides network services directly to applications. In IoT, specialised lightweight protocols are used instead of full HTTP.

  • MQTT: lightweight publish/subscribe for constrained devices over TCP
  • CoAP: RESTful protocol for constrained environments over UDP
  • AMQP: messaging protocol for enterprise IoT platforms
  • HTTP/HTTPS: used where bandwidth and power are not constraints

4. OSI vs TCP/IP — Layer Mapping

OSI Layer

7 — Application→ Application
6 — Presentation→ Application
5 — Session→ Application
4 — Transport→ Transport
3 — Network→ Internet
2 — Data Link→ Network Access
1 — Physical→ Network Access

TCP/IP Layer

Application (4)OSI 5+6+7
Application (4)OSI 5+6+7
Application (4)OSI 5+6+7
Transport (3)OSI 4
Internet (2)OSI 3
Network Access (1)OSI 1+2
Network Access (1)OSI 1+2

5. OSI vs TCP/IP — Key Differences

Feature OSI Model TCP/IP Model
Number of layers 7 4
Developed by ISO (1984) DARPA (1970s)
Nature Conceptual/Reference Practical/Implementation
Transport protocols Defined at Layer 4 TCP and UDP (Layer 3)
Session & Presentation Separate layers (5 & 6) Merged into Application
Physical & Data Link Separate layers (1 & 2) Merged into Network Access
Usage in IoT Theoretical reference for understanding Actual deployment base
Protocol independence High — model is generic Tightly coupled with TCP/IP suite
Reliability Can support both reliable & unreliable Both TCP (reliable) & UDP (unreliable)