IoT Protocols, Networking and Cloud Architectures: CoAP, MQTT, AMQP

Posted on Dec 31, 2025 in Communications Electronic Engineering

CoAP (Constrained Application Protocol)

CoAP (Constrained Application Protocol) is a lightweight communication protocol designed for IoT devices with limited power, memory, and processing ability. It is similar to HTTP but optimized for constrained networks and works on UDP.

Characteristics

• Lightweight and simple
• Works over UDP
• REST-based (supports GET, POST, PUT, DELETE)
• Supports asynchronous communication
• Multicast supported
• Provides security using DTLS
• Designed for constrained devices and low-power networks

Message Format

• Header (4 bytes): Contains version, type, token length, code, message ID
• Token: Matches request and response
• Options: URI, content-format, etc.
• Payload: The actual data carried by the message

Message Types

• CON (Confirmable): Must be acknowledged
• NON (Non-confirmable): No acknowledgment needed
• ACK (Acknowledgment): Response to CON
• RST (Reset): Message cannot be processed

How CoAP Works

The client sends a request (for example, GET) as CON or NON. The server processes the request. The server sends ACK with response for CON messages. NON messages do not need ACK. CoAP supports asynchronous and multicast communication.

IoT Communication Protocols

IoT devices communicate using various protocols depending on power, reliability, and network type. MQTT, MQTT-SN, CoAP, STOMP, and AMQP are popular protocols designed for different communication needs.

• MQTT: Works on TCP. Follows publish/subscribe architecture. Used for sensors sending telemetry data.
• MQTT-SN: Designed for sensor networks. Works without TCP. Supports short topic IDs and sleeping nodes.
• CoAP: Works on UDP. REST-based (GET, POST, PUT, DELETE). Used in low-power IoT environments.
• STOMP: Text-based, human-readable. Works over WebSocket/TCP. Used in chat apps and real-time dashboards.
• AMQP: Binary and highly reliable. Supports queues, routing, exchanges. Used in enterprise and financial systems.

Smart Irrigation System

A smart irrigation system is an IoT-based automatic watering system that uses sensors and controllers to supply water to plants only when required. It helps save water, improve crop growth, and reduce manual effort. An intelligent irrigation system monitors soil and environmental conditions and waters plants automatically.

Key Components

• Soil moisture sensor
• Microcontroller (Arduino, NodeMCU)
• Water pump or solenoid valve
• Relay
• Cloud / IoT connectivity

MQTT (Message Queuing Telemetry Transport)

MQTT is a lightweight IoT protocol that uses a publish/subscribe model. It is designed for low-power devices and works over TCP to ensure reliability.

MQTT Architecture

• Publisher: Sends data/messages to the broker
• Subscriber: Receives messages by subscribing to topics
• Broker: Central server that manages topics, receives messages, and forwards them to subscribers
• Topic: Named channel used to organize messages

Publish/Subscribe Model

MQTT uses a decoupled communication model where publishers and subscribers do not directly communicate. Publishers send messages to a topic at the broker. Subscribers register interest in one or more topics. The broker forwards messages only to interested subscribers.

QoS Levels

• QoS 0 (At most once): Messages delivered once, no acknowledgment, no retry
• QoS 1 (At least once): Messages delivered one or more times, retries until acknowledgment
• QoS 2 (Exactly once): Guaranteed delivery exactly one time, uses a four-step handshake

STOMP (Simple Text Oriented Messaging Protocol)

STOMP is a text-based protocol used for exchanging messages between clients and message brokers. It provides an easy way for applications to send and receive messages using queues and topics.

Communication Model

STOMP uses a client–broker model. Clients connect to a broker using a CONNECT frame. The broker sends back a CONNECTED frame. Clients use SUBSCRIBE to listen to a queue or topic and use SEND to deliver messages to a destination. The broker routes messages to all clients subscribed to that destination. Clients may send ACK or NACK for message confirmation. Finally, clients use DISCONNECT to end the session.

Message Exchange Types

• Point-to-point (Queue): Only one consumer gets the messages
• Publish/Subscribe (Topic): All subscribers receive the messages

STOMP Frame Format

Each STOMP frame has three parts:

1. Command: Defines the action (examples: CONNECT, SEND, SUBSCRIBE, ACK, DISCONNECT)
2. Headers: Key–value pairs providing metadata (examples: dest, content-type, id, ack mode)
3. Body: Optional part that contains the message payload. Ends with the NULL character

6LoWPAN

6LoWPAN stands for IPv6 over Low-Power Wireless Personal Area Networks. It is a communication protocol designed to allow small, low-power IoT devices to transmit IPv6 packets efficiently.

• Compression of IPv6 Packet: IPv6 headers are large (40 bytes). 6LoWPAN compresses them to fit into small 802.15.4 frames.
• Low-Power Support: Enables communication for devices with limited battery, memory, and processing capabilities.
• Works with IEEE 802.15.4: 802.15.4 has very small frame sizes (127 bytes). 6LoWPAN makes IPv6 compatible with them.
• Enables Internet Connectivity: Devices can directly use IPv6 addressing and connect to the internet.
• Supports Mesh Networking: Allows devices to form multi-hop mesh networks for extended coverage.

AMQP (Advanced Message Queuing Protocol)

AMQP defines a complete messaging system for reliable communication in distributed applications. It specifies how messages look, how they are routed, and how reliably they are delivered.

AMQP Message Format

• Properties: Metadata such as message-id, content-type, priority, correlation-id
• Headers: Key-value pairs used for application-specific information
• Body: The actual message content, which may be binary, JSON, or text

AMQP Routing

AMQP defines four types of exchanges for routing:

• Direct Exchange: Routes messages based on exact routing key match
• Topic Exchange: Routes using pattern matching on routing keys
• Fanout Exchange: Sends the message to all bound queues
• Headers Exchange: Routes based on message headers

Delivery Guarantees

• At Most Once: Message may be lost but never duplicated
• At Least Once: Message is delivered but may be duplicated
• Exactly Once: Message is delivered once and only once, ensuring highest reliability

MQTT vs MQTT-SN Features

Amazon Web Services (AWS)

Amazon Web Services supports IoT and data analytics. AWS is widely used for processing IoT datasets, running analytics pipelines, real-time monitoring, and machine learning applications. Its global infrastructure ensures low latency and high performance.

Supports IoT and Data Analytics: AWS is widely used for processing IoT datasets, running analytics pipelines, real-time monitoring, and machine learning applications. Global Infrastructure: AWS operates data centers worldwide, which ensures low latency and high performance.

Key AWS Benefits

• On-demand cloud services including compute, storage, databases, and analytics
• Pay-as-you-go model reduces upfront costs
• Scalability and elasticity for variable workloads
• Wide range of services (EC2, S3, Lambda, RDS, DynamoDB, IoT Core)
• Security features such as encryption, IAM, firewalls, and multi-region backups

Protocol Comparison: HTTP vs MQTT

Protocol Comparison: HTTP vs CoAP

Elastic Analysis

Elastic Analysis is a cloud-based analytics capability that allows resources such as compute, memory, and storage to automatically scale up or down based on data volume and workload. It is especially important for IoT systems because IoT data is unpredictable, large, and often real-time.

1. Automatic Scaling: The system automatically adjusts processing resources depending on workload.
2. Cost Efficiency: Cloud platforms follow a pay-as-you-go model to avoid over-provisioning.
3. Real-Time Performance: Ensures fast dashboards, alerts, and monitoring during data spikes.
4. High Availability and Fault Tolerance: If one server fails, another takes its place to minimize downtime.
5. Elastic Data Pipelines: Data ingestion, transformation, and processing pipelines expand or shrink based on incoming flow.
6. Scalability Across Components: Elasticity applies to compute, storage, network, databases, and analytics services.
7. Suitable for IoT and Big Data: Ideal for large, continuous, and unpredictable sensor data.
8. Example Use Cases: IoT sensor analytics, real-time streaming, e-commerce traffic spikes, machine learning workloads.

Prototyping in IoT and M2M

Prototyping in IoT and M2M is the process of creating an early, working model of a connected device to test feasibility, functionality, and communication. It verifies ideas before full-scale development and helps detect faults early.

Purpose and Methods

• Purpose: Early validation, detect faults early, collect user feedback, reduce development cost
• Rapid prototyping: Uses Arduino, Raspberry Pi
• Simulation and emulation: Tests using software tools
• Iterative development: Continuous improvement
• Key components: Hardware (sensors, microcontrollers), Software (embedded code), Connectivity (Wi-Fi, Bluetooth, LoRa)
• Importance: Saves time and resources, helps refine design, ensures system reliability
• Prototyping in M2M: Tests communication between devices and ensures data flow between sensors, gateways, and servers

Cloud Security Methods

Cloud service providers use multiple security methods to protect data, applications, and networks in the cloud. These techniques prevent unauthorized access, data breaches, and cyberattacks.

• Encryption: Converts data into unreadable code to secure data at rest and in transit
• Identity and Access Management (IAM): Controls who can access cloud resources using roles and permissions
• Firewalls: Protect cloud networks by filtering harmful or unauthorized traffic
• Multi-Factor Authentication (MFA): Requires additional verification such as OTPs along with passwords
• Access Controls: Provides permissions for viewing, editing, or deleting resources
• Security Monitoring: Real-time monitoring to detect suspicious activity and threats
• Compliance: Following standards like ISO, GDPR, HIPAA
• Transport Layer Security (TLS): Protects data transmitted over networks
• Backup and Disaster Recovery: Ensures data is not lost during failures or attacks
• Patch Management: Regular software updates to fix vulnerabilities

Cloud providers combine encryption, access controls, monitoring, firewalls, and compliance to provide strong, multi-layer security. These methods ensure data safety, confidentiality, and reliability in cloud environments.

Amazon Web Services (detailed)

Amazon Web Services (AWS) is a cloud computing platform that offers a wide range of on-demand cloud services such as computing power, storage, databases, and analytics. AWS is one of the world’s most widely used cloud platforms.

• On-Demand Cloud Services: Virtual machines, storage, and databases accessible anytime
• Pay-As-You-Go Model: Users only pay for what they consume
• Scalability and Elasticity: Resources scale based on workload
• Wide Range of Services: EC2, S3, Lambda, RDS, DynamoDB, IoT Core, and more
• Security and Reliability: Encryption, IAM, firewalls, and multi-region backups

Visualization of IoT Data

Visualization of IoT data refers to presenting sensor and device information in clear graphical formats such as charts, dashboards, and graphs. To make the data easy to understand, several design rules should be followed.

• Consistent Design Elements: Use consistent colors, shapes, and fonts
• Clear Labels and Titles: Properly label axes, units, and graphs
• Provide Context: Add explanations, legends, and units
• Avoid Clutter: Remove unnecessary visual elements
• Adaptive Design: Ensure visualization works on mobile, tablets, and desktops
• Regular Updates: Dashboards must show the most recent data
• Appropriate Techniques: Choose graphs that match the data type
• Personalized Dashboards: Different dashboards for managers, engineers, and operations
• Digestible Labels: Use simple descriptions and readable fonts
• Clear Objectives and KPIs: Visualizations should answer specific questions
• Use Real-Time Data: IoT systems benefit from live visualizations

Alert Principles for IoT Dashboards

Alert principles for IoT dashboards ensure notifications are meaningful, clear, and actionable. Well-designed alerts help users quickly identify problems and take necessary actions.

• Clarity: Alerts must be simple and easy to understand
• Prioritization: Use colors or severity labels for urgency
• Contextualization: Include device name, location, and time
• Actionability: Guide users about next steps
• Relevance: Display only meaningful alerts
• Timeliness: Alerts should be generated in real time
• Persistence: Alerts remain until acknowledged or resolved
• Feedback: Allow users to acknowledge, comment, or update status
• Simplicity: Alerts should be short and focused
• Scalability: Support large numbers of devices and notifications

Industrial Internet of Things (I-IoT)

The Industrial Internet of Things (I-IoT) refers to the use of smart sensors, intelligent machines, and advanced communication technologies in industries such as manufacturing, energy, agriculture, and transportation. It helps automate processes, improve efficiency, and support real-time decision making.

Features and Requirements

• High reliability
• Low latency
• Large-scale device deployment
• Support for harsh environments
• Connectivity (Wi-Fi, LPWAN, Ethernet)
• Interoperability (machine-to-machine communication)
• Security against cyber attacks
• Real-time data processing, cloud and edge integration, energy efficiency

Use cases include smart factories, predictive maintenance, smart agriculture, and industrial automation. Compared to general IoT, I-IoT needs higher reliability, lower latency, and industrial-grade durability.

Internet of Behaviors (IoB)

The Internet of Behaviors (IoB) is the concept of collecting and analyzing user behavior data to understand actions, preferences, and needs. It helps organizations improve services by studying how people interact with devices, platforms, and products.

How IoB Works and Uses

• Purpose: Understand customer needs, improve user experience, personalize services
• Sources of Data: Social media activity, location (GPS), purchase history, website usage, health app data
• Process: Data is collected from IoT and digital devices, behavior patterns are analyzed, and insights are used to influence decisions
• Benefits: Personalized recommendations, better customer service, improved decision-making, customer journey analysis
• Applications: Health apps (fitness tracking), online shopping suggestions, smart city services, marketing and advertising
• Challenges: Privacy concerns, data security, ethical issues

Continued Smart Irrigation

Continued smart irrigation

Working Principle

Sensor measures soil moisture. The controller compares with a threshold. If soil is dry, the water pump turns ON. If soil is wet, the pump turns OFF. Data is sent to the cloud for monitoring.

IoT Features

• Remote monitoring
• Smartphone control
• Weather-based watering
• Data analytics for water usage

Advantages and Applications

• Saves water
• Reduces labor
• Prevents over-watering
• Increases crop yield
• Applications: Agriculture, greenhouses, gardens, parks, public plantations

WebSocket

WebSocket is a full-duplex communication protocol used to create a persistent connection between a client and a server. It enables real-time data exchange with low latency. The protocol starts as an HTTP handshake, then the connection upgrades to WebSocket; communication becomes bidirectional and the connection stays open.

Features and Use Cases

• Full-duplex
• Persistent connection
• Low bandwidth usage and event-driven communication
• Use cases: chat apps, live notifications, online multiplayer games, real-time IoT dashboards, stock price updates, collaborative tools
• Advantages: fast, efficient, supports real-time services, less network overhead

ZigBee

ZigBee is a low-power wireless communication technology used for connecting small IoT devices in short-range networks. It is low-cost and designed for low-power operation.

• Features: low data rate, mesh networking, short-range, low power
• Architecture: coordinator, router, end device
• Applications: home automation, smart meters, industrial sensors

HTTP

HTTP is a web communication protocol used between clients and servers to transfer web pages, files, and data. It is a request–response protocol used on the web.

• Characteristics: stateless, text-based, works over TCP, high overhead
• How it works: client sends request, server responds, connection closes
• Applications: websites, APIs, downloading files

Wireless Technologies Comparison

Edge, Fog, and Cloud Computing

Edge, Fog, and Cloud computing are three levels of computing used in IoT systems. They differ based on where data is processed — at the device, near the device, or in the cloud.

Cloud Computing

Cloud provides large-scale storage, processing, and analytics. Data is sent to centralized servers like AWS, Azure, or Google Cloud. Cloud offers high computational power but may introduce latency. It is used for long-term analysis, big data, and machine learning.

Fog Computing

Fog is an intermediate layer between edge devices and the cloud. It uses local servers or gateways to process data near the source, reducing latency and decreasing the burden on the cloud. Examples: IoT gateways and routers with computing power.

Edge Computing

Edge computing performs processing directly on IoT devices or sensors. It provides ultra-fast response as data does not travel far. It works well for time-critical applications like CCTV face detection or autonomous vehicles and reduces the need for constant cloud connectivity.

Physical Design of IoT

The physical design of IoT refers to the hardware components that form an IoT system. It includes devices, sensors, actuators, connectivity, and interfaces that collect data, perform actions, and communicate with the internet.

• Devices: Smart appliances, wearables, machines with sensors and processors
• Sensors: Collect environmental information such as temperature, humidity, motion, or light
• Actuators: Perform actions based on commands (switch devices on/off, control movement)
• Connectivity: Wi-Fi, Bluetooth, ZigBee, cellular networks
• IoT Platforms / Cloud: Store, process, and analyze collected data
• User Interface: Mobile apps, dashboards, or voice interfaces for control and monitoring
• Data Processing Hardware: Microcontrollers or microprocessors (Arduino, Raspberry Pi) for local processing

IoTWF 7-Layer Reference Model

The IoTWF (Internet of Things World Forum) introduced a 7-layer IoT Reference Model to explain how an IoT system works from device level to business level. Each layer has a specific function that helps build efficient and scalable IoT solutions.

1. Physical Devices Layer: Sensors, actuators, and smart devices that collect data
2. Connectivity Layer: Provides communication using Wi-Fi, Bluetooth, ZigBee, cellular and wired networks
3. Edge Computing Layer: Local processing, filtering, and analysis near devices
4. Data Accumulation Layer: Stores large amounts of data using cloud storage and databases
5. Data Abstraction Layer: Organizes, indexes, filters, and processes data for applications
6. Application Layer: Provides IoT applications such as smart homes, healthcare, and industrial automation
7. Collaboration and Processes Layer: Involves user interaction, business rules, decision-making, and workflows

Bluetooth: Classic vs BLE

ZigBee and LoRa Comparison

6LoWPAN Details

6LoWPAN enables IPv6 communication for low-power devices by compressing IPv6 headers to fit into small 802.15.4 frames. This allows limited devices to use IPv6 addressing efficiently and supports mesh networking for extended coverage.