Communication Protocols for the Internet of Things -

Overview

The Internet of Things (IoT) is defined as a global network that intelligently interconnects all objects—whether devices, systems, or humans—with self-configuring capabilities based on standardized and interoperable protocols and formats. Leveraging smart sensors, identification technologies, and computing, IoT is recognized as the next wave of information technology following computers and the internet. IoT supports hundreds of protocols. Among these, wireless protocols play a critical role in IoT development. They are generally categorized into two main types: transmission protocols and communication protocols. Transmission protocols are primarily responsible for networking and communication between devices within a subnet, while communication protocols, which operate on top of the traditional internet TCP/IP protocol stack, manage data exchange and communication between devices over the internet.

The diversity of IoT interface types leads to a wide variety of communication protocols, each with its own applicable scope. For instance, AMQP, JMS, and REST/HTTP are designed for application environments based on Ethernet. Since the foundational protocol of the internet is TCP/IP, the HTTP communication protocol is widely adopted due to its low development cost and high degree of openness. Consequently, many IoT applications are developed based on the HTTP protocol, building IoT protocol standards upon traditional web technologies. The number of protocols used in Industrial IoT is vast; here, we list only the commonly used application layer protocols in Industrial IoT:

MQTT Protocol

MQTT (Message Queuing Telemetry Transport) is an ISO standard (ISO/IEC PRF 20922) message protocol based on the publish/subscribe paradigm (replacing the request/response model commonly used on the internet). It operates over the TCP/IP protocol suite and is designed for remote devices with limited hardware capabilities and poor network conditions, requiring a message broker. The MQTT protocol is lightweight, simple, open, and easy to implement, making it widely applicable and establishing it as a standard protocol for IoT. Due to its simplicity, it is particularly suitable for IoT scenarios requiring low power consumption and limited network bandwidth, including constrained environments such as Machine-to-Machine (M2M) communication and IoT. It is extensively used in satellite link communication for telemetry data, occasionally dialed medical devices, smart homes, and various compact devices.

The main advantages of MQTT are:

MQTT Official Website

Lightweight and efficient, minimizing resources required by clients and network bandwidth.
Supports bidirectional communication between devices and servers. Additionally, it can broadcast messages to groups of things.
Scalable to millions of things.
Specifies Quality of Service (QoS) levels to support message reliability.
Supports persistent sessions between devices and servers, reducing reconnection times required over unreliable networks.
Messages can be encrypted using TLS, and client authentication protocols are supported.

CoAP Protocol

CoAP (Constrained Application Protocol) is a web-like protocol for the IoT world. Many devices in wireless IoT are resource-constrained, with limited memory space and computational power. To address this, the IETF (Internet Engineering Task Force) CoRE (Constrained RESTful Environment) working group developed this RESTful application layer protocol for constrained nodes. It is suitable for one-to-one M2M communication in local area network environments; for example, for small, low-power sensors, switches, valves, and similar components that require remote control or monitoring via standard internet networks. Servers may not respond to unsupported types.

RFC 7252

CoAP is a service layer protocol for resource-constrained Internet devices, such as wireless sensor network nodes. CoAP is designed to translate easily to HTTP for simplified web integration while also meeting specific requirements like multicast support, very low overhead, and simplicity. Multicast, low overhead, and simplicity are crucial for the Internet of Things (IoT) and Machine-to-Machine (M2M) communication, where devices are often deeply embedded and have significantly less memory and power than traditional internet devices. Therefore, efficiency is paramount. CoAP can run on most devices supporting UDP or UDP emulation.

AMQP Protocol (Interoperability)

AMQP (Advanced Message Queuing Protocol) is used for data exchange between business systems such as PLM, ERP, and MES. It was initially applied for transactional message passing between financial systems. In IoT applications, it is primarily suitable for communication and analysis between mobile handheld devices and backend data centers.

AMQP Official Website

AMQP is a binary application layer protocol designed to efficiently support a wide range of messaging applications and communication patterns. It provides flow control, message-oriented communication, with messaging guarantees such as at-most-once (each message is delivered once or never), at-least-once (each message is assured to be delivered, but may be delivered multiple times), and exactly-once (the message always arrives certainly and does so only once), as well as authentication and/or encryption based on SASL and/or TLS. It assumes an underlying reliable transport layer protocol, such as the Transmission Control Protocol (TCP).

The AMQP specification is divided into several layers: (1) a type system, (2) a symmetric asynchronous protocol for transferring messages from one process to another, (3) a standard, extensible message format, and (4) a set of standardized but extensible "messaging capabilities."

REST/HTTP (Loosely Coupled Service Invocation)

At the IoT application level, resources within IoT are often exposed via REST/HTTP to enable services to be invoked by other applications. It is used to achieve loose coupling between client and server interactions, reducing the interaction latency between them.

Advantages: 1. Simple, flexible, and easy to extend. 2. Possesses a mature ecosystem and specifications. 3. Stateless protocol, conducive to implementing distributed clustering.
Disadvantages: Plaintext transmission, all data can be easily obtained. Cannot verify the identities of communicating parties, leading to potential malicious access. Cannot prove the integrity of the message, which might be tampered with.

DDS Protocol (High Reliability, Real-Time)

DDS (Data Distribution Service for Real-Time Systems) is a data distribution service for real-time systems. DDS excellently supports data distribution and device control between devices, as well as data transmission between devices and the cloud. Simultaneously, DDS offers highly efficient real-time data distribution, capable of delivering millions of messages to numerous devices within seconds.

OMG is a computer industry standards consortium; founded in 1989 by 11 companies (including Hewlett-Packard, IBM, Sun Microsystems, Apple Computer, American Airlines, iGrafx, and Data General); responsible for the release and maintenance of DDS versions.

omg

DDS is a network middleware that simplifies complex network programming. It implements a publish-subscribe pattern for sending and receiving data, events, and commands between nodes. Nodes that generate information (publishers) create "topics" (e.g., temperature, position, pressure) and publish "samples." DDS delivers the samples to subscribers who have declared interest in that topic.

DDS provides numerous Quality of Service (QoS) guarantee pathways, meeting the needs of applications such as aerospace and defense, air traffic control, autonomous vehicles, medical devices, robotics, power generation, simulation and testing, smart grid management, transportation systems, and others requiring real-time data exchange.

XMPP Protocol (Instant Messaging)

XMPP (Extensible Messaging and Presence Protocol), originally named Jabber, is a network instant messaging protocol developed by an open-source organization. It is specifically designed for instant messaging (IM), presence information, and contact list maintenance. Based on XML (Extensible Markup Language), it supports near-real-time exchange of structured data between two or more network entities. The protocol is designed for extensibility, offering numerous applications beyond traditional IM in the broader domain of message-oriented middleware, including VoIP, video, file transfer, gaming, remote system monitoring, and other application areas.

XMPP Official Website

Communication Protocols for the Internet of Things

Overview

MQTT Protocol

CoAP Protocol

AMQP Protocol (Interoperability)

REST/HTTP (Loosely Coupled Service Invocation)

DDS Protocol (High Reliability, Real-Time)

XMPP Protocol (Instant Messaging)

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