Enhancing CAN: Higher-Layer Protocols for Advanced Networking

This article is part of our comprehensive SAE J1939 online documentation.

While highly effective in automobiles and small-scale applications, the Controller Area Network (CAN) alone is not ideal for machine automation due to its limitation of only 8 bytes per message. To address this, higher-layer protocols such as CANopen for machine control, DeviceNet for factory automation, and J1939 for vehicles were developed. These protocols extend CAN’s capabilities by enabling true networking functionality, supporting longer message lengths, and allowing master/slave configurations.

To better understand higher-layer protocols, we can refer to the ISO/OSI 7-Layer Reference Model, as illustrated in the diagram below.

ISO/OSI 7-Layer Reference Model

In a standard CAN implementation, there is no direct connection between the Data Link Layer and the Application Layer. Instead, the layers above the Data Link Layer are managed by additional software, which, by definition, constitutes a higher-layer protocol.

When adding software functions between the CAN Data Link Layer and the Application Layer, keep in mind that you may be duplicating functionalities already covered by widely available higher-layer protocols such as CANopen, DeviceNet, and SAE J1939.

Why Are Higher-Layer Protocols Necessary?

Higher-layer protocols are essential because they:

Enable data transport beyond the 8-byte limit per CAN message.
Provide structured communication models, such as the Master/Slave configuration for embedded systems.
Support network management functions, including network start-up, node monitoring, and synchronization.

Popular Higher-Layer Protocols Based on CAN:

CANopen
DeviceNet
SAE J1939

CANopen and DeviceNet are primarily used in industrial control applications. While CANopen is somewhat applicable to vehicle systems, both protocols are highly complex and often considered over-engineered, making them difficult to fully comprehend.

SAE J1939, on the other hand, is an efficiently designed protocol that maximizes the 29-bit CAN message identifier. Instead of relying on an extensive set of protocol functions, SAE J1939 utilizes predefined parameter tables, making the protocol straightforward yet highly effective. It exemplifies good American engineering by following the KISS principle (Keep It Simple, Stupid!), while still being just as powerful as CANopen or DeviceNet.

CANopen

CANopen is a higher-layer protocol built on the Controller Area Network (CAN), designed to standardize communication in embedded control systems. It was originally developed for industrial automation but has since been adopted in various industries, including medical devices, transportation, and off-road vehicles. CANopen extends the basic capabilities of CAN by defining a robust communication framework and device profile specifications.

Key Features

Enhanced Data Management:
- Overcomes CAN’s 8-byte message limit by providing mechanisms for longer data exchanges.
- Supports both real-time data transmission and event-driven communication.
Communication Models:
- Uses a Master/Slave or Producer/Consumer model to organize network communication.
- Provides synchronized and time-triggered communication via Process Data Objects (PDOs) and Service Data Objects (SDOs).
Standardized Device Profiles:
- Defines device profiles for different applications (e.g., motors, sensors, medical devices), ensuring interoperability between manufacturers.
Network Management (NMT):
- Handles network initialization, node monitoring, and error detection.
- Includes Heartbeat and Node Guarding mechanisms for fault detection and recovery.
Flexible and Scalable:
- Suitable for small, single-master networks as well as large, multi-node systems.
- Allows dynamic node addressing for improved network flexibility.

Comparison with Other CAN-Based Protocols

Unlike DeviceNet, which is optimized for factory automation, CANopen provides a more versatile framework suitable for a wide range of embedded applications.
Compared to SAE J1939, CANopen is more complex, offering extensive configuration options and detailed device profiles, whereas J1939 is simpler and designed primarily for heavy-duty vehicles.

Applications of CANopen

Industrial automation (PLC controllers, sensors, actuators).
Medical devices (MRI machines, patient monitoring systems).
Transportation and automotive systems (electric vehicles, railway systems).
Building automation (HVAC, lighting control).

Conclusion

CANopen provides a structured and powerful communication protocol that extends the basic CAN bus capabilities. With its standardized communication models, network management features, and predefined device profiles, CANopen enables interoperability, scalability, and efficient data exchange, making it a preferred choice for complex embedded systems.

DeviceNet

DeviceNet is a higher-layer protocol based on Controller Area Network (CAN), specifically designed for industrial automation. Developed by Allen-Bradley (Rockwell Automation) and now managed by the Open DeviceNet Vendors Association (ODVA), DeviceNet facilitates efficient communication between industrial controllers (PLCs), sensors, actuators, and other automation devices. It standardizes both data exchange and power delivery over a single network, making it a key protocol in modern manufacturing systems.

Key Features

Optimized for Industrial Automation:
- Designed for factory floor applications, including robotics, conveyor systems, and material handling.
- Supports up to 64 nodes per network, ensuring scalability.
Integrated Power and Data Communication:
- DeviceNet transmits both data and power over a single cable, reducing wiring complexity.
- Supports multiple voltage levels (typically 24V DC) to power devices directly.
Robust Network Architecture:
- Uses a Producer/Consumer model instead of traditional Master/Slave communication, allowing more efficient real-time data exchange.
- Supports cyclic, polled, and change-of-state messaging, optimizing network traffic.
Device Profiles and Standardization:
- Defines pre-configured device profiles, ensuring interoperability among different manufacturers.
- Uses object-oriented data structures, simplifying device integration.
Advanced Error Detection and Network Management:
- Includes built-in error checking, diagnostics, and node monitoring for fault tolerance.
- Supports auto-baud rate detection for easy network configuration.

Comparison with Other CAN-Based Protocols

Compared to CANopen, DeviceNet is more focused on factory automation and integrates power and data transmission in a single cable.
Compared to SAE J1939, which is designed for heavy-duty vehicles, DeviceNet is built for industrial control systems with structured device profiles and robust diagnostics.

Applications of DeviceNet

Factory automation (robotics, conveyor systems, packaging machines).
Process control (chemical plants, food and beverage manufacturing).
Material handling (automated storage and retrieval systems).
Industrial safety systems (emergency stop and monitoring devices).

Conclusion

DeviceNet is a powerful and reliable industrial communication protocol that enhances automation efficiency, reduces wiring costs, and improves real-time data exchange. With its plug-and-play capabilities, structured device profiles, and integrated power and data communication, DeviceNet remains a widely adopted solution for modern manufacturing and industrial automation systems.

SAE J1939

This document provides a comprehensive exploration of the J1939 protocol, covering all its features, structure, and applications in detail. Each chapter delves into specific aspects of J1939, including its message structure, data transport mechanisms, and network management functions.

However, in this section, we focus on protocols derived from J1939, which have been adapted for specialized industries. These include:

NMEA 2000 – A marine industry standard based on J1939, designed for communication between shipboard electronic devices, such as GPS systems, navigation instruments, and engine controls.
ISOBUS – A standardized communication protocol for agricultural machinery, enabling seamless interoperability between tractors, implements, and control terminals.
MilCAN – A J1939-based protocol developed for military and aerospace applications, ensuring reliable and secure data exchange in harsh environments, with enhancements for redundancy and deterministic communication.

For a detailed analysis of J1939’s core functionalities, please refer to the following chapters. This section serves as an introduction to its extensions and adaptations in other industries.

NMEA 2000

NMEA 2000 (National Marine Electronics Association 2000) is a higher-layer protocol based on SAE J1939, specifically designed for the marine industry. It standardizes communication between electronic devices on boats and ships, ensuring seamless data exchange between navigation systems, sensors, engines, and other onboard equipment. NMEA 2000 replaces older NMEA 0183 protocols with a modern, multi-device network architecture that supports real-time data sharing.

Key Features

Robust Data Communication:
- Uses Controller Area Network (CAN) for reliable, real-time communication.
- Supports multi-device networking without requiring direct device-to-device wiring.
Plug-and-Play Interoperability:
- Devices from different manufacturers can communicate using standardized messages (Parameter Group Numbers – PGNs).
- Eliminates proprietary communication issues, promoting cross-compatibility.
High Data Efficiency:
- Transmits binary messages instead of text, reducing bandwidth usage.
- Supports long messages using Transport Protocol (TP), overcoming CAN’s 8-byte limit.
Scalability & Flexibility:
- Can support up to 50 nodes per network with a data rate of 250 kbps.
- Allows easy expansion by adding new devices to the common network backbone.
Power and Network Management:
- Provides network-wide power distribution, reducing complex wiring.
- Supports device discovery, configuration, and network status monitoring.

Comparison with Other J1939-Based Protocols

Unlike SAE J1939, which is optimized for land-based heavy vehicles, NMEA 2000 is tailored for marine electronics, with specialized messages for GPS, depth sounders, engine monitoring, and navigation systems.
Compared to ISOBUS (used in agriculture), NMEA 2000 prioritizes environmental durability and marine navigation-specific data handling.

Applications of NMEA 2000

Navigation systems (GPS, autopilot, radar integration).
Marine engine monitoring (fuel levels, RPM, temperature).
Environmental sensors (depth, wind speed, water temperature).
Onboard control systems (lighting, power management).

Conclusion

NMEA 2000 is a highly efficient and standardized communication protocol for modern marine electronics. By leveraging J1939’s proven CAN-based framework, it enables seamless integration of navigation, monitoring, and control systems, making it an essential standard for commercial and recreational marine applications.

ISOBUS

ISOBUS (ISO 11783) is a higher-layer protocol based on SAE J1939, specifically designed for agricultural machinery and equipment. It standardizes communication between tractors, implements, sensors, and control systems, ensuring seamless interoperability between equipment from different manufacturers. ISOBUS enhances precision farming by enabling real-time data exchange, automation, and centralized control.

Key Features

Standardized Communication:
- Provides a universal language for agricultural equipment, ensuring plug-and-play compatibility.
- Uses Parameter Group Numbers (PGNs) for structured data exchange.
Improved Efficiency & Automation:
- Enables automatic machine control for planting, fertilization, and harvesting.
- Supports task management, allowing pre-programmed field operations.
Virtual Terminal (VT) Interface:
- Standardized in-cab display that allows operators to control multiple implements from a single universal terminal.
- Eliminates the need for proprietary control screens for each device.
File Server & Task Controller:
- Allows data logging and exchange between farm management software and machinery.
- Supports precision farming applications, such as variable rate application (VRA).
Network Management & Diagnostics:
- Enables real-time system monitoring, error detection, and remote diagnostics.
- Improves equipment longevity and reduces downtime.

Comparison with Other J1939-Based Protocols

Unlike SAE J1939, which is optimized for heavy-duty road vehicles, ISOBUS is designed for agricultural applications, with specialized messages and automation features.
Compared to NMEA 2000, which focuses on marine electronics, ISOBUS includes task control, file management, and implement standardization, essential for modern farming operations.

Applications of ISOBUS

Tractor-implement communication (seeders, sprayers, harvesters).
Precision agriculture (GPS-guided field operations).
Farm management software integration (data logging, yield mapping).
Automated control systems (variable rate applications, section control).

Conclusion

ISOBUS is a powerful and essential protocol for modern agriculture, enabling interoperability, automation, and data-driven decision-making. By extending J1939’s CAN-based framework, ISOBUS enhances farm efficiency, reduces operational costs, and supports sustainable farming practices.

MilCAN

MilCAN is a higher-layer protocol based on SAE J1939, specifically developed for military and aerospace applications. It enhances the Controller Area Network (CAN) for use in demanding defense environments, ensuring secure, deterministic, and redundant communication in mission-critical systems. MilCAN standardizes data exchange in military vehicles, avionics, and autonomous defense systems, where robustness and reliability are paramount.

Key Features

Deterministic and Reliable Communication:
- Enhances standard CAN arbitration to guarantee real-time data delivery.
- Supports priority-based message scheduling for critical operations.
Redundancy and Fault Tolerance:
- Implements dual-bus redundancy for improved resilience against failures.
- Enables error detection, correction, and recovery mechanisms.
Secure and Robust Network Architecture:
- Designed for harsh environments, resistant to electromagnetic interference (EMI) and cyber threats.
- Supports network encryption and authentication for secure data exchange.
Scalability for Complex Defense Systems:
- Allows multi-node military networks, integrating sensors, actuators, control units, and communication devices.
- Supports dynamic node addressing and reconfiguration.
Interoperability with J1939 and Other Standards:
- Maintains compatibility with J1939 messaging, ensuring easy integration with existing vehicle and aircraft systems.
- Can be adapted for joint military and commercial applications.

Comparison with Other J1939-Based Protocols

Unlike SAE J1939, which is designed for heavy-duty vehicles, MilCAN incorporates security, redundancy, and real-time capabilities, making it suitable for military and aerospace operations.
Compared to NMEA 2000 (marine) and ISOBUS (agriculture), MilCAN prioritizes mission-critical reliability, fault tolerance, and security features.

Applications of MilCAN

Military ground vehicles (tanks, armored personnel carriers).
Aerospace and avionics (unmanned aerial vehicles, helicopters, fighter jets).
Autonomous defense systems (drones, robotic surveillance).
Naval applications (warships, submarines, radar systems).

Conclusion

MilCAN is a mission-critical communication protocol that extends J1939’s capabilities to meet the stringent demands of military and aerospace industries. With its real-time, redundant, and secure architecture, MilCAN ensures robust and fail-safe operations, making it a key standard for modern defense and high-reliability systems.

SAE J1939 Starter Kit and Network Simulator

Our JCOM.J1939 Starter Kit and Network Simulator is designed to allow the experienced engineer and the beginner to experiment with SAE J1939 data communication without the need to connect to a real-world J1939 network, i.e., a diesel engine. It may sound obvious, but you need at least two nodes to establish a network. That fact applies especially to CAN/J1939, where the CAN controller shuts down after transmitting data without receiving a response. Therefore, our jCOM.J1939 Starter Kit and Network Simulator consists of two J1939 nodes, namely our jCOM.J1939.USB, an SAE J1939 ECU Simulator Board with USB Port.

The jCOM.J1939.USB gateway board is a high-performance, low-latency vehicle network adapter for SAE J1939 applications. The board supports the full SAE J1939 protocol according to J1939/81 Network Management (Address Claiming) and J1939/21 Transport Protocol (TP).

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