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Survey of Known Protocols: An Overview of SAE J2056/2 for Vehicle Networking
The SAE J2056-2-2000 Information Report, formally titled Survey of Known Protocols, provides a structured summary comparison of protocols found in manufacturing, automotive, aviation, military, and computer applications. It is intended to serve as a reference for engineers evaluating Class C vehicle network systems—those requiring high data rates and real-time control capability.
The report is not an evaluation but a starting point, offering side-by-side comparisons of attributes such as data rate, bus length, medium access, and error detection. It also defines a standardized format that allows new protocols to be submitted for future revisions, ensuring the document remains relevant as technology evolves.
The Three Classes of Vehicle Communication
The SAE Vehicle Networking Subcommittee has identified three classes of vehicle communication, each serving a distinct purpose:
- Class A – A multiplex system primarily aimed at reducing wiring by transmitting multiple signals (e.g., low-speed body control functions like exterior lamps) over a shared bus instead of individual wires.
- Class B – A multiplex system that enables data transfer between nodes to eliminate redundant sensors and system elements (e.g., sharing parametric data such as vehicle speed).
- Class C – A multiplex system for high data rate signals typically associated with real-time control (e.g., engine controls and anti-skid brakes), enabling distributed control and further wiring reduction.
Each class is designed to support lower-level vehicles, but the focus of SAE J2056/2 is on protocols applicable to Class C applications.
Protocols Surveyed in the Report
The report surveys a range of protocols from multiple industries, each with unique characteristics. The following table lists the protocols included in the survey and their primary application domains.
| Protocol | Primary Application Domain |
|---|---|
| MIL-STD-1553 | Aviation / Military |
| Automotive Bit-Serial Universal-Interface System (ABUS) | Automotive |
| Auto Local Area Network (AutoLAN) | Automotive |
| SAE J1850 | Automotive |
| Controller Area Network (CAN) | Automotive |
| Digital Data Bus (D2B) | Automotive |
| Ethernet (IEEE 802.3) | Computer / General |
| Joint Integrated Avionics Working Group (JIAWG) | Avionics |
| Mini-Manufacturing Automation Protocol (Mini-MAP) | Manufacturing |
| Synchronous Data Link Control / High-Level Data Link Control (SDLC/HDLC) | Computer / Telecom |
| Token Ring (IEEE 802.5) | Computer |
| Token Slot Network | Aviation / Research |
| Vehicle Area Network (VAN) | Automotive |
The report provides detailed examination of attributes such as data rate, bus length, medium access method, electrical characteristics, and error detection. Notably, many protocols do not specify a method for one or more criteria, resulting in entries marked as ‘user defined’ or ‘not specified’. This highlights the need for engineers to tailor aspects to their specific application.
Engineering Design Insights and How to Use This Report
⚠️ Important Note: This report is a summary, not a comprehensive evaluation. It is intended to be a starting point for further research, and the interested reader is encouraged to consult the referenced specifications for complete details.
🛠️ Design Insight: The report includes a standardized form for evaluating a protocol, allowing new protocols to be submitted for consideration in future revisions. This makes it a living document that can adapt to evolving vehicle networking needs.
When using the report, engineers should be aware that many protocols have unspecified attributes, meaning practical implementation often requires custom definition of bus lengths, error handling, or electrical interfaces. The side-by-side comparison table is valuable for quickly identifying which protocols merit deeper investigation based on key parameters like data rate, medium access, or fault tolerance. The report does not recommend any particular protocol; instead, it equips the reader with the necessary references to make an informed decision.
A practical approach is to first identify the required data rate, determinism, and fault tolerance for the application, then use the comparison table to filter candidates. Protocols from non-automotive industries—such as avionics (MIL-STD-1553) or manufacturing (Mini-MAP)—may offer features that are beneficial for automotive Class C systems, so cross-industry consideration is encouraged.
Frequently Asked Questions
- What is the difference between Class A, B, and C?
- Class A is for low-speed body control functions (e.g., lighting), Class B for parametric data sharing (e.g., sensor data), and Class C for high-speed real-time control (e.g., engine management, brakes).
- Which protocol is best for Class C applications?
- The report does not identify a single best protocol. The choice depends on application requirements such as data rate, timing, and reliability. CAN and VAN are popular in automotive, but other protocols like MIL-STD-1553 or Ethernet may be considered for specific needs.
- Why are some attributes listed as ‘user defined’ or ‘not specified’?
- Many protocol specifications leave certain aspects (e.g., bus length, electrical characteristics) open to implementation. Engineers must define these based on the specific system constraints and environment.
- Can I use this report to select a protocol immediately?
- The report is a starting point. It provides a summary comparison, but a detailed evaluation should be performed using the referenced full specifications and application-specific tests.
In summary, SAE J2056-2-2000 is a valuable reference for engineers navigating the landscape of vehicle networking protocols. By presenting a structured survey and standardized comparison format, it aids in the early-stage evaluation of options for Class C systems and beyond.
