Abstract

The rapid evolution of the "Software-Defined Vehicle" (SDV) has necessitated a paradigm shift in how Telematics Control Units (TCUs) communicate with the vehicle’s internal systems. For decades, the Controller Area Network (CAN) has been the industry standard. However, the advent of 5G, C-V2X, and over-the-air (OTA) updates has exposed the bandwidth limitations of CAN. This article provides a comprehensive comparative analysis of CAN-based TCUs versus Diagnostic over IP (DoIP) based TCUs. We explore throughput capabilities, latency, security protocols, and the transition toward Ethernet-based backbones in modern automotive ecosystems.

1. Introduction

The Telematics Control Unit (TCU) serves as the vehicle’s gateway to the outside world. It manages cellular connectivity (LTE/5G), GNSS, and V2X (Vehicle-to-Everything) communications. As vehicles become more autonomous and connected, the volume of data transferred between the TCU and other Electronic Control Units (ECUs) has grown exponentially.

Traditional architectures rely on the CAN (Controller Area Network) bus, a robust but low-bandwidth serial communication protocol. Emerging architectures are shifting toward DoIP (Diagnostic over IP), leveraging Automotive Ethernet (100Base-T1 or 1000Base-T1) to handle the data-heavy requirements of modern telematics.

2. The Legacy: CAN-Based TCUs

2.1 Architecture and Protocol

CAN was designed by Bosch in the 1980s as a multi-master serial bus. In a CAN-based TCU architecture, the unit acts as a node on the bus, broadcasting messages that other ECUs (like the Gateway or BCM) receive.

2.2 Limitations in the 5G Era

• Bandwidth: Standard CAN operates at 500 kbps, while CAN-FD (Flexible Data-rate) reaches up to 5 Mbps. This is insufficient for downloading multi-gigabyte firmware updates or streaming high-definition sensor data.
• Payload Size: CAN frames are limited to 8 bytes (64 bytes for CAN-FD). Segmenting large data packets across multiple frames introduces significant overhead and latency.
• Scalability: As the number of ECUs increases, bus load becomes a critical failure point.

3. The Modern Standard: DoIP-Based TCUs

3.1 What is DoIP?

Diagnostic over IP, standardized in ISO 13400, allows diagnostic messages to be transported over the Internet Protocol (IP) using Ethernet. In a DoIP-based TCU, the interface is no longer a low-speed serial bus but a high-speed Ethernet link.

3.2 Advantages of DoIP

• Massive Throughput: With Automotive Ethernet, TCUs can achieve speeds from 100 Mbps to 10 Gbps.
• OTA Efficiency: Over-the-Air updates that would take hours over CAN can be completed in minutes using DoIP.
• Standardized Stack: Utilizing the TCP/IP stack allows for easier integration with cloud services and standardized security protocols like TLS/SSL.

4. Comparative Technical Analysis

5. Security Considerations

As the TCU is an entry point for cyberattacks, security is paramount.

• CAN Security: CAN lacks built-in encryption. Security often relies on proprietary Message Authentication Codes (MACs) which add significant overhead to the already small frames.
• DoIP Security: By leveraging IP, DoIP can utilize established IT security standards. IPsec and TLS can be implemented to ensure that the data flowing from the TCU to the Gateway is encrypted and authenticated.

6. Case Study: 5G Telematics Implementation

In high-performance automotive projects, the transition to DoIP is a technical necessity. A 5G modem can theoretically download data at speeds exceeding 1 Gbps. If that modem is connected to the vehicle backbone via a 5 Mbps CAN-FD bus, the bus becomes a massive bottleneck. By implementing a DoIP interface, the TCU can distribute data to the Central Gateway at wire-speed, allowing for parallel flashing of multiple ECUs.

7. The Future: Hybrid Architectures

Most modern vehicles currently utilize a hybrid approach. The TCU often maintains a CAN-FD connection for "Keep Alive" signals and low-priority wake-ups, while using a DoIP/Ethernet link for the primary data plane. This ensures backward compatibility while enabling future-proof data rates.

8. Conclusion

The shift from CAN to DoIP marks the transition of the vehicle from a collection of isolated controllers to a distributed high-performance computing platform. While CAN remains relevant for simple sensor data, DoIP is the backbone of the modern TCU. For engineers specializing in device certification and interoperability, mastering the ISO 13400 standard is now as critical as understanding RF performance.

9. References

1. ISO 13400-1:2011. Road vehicles - Communication interface for external equipment and IP - Part 1: General information and use case definition. International Organization for Standardization.
2. ISO 13400-2:2019. Road vehicles - Communication interface for external equipment and IP - Part 2: Transport protocol and network layer services. International Organization for Standardization.
3. ISO 11898-1:2015. Road vehicles - Controller area network (CAN) - Part 1: Data link layer and physical signalling. International Organization for Standardization.
4. 3GPP TS 23.285. Technical Specification Group Services and System Aspects; Architecture enhancements for V2X services. 3rd Generation Partnership Project.
5. 3GPP TS 36.331. Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification.
6. Matheus, K. & Koelzer, S. (2021). Automotive Ethernet (2nd ed.). Cambridge University Press.
7. Tuohy, S., Glavin, M., Jones, E., Trivedi, M., & Kilmartin, L. (2015). "Intra-Vehicle Networks: A Review." IEEE Transactions on Intelligent Transportation Systems, vol. 16, no. 2, pp. 534-545.
8. Smith, C. (2016). The Car Hacker's Handbook: A Guide for the Penetration Tester. No Starch Press.
9. Zimmermann, W. & Schmidgall, R. (2014). Bussysteme in der Fahrzeugtechnik (5th ed.). Springer Vieweg.
10. Correa, A., Al-Hammadi, Y., & Khattak, A. M. (2017). "A Survey on Automotive Ethernet: Standard, Trends and Challenges." IEEE Access, vol. 5.

News Source : Written By: Sunil Sharma