FlexRay Protocol: Advantages and Disadvantages Compared to CAN

This page compares Flexray and CAN, highlighting the advantages and disadvantages of Flexray.

What is Flexray Protocol?

Flexray is an automotive network communication protocol. It was developed by the FlexRay Consortium to provide higher speeds and better reliability compared to CAN and TTP. Flexray is used for various applications, including high-speed data sharing, distributed control, and safety-critical systems.

Figure 1 depicts a Flexray node architecture consisting of a communication controller, a host, a power supply, and two bus drivers.

Image courtesy: FlexRay Consortium

A Flexray cluster can be configured as a single-channel or dual-channel bus network, a single-channel or dual-channel star network, or various hybrid combinations of bus and star topologies. A Flexray cluster consists of at most two channels: channel A and channel B. Each node in the cluster may be connected to either or both channels.

Here are some key features of Flexray:

• Number of channels: 2 (A and B)
• Topology: Bus, Star, Hybrid
• Medium Access: Multi Master, Hybrid TDMA
• It’s an open bus system that supports redundant transmission channels.
• Variable bit rates: 2.5, 5, 8, or 10 Mbps
• It uses a differential NRZ (Non-Return-to-Zero) technique for data encoding. In NRZ signaling, the bit level remains either HIGH or LOW during the entire bit period.
• Nodes: 4 to 22
• It offers static and dynamic data transmission (scalable).
• It supports both electrical and optical physical layers.
• It supports fault-tolerant synchronized global time base.
• It supports AUTOSAR.

Like typical protocol frame structures, the Flexray frame consists of a header, payload, and trailer, as shown in the figure. It carries an 11-bit frame ID, a 255-byte payload, a 24-bit CRC for the payload, and an 11-bit CRC for the header. There’s a field for payload length immediately after the frame ID, as shown.

Benefits or Advantages of Flexray Protocol

Here are the benefits or advantages of Flexray protocol:

• It doesn’t use bit arbitration, unlike CAN. Hence, it offers 10 Mbps speed independent of network length, which is greater than CAN (~1 Mbps).
• It has error detection capability with the use of CRC in the frame.
• It’s a highly flexible protocol.
• It supports different topologies such as bus, star, and combinations of both (i.e., hybrid).
• It offers both synchronous and asynchronous frame transfer with guaranteed frame latency and jitter.

Drawbacks or Disadvantages of Flexray Protocol

Here are the drawbacks or disadvantages of Flexray protocol:

• It’s more expensive compared to CAN (Controller Area Network) and TTP (Time Triggered Protocol).
• It has higher complexity than CAN protocol.
• It has lower operating voltage levels.
• Ethernet is replacing Flexray for bandwidth-intensive and non-safety-critical applications.