Overview
ISO 10681-2:2010 - Road vehicles - Communication on FlexRay - Part 2: Communication layer services defines the communication-layer protocol for FlexRay-based vehicle networks. Implementing the combined OSI network (layer 3) and transport (layer 4) functionality, this part specifies service primitives, message segmentation/reassembly, flow control and acknowledgement behaviors tailored to FlexRay systems. It is intended to enable reliable ECU-to-ECU and diagnostic tester-to-ECU exchanges over FlexRay.
Key topics and technical requirements
- Scope and layering: Maps network and transport services onto a single communication layer (CL) according to OSI principles (referencing ISO/IEC 7498-1 and ISO/IEC 10731).
- Service primitives: Defines standard service calls such as C_Data.request / indication / confirm, C_GetStatus, C_ChangeParameter, C_GetParameter and C_Cancel for transmitting data and managing protocol parameters.
- Message size and segmentation:
- Supports transmission of messages up to 64 kbytes.
- Handles messages with known or unknown but finite lengths.
- Provides segmentation into StartFrame, ConsecutiveFrame and LastFrame and reassembly rules.
- Acknowledgement & retry: Offers both unacknowledged and acknowledged transfer modes, including additional acknowledgement with retry mechanisms and block acknowledgements (FlowControl frames).
- Flow control and framing: Flow status indicators (CTS / WAIT / overflow) and mechanisms for on-the-fly routing and dynamic frame length support.
- Service behaviour rules: Specifies how functional (unacknowledged) vs. confirmed transfers are handled, handling of unexpected formats, and rules for last-frame signaling and buffer handling.
Practical applications and users
Who uses ISO 10681-2:2010:
- Automotive OEM network architects defining FlexRay network behavior.
- ECU suppliers and firmware engineers implementing transport/network services over FlexRay.
- Diagnostic tool and tester vendors interfacing with FlexRay ECUs.
- System integrators and gateway designers managing multi-subnet routing.
Typical applications:
- ECU-to-ECU large-message transfer (e.g., calibration data, firmware chunks).
- Diagnostic session communication between external testers and vehicle ECUs.
- Robust multi-frame messaging with flow control and retransmission across FlexRay subnets.
Related standards
ISO 10681-2:2010 is essential for anyone designing or integrating transport/network services on FlexRay, providing a standardized, interoperable approach to segmented transfers, acknowledgements and dynamic-framing in automotive networks.
