ISO 10681-2:2010

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 10681-1 (General information and use cases)
• FlexRay Communications Systems Protocol Specification (data link layer)
• FlexRay Electrical Physical Layer Specification
• ISO/IEC 7498-1, ISO/IEC 7498-3, ISO/IEC 7498-4, ISO/IEC 10731 (OSI reference models and service conventions)
• ISO 14229 series (application-level diagnostic relevance)

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.