ISO 20794-6:2020

Overview

ISO 20794-6:2020 defines the transport and network layer conformance test plan for the Clock Extension Peripheral Interface (CXPI) used in road vehicles. CXPI is an automotive low‑speed single‑wire network for in-vehicle control applications (e.g., door controls, light switches, HVAC). This part of the ISO 20794 series specifies test procedures that validate the transportation of diagnostic communication, node configuration data and network-layer services as they pass between lower and higher OSI layers.

Keywords: ISO 20794-6, CXPI, transport layer conformance, network layer conformance test plan, automotive network testing, diagnostic communication.

Key Topics and Requirements

The document provides a structured conformance test plan including:

• Concept of operation conformance test plan
  • Test system setup, test conditions, and general test specification considerations.
• Transport layer protocol conformance tests
  • Master and slave node handling of T_PDU and T_PCI fields, including variations in T_PCI type and data length.
  • Specific test cases for extended T_PCI formats and short data fields.
• Network layer services conformance tests
  • N_PDU (node address) specification tests, reception logic tests for particular T_PID/N_NAD combinations, and network-level timeout/error detection (N_As timeout).
• Error detection conformance tests
  • Transport and network layer error detection behaviours and use of error indicator bits.
• Test system and IUT (Implementation Under Test) requirements
  • Configuration parameters, initialization procedures, and criteria for observing results and status report messages.

The standard references OSI conventions and normative standards such as ISO/IEC 7498-1 and other parts of ISO 20794 to ensure consistency with layered communications models.

Practical Applications and Who Uses This Standard

ISO 20794-6:2020 is intended for organizations and professionals involved in automotive network development, verification and certification:

• Automotive OEMs and system integrators validating CXPI-based subsystem interoperability and diagnostic behaviour.
• ECU and sensor manufacturers implementing CXPI transport/network layers who need to demonstrate conformance.
• Test labs and certification bodies running standardized conformance test suites.
• Tool vendors developing test equipment, protocol analyzers and diagnostic interfaces for CXPI.

Using this standard ensures consistent behaviour across nodes, reliable diagnostic transport, and predictable network error handling - supporting interoperability and robust in-vehicle communication.

Related Standards

• ISO 20794-2:2020 (Application layer)
• ISO 20794-3:2020 (Transport and network layer specification)
• ISO 20794-4:2020 (Data link and physical layer)
• ISO 20794-7 and other parts in the ISO 20794 series
• ISO 14229 series (vehicle diagnostic communication)
• ISO/IEC 7498-1 (OSI Basic Reference Model)

Adopting ISO 20794-6:2020 as part of a CXPI compliance program helps ensure standardized test coverage for transport and network layer functions, improving interoperability and diagnostic reliability in automotive systems.