Overview
ISO 21806-2:2020 defines the application layer and presentation layer for Media Oriented Systems Transport (MOST) used in road vehicles. This part of the MOST specification standardizes the device model, registry management, connection management for streaming data, diagnosis and error handling. It also defines the structure of MOST messages (addressing, function block IDs, instance IDs, function IDs, operation types and timing) and the presentation-level data definitions and basic data types.
Keywords: ISO 21806-2:2020, Media Oriented Systems Transport, MOST, application layer, presentation layer, automotive networking, vehicle infotainment.
Key technical topics and requirements
- Device model and node kinds: standardized representations for MOST nodes, remote-controlled nodes and listen-only nodes.
- Function blocks (FBlocks): definitions for FBlock libraries, controllers, instances and function identifiers (FBlockID, InstID, FktID).
- Registry management: central registry behavior, NetworkMaster/NetworkSlave responsibilities and lifecycle (wake-up/startup/shutdown).
- Connection management for streaming data: services for audio/video streaming, source/sink descriptions, streaming connection setup, and compensation for network delay.
- Message structure and addressing: AL-level requirements including 16-bit and 48-bit addressing schemes, addressing semantics and functional addressing uniqueness.
- Operation types and timing: OPType semantics (Set/Get/Start/Result/Error etc.) and timing definitions for reliable timing behavior across the MOST network.
- Presentation layer data types: standardized basic data types, boolean/enum/numeric types, strings, arrays, records and stream types for consistent data serialization.
- Diagnosis and error handling: FBlock configuration status, shutdown reasons, ring break and network diagnosis, overload and over-temperature handling.
- Notification and event mechanisms: event models, notification functions, implicit/automatic notifications and error-related notifications.
Practical applications and who uses it
ISO 21806-2 is essential for:
- Automotive infotainment system architects and software engineers implementing MOST-based media networks.
- ECU and device vendors building compliant MOST function blocks, streaming sources/sinks and registry services.
- Test engineers and tool vendors creating conformance tests, diagnostic tools and network analyzers.
- Systems integrators handling in-vehicle audio/video streaming, telematics and multimedia distribution.
Use cases include in-car audio/video streaming, distributed multimedia control, diagnostics and fault management across MOST ring or Ethernet-based MOST segments.
Related standards
- Other parts of the MOST family (physical, transport and management layers) and complementary automotive networking standards (e.g., SOME/IP, AUTOSAR) for system-level integration and interoperability.
Relevant search terms: ISO 21806-2, MOST application layer, MOST presentation layer, vehicle media transport, automotive streaming protocol, function block registry.
Open preview (PDF)Road vehicles — Media Oriented Systems Transport (MOST) — Part 2: Application layer
