Overview
Reference: ISO 21806-4:2020 - Road vehicles - Media Oriented Systems Transport (MOST) - Part 4: Transport layer and network layer
ISO 21806-4:2020 defines the technical requirements for the MOST transport layer (TL) and network layer (NL) used in automotive multimedia and infotainment networks. The standard specifies the service interface to upper OSI layers, network-layer services, data transport mechanisms for control/packet/streaming data, dynamic node behavior, and network error management. It is part of the ISO 21806 series that maps MOST technology to the OSI reference model for automotive applications.
Key Topics and Technical Requirements
- Service interface to application (upper) layers: standardized APIs, event indications, action requests and parameters for control, packet and streaming services.
- Data type definitions and parameters: message attributes and parameter sets that govern interaction between NL/TL and upper layers.
- Control data transport: handling of small administrative/control messages with specific service behavior and confirmations.
- Packet data transport: packet addressing support including 16‑bit and 48‑bit addressing modes, and separation of packet traffic from streaming and control channels.
- Streaming data mechanisms: allocation, deallocation, connect/disconnect procedures, and reserved bandwidth to ensure low-latency and QoS (synchronous and isochronous streaming).
- Transport layer (TL) functions: data transport mechanisms, services for control and source data, and message attribute management.
- Network layer (NL) functions: node states and state transitions, network error detection & management, timing constraints, startup/shutdown procedures, and NL–data link layer (DLL) interface.
- Network diagnostics: procedures such as Ring Break Diagnosis (Annex A) and mechanisms for network error reporting and recovery.
- Timing and timers: general timing rules and constraints important for synchronous TDM MOST networks.
Applications and Who Uses This Standard
ISO 21806-4:2020 is intended for:
- Automotive OEMs and system architects designing MOST-based infotainment systems.
- Tier‑1/2 suppliers developing MOST interfaces, media controllers, and head‑unit components.
- Embedded network engineers implementing TL/NL stacks and QoS-aware streaming on MOST networks.
- Test houses and conformance labs creating test suites for MOST transport and network behaviors.
- Integrators ensuring interoperability of audio/video, control and packet services in in‑vehicle networks.
Practical benefits include reliable low-latency media transport, predictable QoS for audio/video streams, standardized control-message handling, and robust error management for production vehicles.
Related Standards
- ISO 21806 series (other MOST parts)
- ISO/IEC 7498-1 and ISO/IEC 10731 (OSI model references)
- ISO/IEC/IEEE 8802-3 (Ethernet) - referenced for scalable automotive Ethernet integration
Keywords: ISO 21806-4:2020, MOST, transport layer, network layer, automotive multimedia, QoS, streaming, packet data, network error management.