ISO 21806-6:2020

Road vehicles -- Media Oriented Systems Transport (MOST)

This document specifies technical requirements related to the MOST data link layer functionality. A MOST network is comprised of two or more nodes connected through a physical layer. The data link layer functionality is provided by each node. On each network, all nodes are synchronised and one node provides the system clock. This node is the TimingMaster, while all other nodes are TimingSlaves. The timing configuration of the node (TimingMaster or TimingSlave) determines the tasks that need to be performed on the data link layer. The data link layer specifies the following subjects: — the service interface to the network layer; — the network frame, its areas and indicators; — the different network channels; — the different flow control mechanisms; — the load-adaptive arbitration and the round-robin arbitration; — the different addressing options; — the different cyclic redundancy checks, their usage and the CRC acknowledge; — the frame indicators.

Véhicules routiers -- Système de transport axé sur les médias

Standards Content (sample)

INTERNATIONAL ISO
STANDARD 21806-6
First edition
2020-09
Road vehicles — Media Oriented
Systems Transport (MOST) —
Part 6:
Data link layer
Véhicules routiers — Système de transport axé sur les médias —
Partie 6: Couche de liaison de données
Reference number
ISO 21806-6:2020(E)
ISO 2020
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ISO 21806-6:2020(E)
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© ISO 2020

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ii © ISO 2020 – All rights reserved
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ISO 21806-6:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................vi

Introduction ..............................................................................................................................................................................................................................vii

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols and abbreviated terms ........................................................................................................................................................... 3

4.1 Symbols ......................................................................................................................................................................................................... 3

4.2 Abbreviated terms ............................................................................................................................................................................... 3

5 Conventions ............................................................................................................................................................................................................... 4

6 DLL — Service interface to upper layers ..................................................................................................................................... 4

6.1 DLL — Overview ................................................................................................................................................................................... 4

6.2 DLL — Data type definitions ....................................................................................................................................................... 4

6.3 DLL — Parameters ......... ...................................................................................................................................................................... 5

6.3.1 DLL — Parameters – DLL to TL/NL ................................................................................................................ 5

6.3.2 DLL — Parameters – TL/NL to DLL ................................................................................................................ 6

6.3.3 DLL — Parameters – DLL to TL/NL and TL/NL to DLL ................................................................. 8

6.4 DLL — Event indications and action requests ..........................................................................................................10

6.4.1 DLL — L_EVENT.INDICATE ..................................................................................................................................10

6.4.2 DLL — L_NODE_POSITION.INDICATE ........................................................................................................10

6.4.3 DLL — L_MAXIMUM_NODE_POSITION.INDICATE ..........................................................................10

6.4.4 DLL — L_ACTION.REQUEST ................................................................................................................................10

6.4.5 DLL — L_NETWORK_STARTUP.REQUEST ...............................................................................................11

6.4.6 DLL — L_SET_GROUP_ADDRESS.REQUEST ...........................................................................................11

6.4.7 DLL — L_SET_NODE_ADDRESS.REQUEST ..............................................................................................11

6.4.8 DLL — L_SET_EUI_48.REQUEST ......................................................................................................................11

6.4.9 DLL — L_SET_TRANSMISSION_ATTRIBUTES.REQUEST............................................................12

6.5 DLL — Control Data .........................................................................................................................................................................12

6.5.1 DLL — L_CONTROL_DATA.RECEIVE ............................................................................................................12

6.5.2 DLL — L_CONTROL_DATA.CONFIRM ..........................................................................................................12

6.5.3 DLL — L_CONTROL_DATA.SEND .....................................................................................................................13

6.6 DLL — Packet data ............................................................................................................................................................................13

6.6.1 DLL — 16-bit addressing .......................................................................................................................................13

6.6.2 DLL — 48-bit addressing .......................................................................................................................................14

6.7 DLL — Streaming data ..................................................................................................................................................................15

6.7.1 DLL — L_ALLOCATE.INDICATE .......................................................................................................................15

6.7.2 DLL — L_DEALLOCATE.INDICATE ................................................................................................................15

6.7.3 DLL — L_CONNECT.INDICATE ..........................................................................................................................16

6.7.4 DLL — L_DISCONNECT.INDICATE .................................................................................................................16

6.7.5 DLL — L_SOURCE_DROP.INDICATE ..............................................................................................................16

6.7.6 DLL — L_STREAMING_DATA.RECEIVE ......................................................................................................17

6.7.7 DLL — L_ALLOCATE.REQUEST ........................................................................................................................17

6.7.8 DLL — L_DEALLOCATE.REQUEST .................................................................................................................17

6.7.9 DLL — L_CONNECT.REQUEST ...........................................................................................................................18

6.7.10 DLL — L_DISCONNECT.REQUEST ..................................................................................................................18

6.7.11 DLL — L_STREAMING_DATA.SEND ..............................................................................................................18

7 DLL — Network frame ..................................................................................................................................................................................18

7.1 DLL — General .....................................................................................................................................................................................18

7.2 DLL — Administrative area .......................................................................................................................................................20

7.3 DLL — Source data area ...............................................................................................................................................................20

7.4 DLL — Indicators ...............................................................................................................................................................................21

8 DLL — Channels ..................................................................................................................................................................................................21

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ISO 21806-6:2020(E)

8.1 DLL — Allocation channel ..........................................................................................................................................................21

8.1.1 DLL — General ................................................................................................................................................................21

8.1.2 DLL — Allocation frame structure ................................................................................................................21

8.1.3 DLL — Common allocation channel related subjects ...................................................................23

8.1.4 DLL — Allocation channel related subjects for the TimingMaster ...................................24

8.1.5 DLL — Allocation channel related subjects for a TimingSlave .............................................25

8.1.6 DLL — De-allocating ........................................................................................................................................... .......27

8.1.7 DLL — Source-drop recognition .....................................................................................................................27

8.1.8 DLL — Error handling ..............................................................................................................................................28

8.2 DLL — Control channel ................................................................................................................................................................30

8.2.1 DLL — General ................................................................................................................................................................30

8.2.2 DLL — Control frame structure .......................................................................................................................31

8.3 DLL — Protected system channel ........................................................................................................................................31

8.3.1 DLL — General ................................................................................................................................................................31

8.3.2 DLL — Protected system frame structure ..............................................................................................32

8.4 DLL — Timestamp channel .......................................................................................................................................................34

8.4.1 DLL — General ................................................................................................................................................................34

8.4.2 DLL — Timestamp frame structure .............................................................................................................34

8.4.3 DLL — Behaviour .........................................................................................................................................................35

8.5 DLL — Packet channel ...................................................................................................................................................................35

8.5.1 DLL — General ................................................................................................................................................................35

8.5.2 DLL — Packet frame structure .........................................................................................................................36

8.5.3 DLL — Ethernet data frame structure .......................................................................................................37

8.5.4 DLL — Short packet frame or short Ethernet data frame .........................................................38

8.6 DLL — Synchronous channel ..................................................................................................................................................38

8.6.1 DLL — General ................................................................................................................................................................38

8.6.2 DLL — Synchronous frame structure .........................................................................................................38

8.7 DLL — Isochronous channel ....................................................................................................................................................38

8.7.1 DLL — General ................................................................................................................................................................38

8.7.2 DLL — Isochronous frame structure ...........................................................................................................38

8.8 DLL — Channel frame delay .....................................................................................................................................................39

9 DLL — Flow control.........................................................................................................................................................................................41

9.1 DLL — Pre-emptive acknowledge byte ......... ..................................................................................................................41

9.2 DLL — Early ending .........................................................................................................................................................................41

9.3 DLL — Low-level retries ..............................................................................................................................................................42

10 DLL — Arbitration ............................................................................................................................................................................................42

10.1 DLL — General .....................................................................................................................................................................................42

10.2 DLL — Load-adaptive arbitration .......................................................................................................................................43

10.2.1 DLL — General ................................................................................................................................................................43

10.2.2 DLL — Downstream arbitration .....................................................................................................................46

10.2.3 DLL — Downstream or upstream arbitration .....................................................................................47

10.2.4 DLL — Conditional upstream arbitration ...............................................................................................48

10.3 DLL — Round-robin arbitration ...........................................................................................................................................48

10.3.1 DLL — Basics ...................................................................................................................................................................48

10.3.2 DLL — Ensuring round-robin transmit order .....................................................................................50

10.3.3 DLL — Examples ...........................................................................................................................................................50

11 DLL — Addressing ............................................................................................................................................................................................51

11.1 DLL — General .....................................................................................................................................................................................51

11.2 DLL — 16-bit address types .....................................................................................................................................................52

11.2.1 DLL — General ................................................................................................................................................................52

11.2.2 DLL — Free-up address ..........................................................................................................................................52

11.2.3 DLL — Logical node address ..............................................................................................................................52

11.2.4 DLL — Group address ..............................................................................................................................................52

11.2.5 DLL — Blocking broadcast address .............................................................................................................53

11.2.6 DLL — Non-blocking broadcast address .................................................................................................54

11.2.7 DLL — Node position address ..........................................................................................................................54

11.2.8 DLL — Debug address ..............................................................................................................................................54

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ISO 21806-6:2020(E)

11.3 DLL — 48-bit address types .....................................................................................................................................................55

12 DLL — Cyclic redundancy check (CRC) .......................................................................................................................................55

12.1 DLL — General .....................................................................................................................................................................................55

12.2 DLL — 4-bit CRC .................................................................................................................................................................................55

12.3 DLL — 16-bit CRC ..............................................................................................................................................................................56

12.4 DLL — 32-bit CRC ..............................................................................................................................................................................56

12.5 DLL — CRC usage ......... ......................................................................................................................................................................56

12.6 DLL — CRC acknowledge ............................................................................................................................................................56

Annex A (normative) MOST network configurations .......................................................................................................................58

Annex B (normative) Frame indicators ..........................................................................................................................................................65

Bibliography .............................................................................................................................................................................................................................68

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ISO 21806-6:2020(E)
Foreword

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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

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iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 31,

Data communication.
A list of all parts in the ISO 21806 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO 21806-6:2020(E)
Introduction

The Media Oriented Systems Transport (MOST) communication technology was initially developed at

the end of the 1990s in order to support complex audio applications in cars. The MOST Cooperation was

founded in 1998 with the goal to develop and enable the technology for the automotive industry. Today,

MOST enables the transport of high quality of service (QoS) audio and video together with packet data

and real-time control to support modern automotive multimedia and similar applications. MOST is a

function-oriented communication technology to network a variety of multimedia devices comprising

one or more MOST nodes.
Figure 1 shows a MOST network example.
Figure 1 — MOST network example
The MOST communication technology provides
— synchronous and isochronous streaming,
— small overhead for administrative communication control,
— a functional and hierarchical system model,
— API standardization through a function block (FBlock) framework,
— free partitioning of functionality to real devices,
— service discovery and notification, and
[4]

— flexibly scalable automotive-ready Ethernet communication according to ISO/IEC/IEEE 8802-3 .

MOST is a synchronous time-division-multiplexing (TDM) network that transports different data types

on separate channels at low latency. MOST supports different bit rates and physical layers. The network

clock is provided with a continuous data signal.

1) MOST® is the Registered Trademark of Microchip Technology Inc. This information is given for the convenience

of users of this document and does not constitute an endorsement by ISO.
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ISO 21806-6:2020(E)

Within the synchronous base data signal, the content of multiple streaming connections and control

data is transported. For streaming data connections, bandwidth is reserved to avoid interruptions,

collisions, or delays in the transport of the data stream.

MOST specifies mechanisms for sending anisochronous, packet-based data in addition to control data

and streaming data. The transmission of packet-based data is separated from the transmission of

control data and streaming data. None of them interfere with each other.

A MOST network consists of devices that are connected to one common control channel and packet

channel.

In summary, MOST is a network that has mechanisms to transport the various signals and data streams

that occur in multimedia and infotainment systems.

The ISO standards maintenance portal (https:// standards .iso .org/ iso/ ) provides references to MOST

specifications implemented in today's road vehicles because easy access via hyperlinks to these

specifications is necessary. It references documents that are normative or informative for the MOST

versions 4V0, 3V1, 3V0, and 2V5.

The ISO 21806 series has been established in order to specify requirements and recommendations

for implementing the MOST communication technology into multimedia devices and to provide

conformance test plans for implementing related test tools and test procedures.

To achieve this, the ISO 21806 series is based on the open systems interconnection (OSI) basic reference

[1] [2]

model in accordance with ISO/IEC 7498-1 and ISO/IEC 10731 , which structures communication

systems into seven layers as shown in Figure 2. Stream transmission applications use a direct stream

data interface (transparent) to the data link layer.
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ISO 21806-6:2020(E)
Figure 2 — The ISO 21806 series reference according to the OSI model

The International Organization for Standardization (ISO) draws attention to the fact that it is claimed

that compliance with this document may involve the use of a patent.

ISO takes no position concerning the evidence, validity and scope of this patent right.

The holder of this patent right has assured ISO that he/she is willing to negotiate licences under

reasonable and non-discriminatory terms and conditions with applicants throughout the world. In

this respect, the statement of the holder of this patent right is registered with ISO. Information may be

obtained from the patent database available at www .iso .org/ patents.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights other than those in the patent database. ISO shall not be held responsible for identifying

any or all such patent rights.
© ISO 2020 – All rights reserved ix
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INTERNATIONAL STANDARD ISO 21806-6:2020(E)
Road vehicles — Media Oriented Systems Transport
(MOST) —
Part 6:
Data link layer
1 Scope

This document specifies technical requirements related to the MOST data link layer functionality.

A MOST network is comprised of two or more nodes connected through a physical layer. The data link

layer functionality is provided by each node. On each network, all nodes are synchronised and one node

provides the system clock. This node is the TimingMaster, while all other nodes are TimingSlaves. The

timing configuration of the node (TimingMaster or TimingSlave) determines the tasks that need to be

performed on the data link layer.
The data link layer specifies the following subjects:
— the service interface to the network layer;
— the network frame, its areas and indicators;
— the different network channels;
— the different flow contro
...