Road vehicles -- Media Oriented Systems Transport (MOST)

This document specifies technical requirements related to the MOST transport layer and network layer functionality: — the service interface to application layer; — the network layer services; — the data transport mechanism; — the dynamic behaviour of a node; — the network error management.

Véhicules routiers -- Système de transport axé sur les médias

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Publication Date
17-Sep-2020
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5060 - Close of voting Proof returned by Secretariat
Start Date
29-Jul-2020
Completion Date
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INTERNATIONAL ISO
STANDARD 21806-4
First edition
2020-09
Road vehicles — Media Oriented
Systems Transport (MOST) —
Part 4:
Transport layer and network layer
Véhicules routiers — Système de transport axé sur les médias —
Partie 4: Couche de transport et couche réseau
Reference number
ISO 21806-4:2020(E)
ISO 2020
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ISO 21806-4:2020(E)
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© ISO 2020

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ii © ISO 2020 – All rights reserved
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ISO 21806-4:2020(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

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

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

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

4 Symbols and abbreviated terms ........................................................................................................................................................... 2

4.1 Symbols ......................................................................................................................................................................................................... 2

4.2 Abbreviated terms ............................................................................................................................................................................... 2

5 Conventions ............................................................................................................................................................................................................... 2

6 Transport layer service interface to upper OSI layers ................................................................................................... 3

6.1 Overview of services .......................................................................................................................................................................... 3

6.2 Data type definitions .......................................................................................................................................................................... 3

6.3 Parameters ................................................................................................................................................................................................. 4

6.3.1 Parameters — NL/TL to upper layers ........................................................................................................... 4

6.3.2 Parameters — Upper layers to TL/NL .......................................................................................................... 7

6.3.3 Parameters – NL/TL to upper layers and upper layers to TL/NL ......................................10

6.4 Event indications and action requests .............................................................................................................................12

6.4.1 N_EVENT.INDICATE ....................................................................................................................................................12

6.4.2 N_NODE_POSITION.INDICATE ..........................................................................................................................12

6.4.3 N_MAXIMUM_NODE_POSITION.INDICATE ............................................................................................12

6.4.4 N_NET_INTERFACE_TRANSITION.INDICATE .......................................................................................12

6.4.5 N_DIAGRESULT.INDICATE .....................................................................................................................................13

6.4.6 N_SHUTDOWN_REASON.INDICATE ..............................................................................................................13

6.4.7 N_ACTION.REQUEST ..................................................................................................................................................13

6.4.8 N_NETWORK_STARTUP.REQUEST .................................................................................................................13

6.4.9 N_SET_GROUP_ADDRESS.REQUEST .............................................................................................................14

6.4.10 N_SET_NODE_ADDRESS.REQUEST ................................................................................................................14

6.4.11 N_SET_EUI_48.REQUEST ........................................................................................................................................14

6.5 Control data ............................................................................................................................................................................................14

6.5.1 N_CONTROL_DATA.RECEIVE ..............................................................................................................................14

6.5.2 N_CONTROL_DATA.CONFIRM ............................................................................................................................15

6.5.3 N_SET_MESSAGE_ATTRIBUTES.REQUEST .............................................................................................15

6.5.4 N_CONTROL_DATA.SEND .......................................................................................................................................15

6.6 Packet data ..............................................................................................................................................................................................15

6.6.1 16-bit addressing..........................................................................................................................................................15

6.6.2 48-bit addressing..........................................................................................................................................................16

6.7 Streaming data .....................................................................................................................................................................................16

6.7.1 N_ALLOCATE.INDICATE..........................................................................................................................................16

6.7.2 N_DEALLOCATE.INDICATE ..................................................................................................................................17

6.7.3 N_CONNECT.INDICATE ............................................................................................................................................17

6.7.4 N_DISCONNECT.INDICATE ...................................................................................................................................17

6.7.5 N_SOURCE_DROP.INDICATE ................................................................................................................................17

6.7.6 N_STREAMING_DATA.RECEIVE ........................................................................................................................18

6.7.7 N_ALLOCATE.REQUEST ..........................................................................................................................................18

6.7.8 N_DEALLOCATE.REQUEST ...................................................................................................................................18

6.7.9 N_CONNECT.REQUEST .............................................................................................................................................18

6.7.10 N_DISCONNECT.REQUEST ....................................................................................................................................19

6.7.11 N_STREAMING_DATA.SEND.................................................................................................................................19

7 TL — Transport layer ....................................................................................................................................................................................19

7.1 TL — Overview ....................................................................................................................................................................................19

7.2 TL — Data transport mechanism .........................................................................................................................................19

7.2.1 TL — Transport service ..........................................................................................................................................19

© ISO 2020 – All rights reserved iii
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ISO 21806-4:2020(E)

7.2.2 TL — Service for control data ............................................................................................................................19

7.2.3 TL — Service for source data .............................................................................................................................24

8 NL — Network layer........................................................................................................................................................................................25

8.1 NL — Overview....................................................................................................................................................................................25

8.2 NL — Services .......................................................................................................................................................................................25

8.2.1 NL — States and state transitions ..................................................................................................................25

8.2.2 NL — Network error detection and management ...........................................................................34

8.3 NL — Timing ..........................................................................................................................................................................................39

8.3.1 NL — General ...................................................................................................................................................................39

8.3.2 NL — Timers ....................................................................................................................................................................39

8.3.3 NL — Timing constraints ......................................................................................................................................39

8.3.4 NL — Network startup and changes ...........................................................................................................40

8.3.5 NL — Network shutdown .....................................................................................................................................43

8.3.6 NL — General communication ..........................................................................................................................46

8.4 NL — Data link layer service interface ............................................................................................................................46

Annex A (informative) Ring break diagnosis (RBD) ..........................................................................................................................47

Bibliography .............................................................................................................................................................................................................................56

iv © ISO 2020 – All rights reserved
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ISO 21806-4:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

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).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www .iso .org/ 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.
© ISO 2020 – All rights reserved v
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ISO 21806-4:2020(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
[6]

— 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.
vi © ISO 2020 – All rights reserved
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ISO 21806-4:2020(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] [4]

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.
© ISO 2020 – All rights reserved vii
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ISO 21806-4:2020(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.
viii © ISO 2020 – All rights reserved
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INTERNATIONAL STANDARD ISO 21806-4:2020(E)
Road vehicles — Media Oriented Systems Transport
(MOST) —
Part 4:
Transport layer and network layer
1 Scope

This document specifies technical requirements related to the MOST transport layer and network layer

functionality:
— the service interface to application layer;
— the network layer services;
— the data transport mechanism;
— the dynamic behaviour of a node;
— the network error management.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 21806-1, Road vehicles — Media Oriented Systems Transport (MOST) — Part 1: General information

and definitions
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 21806-1 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
active TimingSlave
TimingSlave that initiates a network startup (3.2)
3.2
network startup

network activity that commences so that all nodes in the MOST network change to s_NetInterface_

Normal_Operation
3.3
network wake-up
process of all nodes in the MOST network exiting s_NetInterface_Sleep
© ISO 2020 – All rights reserved 1
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ISO 21806-4:2020(E)
3.4
network wake-up event
network activity or electrical wake-up line activity
3.5
passive TimingSlave
node that participates in a network startup (3.2), not initiating it
3.6
qualified local wake-up event

local trigger (one that does not affect all devices) that causes exiting s_NetInterface_Sleep

3.7
wake-up event
trigger for exiting s_NetInterface_Sleep
4 Symbols and abbreviated terms
4.1 Symbols
--- empty cell/undefined
L maximum payload length for AMS
AMSmax
L maximum payload length for control data
CMmax
4.2 Abbreviated terms
A: action
AMS application message service
C: condition
ev_
prefix event name
MsgID
message identifier
NL network layer
RBD ring break diagnosis
prefix state name
SegCnt
segment counter
TelID
telegram identifier
TelLen
telegram length
TL transport layer
5 Conventions
[4]

This document is based on OSI service conventions as specified in ISO/IEC 10731 .

2 © ISO 2020 – All rights reserved
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ISO 21806-4:2020(E)
6 Transport layer service interface to upper OSI layers
6.1 Overview of services

Figure 3 shows the transport layer (TL) service interface, which specifies the interface to the upper OSI

[1]
layers, see ISO 21806-2 .
Figure 3 — Service interface to upper OSI layers
6.2 Data type definitions
REQ 4.1 Service interface – Data type definitions
The data types shall be in accordance to:
— Enum: 8-bit enumeration;
— Unsigned Byte: 8-bit unsigned numeric value;
— Unsigned Word: 16-bit unsigned numeric value;
— Unsigned Long: 32-bit unsigned numeric value;
— EUI-48: 48-bit address value;
— Byte Array: sequence of 8-bit aligned data.
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ISO 21806-4:2020(E)
6.3 Parameters
6.3.1 Parameters — NL/TL to upper layers
6.3.1.1 Overview

Table 1 specifies the parameters that are used in the service interface and passed from NL/TL to

upper layers.
Table 1 — Parameters passed from NL/TL to upper layers
Parameter Data type Description
Application_Event
Enum { An event that is reported to
Unlock, the application.
Stable_Lock,
Lock_Flag,
Network_Change_Event,
Shutdown_Flag,
MOST_Output_Off,
Network_Activity
NetInterface_Transition
Enum { A transition between
ev_Wake_Up, NetInterface states
ev_Sleep,
ev_Start_Up,
ev_Diagnosis_Start,
ev_Init_Error_Shutdown,
ev_Init_Diagnosis_Start,
ev_Init_Ready,
ev_Error_Shutdown,
ev_Normal_Shutdown,
ev_Diagnosis_Ready,
ev_Diagnosis_End
DiagResult
Enum { DiagResult of the ring break
No_Error, diagnosis
Ring_Break,
Weak_Signal,
Diagnosis_Inconclusive
Relative_Position Unsigned Byte
Relative position of a node to a
ring break
Shutdown_Reason
Enum { Shutdown reason
No_Result_Available,
No_Fault_Saved,
Sudden_Signal_Off,
Critical_Unlock
Node_Position Unsigned Byte
Position of the node
Maximum_Position Unsigned Byte
Maximum position information
Transmission_Status
Enum { Transmission status that is
Success, reported back to the sender.
Buffer_Full,
CRC_Error,
Wrong_Target
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ISO 21806-4:2020(E)
6.3.1.2 Application_Event

Application_Event corresponds to events that are used to notify the application about changes in lower

layers, which require no additional information.

REQ 4.2 Service interface – Parameters – NL/TL to upper layers – Application_Event

The Application_Event parameter shall be of data type Enum and shall contain the value specified according

to Table 2.
Table 2 — Application_Event values
Enum value Description
Unlock
Unlock event occurred.
Stable_Lock
Stable lock reached.
Lock_Flag
Lock flag detected.
Network_Change_Event
Network change event (NCE) occurred.
Shutdown_Flag
Shutdown flag detected.
Network_Activity_End
Network activity ends.
Network_Activity
Network activity detected.
6.3.1.3 NetInterface_Transition

NetInterface_Transition corresponds to events that are used to notify the application about

transitions from one NetInterface state to another.

REQ 4.3 Service interface – Parameters – NL/TL to upper layers – NetInterface_Transition

The NetInterface_Transition values shall be of data type Enum and shall contain the value specified

according to Table 3.
Table 3 — NetInterface_Transition values
Enum value Description
ev_Wake_Up
The ev_Wake_Up transition from
s_NetInterface_Sleep to s_NetInterface_Off is taken.
ev_Sleep
The ev_Sleep transition from
s_NetInterface_Off to s_NetInterface_Sleep is taken.
ev_Start_Up
The ev_Start_Up transition from
s_NetInterface_Off to s_NetInterface_Init is taken.
ev_Diagnosis_Start
The ev_Diagnosis_Start transition from s_NetInterface_Off to
s_NetInterface_Diagnosis is taken.
ev_Init_Error_Shutdown
The ev_Init_Error_Shutdown transition from s_NetInterface_Init to
s_NetInterface_Off is taken.
ev_Init_Diagnosis_Start
The ev_Init_Diagnosis_Start transition from s_NetInterface_Init to
s_NetInterface_Diagnosis is taken.
ev_Init_Ready
The ev_Init_Ready transition from s_NetInterface_Init to
s_NetInterface_Normal_Operation is taken.
ev_Error_Shutdown
The ev_Error_Shutdown transition from s_NetInterface_Normal_
Operation to
s_NetInterface_Off is taken.
ev_Normal_Shutdown
The ev_Normal_Shutdown transition from s_NetInterface_Normal_
Operation to
s_NetInterface_Off is taken.
ev_Diagnosis_Ready
The ev_Diagnosis_Ready transition from s_NetInterface_Diagnosis to
s_NetInterface_Normal_Operation is taken.
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ISO 21806-4:2020(E)
Table 3 (continued)
Enum value Description
ev_Diagnosis_End
The ev_Diagnosis_End transition from s_NetInterface_Diagnosis to
s_NetInterface_Off is taken.
6.3.1.4 DiagResult

DiagResult corresponds to the possible diagnosis to be provided to the application. The structure

of DiagResult depends on the kind of diagnosis that is performed and should be adopted from the

corresponding specification.
REQ 4.4 Service interface – Parameters – NL/TL to upper layers – DiagResult

The DiagResult values for ring break diagnosis, as specified in Annex A (informative), shall be of data type

Enum and shall contain the value specified according to Table 4.
Table 4 — DiagResult values for ring break diagnosis
Enum value Description
No_Error
No error detected.
Ring_Break
Ring break detected. The result indicates the relative position of ring break
in the Relative_Position parameter.
Weak_Signal
Excessive attenuation detected at the input.
Diagnosis_Inconclusive
The ring break diagnosis inconclusive.
6.3.1.5 Relative_Position

The content of the Relative_Position parameter is relevant if the DiagResult parameter contains the

value Ring_Break.

REQ 4.5 Service interface – Parameters – NL/TL to upper layers – Relative_Position

The Relative_Position parameter shall be of data type Unsigned Byte and shall contain the relative posi-

tion of the node to a ring break.
6.3.1.6 Shutdown_Reason

Shutdown_Reason corresponds to the possible causes of a shutdown to be provided to the application.

REQ 4.6 Service interface – Parameters – NL/TL to upper layers – Shutdown_Reason

The Shutdown_Reason parameter shall be of data type Enum and shall contain the value specified according to

Table 5.
Table 5 — Shutdown_Reason values
Enum value Description
No_Result_Available
Initial value of the shutdown reason.
No_Fault_Saved
Shutdown flag detected before network activity ceased.
Sudden_Signal_Off
Shutdown caused by a sudden signal off (SSO).
Critical_Unlock
Shutdown caused by a critical unlock.
6 © ISO 2020 – All rights reserved
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