ISO 21806-6:2020

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

---------------------- Page: 1 ----------------------
ISO 21806-6:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

---------------------- Page: 2 ----------------------
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
© ISO 2020 – All rights reserved iii

---------------------- Page: 3 ----------------------
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
iv © ISO 2020 – All rights reserved

---------------------- Page: 4 ----------------------
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
© ISO 2020 – All rights reserved v

---------------------- Page: 5 ----------------------
ISO 21806-6:2020(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.
vi © ISO 2020 – All rights reserved

---------------------- Page: 6 ----------------------
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,
1)
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.
© ISO 2020 – All rights reserved vii

---------------------- Page: 7 ----------------------
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.
viii © ISO 2020 – All rights reserved

---------------------- Page: 8 ----------------------
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

---------------------- Page: 9 ----------------------
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
...