ISO 21806-12:2021

INTERNATIONAL ISO
STANDARD 21806-12
First edition
Road vehicles — Media Oriented
Systems Transport (MOST) —
Part 12:
50-Mbit/s balanced media physical
layer
Véhicules routiers — Système de transport axé sur les médias —
Partie 12: Couche physique de support équilibré à 50-Mbit/s
PROOF/ÉPREUVE
Reference number
ISO 21806-12:2021(E)
©
ISO 2021

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ISO 21806-12:2021(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 21806-12:2021(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 . 3
6 Physical layer service interface to OSI data link layer . 3
6.1 Overview . 3
6.2 Data type definitions . 3
6.3 Event indications and action requests . 3
6.3.1 P_EVENT.INDICATE . 3
6.3.2 P_ACTION.REQUEST . 4
6.4 Parameters . 4
6.4.1 PHY_Event . 4
6.4.2 PHY_Request . . 4
7 Basic physical layer requirements . 5
7.1 Logic terminology . 5
7.1.1 Single-ended low-voltage digital signals . 5
7.1.2 Differential signals . 5
7.2 SPs . 5
7.3 Phase variation . 6
7.3.1 General. 6
7.3.2 Wander . 6
7.3.3 Jitter . 6
7.3.4 Clock recovery and reference clock . 7
7.3.5 Link quality . 8
7.3.6 MOST network quality .10
8 MOST50 bPHY requirements .13
8.1 General MOST network parameters .13
8.1.1 MOST network coding .13
8.1.2 Link and interconnect type .15
8.1.3 SP details . . .15
8.1.4 Analogue frontend .16
8.2 Models and measurement methods .17
8.2.1 Golden PLL .17
8.2.2 Jitter filter .18
8.2.3 Stress pattern .18
9 Link specifications .19
9.1 General .19
9.2 SP2 .19
9.3 Electrical link requirements .22
9.3.1 General.22
9.3.2 Electrical interconnect, length and attenuation .22
9.3.3 Characteristic impedance and return loss (RL) .23
9.4 SP3 .25
10 Power-on and power-off .26
10.1 Frequency reference and power supply .26
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10.2 Power supply monitoring circuitry .27
10.3 Electrical transceiver EBC and BEC .27
10.3.1 General.27
10.3.2 BTR requirements.27
10.3.3 EBC requirements .28
10.3.4 EBC power-on and power-off sequence .29
10.3.5 BEC requirements .29
10.3.6 BEC power-on and power-off sequence .31
11 MOST network requirements .31
11.1 SP3 receiver tolerance .31
11.2 TimingMaster delay tolerance .32
11.3 Environmental considerations and requirements .32
12 Bit rate and frequency tolerance .33
Bibliography .34
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ISO 21806-12:2021(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.
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ISO 21806-12:2021(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
[2]
— 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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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.
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.
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] [3]
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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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.
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INTERNATIONAL STANDARD ISO 21806-12:2021(E)
Road vehicles — Media Oriented Systems Transport
(MOST) —
Part 12:
50-Mbit/s balanced media physical layer
1 Scope
This document specifies the 50-Mbit/s balanced media physical layer for MOST (MOST50 bPHY), a
synchronous time-division-multiplexing network.
This document specifies the applicable constraints and defines interfaces and parameters, suitable for
the development of products based on MOST50 bPHY. Such products include electrical interconnects,
integrated receivers, transmitters, electrical to balanced media converters, and balanced media to
electrical converters.
This document also establishes basic measurement techniques and actual parameter values for
MOST50 bPHY.
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
2)
JEDEC No. JESD8C.01, Interface Standard for Nominal 3 V/3,3 V Supply Digital Integrated Circuits
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
balanced media
BM
unshielded or shielded twisted pair cable
3.2
BEC
balanced media to electrical converter
MOST component that converts a balanced media (3.1) signal into an electrical signal
2) Available at https:// www .jedec .org/ .
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3.3
EBC
electrical to balanced media converter
MOST component that converts an electrical signal into a balanced media (3.1) signal
4 Symbols and abbreviated terms
4.1 Symbols
--- empty table cell or feature undefined
J transferred jitter
tr
N number of bits per frame
BPF
ρ network frame rate
Fs
σ standard deviation
t TimingMaster delay tolerance
MDT
t unit interval
UI
ρ bit rate
BR
T ambient temperature
A
V output high voltage
OH
V output low voltage
OL
4.2 Abbreviated terms
AC alternating current
AFE analogue frontend
BEC balanced media to electrical converter
BM balanced media
BPF bits per frame
bPHY balanced media physical layer
BR bit rate
BTR balanced media transceiver
DC direct current
DCA DC adaptive
DDJ data-dependant jitter
DLL data link layer
DSV digital sum value
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EBC electrical to balanced media converter
ECU electronic control unit
EMC electromagnetic compatibility
EMI electromagnetic interference
MNC MOST network controller
PCB printed circuit board
PDF probability density function
PHY physical layer
PLL phase locked loop
PSD power spectrum density
RBW resolution bandwidth
RL return loss
RMS root mean square
Rx data encoded digital bit stream being received
SP[n] specification point
Tx data encoded digital bit stream being transmitted
UI unit interval
5 Conventions
[3]
This document is based on OSI service conventions as specified in ISO/IEC 10731 .
6 Physical layer service interface to OSI data link layer
6.1 Overview
The physical layer (PHY) service interface specifies the abstract interface to the OSI data link layer
[4]
(DLL), see ISO 21806-6 .
6.2 Data type definitions
The data type Enum is defined as an 8-bit enumeration.
6.3 Event indications and action requests
6.3.1 P_EVENT.INDICATE
The PHY shall use P_EVENT.INDICATE to indicate the occurrence of an event to the DLL.
P_EVENT.INDICATE{
  PHY_Event
}

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6.3.2 P_ACTION.REQUEST
P_ACTION.REQUEST shall trigger the execution of a request.
P_ACTION.REQUEST {
  PHY_Request
}

6.4 Parameters
6.4.1 PHY_Event
Table 1 specifies the PHY_Event parameter, which notifies the DLL about events.
Table 1 — Parameter passed from PHY to DLL
Parameter Data type Description
PHY_Event
Enum { An event that is reported to the DLL.
  PHY_Output_Off,
  PHY_Network_Activity
}
Table 2 specifies the parameter values for the PHY_Event Enum.
Table 2 — PHY_Event Enum values
Enum value Description
PHY_Output_Off
MNC transmit terminal is switched off.
PHY_Network_Activity
Network activity is detected at the MNC receive terminal.
6.4.2 PHY_Request
Table 3 specifies the PHY_Request parameter, which is passed from DLL to PHY.
Table 3 — Parameter passed from DLL to PHY
Parameter Data type Description
PHY_Request
Enum { A request from the DLL
  cmd_Output_Off,
  cmd_Output_On,
  cmd_Open_Bypass,
}
Table 4 specifies the parameter values for the PHY_Request Enum.
Table 4 — PHY_Request Enum values
Enum value Description
cmd_Output_Off
Switching off the MNC transmit terminal is requested. By default, it is off.
cmd_Output_On
Switching on the MNC transmit terminal is requested. By default, it is off.
cmd_Open_Bypass
Opening the bypass is requested. By default, the bypass is closed.
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7 Basic physical layer requirements
7.1 Logic terminology
7.1.1 Single-ended low-voltage digital signals
For the parameters provided in JEDEC No. JESD8C.01, Table 5 defines the corresponding terms for
single-ended signals used in this document. These terms are used to describe the logic states of signals
/RST and STATUS.
Table 5 — Terms for single-ended signals
Term Corresponding JEDEC parameter
Low
V (output low voltage)
OL
Logic 0
High
V (output high voltage)
OH
Logic 1
7.1.2 Differential signals
Table 6 explains the expressions used to describe the logic states of the differential data signals.
Table 6 — Differential signals
Expression Description
Disabled
The P and N terminals are in a high impedance state. Small leakage currents may exist which
can cause an indeterminate voltage on the line/load.
Off
Enabled Both the P and N terminals are driving the line / load. The outputs may be in a transitioning
phase or in the process to settle differential amplitude as well as common mode. The defined
On
link quality parameter requirements may not be met.
Valid MOST data DCA encoded data that meets defined link quality parameters and bit rate requirements.
7.2 SPs
A physical connection of two MOST devices is called a link. Measurements are taken at specific locations
along a link. These locations are called SPs. The location of the SPs is shown in Figure 3.
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Key
1 SP1
2 SP2
3 SP3
4 SP4
Figure 3 — Location of SPs along a link
SPs define interfaces that are boundaries between a transmitting and a receiving MOST component.
For each of those interfaces, a set of requirements and properties is defined (e.g. signal timing, signal
amplitude, connector interface drawings). SP1 and SP4 are located between a MOST network controller
(MNC) and the corresponding transceiver. SP2 and SP3 are located between transceivers and a wiring
harness.
For MOST components that are located between two adjacent SPs, requirements and properties can
be derived. The definitions of the second SP of the pair specify the component's output performance to
be achieved, considering input conditions as defined in the first SP. For example, a transmit converter
component specification can be derived from SP1 and SP2. Receive converter component requirements
are covered by SP3 and SP4. Wiring harness requirements can be derived from SP2 and SP3.
In addition to the definitions of the SPs for a point-to-point link, this document defines requirements
covering the stability of the MOST network. Examples are requirements regarding jitter transfer
through MOST devices, jitter accumulation through the MOST network, and power state transitions.
The specified parameters in this document are minimum values to ensure functionality of the MOST
network in a wide range of environmental conditions.
7.3 Phase variation
7.3.1 General
Data stream timing and distortion cause phase variation.
7.3.2 Wander
Wander consists of any phase variation from 0 Hz to 10 Hz. All active MOST components in the MOST
network create wander. Wander is a function of the temperature drift and propagates from node to
node. Typically, wander does not affect alignment jitter eye masks.
NOTE It is possible that wander impacts the TimingMaster.
7.3.3 Jitter
Jitter is any phase variation of frequencies above 10 Hz. Every MOST component and the transmission
medium create jitter in the MOST n
...