ISO 21806-11:2021

Road vehicles - Media Oriented Systems Transport (MOST) - Part 11: 150-Mbit/s coaxial physical layer conformance test plan

This document specifies the conformance test plan for the 150-Mbit/s coaxial physical layer for MOST (MOST150 cPHY), a synchronous time-division-multiplexing network. This document specifies the basic conformance test measurement methods, relevant for verifying compatibility of networks, nodes, and MOST components with the requirements specified in ISO 21806‑10.

Véhicules routiers — Système de transport axé sur les médias — Partie 11: Plan d'essais de conformité de la couche coaxiale physique à 150 Mbit/s

General Information

• Status: Published
• Publication Date: 30-May-2021
• ICS: 43.040.15 - Car informatics. On board computer systems
• Technical Committee: ISO/TC 22/SC 31 - Data communication
• Drafting Committee: ISO/TC 22/SC 31/WG 3 - In-vehicle networks
• Current Stage: 6060 - International Standard published
• Start Date: 31-May-2021
• Due Date: 21-May-2022
• Completion Date: 31-May-2021

Overview

ISO 21806-11:2021 specifies the conformance test plan for the 150-Mbit/s coaxial physical layer of Media Oriented Systems Transport (MOST150 cPHY). The standard defines measurement methods and test procedures to verify that MOST networks, nodes, and components comply with the physical-layer requirements referenced in ISO 21806‑10. It focuses on electrical and coaxial-layer behavior for a synchronous time-division-multiplexing automotive network using a 150‑Mbit/s coaxial interconnect.

Key topics and technical requirements

ISO 21806-11:2021 covers a comprehensive set of physical-layer conformance topics, including:

• Operating conditions and measurement tools: required test environment, instrumentation accuracy and calibration for conformance testing.
• Electrical characteristics: tests for LVDS and LVTTL signalling relevant to MOST150 cPHY inputs and outputs.
• Coaxial characteristics: measurement procedures for attenuation, characteristic impedance, return loss (RL) of cables, connectors and PCB interfaces.
• Signal points and stimuli: definitions and generation of SP2/SP3/SP4 stimuli, pattern and arbitrary signal generation, noise injection for stress tests.
• Timing and jitter: methods to measure phase variation, alignment jitter (AJ), transferred jitter (TJ), and timing master delay tolerance.
• Test set-ups: detailed configurations for simplex, duplex and dual-simplex devices; directional coupler usage; compensation setups for duplex measurements.
• Power sequencing and control signals: power‑on/power‑off behavior, wake-up and shutdown functional tests, ECC/CEC parameter measurements.
• System performance & limited conformance: receiver tolerance, port delay drift measurement, limited physical-layer conformance for development tools and restricted-access test scenarios.
• Normative annexes: stress conditions, duplex compensation, two-port node test procedures.

Note: The document references the normative requirements in ISO 21806‑10 for compatibility verification.

Practical applications and who uses this standard

ISO 21806-11:2021 is intended for organizations involved in the development, verification and deployment of MOST150 coaxial physical-layer components and systems:

• Automotive OEMs and system architects verifying network-level interoperability and compliance.
• Tier‑1 and Tier‑2 suppliers designing ECUs, transceivers, connectors, and coaxial harnesses for MOST150.
• Test houses and conformance laboratories implementing standardized test plans and reporting conformance results.
• R&D and validation teams performing lab and field characterization of signal integrity, jitter, and connector/cable performance.

Using this standard helps ensure reliable in-vehicle multimedia and data transport over 150‑Mbit/s coaxial links by establishing repeatable, traceable test methods for physical-layer conformance.

Related standards

• ISO 21806‑10 - MOST150 specifications (normative reference for physical-layer requirements)
• MOST family specifications (Media Oriented Systems Transport) - system and protocol context for MOST150 cPHY

Keywords: ISO 21806-11:2021, MOST150 cPHY, 150-Mbit/s coaxial, conformance test plan, physical layer testing, automotive network test, coaxial impedance, jitter measurement.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21806-11
First edition
2021-05
Road vehicles — Media Oriented
Systems Transport (MOST) —
Part 11:
150-Mbit/s coaxial physical layer
conformance test plan
Véhicules routiers — Système de transport axé sur les médias —
Partie 11: Plan d'essais de conformité de la couche coaxiale physique
à 150 Mbit/s
Reference number
©
ISO 2021
© ISO 2021
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

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 Operating conditions and measurement tools, requested accuracy .4
6.1 Operating conditions . 4
6.2 Apparatus — Measurement tools, requested accuracy . 4
7 Electrical characteristics . 4
7.1 Test according to LVDS . 4
7.2 Test according to LVTTL . 5
8 Coaxial characteristics . 5
8.1 High/low detection at SP2 . 5
8.2 Transition times at SP2 . 5
8.3 Steady state amplitude at SP2 . 6
8.4 Attenuation of coaxial interconnect . 7
8.4.1 General. 7
8.4.2 Coefficient values based on attenuation measurements . 7
8.4.3 Fitting of corridor . 7
8.4.4 Attenuation test set-up . 7
8.4.5 Test procedure . 8
8.5 RL of connectors and couplers .13
8.6 Characteristic impedance of coaxial cable .13
8.7 RL of coaxial interconnect .13
8.8 RL of PCB interfaces .15
8.9 Stimulus creation for SP3 .16
8.9.1 General.16
8.9.2 Pattern generator .16
8.9.3 Arbitrary signal generator .17
8.9.4 Attenuator . . .17
8.9.5 Cable or analogue representation .17
8.9.6 Noise generator . .18
8.9.7 Creating a stimulus for SP3 for simplex applications .18
8.9.8 Creating a stimulus for SP3 for duplex applications .20
9 Measurement of phase variation .23
9.1 General .23
9.2 Measuring alignment jitter .25
9.3 Measuring transferred jitter .27
10 Test set-ups.30
10.1 General .30
10.2 Graphical symbols and descriptions .30
10.2.1 Pattern generator SP1 .30
10.2.2 SP3 stimulus .30
10.2.3 Standalone simplex ECport under test .31
10.2.4 Integrated simplex ECport under test .31
10.2.5 Standalone simplex CEport under test .32
10.2.6 Integrated simplex CEport under test .32
10.2.7 Duplex ECport under test .33
10.2.8 Duplex CEport under test .34
10.3 Set-ups for dual simplex .34
10.3.1 General.34
10.3.2 SP2 signal quality measurement for simplex .34
10.3.3 SP4 jitter measurement (AJ and TJ) for simplex.36
10.4 Set-ups for duplex .37
10.4.1 General.37
10.4.2 Directional couplers .37
10.4.3 SP2 signal quality measurement for duplex .40
10.4.4 SP4 jitter measurement (AJ and TJ) for duplex .42
11 Power-on and power-off .44
11.1 General .44
11.2 Measuring ECC parameters .45
11.2.1 Measuring ECC parameters – Test set-up .45
11.2.2 Measuring ECC parameters – Signal charts .46
11.2.3 Measuring ECC parameters – Test sequences .47
11.3 Measuring CEC parameters .51
11.3.1 Measuring CEC parameters – Test set-up .51
11.3.2 Measuring CEC parameters – Signal charts .53
11.3.3 Measuring CEC parameters – Test sequences .53
12 Detecting bit rate (frequency reference) .57
13 System performance .57
13.1 General .57
13.2 SP4 receiver tolerance .57
13.3 TimingMaster delay tolerance .58
14 Conformance tests of 150-Mbit/s coaxial physical layer .61
14.1 Location of interfaces .61
14.2 Control signals .64
14.3 Limited access to specification points .65
14.4 Parameter overview .66
15 Limited physical layer conformance .66
15.1 Overview .66
15.2 Test set-ups 1 and 2 .67
15.3 Generating test signals for the IUT input section SP3 .68
15.4 Analysis of test results .69
15.5 Test flow overview .69
15.6 Measurement of SP3 input signal of the IUT .70
15.7 Measurement of SP2 output signal of the IUT .71
15.8 Measurement of RL .72
15.9 Functional test of wake-up and shutdown .72
16 Direct physical measuring accuracy.72
17 Measurement of Port1 delay drift .73
Annex A (informative) Limited physical layer conformance for development tools .74
Annex B (normative) SP3 stress conditions .75
Annex C (normative) Compensation set-up for MOST150 cPHY duplex .76
Annex D (informative) Test procedure for 2-port nodes .80
Bibliography .84
iv © ISO 2021 – All rights reserved

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.
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.
MOST® is the registered trademark of Microchip Technology Inc. This information is given for the convenience of users of this document and does
1)
not constitute an endorsement by ISO.
vi © ISO 2021 – All rights reserved

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 an isochronous, 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] [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.
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 2021 – All rights reserved

INTERNATIONAL STANDARD ISO 21806-11:2021(E)
Road vehicles — Media Oriented Systems Transport
(MOST) —
Part 11:
150-Mbit/s coaxial physical layer conformance test plan
1 Scope
This document specifies the conformance test plan for the 150-Mbit/s coaxial physical layer for MOST
(MOST150 cPHY), a synchronous time-division-multiplexing network.
This document specifies the basic conformance test measurement methods, relevant for verifying
compatibility of networks, nodes, and MOST components with the requirements specified in
ISO 21806-10.
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
ISO 21806-10, Road vehicles — Media Oriented Systems Transport (MOST) — Part 10: 150-Mbit/s coaxial
physical layer
ISO 20860-2, Road vehicles — 50 ohms impedance radio frequency connection system interface — Part 2:
Test procedures
EN 50289-1-8, Communication cables — Specifications for test methods — Part 1-8: Electrical test
methods — Attenuation
EN 50289-1-11, Communication cables — Specifications for test methods — Part 1-11: Electrical test
methods — Characteristic impedance, input impedance, return loss
2)
No JEDEC JESD8C.01, interface Standard for Nominal 3 V/3.3 V Supply Digital Integrated Circuits
3)
TIA/EIA-644-A-2001, Electrical Characteristics of Low-Voltage Differential Signaling (LVDS) interface
Circuits
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21806-1, ISO 21806-10 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
2) Available at https:// www .jedec .org/ .
3) Available at https:// www .tiaonline .org/ standards/ .
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
intersymbol interference
disturbance due to the overflowing into the signal element representing a wanted digit of signal
elements representing preceding or following digits
[SOURCE: IEC Electropedia 702-08-33]
4 Symbols and abbreviated terms
4.1 Symbols
--- empty table cell or feature undefined
A DC attenuation
DC_loss
F frequency
ρ network frame rate
Fs
ρ bit rate
BR
ν transferred jitter, calculated using the root-mean-square method
RMS
L return loss
RL
V voltage at the LVDS receive terminal P
RXP
V voltage at the LVDS receive terminal N
RXN
V voltage at the LVDS transmit terminal P
TXP
V voltage at the LVDS transmit terminal N
TXN
t time
T temperature
T ambient temperature
A
T typical temperature
Typ
t start of measurement time
SLS
t end of measurement time
SLE
4.2 Abbreviated terms
AC alternate current
AFE analogue frontend
AJ alignment jitter
BR bit rate
BW bandwidth
2 © ISO 2021 – All rights reserved

CEC coaxial electrical converter
CEport coaxial electrical port (combination of AFE and CEC)
Cfg configuration
CTR coaxial transceiver
DC direct current
DSO digital sampling oscilloscope
EMD equilibrium mode power distribution
ECC electrical coaxial converter
ECport electrical coaxial port (combination of AFE and ECC)
IUT implementation under test
MNC MOST network controller
MTCM MOST150 cPHY tester cable model
Mux multiplexer
PCB printed circuit board
PG pattern generator
PHYSTT physical layer stress test tool
PLL phase lock loop
RMS root mean square
SDA serial data analyser
SLE signal level end
SLS signal level start
SMD surface mount device
SP specification point
TDR time-domain reflectometer
TJ transferred jitter
UI unit interval
VCM common mode voltage
VNA vector network analyser
5 Conventions
[3]
This document is based on OSI service conventions as specified in ISO/IEC 10731 .
6 Operating conditions and measurement tools, requested accuracy
6.1 Operating conditions
Temperature range for MOST components: T = -40 °C to +105 °C according to ISO 21806-10:2021, 11.3.
A
Voltage range for MOST components: V and V , with an operating range of 3,3 V ± 0,165 V
CCCN CCSW
according to ISO 21806-10:2021, Clause 10.
NOTE There are functional requirements for the ECC within an extended voltage supply range according to
ISO 21806-10.
6.2 Apparatus — Measurement tools, requested accuracy
Apart from the measurement tools listed in this subclause, depending on the chosen test method and
method to generate stimuli for the test, further equipment is necessary (e.g. electrical attenuator,
discrete filter module to emulate cable transfer function, etc.). Performance requirements of such
equipment depend on the use case.
The following list provides the measurement tools.
6.2.1 Oscilloscope
— digital sampling oscilloscope;
— sampling rate ≥ 10 gigasample/s;
— bandwidth ≥ 1,5 GHz;
— sampling memory ≥ 10 megasample;
— active probe (single-ended, differential).
6.2.2 VNA or TDR (TDR bandwidth ≥ 3,5 GHz).
6.2.3 Ampere meter
— accuracy ≤ 2 µA;
— trigger input (for timing measurements).
[7]
6.2.4 Pattern generator for generating MOST150 cPHY stress pattern
— bandwidth 300 Mbit/s;
— trigger output (for timing measurements).
6.2.5 Directional coupler (for duplex set-ups only), the required performance levels are discussed
in 10.4.2.
7 Electrical characteristics
7.1 Test according to LVDS
Testing of MOST devices or MOST components shall be performed according to the measurement
methods and set-ups specified in TIA/EIA-644-A-2001. Parameters and their respective limits are also
derived from TIA/EIA-644-A-2001, with the exception of common mode voltage (V ) as specified in
CM
ISO 21806-10:2021, 12.1.
4 © ISO 2021 – All rights reserved

7.2 Test according to LVTTL
Testing of MOST devices or MOST components shall be performed in accordance with JEDEC No.
JESD8C.01.
8 Coaxial characteristics
8.1 High/low detection at SP2
[7]
To determine high/low levels, the MOST150 cPHY stress pattern shall be used. At least 500 pulses
(5 UI or 6 UI) shall be extracted out of the measured data. Extraction can be done by triggering on
pulse width ranges or by software-based selection on a prior acquired waveform. The statistical mean
of all amplitude samples lying in the slice between the start of measurement (t ) and the end of
SLS
measurement (t ) for all acquired high pulses is defined as high. The statistical mean of all amplitude
SLE
samples lying in the slice between t and t for all acquired low pulses is defined as low. t and t
SLS SLE SLS SLE
are defined in this document and shown in Table 1.
Table 1 — Signal level measurement interval
Measurement region Value Unit
t 1,00 UI
SLS
t 3,00 UI
SLE
The measured amplitudes (high and low) are an integral part of further measurements at SP2.
Figure 3 defines the high/low detection at SP2.
Figure 3 — High/low detection at SP2
8.2 Transition times at SP2
The transition times (rise and fall) are detected as the time of an edge when transitioning through the
level range of 20 % and 80 % of the amplitude (high and low, see 8.1). Therefore, high/low detection
shall be performed before transition times are determined.
To ensure non-ambiguous measurements the method described below is recommended and applied as
a reference procedure in the case of discrepancies.
Formula (1) and Formula (2) define the amplitude threshold levels.
hb=− bb×02, + (1)
()
 
20 10 0
hb=−bb×08, + (2)
() 
80  10  0
where
h is the 20 % threshold of the amplitude;
h is the 80 % threshold of the amplitude;
b is the signal level when a logic 0 is being transmitted (low);
b is the signal level when a logic 1 is being transmitted (high).
Figure 4 shows an example for the detection of rise-time.

a
High.
b
Low.
c
80 % threshold.
d
20 % threshold.
e
Rise at trigger level.
Figure 4 — Example for detection of rise-time
Measured transition times are smaller than the specified limit in ISO 21806-10:2021, 9.4. MOST150
[7]
cPHY stress pattern should be used as data signal.
8.3 Steady state amplitude at SP2
Following the method in 8.1, the steady state amplitude is the difference between high and low.
6 © ISO 2021 – All rights reserved

8.4 Attenuation of coaxial interconnect
8.4.1 General
ISO 21806-10 specifies the attenuation requirements for a coaxial interconnect, formed of one or
more cables and the associated couplers and harness connectors. The maximum total length of the
interconnect is 15 m. The attenuation of such an interconnect is frequency dependent. ISO 21806-10
specifies an idealized, frequency dependent attenuation function with the coefficients A and F
DC_loss skin
in Formula (3)
F
AF =−A − (3)
()
DC_loss
F
skin
where
A is the attenuation;
A represents the DC attenuation;
DC_loss
F is the frequency;
F represents the skin effect losses.
skin
Attenuation requirements are limited to the frequency range between 1 MHz and 450 MHz and the
absolute attenuation is allowed to vary, as long as specific requirements are met (see 8.4.5).
8.4.2 Coefficient values based on attenuation measurements
It is determined that the coefficient values calculated (as described below) based on attenuation
measurements for the IUT are within the specified limits:
— A < 0,5 dB;
DC_loss
6 2
— F > 9,2 × 10 Hz/dB .
skin
8.4.3 Fitting of corridor
With the evaluated coefficients and the given attenuation function, an idealized attenuation
curve can be constructed, which approximates the characteristics of the measured interconnect.
ISO 21806-10:2021, 9.4.1 mandates that the difference between data-points of the constructed and the
measured attenuation curve (residues) is smaller than ±1 dB.
Attenuation requirements described above apply to the complete temperature range, automotive
environmental conditions, and lifetime.
NOTE Although attenuation always reduces signal strength, attenuation in MOST150 cPHY is specified with
positive values (e.g. A < 0,5 dB).
DC_loss
8.4.4 Attenuation test set-up
Figure 5 specifies the attenuation test set-up.
Key
1 attenuation
2 return loss
3 coaxial interconnect
Figure 5 — Attenuation test set-up
8.4.5 Test procedure
8.4.5.1 General
The test procedure shall start with the measurement of the attenuation characteristic over frequency
for an IUT.
This is usually done with a VNA, using a 2-port arrangement. The VNA measures attenuation from
port 1 to port 2 and vice versa.
The frequency sweep shall produce at least 40 data points per decade, logarithmically distributed.
The measurement procedure shall be performed according to EN 50289-1-8.
8.4.5.2 Data acquisition
Figure 6 shows the data acquisition for an IUT cable length of 15 m. See 8.4.2 for A and F
DC_loss skin
specification limits.
8 © ISO 2021 – All rights reserved

Key
A attenuation [dB]
F frequency [Hz]
a
Acquired data in frequency range 1 MHz to 450 MHz.
b
MOST150 cPHY specification limits: idealized attenuation characteristic based on worst case coefficients
A and F .
DC_loss skin
Figure 6 — Data acquisition
8.4.5.3 Data fitting
A least square fitting algorithm fits the measured data to the given attenuation function, resulting in
7 2
values for A and F . The evaluated coefficients A < 0,07 dB and F > 1,62 × 10 Hz/dB
DC_loss skin DC_loss skin
are within the specified limits according to 8.4.2.
Figure 7 shows the data fitting for an IUT cable length of 15 m.
Key
A attenuation [dB]
F frequency [Hz]
a
Idealized attenuation curve approximating the measured performance of the IUT (attenuation function, with
coefficients as determined by the fit).
b
MOST150 cPHY specification limits: idealized attenuation characteristic based on worst case coefficients
A and F .
DC_loss skin
c
Acquired data in frequency range 1 MHz to 450 MHz.
Figure 7 — Data fitting
8.4.5.4 Attenuation conformance
Figure 8 shows the attenuation conformance as specified in ISO 21806-10:2021, 9.4.1 and the residues
for an IUT cable length of 15 m. Residue, in this context, refers to the deviation of a measured sample
from the idealized curve for each frequency step.
A least square fitting algorithm fits the measured data to the given attenuation function, resulting in
7 2
values for A and F . The evaluated coefficients A < 0,07 dB and F > 1,62 × 10 Hz/dB
DC_loss skin DC_loss skin
are within the specified limits according to 8.4.2.
It is verified that:
— the measured samples are within the attenuation conformance corridor and
— the minimum and maximum values for residues, -0,16 dB and 0,19 dB, respectively, are within the
limits specified in ISO 21806-10:2021, 9.4.1.
10 © ISO 2021 – All rights reserved

Key
A attenuation [dB]
F frequency [Hz]
Y fit residue [dB]
a
Idealized attenuation curve approximating the measured performance of the IUT (attenuation function, with
coefficients as determined by the fit).
b
MOST150 cPHY specification limits: idealized attenuation characteristic based on worst case coefficients
A and F .
DC_loss skin
c
Acquired data in frequency range 1 MHz to 450 MHz.
d
Attenuation conformance corridor.
e
Fit residue.
Figure 8 — Attenuation conformance
The A and F coefficient limits restrict the allowed attenuation span. The attenuation
DC_loss skin
conformance corridor ensures that the transfer characteristic of the IUT follows a transfer function of
coaxial cables. As a result, signal passing such interconnect and being consecutively equalized (based
on coaxial cable attenuation function) maintains a flatness of ±1 dB.
Particular coaxial interconnect configuration exhibits individual attenuation characteristics and is
thus characterized by their respective individual A and F coefficients. The values of those
DC_loss skin
coefficients depend on the cable type used and the total length of each specific interconnect tested.
Coaxial interconnect/segments with shorter length have lower attenuation and therefore lower A
DC_loss
and larger F . Interconnects with identical configuration can produce different coefficient sets.
skin
Cable attenuation varies with temperature. This is mainly contributed by the temperature dependent
conductance of the conductor’s material (copper). Therefore, coefficients for a given interconnect vary
over temperature.
Extrapolation of coefficient values for different cable lengths is defined in Formula (4) and Formula (5).
A
DC_lossm_ eas
Al()=×l (4)
DC_loss
l
IUT
where
A represents the DC attenuation;
DC_loss
A is the result of a fit on measured data;
DC_loss_meas
l is the length of measured interconnect;
IUT
l is the desired length coefficients are extrapolated to.
F
skin_meas
Fl()=×l (5)
skin IUT
l
where
F represents skin effect losses;
skin
F represents skin effect losses as a result of a fit on measured data;
skin_meas
l is the length of measured interconnect;
IUT
l is the desired length coefficients are extrapolated to.
Table 2 shows an example using coefficient limits.
Table 2 — Example using coefficient limits
Measured Extrapolated
l : 15 m l extrapolated: 5 m
IUT IUT
A : 0,500 dB A (l): 0,167 dB
DC_loss_meas DC_loss
6 2 7 2
F : 9,2 × 10 Hz/dB F (l): 8,28 × 10 Hz/dB
skin_meas skin
l : 5 m l extrapolated: 15 m
IUT IUT
A : 0,167 dB A (l): 0,500 dB
DC_loss_meas DC_loss
7 2 6 2
F : 8,28 × 10 Hz/dB F (l): 9,2 × 10 Hz/dB
skin_meas skin
8.4.5.5 Impact of attenuation on data signal
ISO 21806-10:2021, 9.4.1 specifies the attenuation characteristic of coaxial interconnect which
follows a function of frequency. Therefore, the spectrum of a data signal being fed into such channel is
attenuated in a non-uniform manner. Attenuation affects high frequencies more than low frequencies.
In consequence, transition times decrease. Shorter pulses of the signal might not achieve full amplitude
swing anymore. The effect is called intersymbol interference.
The graph in Figure 9 gives an example: the SP2 signal starts with uniform amplitude on all pulses (V
ss2
in ISO 21806-10:2021, 9.3). The SP3 signal shows the resulting signal shape after passing the coaxial
interconnect (typical coaxial cable, 15 m, same cable as used for analysis of link attenuation in 8.4.4).
Figure 9 shows the measurement of attenuation of coaxial interconnects.
12 © ISO 2021 – All rights reserved

Key
1 amplitude at SP2
2 minimum amplitude at SP3
3 maximum amplitude at SP3
Figure 9 — Measurement of attenuation of coaxial interconnects
8.5 RL of connectors and couplers
RL affects all types of connectors in the coaxial link, i.e. inline-couplers, harness connectors as well
as ECU connectors. Testing of such connectors and couplers shall be performed in accordance with
ISO 20860-2. The frequency range of interest for MOST150 cPHY is defined with 1 MHz to 450 MHz,
which is only a sub-set of the requested bandwidth in ISO 20860-2.
8.6 Characteristic impedance of coaxial cable
Measurement of characteristic impedance of coaxial cables shall be performed according to EN 50289-
1-11.
8.7 RL of coaxial interconnect
A coaxial interconnect is formed of one or more cables and the associated couplers and harness
connectors. RL of a coaxial interconnect characterizes the frequency dependent signal reflection ratio,
due to accumulated impedance mismatch throughout the whole length of that interconnect, measured
at each of its ends.
RL shall b
...