INTERNATIONAL ISO
STANDARD 4426
First edition
Intelligent transport systems —
Lower layer protocols for usage in the
European digital tachograph
Systèmes de transport intelligents - Protocoles de couche basse pour
utilisation dans le cadre du chrono tachygraphe numérique européen
PROOF/ÉPREUVE
Reference number
ISO 4426:2021(E)
ISO 2021
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ISO 4426:2021(E)
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ISO 4426:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

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

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

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

4 Abbreviated terms and symbols .......................................................................................................................................................... 8

5 Digital tachograph interrogation .....................................................................................................................................................10

5.1 General ........................................................................................................................................................................................................10

5.2 SDTC protocol stack .........................................................................................................................................................................11

5.2.1 Simplified OSI layered ..............................................................................................................................................11

5.2.2 SDTC L1 .................................................................................................................................................................................11

5.2.3 SDTC L2 .................................................................................................................................................................................11

5.2.4 SDTC L7 .................................................................................................................................................................................11

5.3 SDTC profiles .........................................................................................................................................................................................11

6 Test methods ..........................................................................................................................................................................................................11

Annex A (normative) SDTC physical layer ....................................................................................................................................................13

Annex B (normative) SDTC data link layer ..................................................................................................................................................18

Annex C (normative) SDTC application layer ............................................................................................................................................53

Annex D (normative) SDTC profiles ....................................................................................................................................................................56

Bibliography .............................................................................................................................................................................................................................65

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ISO 4426:2021(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 204, Intelligent transport systems.

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 4426:2021(E)
Introduction

This document is designed to encompass communication requirements in support of the Smart Digital

[23]
Tachograph (SDT) as identified by Regulation 2016/799 of the European Union .

This document specifies SDT Communications (SDTC). SDTC is the application of CEN Dedicated Short

Range Communication (DSRC) for SDT. See the following:

— EN 12253, Road transport and traffic telematics — Dedicated short-range communication — Physical

[1]
layer using microwave at 5,8 GHz

— EN 12795, Road transport and traffic telematics — Dedicated Short Range Communication (DSRC) —

[2]
DSRC data link layer: medium access and logical link control

— EN 12834, Road transport and traffic telematics — Dedicated Short Range Communication (DSRC) —

[3]
DSRC application layer

— EN 13372, Road transport and traffic telematics — Dedicated short-range communication — Profiles

[4]
for RTTT applications

Complementing the standardized specifications and descriptions, several private documents describe

this dedicated short range semi-passive communication technology in an informative manner, providing

additional detailed explanations and implementation hints. See for example:
[24]
— DSRC tutorial published by ESF GmbH in July 2003 (publicly available) ;
[25]

— GSS industry specification published in August 2003 (no longer available from the authors;

essential content is now available in ISO 15509);

It is to be noted that the abovementioned private documents provide information that can be essential

to easily achieving interoperability with existing DSRC equipment and optimum performance.

[1]

EN 12253 deals with the physical layer of the DSRC protocol stack presented in Figure 1; i.e. it

comprises requirements for Open Systems Interconnection (OSI) Layer 1 at 5,8 GHz for DSRC.

Figure 1 — DSRC protocol stack
[1]

EN 12253 does not include associated measurement procedures for verification of the requirements.

[12] [13]

Test methods for conformity are provided in ETSI EN 300674-1 , ETSI EN 300674-2-1 and ETSI

[14]
EN 300674-2-2 .
[1]

EN 12253 caters for on-board units based on transponder technologies. Furthermore, it allows for

mixed time, frequency and space division multiple access approaches.
[1]

EN 12253 is conceived for the 10 MHz part (i.e. 5,795 GHz to 5,805 GHz) of the ISM band at 5,8 GHz

[10]

which is recommended by ECC/DEC(01)01 . An additional sub-band (5,805 GHz - 5,815 GHz) may be

allocated on a national basis. National restrictions on the usage of these frequency bands can apply

[11]
according to CEPT/ERC REC 70-03 .
[2]

EN 12795 gives the architecture and services offered by the DSRC data link layer.

[3]

EN 12834 and the almost identical ISO 15628 give the architecture and services offered by the DSRC

application layer.
[4]
EN 13372 deals with the interlayer management of the DSRC protocol stack.

Figure 2 illustrates the global data flow between the elements of the SDTC stack, (physical layer, data

link layer and application layer) and the SDT application.
Figure 2 — Architecture and data flow of the SDTC stack
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INTERNATIONAL STANDARD ISO 4426:2021(E)
Intelligent transport systems — Lower layer protocols for
usage in the European digital tachograph
1 Scope

This document specifies communication requirements in support of the Smart Digital Tachograph

[23]
(SDT) as identified by Regulation 2016/799 of the European Union .
The specification covers:
— the physical layer at 5,8 GHz for SDT communications (SDTC);
— the data link layer (DLL) of SDTC;
— the application layer of SDTC;

— SDTC profiles which provide coherent sets of communication tools for applications based on SDTC.

This document provides further information beneficial for the design and development of SDTC

equipment.
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 15628, Intelligent transport systems — Dedicated short range communication (DSRC) — DSRC

application layer

ISO/IEC 13239, Information technology — Telecommunications and information exchange between

systems — High-level data link control (HDLC) procedures
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
adjacent channel
neighbouring SDTC channel for use by two or more emissions

Note 1 to entry: It is possible that a SDTC channel has either one of two adjacent channels.

3.2
antenna bore sight direction
direction of maximum antenna gain
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ISO 4426:2021(E)
3.3
application

set of processes including related functions and structured data that uses the services offered by the

SDTC communication stack
3.4
beacon service table
BST
data structure transmitted by the fixed equipment indicating available services
3.5
bit error ratio

averaged number of erroneous bits relative to the total number of transmitted bits

3.6
co-channel
refers to the use of the same SDTC channel by two or more emissions
3.7
communication initialization
procedure used to establish communication between an RSU and a newly arrived OBU

Note 1 to entry: Terms prefixed with D present downlink parameters; downlink parameters apply to transmission

of data from RSU to OBU.
3.8
D1 — carrier frequencies

number and values of the downlink carrier frequencies, which are equal to the frequencies of the CW,

transmitted by the RSU and used by transponder OBUs for uplink communication

Note 1 to entry: Each carrier frequency is the centre frequency of a downlink channel.

3.9
D1a — tolerance of carrier frequencies
maximum deviation of the carrier frequency resulting from any cause
Note 1 to entry: It is expressed in parts per million (ppm)

EXAMPLE ±1 ppm of a 5,8 GHz carrier allows for the carrier frequency to be in the range of 5,8 GHz ± 5,8 kHz.

3.10
D2 — RSU transmitter spectrum mask

maximum allowed power within a defined frequency band emitted by the RSU transmitter

3.11
D3 — OBU minimum frequency range
minimum range of frequencies that has to be received by the OBU receiver
3.12
D4 — maximum E.I.R.P.
maximum allowed value of E.I.R.P.
3.13
D4a — angular E.I.R.P. mask

E.I.R.P. as a function of the angle Θ, where Θ indicates the angle relative to a vector perpendicular to the

road surface, pointing downwards
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ISO 4426:2021(E)
3.14
D5 — polarization

locus of the tip of the vector of the electrical field strength in a plane perpendicular to the transmission

vector

EXAMPLE Horizontal and vertical linear polarization and left- and right-hand circular polarization.

3.15
D5a — cross-polarization
ellipticity of polarization

antenna designed to transmit left-hand circular waves, which can transmit some right-hand circular

waves in addition

Note 1 to entry: Cross-polar discrimination (XPD) is defined as the ratio between left- and right-hand circular

power, P /P , when the total power transmitted is P + P . XPD is related to the ellipticity of polarization.

LHC RHC LHC RHC
3.16
D6 — modulation
keying of the carrier wave by coded data

EXAMPLE Amplitude shift keying (ASK), phase shift keying (PSK), frequency shift keying (FSK) and linear

amplitude modulation (AM).
3.17
D6a — modulation index

ratio of the variation of the modulation parameter (frequency, amplitude, phase) caused by the

modulation signal (data signal)

EXAMPLE Given the minimum and maximum values V and V of the envelope amplitude V of the

max min
modulated signal, the amplitude modulation index m is defined as:
VV−
maxmin
m= .
VV+
maxmin
3.18
D7 — data coding

downlink base band signal presentation, i.e. a mapping of logical bits to physical signals

EXAMPLE Bi-phase schemes (Manchester, FM0, FM1, differential Manchester), NRZ and NRZI. NRZI: No

transition at beginning of "1" bit, transition at beginning of "0" bit, no transition within bit.

3.19
D8 — bit rate
number of bits per second, independent of the data coding
3.20
D8a — tolerance of bit clock

maximum downlink deviation of the bit clock resulting from any cause, expressed in ppm

EXAMPLE 100 ppm of 500 kbit/s allows for the bit clock to be in the range of 500 kHz ± 50 Hz.

3.21
D9 — bit error ratio for communication

maximum allowed bit error ratio valid within the dynamic range of the receiver as defined by D11a and

D11b
3.22
D10 — wake-up trigger for OBU
signal which:

a) indicates to the OBU that it is within a communication zone, i.e. that it can now communicate with

an RSU;
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ISO 4426:2021(E)
b) switches the OBU main circuitry from sleep mode to the active mode

Note 1 to entry: This is a feature to allow the OBU to save battery power. It is not mandatory for an OBU to use a

wake-up process.
3.23
D10a — maximum start time

maximum time between the reception of the wake-up trigger and the time when the OBU has switched

to the active mode
3.24
D11 — communication zone

spatial region within which the incident power of the OBU has a dynamic range as defined by D11a and

D11b
3.25
D11a — power limit for communication (upper)

upper level of incident power referred to a lossless isotropic antenna (0 dB) in front of the OBU

Note 1 to entry: This is the level below which, subject to D11b, communication is guaranteed with a specified

bit error ratio. Communication can take place above this limit, but is not guaranteed. Together with D11b it also

specifies the minimum dynamic range of the OBU receiver. Power values are measured without any additional

losses due to rain or misalignment.
3.26
D11b — power limit for communication (lower)

lower level of incident power referred to a lossless isotropic antenna (0 dB) in front of the OBU

Note 1 to entry: This is the level above which, subject to D11a, communication is guaranteed with a specified

bit error ratio. Communication can take place below this limit, but is not guaranteed. Together with D11a it also

specifies the minimum dynamic range of the OBU receiver. Power values are measured without any additional

losses due to rain or misalignment
3.27
D12 — cut-off power level of OBU

incident power that is lower than the specified cut-off power level that does not result in communication

3.28
D13 — preamble
specific downlink layer 1-bit pattern

Note 1 to entry: Preamble is the bit pattern transmitted immediately before a frame.

3.29
D13a — preamble length
length of the downlink preamble measured in number of bits
3.30
D13b — preamble wave form
signal shape of the preamble
3.31
D13c — trailing bits
sequence of bits transmitted after the end flag of the data link layer
3.32
downlink
communication channel on which the fixed equipment transmits its information
3.33
downlink communication
communication from the RSU to the OBU
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ISO 4426:2021(E)
3.34
equivalent isotropically radiated power
E.I.R.P.

signal power fed into an ideal lossless antenna radiating equally in all directions that generates the

same power flux at a reference distance as the one generated by a signal fed into the antenna under

consideration in a predefined direction within its far field region
3.35
fixed equipment

fixed communication facility with one or more downlink channels and, optionally, one or more uplink

channels

Note 1 to entry: Normally the fixed equipment is installed at a fixed location, but it may be installed on a mobile

platform.
3.36
interlayer management

assembly of communication parameters of all protocol layers such that a consistent communication

protocol is provided
3.37
link identifier
LID
unique address used for addressing the mobile equipment
3.38
mobile equipment

mobile communication facility capable of receiving information from the fixed equipment on the

downlink and, optionally, also capable of transmitting information to the fixed equipment on the uplink

Note 1 to entry: The mobile equipment normally corresponds to the vehicle’s communication unit.

3.39
on-board unit
OBU

physical assembly that is located and operated in or on the vehicle to transmit and/or receive SDTC

signals

Note 1 to entry: An OBU may be in a form that is removable from the vehicle, or mountable in or on any part of

the vehicle structure, or bonded to a part of the vehicle, or an integral part of a vehicle component, such as a

windscreen, bumper or licence plate. In this document, parameters that refer to an OBU relate to the form that

the OBU takes as it is supplied to the vehicle manufacturer or constructor.
Note 2 to entry: An OBU is an alternative descriptor to Mobile Equipment.
3.40
roadside unit
RSU
SDTC equipment usually residing by the side of the road or overhead the road
Note 1 to entry: An RSU is an alternative descriptor to Fixed Equipment.
3.41
SDTC channel

frequency band for SDTC indicated by reference to the downlink centre frequency of one of up to four

frequency bands with 5 MHz width each
3.42
SDTC profile

consistent and standardized set of cross layer parameters controlling the behaviour of the SDTC

interface point between data link layer and application layer, that has a unique link identifier and that

allows layers to communicate
3.44
smart digital tachograph communication
SDTC
CEN DSRC applied for the Smart Digital Tachograph (SDT)
[23]

Note 1 to entry: This is as identified by Regulation 2016/799 of the European Union .

3.45
termination
procedure used to terminate communication between an RSU and an OBU
3.46
U1 — sub-carrier frequencies

number and values of the uplink sub-carrier frequencies, i.e. the frequency separation from the centre

of the uplink side band to the centre of the corresponding downlink band
3.47
U1a — tolerance of sub-carrier frequencies
maximum deviation of the sub-carrier frequency resulting from any cause

EXAMPLE 1 % of 1,5 MHz sub-carrier allows for the sub-carrier frequency to be in the range of

1,5 MHz ± 15 kHz.

Note 1 to entry: Normally this is expressed in percentage (%) or in parts per million (ppm) of the sub-carrier

frequency.

Note 2 to entry: Terms prefixed with U present uplink parameters; uplink parameters apply to transmission of

data from OBU to RSU.
3.48
U1b — use of side bands
specification of the use of the uplink side bands

Note 1 to entry: Data can be modulated on the upper side band only, or the lower side band only, or on both side

bands. In principle, different data can be modulated on the two side bands.
3.49
U2 — OBU transmitter spectrum mask

maximum allowed power emitted by the OBU transmitter within a defined frequency band

3.50
U4 — maximum single side band E.I.R.P. (bore sight)

maximum E.I.R.P. transmitted by the OBU within a single side band, measured at the maximum incident

power defined by D11a

Note 1 to entry: For a non-isotropic OBU antenna the single side band E.I.R.P varies with the direction of the

incident power and the direction in which the emitted power is measured.
3.51
U4a — maximum single side band E.I.R.P. (bore sight)

measurement when the incident power is in bore sight and the emitted power is measured in bore sight

3.52
U4b — maximum single side band E.I.R.P. (35°)

measurement when the incident power is in bore sight and the emitted power is measured at any angle

not less than 35° away from bore sight
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ISO 4426:2021(E)
3.53
uplink parameter indicating the uplink polarization
3.54
U5 — cross-polarization
uplink parameter indicating the cross-polarization
3.55
U6 — sub-carrier modulation
keying of the sub-carrier wave by coded data

EXAMPLE Amplitude shift keying (ASK), phase shift keying (PSK), and frequency shift keying (FSK).

Note 1 to entry: U6b is not used.
3.56
U6b — duty cycle
ratio of the length of high or low pulses to the duration of a complete cycle

Note 1 to entry: In NRZI a sequence of zero bits results in a pulse of alternating high- and low-level sections. A

low-level section and the adjacent high-level section constitute a cycle of the pulse. The nominal duration of such

a single section is equal to the bit duration. The cycle duration is twice the bit duration. The duty cycle is the ratio

of the duration of the high-level section to the cycle duration.
3.57
U6c — modulation on carrier
keying of the carrier wave by the modulated sub-carrier
3.58
U7 — data coding

uplink base band signal presentation, i.e. a mapping of logical bits to physical signals

3.59
U8 — bit rate
number of bits per second, independent of the data coding
3.60
U8a — tolerance of symbol clock

maximum uplink deviation of the bit clock resulting from any cause, expressed in ppm

3.61
U9 — bit error ratio for communication
maximum allowed bit error ratio valid within the dynamic range of the receiver
3.62
U11 — communication zone

spatial region within which the OBU is situated such that its transmissions are received by the RSU

with a bit error ratio of less than a specified value
3.63
U12 — conversion gain

difference between OBU E.I.R.P. within one side band and the carrier incident power on OBU

3.64
U13 — preamble
specific uplink layer 1-bit pattern
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ISO 4426:2021(E)
3.65
U13a — preamble length
length of the uplink preamble

Note 1 to entry: Preamble length is measured either in multiples of symbols or in seconds.

3.66
U13b — trailing bits
sequence of bits transmitted after the end flag of the data link layer
3.67
uplink
communication channel on which mobile equipment transmits its information
3.68
uplink communication
communication from the OBU to the RSU
3.69
vehicle service table
VST
data structure transmitted by the OBU to indicate available services
3.70
window

period of time during which the physical medium is allocated either to the fixed equipment or to the

mobile equipment
4 Abbreviated terms and symbols
2-PSK binary phase shift keying
ACK acknowledge
ACn acknowledged command with sequence bit n
ADU application data unit
AM amplitude modulation
APDU application protocol data unit
ASDU application service data unit
ASK amplitude shift keying
C/R command/response
CEN European Committee for Standardization
CEPT European Conference of Postal and Telecommunications Administrations
CW continuous wave
DLL data link layer
DSRC dedicated short-range communication
EC European Commission
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ISO 4426:2021(E)
EDTC European digital tachograph communication
EFC electronic fee collection
EN European Standard
ERC European Radiocommunications Committee
ERM electromagnetic compatibility and radio spectrum matters
ETSI European Telecommunications Standards Institute
F final
FCS frame check sequence
FE fixed equipment
FM0 / FM1 bi-phase coding scheme, bit inverse to FM1 / FM0
FSK frequency shift keying
HDLC high-level data link control
ISM industrial, scientific, medical
L1 layer 1 of SDTC (physical layer)
L2 layer 2 of SDTC (data link layer)
L7 layer 7 of SDTC (application layer)
LLC logic link control
LPDU link layer protocol data unit
LSB least significant bit
LSDU link layer service data unit
M modifier function bit
MAC medium access control
ME mobile equipment
MSB most significant bit
NRZ non-return to zero
NRZI non-return to zero inverted
OSI open systems interconnection
P poll
P/F poll/final
PICS protocol implementation conformance statement
PDU protocol data unit
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ISO 4426:2021(E)
PPDU physical layer protocol data unit
PSDU physical layer service data unit
ppm parts per million
PSK phase shift keying
R response
R&TTE radio and telecommunications terminal equipment
RR response request
RTTT road transport and traffic telematics
TDMA time division multiple access
TSS&TP test suite structure and test purposes
UI unnumbered information
V receive state variable (LLC)
V transmit state variable (LLC)
XPD cross-polar discrimination
5 Digital tachograph interrogation
5.1 General

A regulatory device such as a smart tachograph needs to offer an interface for interrogation by

authorized officers. Such an interface may be carried through a physical connector, or via a wireless

communication interface. When the second option is chosen, stringent requirements of confidentiality

and, in general, security, arise.

A DSRC helps in satisfying these security requirements because of its localized nature and because of

the experience already gained in securing this type of links. This is one of the reasons the specification

of the application for digital tachograph interrogation in ISO 15638-9 is based on this type of

communication mechanism.

Some legislations require that a radio link shall be available in smart tachograph devices, such as in

[21]

Europe, where Regulation 165/2014 requires that "In order to facilitate targeted roadside checks by

the competent control authorities, tachographs installed in vehicles … shall be able to communicate to those

authorities while the vehicle is in motion".
The right to allocate frequencies for DSRC and to determ
...

ISO/PRF 4426

Intelligent transport systems -- Lower layer protocols for usage in the European digital tachograph

Intelligent transport systems -- Lower layer protocols for usage in the European digital tachograph

Systèmes de transport intelligents - Protocoles de couche basse pour utilisation dans le cadre du chrono tachygraphe numérique européen

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Intelligent transport systems -- Lower layer protocols for usage in the European digital tachograph

Systèmes de transport intelligents - Protocoles de couche basse pour utilisation dans le cadre du chrono tachygraphe numérique européen

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