IEC 61784-3:2016/AMD1:2017

IEC 61784-3 ®
Edition 3.0 2017-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
A MENDMENT 1
AM ENDEMENT 1
Industrial communication networks – Profiles –
Part 3: Functional safety fieldbuses – General rules and profile definitions

Réseaux de communication industriels – Profils –
Partie 3: Bus de terrain de sécurité fonctionnelle – Règles générales et
définitions de profils
IEC 61784-3:2016-05/AMD1:2017-08(en-fr)

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IEC 61784-3 ®
Edition 3.0 2017-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
A MENDMENT 1
AM ENDEMENT 1
Industrial communication networks – Profiles –

Part 3: Functional safety fieldbuses – General rules and profile definitions

Réseaux de communication industriels – Profils –

Partie 3: Bus de terrain de sécurité fonctionnelle – Règles générales et

définitions de profils
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 25.040.40; 35.100.05 ISBN 978-2-8322-4585-9

– 2 – IEC 61784-3:2016/AMD1:2017
© IEC 2017
FOREWORD
This amendment has been prepared by subcommittee 65C: Industrial networks, of IEC
technical committee 65: Industrial-process measurement, control and automation.
The text of this amendment is based on the following documents:
FDIS Report on voting
65C/879/FDIS 65C/886/RVD
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the stability date indicated on the IEC website under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
_____________
© IEC 2017
INTRODUCTION
This Amendment 1 discusses the concepts of implicit data safety mechanisms for use in
functional safety communications protocols (FSCPs) as specified in IEC 61784-3:2016.
3 Terms, definitions, symbols, abbreviated terms and conventions
3.1 Terms and definitions
Add the following new terms and definitions 3.1.56 and 3.1.57:
3.1.56
explicit data
data that is transmitted
3.1.57
implicit data
additional data that is not transmitted but is known to the sender and receiver
[SOURCE: IEC 62280:2014, 3.1.25]
3.2 Symbols and abbreviated terms
Add two new Subclauses 3.2.1 and 3.2.2, as specified below.
3.2.1 Abbreviated terms
Move the existing list of symbols and abbreviated terms to this new Subclause 3.2.1.
Delete “Pe” and “RP” from the existing list of abbreviated terms. Add, in alphabetical order, in
the list of abbreviated terms the following new abbreviated terms:
A-code Authenticity code
T-code Timeliness code
3.2.2 Symbols
Add, in this new Subclause 3.2.2 the following list of symbols:
A Weight distribution of the code: number of valid
k
codewords having k bits set to “one”
e Bit length of explicit data
err Bitwise disjunction of impl and impl
impl S R
expl Explicit data
expl Explicit data in the receiver
R
expl Explicit data in the sender
S
FCS Frame check sequence calculated in the receiver
C
FCS Frame check sequence received
R
FCS Frame check sequence sent
S
i Bit length of implicit data
ID Incorrect delivery
impl Implicit data in the receiver
R
impl Implicit data in the sender
S
– 4 – IEC 61784-3:2016/AMD1:2017
© IEC 2017
n Bit length of SPDU
P Bit error probability
e
P Probability of incorrect delivery
ID
r Bit length of FCS (degree of generator polynomial)
RP Residual error probability
Add, after Annex F, the following new informative Annex G:

© IEC 2017
Annex G
(informative)
Implicit data safety mechanisms for IEC 61784­3 functional
safety communication profiles (FSCPs)
G.1 Overview
Annex G discusses the concepts of implicit data safety mechanisms for use in functional
safety communications protocols (FSCPs) as specified in this standard. Implicit data is that
which is not explicitly transmitted in a PDU. Instead, the implicit data values are known by
both the sender (source) and the receiver (sink). Implicit data values are validated by the
value of one or more transmitted frame check sequence(s) (FCS) which are calculated using
an overall data string comprised of the implicit data string appended with the explicit data
string. Because the implicit data is not transmitted, the load on the transmission media is
reduced.
Today, the FSCPs that use implicit data mechanisms do so in order to communicate complete
or partial timeliness codes (T-codes) and/or authenticity codes (A-codes), see Annex E.
These FSCPs also use cyclic redundancy check (CRC) algorithms for the frame check
sequence (FCS) exclusively. Therefore, Annex G is limited to the analysis of implicitly
transmitted T-codes and A-codes using CRC-algorithms.
According to Clause E.8, with regard to implicit data, "Due to the various possible approaches
generic formulae cannot be provided. It is up to the individual FSCP to prove sufficient
residual error probabilities." In the hope of advancing IEC 61784-3 for the next edition and
beyond, the subject of this new Annex G is to improve the understanding of formulating
models for the residual error probabilities of FSCPs using CRC-algorithms to implicitly
transmit T-codes and A-codes when a single FCS code is used by the protocol.
Presented in Annex G are two formulae examples, applicable for two special cases, and from
which a better understanding is promoted for the development of additional (specific and
general) formulae.
Also presented is a summation method generally applicable when conditional weight
distributions for implicit data error patterns are known and can be quantified in a way either
leading to a closed-form solution, or suitable for iterative summation with a reasonably
bounded execution time.
G.2 Basic principles
Calculations in Annex G also use the binary symmetric channel (BSC) model as specified in
Annex B.
NOTE 1 Although it does not take into account burst errors, the BSC model with a sufficiently conservative bit
error probability is so far the most practical known for use in probability calculations needed for the determination
of the FSCP residual error rate.
Figure G.1 shows the basic principle of an FSCP using single FCS protection mechanisms
involving implicit data. In the sender, a CRC-checksum over the implicit data impl
S
concatenated with the explicit data expl is generated, resulting in a frame check sequence
S
FCS . When multiple FCS codes are used in an FCSP format, the calculation shall be done
S
for each FCS code. While expl and FCS are explicitly transmitted over the black channel,
S S
impl is not transmitted, but impacts the value of the FCS . Therefore, it can only contain
S S
data whose value is already known to the receiver. Implicit data is used to detect e.g. SPDUs
which were misdirected in either space (“authentication error”) or time (“timeliness error”).
This is accomplished by deriving the implicit data from the A-code (e.g. connection identifier)
and/or the T-code (e.g. sequence number) of an SPDU.

– 6 – IEC 61784-3:2016/AMD1:2017
© IEC 2017
NOTE 2 Initialization details are addressed in F.12.1.
Sender Receiver
expl
S
impl
R
impl
S
CRC CRC
calculation calculation
impl expl
R R
impl expl
S S
?
FCS
C
ok
expl FCS
S S
expl FCS
R R
expl FCS
Black channel
SPDU
IEC
Key Symbols are specified in 3.2.2
Figure G.1 – FSCP with implicit transmission of authenticity
and/or timeliness codes
When the SPDU comprising expl and FCS is delivered to the FSCP-layer in the receiver, it
may contain transmission errors, i.e. the value delivered may differ from the value sent. For
discrimination, the symbols expl and FCS are used in the receiver.
R R
The expected value of the implicit data is called impl . In the error free case, this expectation
R
is identical to impl . In case of, for example, a misdirected SPDU, impl and impl may differ.
S R S
The receiver generates one or more frame check sequence(s) FCS by building a CRC-
C
checksum over the concatenation of impl and expl . When each FCS is identical to its
R R C
corresponding FCS , it is assumed that no error occurred. Otherwise an error has been
R
detected.
The lengths of the bitstrings for a
...