SIST EN 62056-4-7:2017

SLOVENSKI STANDARD
SIST EN 62056-4-7:2017
01-februar-2017
1DGRPHãþD
SIST EN 62056-47:2007
,]PHQMDYDSRGDWNRYSULPHUMHQMXHOHNWULþQHHQHUJLMH1L]'/06&26(0GHO
7UDQVSRUWQDSODVW'/06&26(0]DRPUHåMD,3
Electricity metering data exchange - The DLMS/COSEM suite - Part 4-7: DLMS/COSEM
transport layer for IP networks
Datenkommunikation der elektrischen Energiemessung - DLMS/COSEM - Teil 4-7:
DLMS/COSEM Transportschicht für IP-Netzwerke
Échange des données de comptage de l'électricité - La suite DLMS/COSEM - Partie 4-7:
Couche transport DLMS/COSEM pour réseaux IP
Ta slovenski standard je istoveten z: EN 62056-4-7:2016
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
35.100.40 Transportni sloj Transport layer
91.140.50 Sistemi za oskrbo z elektriko Electricity supply systems
SIST EN 62056-4-7:2017 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

SIST EN 62056-4-7:2017

---------------------- Page: 2 ----------------------

SIST EN 62056-4-7:2017


EUROPEAN STANDARD EN 62056-4-7

NORME EUROPÉENNE

EUROPÄISCHE NORM
December 2016
ICS 17.220; 35.110; 91.140.50 Supersedes EN 62056-47:2007
English Version
Electricity metering data exchange - The DLMS/COSEM suite -
Part 4-7: DLMS/COSEM transport layer for IP networks
(IEC 62056-4-7:2015)
Échange des données de comptage de l'électricité - La Datenkommunikation der elektrischen Energiemessung -
suite DLMS/COSEM - Partie 4-7: Couche transport DLMS/COSEM - Teil 4-7: DLMS/COSEM Transportschicht
DLMS/COSEM pour réseaux IP für IP-Netzwerke
(IEC 62056-4-7:2015) (IEC 62056-4-7:2015)
This European Standard was approved by CENELEC on 2015-06-24. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.


European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
 Ref. No. EN 62056-4-7:2016 E

---------------------- Page: 3 ----------------------

SIST EN 62056-4-7:2017
EN 62056-4-7:2016
European foreword
The text of document 13/1570/CDV, future edition 1 of IEC 62056-4-7, prepared by IEC/TC 13
"Electrical energy measurement and control" was submitted to the IEC-CENELEC parallel vote and
approved by CENELEC as EN 62056-4-7:2016.

The following dates are fixed:
(dop) 2017-06-09
• latest date by which the document has to be
implemented at national level by
publication of an identical national
standard or by endorsement
• latest date by which the national (dow) 2019-12-09
standards conflicting with the
document have to be withdrawn

This document supersedes EN 62056-47:2007.

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.

This document has been prepared under a mandate given to CENELEC by the European Commission
and the European Free Trade Association.

Endorsement notice
The text of the International Standard IEC 62056-4-7:2015 was approved by CENELEC as a
European Standard without any modification.
2

---------------------- Page: 4 ----------------------

SIST EN 62056-4-7:2017
EN 62056-4-7:2016
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications

The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.

NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.

NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu

Publication Year Title EN/HD Year

IEC 60050-300 2001 International Electrotechnical Vocabulary - -
(IEV) - Electrical and electronic
measurements and measuring instruments
- Part 311: General terms relating to
measurements -
Part 312: General terms relating to
electrical measurements -
Part 313: Types of electrical measuring
instruments -
Part 314: Specific terms according to the
type of instrument
IEC/TR 62051 1999 Electricity metering - Glossary of terms - -
IEC/TR 62051-1 2004 Electricity metering - Data exchange for - -
meter reading, tariff and load control -
Glossary of terms -
Part 1: Terms related to data exchange
with metering equipment using
DLMS/COSEM
1)
IEC 62056-5-3 2013 Electricity metering data exchange - EN 62056-5-3 2014
The DLMS/COSEM suite -
Part 5-3: DLMS/COSEM application layer
2)
IEC 62056-6-2 2013 Electricity metering data exchange - EN 62056-6-2 2013
The DLMS/COSEM suite -
Part 6-2: COSEM interface classes
IEC 62056-9-7 2013 Electricity metering data exchange - EN 62056-9-7 2013
The DLMS/COSEM suite -
Part 9-7: Communication profile
for TCP-UDP/IP networks
STD 0006 -  User Datagram Protocol - -
STD 0007 -  Transmission Control Protocol - -


1)
Superseded by EN 62056-5-3:2016 (IEC 62056-5-3:2016): DOW = 2019-12-09.
2)
Superseded by EN 62056-6-2:2016 (IEC 62056-6-2:2016): DOW = 2019-12-09.
3

---------------------- Page: 5 ----------------------

SIST EN 62056-4-7:2017

---------------------- Page: 6 ----------------------

SIST EN 62056-4-7:2017




IEC 62056-4-7

®


Edition 1.0 2015-05




INTERNATIONAL



STANDARD




NORME



INTERNATIONALE
colour

inside










Electricity metering data exchange – The DLMS/COSEM suite –

Part 4-7: DLMS/COSEM transport layer for IP networks




Échange des données de comptage de l'électricité – La suite DLMS/COSEM –

Partie 4-7: Couche transport DLMS/COSEM pour réseaux IP

















INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE


INTERNATIONALE




ICS 17.220; 35.110; 91.140.50 ISBN 978-2-8322-2609-4



Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

---------------------- Page: 7 ----------------------

SIST EN 62056-4-7:2017
– 2 – IEC 62056-4-7:2015  IEC 2015
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviations . 8
3.1 Terms and definitions . 8
3.2 Abbreviations . 8
4 Overview . 9
5 The DLMS/COSEM connection-less, UDP-based transport layer . 10
5.1 General . 10
5.2 Service specification for the DLMS/COSEM UDP-based transport layer . 11
5.2.1 General . 11
5.2.2 The UDP-DATA service . 12
5.3 Protocol specification for the DLMS/COSEM UDP-based transport layer . 14
5.3.1 General . 14
5.3.2 The wrapper protocol data unit (WPDU) . 14
5.3.3 The DLMS/COSEM UDP-based transport layer protocol data unit . 15
5.3.4 Reserved wrapper port numbers (wPorts) . 16
5.3.5 Protocol state machine . 16
6 The DLMS/COSEM connection-oriented, TCP-based transport layer . 16
6.1 General . 16
6.2 Service specification for the DLMS/COSEM TCP-based transport layer . 17
6.2.1 General . 17
6.2.2 The TCP-CONNECT service . 18
6.2.3 The TCP-DISCONNECT service . 21
6.2.4 The TCP-ABORT service . 23
6.2.5 The TCP-DATA service . 24
6.3 Protocol specification for the DLMS/COSEM TCP-based transport layer . 26
6.3.1 General . 26
6.3.2 The wrapper protocol data unit (WPDU) . 26
6.3.3 The DLMS/COSEM TCP-based transport layer protocol data unit . 27
6.3.4 Reserved wrapper port numbers . 27
6.3.5 Definition of the procedures . 27
Annex A (informative) Converting OSI-style TL services to and from RFC-style TCP
function calls. 32
A.1 Transport layer and TCP connection establishment . 32
A.2 Closing a transport layer and a TCP connection . 33
A.3 TCP connection abort . 34
A.4 Data transfer using the TCP-DATA service . 35
INDEX . 37
Bibliography . 38

Figure 1 – DLMS/COSEM as a standard Internet application protocol . 9
Figure 2 – Transport layers of the DLMS/COSEM_on_IP profile . 10
Figure 3 – Services of the DLMS/COSEM connection-less, UDP-based transport layer . 12

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

SIST EN 62056-4-7:2017
IEC 62056-4-7:2015  IEC 2015 – 3 –
Figure 4 – The wrapper protocol data unit (WPDU) . 15
Figure 5 – The DLMS/COSEM connection-less, UDP-based transport layer PDU (UDP-
PDU) . 15
Figure 6 – Services of the DLMS/COSEM connection-oriented,TCP-based transport
layer . 18
Figure 7 – The TCP packet format . 27
Figure 8 – TCP connection establishment . 28
Figure 9 – TCP disconnection . 29
Figure 10 – Data transfer using the DLMS/COSEM TCP-based transport layer . 30
Figure 11 – High-level state transition diagram for the wrapper sublayer . 31
Figure A.1 – TCP connection state diagram . 32
Figure A.2 – MSC and state transitions for establishing a transport layer and TCP
connection . 33
Figure A.3 – MSC and state transitions for closing a transport layer and TCP
connection . 34
Figure A.4 – Polling the TCP sublayer for TCP abort indication . 34
Figure A.5 – Sending an APDU in three TCP packets . 35
Figure A.6 – Receiving the message in several packets . 36

Table 1 – Reserved wrapper port numbers in the UDP-based DLMS/COSEM TL . 16

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

SIST EN 62056-4-7:2017
– 4 – IEC 62056-4-7:2015  IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

ELECTRICITY METERING DATA EXCHANGE –
THE DLMS/COSEM SUITE –

Part 4-7: DLMS/COSEM transport layer for IP networks

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The International Electrotechnical Commission (IEC) draws attention to the fact that it is claimed that compliance
with this International Standard may involve the use of a maintenance service concerning the stack of protocols on
which the present standard IEC 62056-4-7 is based.
The IEC takes no position concerning the evidence, validity and scope of this maintenance service.
The provider of the maintenance service has assured the IEC that he is willing to provide services under
reasonable and non-discriminatory terms and conditions for applicants throughout the world. In this respect, the
statement of the provider of the maintenance service is registered with the IEC. Information may be obtained from:

DLMS User Association
Zug/Switzerland
www.dlms.com

---------------------- Page: 10 ----------------------

SIST EN 62056-4-7:2017
IEC 62056-4-7:2015  IEC 2015 – 5 –
International Standard IEC 62056-4-7 has been prepared by IEC technical committee 13:
Electrical energy measurement and control.
This first edition cancels and replaces IEC 62056-47 published in 2006. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) This standard is applicable now both for IP4 and IPv6 networks;
b) Latest editions of the IEC 62056 suite are referenced.
c) DLMS/COSEM IANA-registered port numbers added.
The text of this standard is based on the following documents:
CDV Report on voting
13/1570/CDV 13/1595/RVC

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62056 series, published under the general title Electricity metering
data exchange – The DLMS/COSEM suite, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site 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.

---------------------- Page: 11 ----------------------

SIST EN 62056-4-7:2017
– 6 – IEC 62056-4-7:2015  IEC 2015
INTRODUCTION
This standard specifies the DLMS/COSEM transport layer for IP (IPv4 or IPv6) networks. It
shall be read together with IEC 62056-9-7:2013, Electricity metering data exchange – The
DLMS/COSEM suite – Part 9-7: Communication profile for TCP-UDP/IP networks.

---------------------- Page: 12 ----------------------

SIST EN 62056-4-7:2017
IEC 62056-4-7:2015  IEC 2015 – 7 –
ELECTRICITY METERING DATA EXCHANGE –
THE DLMS/COSEM SUITE –

Part 4-7: DLMS/COSEM transport layer for IP networks



1 Scope
This part of IEC 62056 specifies a connection-less and a connection oriented transport layer
(TL) for DLMS/COSEM communication profiles used on IP networks.
These TLs provide OSI-style services to the service user DLMS/COSEM AL. The connection-
less TL is based on the Internet Standard User Datagram Protocol (UDP). The connection-
oriented TL is based on the Internet Standard Transmission Control Protocol (TCP).
The DLMS/COSEM TL consists of the UDP or TCP transport layer TCP and an additional
sublayer, called wrapper.
Annex A shows how the OSI-style TL services can be converted to and from UDP and TCP
function calls.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050-300:2001, International Electrotechnical Vocabulary (IEV) – Electrical and
electronic measurements and measuring instruments – Part 311: General terms relating to
measurements − Part 312: General terms relating to electrical measurements − Part 313:
Types of electrical measuring instruments − Part 314: Specific terms according to the type of
instrument
IEC TR 62051:1999, Electricity metering – Glossary of terms
IEC TR 62051-1:2004, Electricity metering – Data exchange for meter reading, tariff and load
control – Glossary of terms – Part 1: Terms related to data exchange with metering equipment
using DLMS/COSEM
IEC 62056-5-3:2013, Electricity metering data exchange – The DLMS/COSEM suite –
1
Part 5-3: DLMS/COSEM application layer
IEC 62056-6-2:2013, Electricity metering data exchange – The DLMS/COSEM suite –
2
Part 6-2: COSEM interface classes
______________
1
Edition 2 of IEC 62056-5-3 to be published.
2
Edition 2 of IEC 62056-6-2 to be published.

---------------------- Page: 13 ----------------------

SIST EN 62056-4-7:2017
– 8 – IEC 62056-4-7:2015  IEC 2015
IEC 62056-9-7:2013, Electricity metering data exchange – the DLMS/COSEM suite –
Part 9-7: Communication profile for TCP-UDP/IP networks
STD 0006, User Datagram Protocol. Edited by Jon Postel, August 1980. Available from:
http://www.faqs.org/rfcs/std/std6.html
STD 0007, Transmission Control Protocol. Edited by Jon Postel, September 1981. Available
from: http://www.faqs.org/rfcs/std/std7.html
NOTE See also Bibliography for other related Internet RFCs.
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-300,
IEC TR 62051 and IEC TR 62051-1 apply as well as the following:
3.1.1
application process
an element within a real open system which performs the information processing for a
particular application
[SOURCE: ISO/IEC 7498-1: 1994, 4.1.4]
3.1.2
application entity
system-independent application activities that are made available as application services to
the application agent, e.g., a set of application service elements that together perform all or
part of the communication aspects of an application process
3.2 Abbreviations
APDU Application Layer Protocol Data Unit
AL  Application Layer
AP  Application Process
AE  Application Entity
COSEM COmpanion Specification for Energy Metering
DHCP Dynamic Host Configuration Protocol
DLMS Device Language Message Sepcification
COSEM_on_IP The TCP-UDP/IP based COSEM communication profile
FTP  File Transfer Protocol
HTTP  HyperText Transfer Protocol
IANA  Internet Assigned Numbers Authority
IP  Internet Protocol
PDU  Protocol Data Unit
PAR  Positive Acknowledgement with Retransmission
SNMP Simple Network Management Protocol
TCP  Transmission Control Protocol
TFTP  Trivial File Transfer Protocol
TL  Transport Layer
UDP  User Datagram Protocol

---------------------- Page: 14 ----------------------

SIST EN 62056-4-7:2017
IEC 62056-4-7:2015  IEC 2015 – 9 –
WPDU Wrapper Protocol Data Unit
4 Overview
In the DLMS/COSEM_on_IP profiles, the DLMS/COSEM AL uses the services of one of these
TLs, which use then the services of the Internet Protocol (IP) network layer to communicate
with other nodes connected to the abstract IP network.
When used in these profiles, the DLMS/COSEM AL can be considered as an Internet standard
application protocol (like the well-known HTTP, FTP or SNMP) and it may co-exist with other
Internet application protocols, as it is shown in Figure 1.
Application / Data models
WEB COSEM
Files
pages interface model
Standard application protocols

DLMS/COSEM AL
...
e.g. FTP e.g. HTTP
ACSE + xDLMS
Wrapper
Internet Transport Layer (UDP or TCP)
Internet Network Layer (IP)
Convergence / Adaptation Layer
Data Link Layer
Physical Layer
IEC

Figure 1 – DLMS/COSEM as a standard Internet application protocol
For DLMS/COSEM, the following port numbers have been registered by the IANA. See
http://www.iana.org/assignments/port-numbers.
• dlms/cosem 4059/TCP DLMS/COSEM
• dlms/cosem 4059/UDP DLMS/COSEM
As the DLMS/COSEM AL specified in IEC 62056-5-3 uses and provides OSI-style services, a
wrapper has been introduced between the UDP/TCP layers and the DLMS/COSEM AL.
Therefore, the DLMS/COSEM TLs consist of a wrapper sublayer and the UDP or TCP TL. The

---------------------- Page: 15 ----------------------

SIST EN 62056-4-7:2017
– 10 – IEC 62056-4-7:2015  IEC 2015
wrapper sublayer is a lightweight, nearly state-less entity: its main function is to adapt the
OSI-style service set, provided by the DLMS/COSEM TL, to UDP or TCP function calls and
vice versa.
In addition, the wrapper sublayer has the following functions:
• it provides an additional addressing capability (wPort) on top of the UDP/TCP port;
• it provides information about the length of the data transported. This feature helps the
sender to send and the receiver to recognize the reception of a complete APDU, which
may be sent and received in multiple TCP packets.
As specified in IEC 62056-9-7:2013, Clause 6, the DLMS/COSEM AL is listening only on one
UDP or TCP port. On the other hand, as defined in IEC 62056-6-2:2013, 4.7, a DLMS/COSEM
physical device may host several client APs or server logical devices. The additional
addressing capability provided by the wrapper sublayer allows identifying these APs.
The structure of the DLMS/COSEM TL and their place in COSEM_on_IP is shown in Figure 2.

COSEM Application Process
COSEM Application Process
TCP Connection
Manager
COSEM application COSEM application
layer services layer services
DLMS/COSEM Application Layer DLMS/COSEM Application Layer
DLMS/COSEM
DLMS/COSEM connectionless TCP-
connection-oriented
transport services ABORT.ind
transport services
UDP-DATA.req/.ind/(.cnf)
TCP-DATA.req/.ind/(.cnf)
DLMS/COSEM UDP-based Transport Layer DLMS/COSEM TCP-based Transport Layer
Wrapper Wrapper
TCP function calls
UDP function calls
active/passive OPEN,
SEND, RECEIVE
SEND, RECEIVE
Internet UDP Internet TCP


IP and lower layers
IP and lower layers
a) the UDP-based profile b) the TCP-based profile
IEC
Figure 2 – Transport layers of the DLMS/COSEM_on_IP profile
The service user of both the UDP-DATA and the TCP-DATA services is the DLMS/COSEM
AL. On the other hand, the service user of the TCP-CONNECT and TCP-DISCONNECT
services is the TCP Connection Manager Process. The DLMS/COSEM TCP-based TL also
provides a TCP-ABORT service to the service user DLMS/COSEM AL.
5 The DLMS/COSEM connection-less, UDP-based transport layer
5.1 General
The DLMS/COSEM connection-less TL is based on the User Datagram Protocol (UDP) as
specified in STD 0006.
TCP-CONNECT services
TCP-DISCONNECT services

---------------------- Page: 16 ----------------------

SIST EN 62056-4-7:2017
IEC 62056-4-7:2015  IEC 2015 – 11 –
UDP provides a procedure f
...