ISO 3531-1:2022

INTERNATIONAL ISO
STANDARD 3531-1
First edition
2022-04
Financial services — Financial
information eXchange session layer —
Part 1:
FIX tagvalue encoding
Reference number
© ISO 2022
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 FIX tagvalue message syntax . 2
4.1 Character encoding . 2
4.2 Field syntax . 2
4.2.1 Tag (field identifier) . 2
4.2.2 Tag delimiter . 2
4.2.3 Field value . 2
4.2.4 Field delimiter . 2
4.2.5 Well-formed field. 2
4.2.6 Example of a FIX tagvalue message . 3
4.3 Message structure . 3
4.3.1 General . 3
4.3.2 Message type . 3
4.3.3 Field presence . 3
4.3.4 Field sequence . . 3
4.3.5 Message delimiter . 4
4.3.6 Components . 4
4.3.7 Groups and repeating groups . . 4
4.3.8 Encoded data fields . 6
5 Standard header and trailer .7
5.1 General . 7
5.2 Standard header . 7
5.2.1 General . 7
5.2.2 Body length calculation . 7
5.2.3 Standard header definition . 7
5.3 Standard trailer . 8
5.3.1 Standard trailer definition . 8
5.3.2 Checksum . 8
6 FIX tagvalue datatypes.8
6.1 General . 8
6.2 Value space . 8
6.3 Lexical space . 8
6.3.1 General . 8
6.3.2 Character encoding . 9
6.3.3 Lexical encoding for FIX datatypes . 9
6.3.4 XML data .15
7 Code sets .15
7.1 General . 15
7.2 Underlying value type .15
7.2.1 General .15
7.2.2 Internal code sets .15
7.2.3 External code sets .15
Annex A (informative) Checksum calculation .16
Bibliography .17
iii
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
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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
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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 FIX Trading Community (as FIX Session Layer Technical Specification)
and drafted in accordance with its editorial rules. It was assigned to Technical Committee ISO/TC 68,
Financial services, Subcommittee SC 9, Information exchange for financial services, and adopted under
the “fast-track procedure”.
A list of all parts in the ISO 3531 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.
iv
Introduction
FIX session protocol was written to be independent of any specific communications protocol (e.g. X.25,
async, TCP/IP) or physical medium (e.g. copper, fibre, satellite) chosen for electronic data delivery. It
offers a reliable stream where a message is delivered once and in order. The FIX session layer is designed
to survive and resume operation in the event of the loss of transport level connections caused by any
type of failure, including network outage, application failure or computer hardware failures.
The session layer is concerned with the ordered delivery of data while the application level defines
business-related data content. This document focuses on the ordered delivery of data using the “FIX
session protocol”.
The FIX session protocol is implemented using the FIX tagvalue encoding syntax for the standard
header, standard trailer and the session level messages which make up the FIX session protocol. It is
possible to send messages encoded using other FIX-defined encodings (e.g. FIXML, SBE, JSON, GPB,
ASN.1) or other non-FIX-defined encodings (e.g. XML, FpML, ISO 20022 XML, JSON).
The Financial Information eXchange tagvalue encoding is the original encoding used for FIX messages.
The tagvalue encoding is the encoding used by the FIX session layer; it corresponds to the Presentation
Layer of the ISO Open Systems Interconnection model. The encoding uses an integer number known as
a tag to identify the field, followed by the “=” character (hexadecimal 0x3D), then the value of that field
encoded in the ISO/IEC 8859-1 character set. Each tagvalue pair is separated by the Start of Heading
control character (hexadecimal value 0x01), which is defined by ISO/IEC 6429. The tagvalue
encoding also
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