FIX Session Protocol submitted to ISO

The FIX Global Technical Committee (GTC) is pleased to announce the submission of the FIX tagvalue encoding standard and the FIX session layer standard (including session testcases) to the International Organization for Standardization (ISO) for standardization. The submission has been made to the ISO/TC68/SC 9 subcommittee (Information exchange for financial services) as a Draft International Standard (DIS). ISO 3531 has been assigned to identify the FIX Session Protocol standard.


The FIX tagvalue encoding and the FIX session protocol were defined as part of the very first published FIX Version 2.7 back in 1994. The financial industry has enjoyed the benefits of these technical standards for a few decades now. They are well proven and used on a global scale across asset classes.

ISO standards are recognized and accepted globally. Many countries and regulators have expressed a strong preference for ISO based standards in recent years. FIX is the de facto global standard for electronic trading. It seems appropriate to have our global de facto standards recognized as ISO standards.

FIX tagvalue encoding (ISO 3531-1)

FIX 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 8859-1 character set. Each tagvalue pair is separated by the Start of Heading control character <SOH> (hexadecimal value 0x01), which is defined by ISO 6429:1992. The tagvalue encoding also supports the encoding of binary and multibyte character data in certain encoded data fields that are preceded by a Length field.

The GTC has refactored and enhanced the original specification without making any changes to the standards themselves. The FIX datatypes are now described in terms of their value space as well as in terms of their lexical space, i.e. the actual wire format. Multiple sequence diagrams have been added to the FIX session layer specification.

The technical specification is available for download or as an online version.

FIX session layer (ISO 3531-2)

The FIX session layer provides reliable and recoverable messaging for electronic trading. The protocol is intended for use by asset managers, trading firms, brokerages, trading venues, clearing houses, custodians, depositories, asset servicers, among others involved in the trading life cycle activities of a wide range of financial instruments. The FIX session layer functionality is a realization of the ISO/IEC 7498-1:1994 Open System Interconnection basic reference model level 5 session layer.

The FIX session layer standard has been integrated into a single refactored volume with  multiple session profiles, which describe specific realizations of the FIX session layer. The FIX session layer standard covers the session protocols defined as part of the FIX application versions FIX 4.2 and FIX 4.4 as well as the specification of FIXT. A new session profile called Lightweight FIXT has been added which simplifies the standard for those that do not require application message recovery by the session layer..

The technical specification is available for download or as an online version.

FIX session testcases (ISO 3531-3)

The FIX session testcases provide a set of compliance tests applicable to all versions of the FIX session layer standard. They were last revised September 20, 2002 at which time FIX version 4.3 with Errata 20020930 was the latest version of the FIX Protocol. The testcases are from the perspective of the FIX system being tested. The FIX system receives the “Condition / Stimulus” and is expected to take the appropriate action as defined by “Expected Behavior”.

The technical specification is available for download or as an online version.

ISO submission process

The FIX Trading Community is a liaison “A” organization to the ISO TC 68 committee for financial services. FIX also is a liaison “A” organization to the ISO TC 68/SC 9 subcommittee on information exchange and ISO TC 68/SC 8 subcommittee on reference data. The ISO directives, the governance rules of ISO, permits national standards bodies and liaison organizations, such as FIX, to submit existing non-ISO developed standards for inclusion as international standards. The ISO directives provide for a “fast track” submission process. The “fast track” process only bypasses the working group phase of the process. The reasoning being that the standard is already developed and in use, what remains is to have the standard balloted by national standards body members of ISO for approval. The overall approval process includes document preparation and translation into the ISO supported languages, balloting by national standards bodies, then publication. This process is expected to take between six months to one year to complete.

Impact on the FIX Trading Community

In practical terms for the FIX Trading Community there is an immediate benefit of higher quality standards documents that should lead to improved interoperability between implementations because vagueness and ambiguity has been reduced. The governance and evolution of the standard remains within the FIX Trading Community. ISO requires a five-year systematic review of each standard, which of course will require FIX Trading Community involvement and leadership. It is hoped that the adopters of FIX standards will benefit from the certainty of the ISO standardization process and the value of ISO branding.

The FIX application layer messages (the business messages) are not being submitted for ISO standardization at this time. A separate long-term effort, which has been ongoing since 2007, to find a path for inclusion of the FIX application layer messages as part of the ISO 20022 messaging standard continues. The FIX Trading Community remains committed to harmonization and interoperability with the ISO 20022 messaging standard.