ZagTrader

FIX Protocol Tag 8: BeginString

Identifies the start of a new message and the protocol version, for example FIX.4.2, FIX.4.4 or FIXT.1.1 for FIX 5.0 sessions. It is always the first field of a message and is never encrypted.

Tag number
8
Data type
STRING
FIX versions
FIX 4.0 to 5.0 SP2 and FIXT 1.1
Location
Standard header

Practical notes on BeginString

BeginString names the protocol version of the session. It is always the first field of every message.

  • FIX 4.x sessions send FIX.4.0 to FIX.4.4. FIX 5.0, 5.0 SP1 and 5.0 SP2 sessions send FIXT.1.1, the session-layer version, and give the application version in DefaultApplVerID (1137) on the Logon.
  • The value must match the session configuration on both sides. Engines use it, together with the CompIDs, to find the session a message belongs to.

Common mistakes

  • FIX.5.0SP2 is not a valid BeginString. Use FIXT.1.1.
  • A Logon with the wrong BeginString is refused; QuickFIX answers with a Logout reading "Incorrect BeginString".

Changes between FIX versions

  • FIXT.1.1 arrived with FIX 5.0, when the session layer was split from the application messages.

See also:FIXT.1.1 and ApplVerID errorsFIXT.1.1 and ApplVerID explained

Tag 8 in each FIX version

Values and message usage as defined in a specific version.

Data type

STRING: Text of printable characters. It cannot contain the SOH delimiter.

Valid values

6 enumerated values across all FIX versions.

ValueMeaning
FIX.4.2FIX 4.2
FIX.4.4FIX 4.4
FIXT.1.1FIXT 1.1 (session layer for FIX 5.0 and later)
FIX.4.0FIX 4.0
FIX.4.1FIX 4.1
FIX.4.3FIX 4.3

Example

8=FIX.4.4

Illustrative value. In a message, fields are separated by the SOH character (0x01), often shown as | or ^ in logs.

Decode a message with this tag

Message types that use tag 8

BeginString belongs to the standard message header, which every FIX message carries, so it is not listed against individual message types.

Field and message data comes from the QuickFIX data dictionaries for FIX 4.0 to 5.0 SP2 and FIXT 1.1, used under the QuickFIX Software License. This product includes software developed by quickfixengine.org (http://www.quickfixengine.org/). Enumerated value names are converted to plain text for reading.