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FIX 4.4 Protocol Overview

The Financial Information eXchange (FIX) protocol is an open, widely used messaging standard for the electronic exchange of trade-related information.\ Version FIX 4.4, remains one of the most adopted versions across the financial industry.

Key Features

  • Transport-independent: FIX defines the message structure, not the transport. TCP/IP is most common, but other transports are possible.
  • Human-readable format: Messages are ASCII-based key--value pairs (tag=value).
  • Low latency: Optimized for fast and reliable real-time trading communication.
  • Extensible: Supports custom tags while keeping compatibility with the standard.
  • Wide adoption: Used by brokers, exchanges, asset managers, and banks worldwide.

Message Structure

Each FIX message is composed of fields separated by the delimiter SOH (ASCII 0x01):

8=FIX.4.4|9=176|35=D|49=CLIENT1|56=BROKER1|34=215|52=20250912-15:32:10.123|
11=12345|21=1|55=EUR/USD|54=1|38=100000|40=2|44=1.2345|59=0|10=128|

Where: - 8 -- BeginString (FIX.4.4) - 9 -- BodyLength - 35 -- MsgType (e.g., D = New Order -- Single) - 49 -- SenderCompID - 56 -- TargetCompID - 11 -- ClOrdID - 55 -- Symbol - 54 -- Side (1 = Buy, 2 = Sell) - 38 -- OrderQty - 40 -- OrdType (2 = Limit) - 44 -- Price - 59 -- TimeInForce (0 = Day) - 10 -- CheckSum

Common Message Types in FIX 4.4

  • D -- New Order -- Single\
  • F -- Order Cancel Request\
  • G -- Order Cancel/Replace Request\
  • 8 -- Execution Report\
  • 9 -- Order Cancel Reject\
  • A -- Logon\
  • 5 -- Logout\
  • 0 -- Heartbeat\
  • 1 -- Test Request

Sessions in FIX

FIX sessions are managed via session-level messages: - Logon (A) -- starts the session - Heartbeat (0) -- keeps the session alive - Test Request (1) -- checks connectivity - Resend Request (2) -- recovers lost messages - Sequence Reset (4) -- resets message sequence - Logout (5) -- ends the session

Each session is identified by: - SenderCompID - TargetCompID - Message sequence numbers

Advantages of FIX 4.4

  • Standardization: Industry-wide acceptance ensures interoperability.
  • Transparency: Clear, auditable trade messages.
  • Flexibility: Supports multiple asset classes -- equities, FX, derivatives, fixed income.
  • Extensibility: Custom tags allow broker-specific functionality.
  • Backward compatibility: FIX 4.4 is compatible with many 4.x implementations.

Limitations

  • Verbose compared to binary protocols (e.g., FIX/FAST, FIXP).
  • Requires careful session management (sequence numbers, heartbeats).
  • Less suited for ultra-low latency environments compared to newer protocols.

Resources

Next Steps

In this documentation you will find: - Implementation details of FIX-like commands in the Commands class. - Mapping of internal API methods to FIX 4.4 message types. - Examples of usage and integration with trading systems.