The Financial Information eXchange (FIX) protocol has been the backbone of electronic trading since the 1990s. As markets evolved, so did FIX—and the jump from FIX 4.4 to FIX 5.0 represents one of the most significant architectural changes in the protocol's history.
The Evolution of FIX
FIX 4.x versions (4.0 through 4.4) were incremental improvements that maintained backward compatibility. Each version added new message types and fields, but the fundamental architecture remained the same. FIX 4.4, released in 2003, became the de facto standard for most trading venues.
FIX 5.0, released in 2006, took a different approach. Rather than just adding features, FIX 5.0 restructured the protocol to be more modular, extensible, and better suited for modern trading environments.
Key Architectural Differences
Transport Independence
FIX 4.x versions bundled the session layer with the application layer. In FIX 5.0, these are separated. The session layer is handled by FIXT (FIX Transport), allowing the application messages to be transported over different protocols.
This means you can use FIX 5.0 application messages over TCP, UDP multicast, or even proprietary binary protocols—giving firms more flexibility in optimizing for their specific latency and throughput requirements.
Message Structure
FIX 5.0 introduced a more modular message structure with components and component groups. This makes messages more organized and easier to extend without breaking compatibility.
For example, the Parties component in FIX 5.0 standardizes how counterparty information is represented across all message types, whereas FIX 4.4 had different approaches in different messages.
Performance Considerations
While FIX 5.0 messages can be slightly larger due to better structuring, the transport independence allows for optimizations that weren't possible in FIX 4.4:
- •Binary encoding: FIX 5.0 messages can be encoded in binary formats like SBE (Simple Binary Encoding), reducing message size by 50-70%
- •Multicast support: Market data can be distributed via UDP multicast, reducing network load
- •Session multiplexing: Multiple logical sessions over a single TCP connection
Migration Considerations
Migrating from FIX 4.4 to FIX 5.0 requires careful planning. Key considerations include:
- •Message Mapping: Many FIX 4.4 messages have direct equivalents in FIX 5.0, but some fields have moved or been renamed
- •Session Management: The FIXT session layer uses different message types than FIX 4.4
- •Testing Requirements: Counterparty certification is typically required when changing FIX versions
- •Dual Support Period: Plan for a period where you support both versions during migration
Why Modern Exchanges Choose FIX 5.0
New exchanges like TXSE are standardizing on FIX 5.0 for several reasons:
- •Future-proofing: FIX 5.0's modular design makes it easier to add new functionality
- •Performance options: Transport independence enables latency optimizations
- •Industry direction: FIX 5.0 is the recommended standard by FIX Trading Community
- •Better security: FIX 5.0 includes improved security extensions
Conclusion
While FIX 4.4 remains widely used, the industry is steadily moving toward FIX 5.0. If your firm is still running FIX 4.4 infrastructure, now is a good time to evaluate a migration—especially if you're planning to connect to new venues like TXSE.