AS2 and AS4 EDI Protocol Comparison

AS2 has been one of the standards used for many years in the world of B2B integration. However, AS4 is increasingly being used, especially in e-invoicing, e-waybills, and international B2B projects.In this blog, I discuss the AS2 vs AS4 comparison in terms of architecture, security, operational ease, and future perspective.

What is AS2?

AS2 (Applicability Statement 2) is a protocol that enables secure B2B data transfer over HTTP/HTTPS. AS2 enhances security and enables real-time confirmation and processing. This increases transaction efficiency, making it a standard for EDI and other data transfers. AS2 supports all file types and offers message signing for authentication.AS2 increases traceability by requiring Message Status Notifications (MDN). These notifications confirm successful transfers and full message delivery. It offers options including synchronous and asynchronous feedback.

What is AS4?

AS4 is a modernized version of AS2 and is based on the OASIS + ebMS 3.0 standards. AS4's SOAP and Web Services-based structure is its most important distinguishing feature from AS2. It uses WS-Security features such as message encryption, digital signatures, acknowledgments, and retry mechanisms, and supports large attachments.

AS2 vs AS4: Security Comparison

While both encryption and digital signatures are available, certificate management is simpler in AS2 and more complex in AS4.AS4 is more robust, especially in projects with legal binding and audit requirements.

Message Delivery and Reliability (MDN vs Reliable Messaging) 

• AS2

o    MDN (Sync / Async)o   MDN parse errors are commono    The question “Did the MDN arrive or not?” creates operational overhead

• AS4

o    Reliable Messaging (Retry, Sequence, Acknowledgement)o    Similar to MDN but with a more robust structureo    More reliable for large-volume messages

What Changes in AS4?

• Less “manual intervention”
• Clearer error messages
• Stricter compliance with standards
• But: setup & configuration is more difficult

Should You Choose AS2 or AS4? 

Choose AS2:

• Existing PO system is in place
• Counterparty uses AS2
• EDI / retail / logistics integration
• Rapid deployment is important
• Low/medium volume

Choose AS4:

• Regulatory (e-invoice, e-delivery) projects
• European / Peppol compliance
• High volume & critical messaging
• Long-term architectural goal
• Integration Suite or new platform plan exists

Will AS4 Replace AS2 in B2B Integration? 

AS2 is not dead, but it is starting to be seen as “legacy” in new projects.

• SAP's strategic focus: SAP Integration Suite + AS4
• European e-transformation projects: AS4 + Peppol
• AS4 is inevitable for companies transitioning from SAP PO to Integration Suite

In summary, if you have a system running on SAP PO today, AS2 still makes sense.But if you are building a new B2B architecture, especially if there are European regulations, AS4 may be a better investment in the long run.

AS2 vs AS4: Key Differences and Applications

The following table compares the AS2 and AS4 protocols in terms of architecture, message reliability, operational complexity, and application areas, clearly showing which standard is more suitable for which scenario.