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AS4 for Dummies - Part V: Are you ready for AS4?

This blog post series aims to provide an introduction to AS4, a recent B2B messaging standard. It provides the basic insights on how AS4 establishes a reliable and secure message exchange between trading partners. This is a jump start to get to know the ins and outs of the standard, as the specifications are quite complex to understand without any prior introduction.

If you are active in B2B/B2C messaging, then AS4 is definitely coming your way! Make sure you are prepared.

AS2 Comparison

As AS4 is inspired by AS2, both are often considered in message exchange over the internet. On a high level, they are very similar, however there are some key differences that you should be aware of in order to make a profound decision on this matter. Let’s have a look!

Common Characteristics

These are the most important common characteristics of AS2 and AS4:

  • Payload agnostic: both messaging protocols are payload agnostic, so they support any kind of payload to be exchanged: XML, flat file, EDI, HL7, PDF, binary…
  • Payload compression: AS2 and AS4 support both compression of the exchanged messages, in order to reduce bandwidth. It’s however done via totally different algorithms.
  • Signing and encryption: the two protocols support both signing and encryption of the exchanged payloads. It’s a trading partner agreement whether to apply it or not.
  • Non-repudiation: the biggest similarity is the way non-repudiation of origin and receipt are achieved. This is done by applying signing and using acknowledgement mechanisms.

Technology Differences

The common characteristics are established by using totally different technologies:

  • Message packaging: within AS2, the message packaging is purely MIME based. In AS4, this is governed by SOAP with Attachments, a combination of MIME and SOAP.
  • Security: AS2 applies security via the S/MIME specifications, whereas AS4’s security model is based on the well-known WS-Security standard.
  • Acknowledgements: in AS2 and AS4, acknowledgements are introduced to support reliable messaging and non-repudiation of receipt. In AS2 this is done by so-called Message Disposition Notifications (MDN), AS4 uses signed Receipts.

AS4 Differentiators

These are the main reasons why AS4 could be chosen, instead of AS2. If none of these features are applicable to your scenario, AS2 might be the best option as it is currently more known and widely adopted.

  • Support for multiple payloads: AS4 has full support for exchanging more than one business payload. Custom key/value properties for each payload are available.
  • Support for native web services: being built on top of SOAP with Attachments, AS4 offers native web service support. It’s a drawback that SwA is not supported out-of-the-box by .NET.
  • Support for pulling: this feature is very important if message exchange is required with a trading partner that cannot offer high availability or static addressing.
  • Support for lightweight client implementations: three conformance clauses are defined within AS4, so client applications must not support immediately the full AS4 feature stack.
  • Support for modern crypto algorithms: in case data protection is an important aspect, AS4 can offer more modern and less vulnerable crypto algorithms.
  • Support for more authentication types: AS4 supports username-password and X.509 authentication. There is also a conformance clause on SAML authentication within AS4.

Getting Started

Are you interested to learn more on AS4?

From an architecture / specifications perspective it’s good to have a look at the related OASIS standards. This includes the ebMS 3.0 Core Specifications and the AS4 profile of ebMS 3.0. In case you are more interested on how an AS4 usage profile could be described between trading partners, this ENTSOG AS4 Usage Profile is a great example.

If you’re more developer oriented, it’s good to have a look at Holodeck B2B. It is a java-based open-source software that fully supports the AS4 profile. Some sample files provide you a head start in creating your first AS4 messages. Unfortunately SOAP with Attachments or AS4 is not supported out-of-the-box within Microsoft .NET.

Can we help you?

Codit is closely involved with AS4. It is represented in the OASIS ebXML Messaging Services TC by Toon Vanhoutte, as a contributing member. In this way, Codit keeps a close eye on the evolution of the AS4 messaging standard. Throughout several projects, Codit has gained an extended expertise in AS4. Do not hesitate to contact us if you need any assistance on architecture, analysis or development of your AS4 implementation.

Within our R&D department, we have developed a base .NET library with support for the main AS4 features. In the demo for Integration Monday, this library was plugged into the BizTalk Server engine in order to create AS4 compatible messages. At the time of writing, Codit is defining its AS4 offering. If you would like to be informed about the strategy of Codit when it comes to AS4, please reach out to us. We will be more than happy to exchange ideas.

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