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During phase 2 of the AS2-AS4 Theme release (TR AS2-AS4) we encountered problems when market parties tried to migrate from the AS2 protocol to the AS4 protocol. Our investigation shows that the issue had been caused by a certain content type.

Investigation into cause of problem
We decided to temporarily halt the theme release back in February. This has given us enough time to investigate why the transition from AS2 to AS4 has not flowed smoothly. Before the investigation started, we thought the problems were being caused by differences between version 3.0 and version 3.5 of the ENTSO-G AS4 profile.

Difference in content type
Having analysed the two versions of the ENTSO-G Q&A, it appears there is only 1 difference between version 3.0 and version 3.5. And this difference is the content type, which relates to how messages are packaged for security purposes.

Gzip content used as basis
When constructing the Nexus central hub in 2017, a Q&A for AS4 has been consulted that had been compiled by European organisation ENTSO-G. This was done to identify the most commonly used content type. It transpired that content types Gzip and Octet-stream were both possible. Because the national grid operator for gas uses Gzip, a decision was made to opt for this content type when constructing the hub.

Transition to Octet-stream content
In 2016, ENTSO-G updated its Q&A for AS4. From that moment, only Octet-stream content was permitted. This means the hub must switch from Gzip content to Octet-stream content, in ENTSO-G AS4 profile version 3.0 as well as version 3.5. Unfortunately, this also applies to you as market party. Do you use Gzip content for your AS4 messages? Then you and other market parties will have to switch to Octet-stream in a controlled manner. Before making the switch, you will be given the opportunity to test whether everything works properly. The switch will be supervised by the project team of NEDU and EDSN, and will be supported by the system integrator.

Finalisation Request for Change
Because the switch to Octet-stream is mandatory, NEDU is working on a Request for Change (RFC) for issue TC034. This RFC must be finalised during the NEDU General Meeting of Members of 3 July 2019.

More information
If there are any new developments, we will inform you once again via the newsletter. If you have specific questions, please send them to

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