AS4 (Applicability Statement 4) is a protocol for standardized message exchange between gas transmission system operators and their counterparties in Europe. It is used for balancing and congestion management. Unlike the AS2 (Applicability Statement 2) protocol previously used for these processes, AS4 is based on web services. The data exchange format used is Edig@s-XML with the following standard messages:
- NOMINT (balancing)
- NOMRES (balancing) and
- CHACAP (congestion management)
Based on EU Regulation 2015/703 of 30 April 2015 establishing a network code with rules for interoperability and data exchange, the AS4 and Edig@s-XML message formats are mandatory for these communication processes in gas trading – in many European countries, such as Sweden, Germany, Denmark, and Italy, since the end of 2017 or the beginning of 2018:
- Nomination limit for congestion management (CHACAP)
- Nomination, re-nomination, and confirmation thereof for balancing group management (NOMINT, NOMRES)
This applies to all market participants who submit nominations to the respective transmission system operators at border or market area transition points, and these nominations are matched. receive or a capacity inventory report concerning these points.
In this context, ENTSOG (European Network of Gas Transmission System Operators) has defined a specific subset that details communication via AS4 and standardizes the connection of the various market participants (AS4 Usage Profile).