If you finally choose to work through a Participant Aggregator you can see below the list of them with their functionalities (also Portal IAG as an Aggregator).
The following tables show a comprehensive list of all the Aggregators as Service Providers in NDC.
Please, note that whenever a new Aggregator is added up to the list and/or an existing Aggregator includes any new functionality/Service, the downloadable PDF is updated.
Following, the downloadable version containing the above-mentioned information: