The illustration is for Replication Request Mode for Dataguard.
It shows squares for two data centers labeled Local and Remote. Each data center square has the database DB-a and one recovery appliance, labeled RA-x and RA-y.
The local database has an arrow going to its RA-x for backups, and second bi-direction arrow going to the remote database, labeled Data Guard Redo.
The local RA-x has an arrow to RA-y in Munich, indicating REQUEST_ONLY=TRUE.
The remote RA-y has an arrow going to the local RA-x for RA Catalog Reconsile.
The remote RA-y has an arrow to the local RA-x, indicating Backups Replicated to Synch with Current State.