The image shows an OCI Region with an Availability Domain containing a VCN. The VCN consists of a

Subnet A Server hosting one Iris and three Hemera instances.
Subnet B Database hosting Oracle Exadata Database Service on Dedicated Infrastructure. The Hemera instances are connected to the Oracle Exadata Database Service on Dedicated Infrastructure.

The VCN is connected to an Oracle Services Network via a Service Gateway.

External meters connect to Customer Premises Equipment. The On-premises setup is connected to Iris via Site to Site VPN or FastConnect through a DRG.