The image shows the architecture of a multi-region NoSQL setup. There are three regions in this example:

London region, referred as Region 1 with four shards.
Frankfurt region, referred as Region 2 with three shards.
Dublin region, referred as Region 3 with two shards.

Each region has a Cross-Region Service. All the regions are connected with each other using the Cross-Region Service via NoSQL Streams. There is one inbound and one outbound NoSQL stream between every two regions, that is, between London and Frankfurt, Frankfurt and Dublin, and Dublin and London.