Server to Server interactions in the Client Server model are interactions in which one Server acts as a Client of another Server. Server to Server interactions allow for the development of servers that:
- exchange information with each other on a peer-to-peer basis, this could include redundancy or remote Servers that are used for maintaining system wide type definitions (see Figure 6),
- are chained in a layered architecture of Servers to provide:
- aggregation of data from lower-layer Servers,
- higher-layer data constructs to Clients, and
- concentrator interfaces to Clients for single points of access to multiple underlying Servers.
Figure 6 illustrates interactions between Servers.
Figure 6 – Peer-to-peer interactions between Servers
Similar peer-to-peer interactions can also be accomplished using the OPC UA PubSub model where each peer Application is both a Publisher and a Subscriber.
Figure 7 extends the previous example and illustrates the chaining of Servers together for vertical access to data in an enterprise.