The UA AddressSpace supports references between Nodes that exist in different Server AddressSpace spaces. These references are specified with a ExpandedNodeId that includes the URI of the Server which owns the Node. A Client that wishes to follow a reference to an external Node should map the ApplicationUri onto an EndpointUrl that it can use. A Client can do this by using the GlobalDiscoveryServer that knows about the Server. The process of connecting to a Server containing a remote Node is illustrated in Figure 36.
Figure 36 – Following References to Remote Servers
If a GDS not available Client may use other strategies to find the Server associated with the URI.