13.2.1 Locating Server via GDS

If a GDS address (GlobalDiscoveryServers) is defined (see 6.7.2), the GDS is queried to find the Server. If an array of GDS addresses is provided each GDS in the list is tried until the Server is located. If the Server is not found, an error could be reported or the server could be contacted directly.

The Server is located following the standard procedure as defined in OPC 10000-12, i.e., QueryApplications, GetEndpoints, OpenSecureChannel, CreateSession and ActivateSession on the Server Address with the specified SecurityMode (see 9.2.2 for the description of the provided Server information).

Figure 64 - Client connection process

If the Server is the same Server that the ConnectionManager resides on, the EstablishConnections Method may be invoked by vendor-specific means, and all portable node identifiers can be resolved locally.

The Session established by the ConnectionManager shall support the use of authentication and/or encryption. This includes:

Application Authentication based on security mode and policy

The use of Roles (this may require user authentication or specific ApplicationInstance certificates)

If SecurityPolicyUri contains an empty or null string, the EndpointDescription on the Server with the highest SecurityLevel of the ones supported by the ConnectionManager and matching the requested SecurityMode (see 9.2.2) shall be chosen. If it is not an empty or null string, the EndpointDescription matching the requested SecurityMode and SecurityPolicyUri (see 9.2.2) shall be chosen. The complete process, including NodeId resolution, is illustrated in Figure 64.