The discovery process allows applications to find other applications on the network and then discover how to connect to them. Note that this discussion builds on the discovery related concepts defined in OPC 10000-4. Discoverable applications are generally Servers, however, some Clientswill support reverse connections as described in OPC 10000-6and want Serversto be able to discover them.
Clientsand Serverscan be on the same host, on different hosts in the same subnet, or even on completely different locations in an administrative domain. The following clauses describe the different configurations and how discovery can be accomplished.
The Discovery Servicesare specified in OPC 10000-4. They are implemented by individual Serversand by dedicated DiscoveryServers. The following dedicated DiscoveryServersprovide a way for applications to discover registered OPC UA applications in different situations:
- A LocalDiscoveryServer(LDS) maintains discovery information for all applications that have registered with it, usually all applications available on the host that it runs on.
- A LocalDiscoveryServerwith the MulticastExtension(LDS-ME) maintains discovery information for all applications that have been announced on the local MulticastSubnet.
- A GlobalDiscoveryServer(GDS) maintains discovery information for applications available in an administrative domain.