Each host that could have multiple discoverable applications installed should have a standalone LocalDiscoveryServer installed. The LocalDiscoveryServer shall expose one or more Endpoints which support the FindServers and GetEndpoints services defined in OPC 10000-4 for all applications on the host. In addition, the LocalDiscoveryServer shall provide at least one Endpoint which implements the RegisterServer service for these applications .
In systems (usually embedded systems) with exactly one Server installed this Server may also be the LDS (see 4.2.3).
An LDS-ME will announce all applications that it knows about on the local MulticastSubnet. In order to support this, a LocalDiscoveryServer supports the RegisterServer2 Service defined in OPC 10000-4. For backward compatibility a LocalDiscoveryServer also supports the RegisterServer Service which is defined in OPC 10000-4.
Each host with OPC UA Applications (Clients and Servers) installed should have a LocalDiscoveryServer with a MulticastExtension.
The MulticastExtension incorporates the functionality of the mDNS Responder described in the Multicast DNS (mDNS) specification (see mDNS). In addition the LocalDiscoveryServer that supports the MulticastExtension supports the FindServersOnNetwork Service described in OPC 10000-4.