OPC UA: what does an LDS installation do?
Considering these 2 settings:
- Machine with 3 OPC UA servers.
- Machine with 3 OPC UA and LDS servers.
What's the difference in functionality? In particular, I would like to know:
- Is LDS required?
- What is the practical difference between discovering the server, connecting it, and connecting directly to the server endpoint without discovery?
- What does an LDS installation do?
(All of this, indicating the relevant OPC UA specifications, if applicable, please)
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Is LDS required?
No, installing LDS is optional. Especially on small / embedded devices, you might not even be able to install anything other than the OPC UA server.
What is the practical difference between discovering the server, connecting it to it, and connecting directly to the server endpoint without being discovered?
With LDS running on the standard port (4840), you can discover all of the servers on a computer without knowing their endpoint URLs. Without LDS, there is no way to connect to the server without knowing the URL.
As noted, the presence of LDS makes discovery (very) a little slower, as you need to establish a connection to both the LDS and the server.
If there is only one server running on the computer, you can set that server's port to 4840, so clients discovering on the computer find the server without needing to know the configured port.
What does an LDS installation do?
It just lets you discover all the servers running on the computer without knowing all of its different endpoint URLs.
Future releases will contain enhancements that pass this information through Zeroconf, so each LDS will have a list of all OPC UA servers on the local network.
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