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Usage of namespace index 1

March 10, 2022
17:49, EET

rocket science

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March 16, 2017

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Hi all,

according to the OpcUa reference (https://reference.opcfoundation.org/v104/Core/docs/Part5/6.3.1/) the namespace with index 0 and 1 are reserved:

>> Index 0 is reserved for the OPC UA namespace, and index 1 is reserved for the local Server.
and
>> The URI of the ServerArray with Index 0 shall be identical to the URI of the NamespaceArray with Index 1, since both represent the local Server.

I’m just asking myself, what is the practical use of this namespace with index 1 ?

When comparing different OpcUa servers, I can see that the URI of namespace index 1 looks something like:

[1] urn:’the local server hostname’:UnifiedAutomation:UaServerCpp
[1] urn:’the local server hostname’:OPCUA:SimulationServer
[1] urn:’the local server hostname’:Kepware.KEPServerEX.V6:UA Server

So in every server I check, I haven’t found any node in this namespace 1.

From client point of view it makes no sense to have any node in the namespace 1, as the URI is dependent on which physical machine the server is running.

Can you help me to understand for which use cases a node shall be provided at the namespace 1?

Thanks!

March 11, 2022
10:57, EET

Bjarne Boström

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April 3, 2012

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Hi,

Typically it is (just) used for the diagnostics nodes, but nothing prevents you from having all the “real nodes” of the server there. And nothing sort of prevents the 2+ indexes behaving the same way, it just depends on the uri that it is a well known uri or not.

Most likely the diagnostics is either off by default (this is typical) or that they are not supported in those servers. In our SimulationServer they are by default on and you can look via SimulationServer’s Address Space tab below Root/Objects/Server/ServerDiagnostics/SessionsDiagnosticsSummary/* you would find a node per active Session (the summary nodes are in 0 as they are well-known, the nodes per individual session are in 1).

You can think of 0 being static and every node there is driven by the base Nodeset thus the diagnostics nodes could not be there (since they could conflict with e.g. a future type addition etc.).

Then there is 100s of things (skipping here) regarding aggregation and separating type namespaces from instance namespaces and should you use or not use an unique namespace per server for instaces.

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