Analyse data transfert between opc server and Ua client with wireshark

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Flesher
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Analyse data transfert between opc server and Ua client with wireshark

Post by Flesher »

hello,

I use the UA client to implement the data subscriptions function of a UA OPC server.
With wireshark, I check if the frames are sent only when the data value changes.
I have the trame ReadRequest/ReadResponse every 5 secondes.
I want to know the significtifation of the trame ReadRequest/ReadResponse and PublishRequest/PublishResponse

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Re: Analyse data transfert between opc server and Ua client with wireshark

Post by Support Team »

Hello,

when you analyse the wireshark, is the PublishRequest/PublishResponse looking at "the same items" than the ReadRequest/ReadResponse is asking for?
If not, the "Read" is probably serving a different purpose (and for a different set of nodes).

However, subscribe for change notification plus cyclic read every 5sec on the same tags, makes not much sense.

Please deeply look into the wireshark and make an educated guess.
Best regards
Unified Automation Support Team

Flesher
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Re: Analyse data transfert between opc server and Ua client with wireshark

Post by Flesher »

Hello,

I don't know how to change the cyclic read.
However, I think that the publishRequest/PublishResponse is the minimal intervalle of emission that i have configured in OPC UA serveur of my PLC 1500

The goal is to limit the traffic between the OPC UA server of my PLC and the UA client.

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Re: Analyse data transfert between opc server and Ua client with wireshark

Post by Support Team »

Hello,

the cyclic read in UaExppert is checking health of connected UA server. Any client can do what he wants, the UaExpert is doing health check with cyclic read. This cyclic read has nothing to do with the data items you are subscribing for, that is different items and differend purpose.

The data items you have subscribed for will only get PublishResponse when they have changed (their value/timestamp/status). If they have not changed you will have no traffic (except from time to time sending a keepalive, which is an empty PublishResponse). The keep alive traffic can be configured with the Publish interval and subscription settings. This is the "minimum" traffic you can get !
Best regards
Unified Automation Support Team

Flesher
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Re: Analyse data transfert between opc server and Ua client with wireshark

Post by Flesher »

hello,

I'm not undestand why the PublishResponse come before the PublishRequest.

however, the ReadRequest come before the ReadResponse

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Re: Analyse data transfert between opc server and Ua client with wireshark

Post by Support Team »

Hello,

you can be sure that you are NOT getting the response "before" the request, because that would be technically nonsense.

Most likely you are not reading the wireshark correctly. Please start reading from very first beginning, and you will see that there is "first" the request and "thereafter" the corresponding response, and then (quickly) comming the "next" request. If you had read the UA spec, you would know that there are sequence numbers in every ping/pong which will be in sequence for sure.

Best way to analyse is to use UaExpert and one of our demo servers which behaves correctly.
Best regards
Unified Automation Support Team

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