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Bandwidth Requirement for OPC UA
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Meghnad Natekar
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10/15/2020 - 08:16
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I would like to understand how to calculate bandwidth for OPC UA. We have around 80000 tags to exchange and I would like to know how much network bandwidth is needed.

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Randy Armstrong
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10/15/2020 - 09:39
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UA is exception based so no data is transmitted if the value does not change.

You can also specify deadbands for each item which can reduce data transmission even if the value changes by a small amount.

UA also allows you to suppress information such as the Timestamps which further reduces network requirements.

Lastly, datachanges are bundled into network messages. More datachanges in a single message means lower bandwidth but higher latency.

So to answer you question you need to know:

1) DataTypes of your 80K items;

2) How frequently they change;

3) The maximum delay between the change and receiving the update;

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Meghnad Natekar
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10/15/2020 - 20:58
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Randy Armstrong said
UA is exception based so no data is transmitted if the value does not change.

You can also specify deadbands for each item which can reduce data transmission even if the value changes by a small amount.

UA also allows you to suppress information such as the Timestamps which further reduces network requirements.

Lastly, datachanges are bundled into network messages. More datachanges in a single message means lower bandwidth but higher latency.

So to answer you question you need to know:

1) DataTypes of your 80K items;

2) How frequently they change;

3) The maximum delay between the change and receiving the update;

  

Hi Randy

Thanks for detailed explanation.

I would assume below 

1) 70% of tags are digital inputs and 30% analog inputs i.e. 56000 Digital and 24000 Analog.

2) Analog Data Change - 1 Min per signal ; Digital Data Change - 1 Hr per signal

3) Max delay between the change and receeving the update - 3 sec

 

If you can provide further guidelines, I can then create a template to calculate bandwidth requirements which can be tuned as further details are available.

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Randy Armstrong
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10/16/2020 - 20:08
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You need 1 publish request per 3sec with about 1248 data changes per message.

Data changes per message with timestamp are 16*3 * sizeof(byte) for digital and 400*3 * sizeof(double) for analog + 8 byte timestamp + 2 byte encoding id + 4 byte client handle.

Or 27K per message not including message overhead which should be insignificant compared to the data.

This gives you ~9K/sec average bandwidth requirements.

You need to think about peak requirements as well since real systems can have bursts of changes.

However, the nice thing about UA it includes flow control which allows clients to sacrifice latency to ensure the network does not get overloaded.

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Meghnad Natekar
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10/18/2020 - 22:37
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Randy Armstrong said
You need 1 publish request per 3sec with about 1248 data changes per message.

Data changes per message with timestamp are 16*3 * sizeof(byte) for digital and 400*3 * sizeof(double) for analog + 8 byte timestamp + 2 byte encoding id + 4 byte client handle.

Or 27K per message not including message overhead which should be insignificant compared to the data.

This gives you ~9K/sec average bandwidth requirements.

You need to think about peak requirements as well since real systems can have bursts of changes.

However, the nice thing about UA it includes flow control which allows clients to sacrifice latency to ensure the network does not get overloaded.

  

Thank Randy for this detailed explaination.

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