Multiple subscription management

[SimoneMaffei98]

Hi Thomas,
I'm here again.
I would like to use subscription but it has some limits.
I would like to read 10000 variables but i can subscribe only 2000.
Is it possible to make for exemple 5 subscription with the same connestion? I tried but it seems not working, first time connect but then it gives me errors.

Thank you.

[thomas-v2]

What value do you get in CommRessources.PlcSubscriptionsMax? This value is decreased by the number of subscribed variables you add. The other two values PlcAttributesMax and SubscriptionMemoryMax are decreased as well, but by a different amount. I haven't done much testing on this. But I believe these values have to be in the limits. But PlcSubscriptionsMax is the easiest limit to calculate, if you are above this, you must switch to poll mode (WinCC for example is doing this also this way).

You can make multiple subscriptions on a single connection, but not with the code I have in the Subscription.cs file. For a new subscription the m_SubscriptionRelationId must be increased when creating the new subscription, and the returned new m_SubscriptionObjectId must be stored, to know when a notification arrives to which subscription the data belongs to. And to modify or delete the subscription. This needs more analyzing and testing how this in detail needs to be handled.

[SimoneMaffei98]

Hi Thomas,
regarding polling, I don’t like it very much: it’s too slow and cumbersome. When there are many variables, reading becomes extremely slow; moreover, on the PLCs I have here it is only possible to read up to 100 variables at a time.

I have instead found a way to make multiple subscriptions work properly, and I am still running some tests.

Just for your information: the issue I had was that during SubscriptionCreate, at a certain point
WaitForNewS7plusReceived(m_ReadTimeout);
is called, followed by
var createObjRes = CreateObjectResponse.DeserializeFromPdu(m_ReceivedPDU);.

On the second subscription, however, it failed because it received a notification result instead of the subscription creation response.

If you want, I can send you the updated class here.

Thank you very much for your help.