Significance of the create_subscription parameter

[dibyendumca]

Hello,
Can anybody explain the significance of the 1st parameter of the client function 'CREATE_SUBSCRIPTION' ?

handler = SubscriptionHandler()
client.create_subscription(500, handler)

What this value 500 means exactly?
What will happen if we increase or decrease this value?

[schroeder-]

The first parameter is publishing interval. For a complete description see opc ua ref.
A simple explanation is that is the interval in ms(milliseconds), in which the server checks if a monitored item has changed, in your subscription. Lowering only works if the samplingrate of a VariableNode is lower than the publishing interval.

[dibyendumca]

I am getting the below line in the console as and when I am running a Server module of an ASYNCUA.

Subscription Subscription(id:78) has expired, publish cycle count(10001) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10002) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10003) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10003) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10004) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10005) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10006) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10007) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10008) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10009) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10010) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10011) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10012) > lifetime count (10000)
......
Subscription Subscription(id:78) has expired, publish cycle count(66106) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66107) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66107) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66108) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66109) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66110) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66110) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66111) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66112) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66112) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66113) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66114) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66115) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66116) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66117) > lifetime count (10000)

May I know what is this about?

[AndreasHeine]

I am getting the below line in the console as and when I am running a Server module of an ASYNCUA.

Subscription Subscription(id:78) has expired, publish cycle count(10001) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10002) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10003) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10003) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10004) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10005) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10006) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10007) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10008) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10009) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10010) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10011) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(10012) > lifetime count (10000)
......
Subscription Subscription(id:78) has expired, publish cycle count(66106) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66107) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66107) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66108) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66109) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66110) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66110) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66111) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66112) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66112) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66113) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66114) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66115) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66116) > lifetime count (10000)
Subscription Subscription(id:78) has expired, publish cycle count(66117) > lifetime count (10000)

May I know what is this about?

https://reference.opcfoundation.org/v104/Core/docs/Part4/5.13.1/

Subscriptionshave a lifetime counter that counts the number of consecutive publishing cycles in which there have been no Publishrequests available to send a Publishresponse for the Subscription. Any Servicecall that uses the SubscriptionIdor the processing of a Publishresponse resets the lifetime counter of this Subscription. When this counter reaches the value calculated for the lifetime of a Subscriptionbased on the MaxKeepAliveCount parameter in the CreateSubscription Service(5.13.2), the Subscriptionis closed. Closing the Subscriptioncauses its MonitoredItemsto be deleted. In addition the Servershall issue a StatusChangeNotification notificationMessagewith the status code Bad_Timeout. The StatusChangeNotification notificationMessagetype is defined in 7.20.4.

[AndreasHeine]

it basically means that the client does not send any publishrequest for a while!
Client -> PublishRequest -> Server -> Subscription
if no data:
Subscription -> Server -> KeepAlive -> Client
then the client needs to send a new PublishRequest!
but in your case this does not happen with "Subscription(id:78)"!

edit:

it often happens if the publishinterval is to small e.g. <500ms and you have "static" data like configuration parameters which do not change frequently... so you will get many keepalives...

[JamesTev]

@AndreasHeine I am having a similar problem to the one mentioned above. Your note "it often happens if the publishinterval is to small" seems like it might be the cause for me as I have some variables that may not change for many hours, despite my subscription period being 500ms. What do you suggest I do to get around this? And how can I catch subscriptions being deleted?

[AndreasHeine]

you can add the servertime variable to the subscription! wich would be the easiest fix.

https://www.linkedin.com/pulse/brief-introduction-opc-ua-subscriptions-andreas-heine-3pc6e?utm_source=share&utm_medium=member_android&utm_campaign=share_via