Hello,

As it was already raised in description of https://apps.opcfoundation.org/mantis/view.php?id=33 there is an issue with the KeepAliveCounter management regarding the description of the MaxKeepAliveCount parameter in the service:

• requestedMaxKeepAliveCount (table 86 of part4 v1.03): "When the publishing timer has expired this number of times without requiring any NotificationMessage to be sent, the Subscription sends a keep-alive Message to the Client."
• Table 83 part 4 v1.03 state changes (on publishing timer expiration) are:
  • #9: NORMAL -> KEEP ALIVE: no notification to send => keep alive timer reset
  • #15: KEEP ALIVE -> KEEP ALIVE: no notification to send && KeepAliveCounter == 1 => send a keep alive + keep alive timer reset
  • #16: KEEP ALIVE -> KEEP ALIVE: no notification to send && KeepAliveCounter > 1 => KeepAliveCounter decremented

Example of execution using the above definition:
Init: state = NORMAL && MaxKeepAliveCount = 2
Cycle 1: transition #9 => state = KEEP ALIVE && KeepAliveCounter = 2
Cycle 2: transition #16 => state = KEEP ALIVE && KeepAliveCounter = 1
Cycle 3: tranisition #15 => SEND KEEP ALIVE && state = KEEP ALIVE && KeepAliveCounter = 2
Cycle 4: transition #16 => state = KEEP ALIVE && KeepAliveCounter = 1
Cycle 5: transition #15 => SEND KEEP ALIVE && state = KEEP ALIVE && KeepAliveCounter = 2

As you can see, starting from NORMAL state there is 3 publishing timer expiration (cycles 1-2-3) before a KeepAlive is sent whereas starting from KEEP ALIVE state we only have 2 publishing timer expiration (cycles 4-5) before a KeepAlive is sent as expected due to MaxKeepAliveCount value configured.

Therefore to be compliant with the description of requestedMaxKeepAliveCount in table 86, the state transition #9 shall reset the KeepAliveCounter but it shall also decrement it after the reset in the same transition.

Best regards