how do scom subscriptions work?

I'm writing a connector into SCOM using a subscription, and trying to find out if I have a bug or not开发者_高级运维:

Do subscriptions work like a feed, so that they return me all the current alarms in the system? Or do they just fire off when a new alarm happens?

My connector polls the subscription every 30 seconds and sometimes doesn't return any alarms, so I'm hoping the reason is there are no new alarms in the system since I last polled it.

Can anyone confirm this for me?

Thanks,

After doing some testing, I've found that subscriptions will only send you new alerts since you last checked in.