The maintenance window is regulated by ICE. All the details about the maintenance window can be found in the section "8. Feed Availability and Maintenance Window" of the ICE iMpact Multicast Feed Technical Specification.

As far as session number is changed after the maintenance window the Handler activates full recovery procedure to refresh the product definitions and the market state.

The Handler doesn't provide any mechanism to notify when the maintenance window starts or ends. A user application should handle this period of inactivity on its own.

After the maintenance window, the number of product definitions could be changed. The Handler keeps all the product definitions downloaded at the beginning when the Start(ICollection<MarketSubscription>) method is called and uses this set at market state recovery. This means that if at least one product definition is removed after the maintenance window, the Handler won't be able to finish market state recovery as it will keep waiting for snapshot messages for the product definitions that are no longer available. To avoid this situation full restart of the Handler is required.