Demand is Communicated to External Systems 

Answer

This flag is available in the pop-up when you try to create a new demand.

This flag has a use case only for those Nodes that track supplies externally. In such cases Sterling uses GetExternalSupply user exit to get the supplies from external systems to calculate the availability. Now the supply quantity returned from this UE is actually the available quantity which is calculated by excluding the demands with demand type that has CommunicatedDemand=Y. (ie "Demand Is Communicated to External System" flag is checked)

For an external system that already considered "communicated demands" (Demands communicated from Sterling) in its supply picture, the IgnoreCommunicatedDemands flag can be passed in the output of the getExternalSupply user exit. This implies that Sterling should ignore all demands with demand type that has CommunicatedDemand=Y during availability calculation because the supply picture provided by external system already excluded the quantities for such demands.

To explain this with an example:

Say Sterling maintains following Demand types: (All the supplies being maintained externally)

-- Open Order
-- Backordered
-- Allocated
-- Scheduled

And the external system maintains only "Scheduled" Demand type, ie "Demand Is Communicated to External System" flag is checked only for "Scheduled" demand type.

Now say the Inventory Picture available to Sterling is:

Allocated = 2
Scheduled = 3

External Inventory Picture:

Onhand=10 (Supply)
Scheduled=3 (Demand)

Now GetExternalSupply UE will pass only 7 as the Onhand quantity and use this to calculate the availability. Now if IgnoreCommunicatedDemands flag is passed as Y from the UE, then Sterling will ignore the "Scheduled" demand type available to Sterling and calculate the availability as 7-2=5.
But if IgnoreCommunicatedDemands is passed as N, then Sterling will consider all the demand types to calculate availability. In this case availability = 7-2-3 = 2.