[FedCom] US Postal Wide Area Radio Comm System Operation?

[Ken]

409.9375 Repeater P25/Digital  (mobiles in the clear, dispatch encrypted, 
usually, it's the opposite way!!!)

Earlier this evening monitored 2 units (unit identifiers 4 digits, no alpha) 
were advising dispatch that they were responding to a specific Boston Post 
Office.

Now, I'm wondering IF all the repeaters in the region are automatically 
keyed up when any mobile/portable unit and/or dispatch uses the system OR is 
a local repeater (within the system) keyed up only if there's a unit close 
by?


Ken
Springfield MA Monitoring Area