How an operator decides which is trusted node or which is non-trusted node?

Question

In LTE we have a node called ePDG which is used to connect trusted with non-trusted network elements. How an operator decides which is trusted or which is non-trusted.

Answer 1

Definition of trusted and nontrauted is simple same business entity is trusted and different business entity is non-trusted.

Assume you have two network one is CDMA and another is LTE, when both need to interwork and own by the same business entity then you need e-PDG if same then don't require e-PDG.