Question: What type of transactions does the protocol crossing the Ro reference point support?
Option 1: Only real-time transactions
Option 2: Only non-real-time transactions
Option 3: Both real-time and non-real-time transactions
Option 4: Neither real-time nor non-real-time transactions
Explanation: The protocol crossing the Ro reference point supports real-time transactions, as stated in the capabilities required for this reference point. Real-time transactions are essential for online charging, where immediate response is necessary to grant or reject network resource usage.