Question: In the context of the Gxx application defined by 3GPP, what role does the PCRF (Policy and Charging Rules Function) assume when interacting with the Diameter protocol over the Gxx interface?
Option 1: Diameter Client, requesting QoS rules for transport plane network resources
Option 2: Diameter Relay Agent, forwarding requests between different realms
Option 3: Diameter Proxy Agent, modifying messages to suit different applications
Option 4: Diameter Server, handling QoS Rule requests for a particular realm
Explanation: According to the defined protocol support for the Gxx application, the PCRF acts as a Diameter server. This means it is responsible for handling and responding to QoS (Quality of Service) Rule requests, which are crucial for managing network resources within its realm.