Question: When the PCRF (Policy and Charging Rules Function) receives a CCR command with CC-Request-Type AVP set to "INITIAL_REQUEST" for an APN dedicated for IMS, how does it derive the ARP (Allocation and Retention Priority) for the default bearer if the IMS Signalling Priority is set?
Option 1: The PCRF assigns a fixed, high ARP value for all IMS signalling bearers.
Option 2: The PCRF derives the ARP without considering the IMS Signalling Priority.
Option 3: The PCRF uses the MPS EPS Priority and MPS Priority Level to determine the ARP.
Option 4: The PCRF assigns an ARP corresponding to Multimedia Priority Service (MPS) for the default bearer.
Explanation: According to the provided context, when the IMS Signalling Priority is set and the Called-Station-Id AVP corresponds to an APN dedicated for IMS, the PCRF shall assign an ARP corresponding to MPS for both the default bearer and the PCC Rules corresponding to the IMS signalling bearer. This ensures prioritized handling of IMS traffic, reflecting the importance of maintaining high-quality service for such communications.