Question: In a scenario where the Subscription-Id Attribute Value Pair (AVP) is not received, how does the Policy and Charging Rules Function (PCRF) perform Gateway Control Session to Gx session linking?
Option 1: By solely relying on the International Mobile Subscriber Identity (IMSI) extracted from the S1-AP protocol
Option 2: Using either the User-Equipment-Info AVP or, if supported, the User-Equipment-Info-Extension AVP
Option 3: Automatically falling back to a default Gx session without any specific user equipment identification
Option 4: Requesting retransmission of the Subscription-Id AVP before proceeding with session linking
Explanation: This is correct because, according to the specified procedure for when the Subscription-Id AVP is not received, the PCRF utilizes alternative attributes (User-Equipment-Info AVP or User-Equipment-Info-Extension AVP if its feature is supported) for linking Gateway Control Sessions to Gx sessions. This approach ensures session management can proceed without the primary identifier, leveraging available user equipment information instead.