Question: What is the purpose of using an Alternative Format of W-APN Operator Identifier?
Option 1: To enable roaming between different public land mobile networks (PLMNs)
Option 2: To provide a unique identifier for the PDG serving the W-APN
Option 3: To accommodate situations where the PDG is located in a network not part of the GRX
Option 4: To simplify the configuration of W-APN Operator Identifiers
Explanation: The Alternative Format of W-APN Operator Identifier is required when the PDG serving the W-APN is located in a network that is not part of the GRX (Interoperator IP backbone). This is because the default Operator Identifier described in clause 14.7.2 is not available for use in such situations, due to the restriction originating from the ".3gppnetwork.org" domain being only available in GRX DNS for actual use.