Question: What is the format of the External Group Identifier that identifies a group made up of one or more subscriptions associated to a group of IMSIs?
Option 1: Local Identifier + Domain Identifier
Option 2: IMSI + MSISDN
Option 3: Group Name + Realm Name
Option 4: <Local Identifier>@<Domain Identifier>
Explanation: The External Group Identifier has a specific format that includes the Local Identifier and the Domain Identifier, separated by the "@" symbol. This format makes the External Group Identifier globally unique.