Question: What form shall a Subscription Permanent Identifier (SUPI) take when it contains a network-specific identifier, as defined in the 3GPP specifications?
Option 1: A globally unique identifier using the IMSI format.
Option 2: A Network Access Identifier (NAI) using the NAI RFC 7542 based user identification.
Option 3: A combination of a GCI and an operator identifier of the 5GC operator.
Option 4: A random string generated by the UE.
Explanation: According to the 3GPP specifications, when a SUPI contains a network-specific identifier, it shall take the form of a Network Access Identifier (NAI) using the NAI RFC 7542 based user identification. This is specified in TS 23.003 and ensures that the SUPI can be used for private networks as defined in TS 22.261.