Question: What is the format for deriving a Temporary Public User Identity for a Stand-alone Non-Public Network (SNPN) subscriber with an IMSI-based SUPI type in 3GPP systems?
Option 1: sip: appended with a username and domain portion equal to the IMSI, without any additional network identifiers.
Option 2: sip: followed by a random username and a static domain 3gppnetwork.org
Option 3: sip: appended with a username (IMSI-derived Private User Identity) and a domain portion that includes ims., followed by nid<NID> of the SNPN, then mnc<MNC>, mcc<MCC>, and finally .3gppnetwork.org
Option 4: sip: prefixed to a Network-Specific Identifier (NAI) in its entirety, without breaking down into username and realm portions.
Explanation: For SNPN subscribers identified by an IMSI-based SUPI, the Temporary Public User Identity derivation must include the network identifier (NID) of the SNPN, inserted between ims. and mnc<MNC> in the domain portion, reflecting the specific network affiliation.