The HA-APN is composed of two parts as follows:
The HA-APN Network Identifier; this defines to which external network the HA is connected.
The HA-APN Operator Identifier; this defines in which PLMN the HA serving the HA-APN is located.
TS 23.003, clause 21.2
The Home Network Realm/Domain shall be an Internet domain name in the form of:
"<MNC>" and "<MCC>" fields correspond to the MNC and MCC of the operator's PLMN.
Both the "<MNC>" and
"<MCC>" fields are 3 digits long.
If the MNC of the PLMN is 2 digits, then a zero shall be added at the beginning.
TS 23.003, clause 19.2