In order to support A12 authentication, matching A12 credentials (i.e., an A12 Network Address Identifier (NAI) and A12 CHAP key) must be provisioned into the AT and the user's home AAA server.
A12 authentication is important for roaming since all participating operators in the IRT have agreed to support it.
If A12 credentials are not provisioned into an AT, that AT will not be able to access any visited network that performs A12 authentication.
In addition, the Mobile Node Identifier (MN ID) is obtained from the AN-AAA during successful A12 authentication.
If A12 authentication is not performed, the MN ID must be somehow derived and such handoffs may not be possible without establishing a new Point-to-Point Protocol (PPP) session.