Question: What happens when the SMF+PGW-C receives a re-authentication request from the DN-AAA Server while the UE is in EPS?
Option 1: The SMF+PGW-C initiates PDN connection release immediately.
Option 2: The SMF+PGW-C informs the DN-AAA Server that the UE is not available for re-authentication at the moment and does not initiate PDN connection release.
Option 3: The SMF+PGW-C performs re-authentication with the UE over EPS.
Option 4: The SMF+PGW-C ignores the re-authentication request from the DN-AAA Server.
Explanation: According to the text, when the SMF+PGW-C receives a re-authentication request from the DN-AAA Server while the UE is in EPS, it informs the DN-AAA Server that the UE is not available for re-authentication at the moment and does not initiate PDN connection release. This is because there is no support of the related signalling in EPS, and the SMF+PGW-C should not take any action without the DN-AAA Server's decision based on local policy.