Question: What is the responsibility of the PDN GW when an IPv4 address is allocated from an external PDN?
Option 1: The PDN GW is responsible for allocating and releasing the IPv4 address, but not obtaining it from the external PDN.
Option 2: The PDN GW is responsible for obtaining, allocating, renewing, and releasing the IPv4 address from the external PDN.
Option 3: The PDN GW is only responsible for releasing the IPv4 address, but not obtaining or allocating it.
Option 4: The PDN GW has no responsibility when an IPv4 address is allocated from an external PDN.
Explanation: According to the text, when an IPv4 address is allocated from an external PDN, it is the PDN GW's responsibility to obtain the IPv4 address from the external PDN and to allocate, renew, and release the IPv4 address. This can be done using DHCPv4, RADIUS, or Diameter protocols.