Question: Which of the following IP versions is mandatory for the outer GTPv1-U packet layer to support, as per the specified requirements?
Option 1: IPv4 as defined by IETF RFC 791
Option 2: IPv6 as defined by IETF RFC 8200
Option 3: Both IPv4 and IPv6 with equal priority
Option 4: Neither IPv4 nor IPv6, as it depends on the network architecture
Explanation: According to the specifications, the outer GTPv1-U packet layer shall support IPv4, indicating a mandatory requirement. In contrast, support for IPv6 is recommended but not obligatory.