The entry is created:
1. When a path between a GGSN and SGSN is setup.
2. Or, when a path between the GGSN and the charging
gateway is setup.
3. Or, when a path between GGSN and the MAP converting GSN
is setup.
The entry is deleted when the path is released, or echo
test message on the path times out after certain retry number
defined as cGtpN3Request.