Section: 5.3.1.2.4 IPv4 address allocation, renewal and release and IPv4 parameter configuration via DHCPv4
Content: When the PLMN allocates an IPv4 address, it is the PDN GW responsibility to allocate, renew and release the IPv4 address. When external PDN allocation is used, the PDN GW functions as a DHCPv4 server towards the UE. The PDN GW may act as a DHCP Client when interacting with a DHCPv4 server in the external PDN in order to obtain, renew and release the IPv4 address and to obtain the configuration parameters. Or, if RADIUS or Diameter is used towards the external PDN as described in TS 29.061[ Interworking between the Public Land Mobile Network (PLMN) supporting packet based services and Packet Data Networks (PDN) ]  [38], the IPv4 address and the requested configuration parameters can be obtained, renewed and released as part of these procedures. If dynamic policy provisioning is deployed, and the PCRF was not informed about the IPv4 address at IP-CAN session establishment, the PDN GW shall initiate an IP-CAN Session Modification procedure to inform the PCRF about an allocated IPv4 address. If the IPv4 address is released, the PDN GW shall inform the PCRF about the de-allocation of an IPv4 address. If the UE sends DHCPv4 lease renewal message to renew the lease of the allocated IPv4 address, the PDN GW shall renew the lease of the allocated IPv4 address. If the IPv4 address was obtained from an external PDN, the PDN GW shall perform the DHCPv4 lease renewal procedure with the external PDN if DHCPv4 was used for obtaining IPv4 address from external PDN. If Diameter or RADIUS procedures where used to obtain the IPv4 address from external PDN, the PDN GW may perform corresponding update procedures as applicable. If the external PDN extends lease of the allocated IPv4 address, the PDN GW responds accordingly to the UE. Otherwise, if the external PDN does not extend the lease of the allocated IPv4 address, the PDN GW responds with the remaining lease time of the IPv4 address. If there is no PDN address allocated to the UE for this PDN connection, the PDN GW shall perform PDN GW initiated bearer deactivation procedure as defined in clause 5.4.4.1. If the UE sends DHCPv4 release message to release the allocated IPv4 address for the PDN connection, the PDN GW may any time thereafter release the IPv4 address. If the PDN connection has no allocated PDN address, the PDN GW may at any time initiate PDN GW initiated bearer deactivation procedure as defined in clause 5.4.4.1. NOTE: If the PDN type is IPv4v6 the release of the allocated IPv4 address does not mean that there is no allocated PDN address for the PDN connection, as the IPv6 prefix still remains allocated to that PDN connection. If the PDN connection is released without any DHCPv4 release signalling with the UE, the UE and the PDN GW shall release the IPv4 address implicitly, as soon as the PDN connection is released. After releasing the IPv4 address, the PDN GW should not assign that IPv4 address to any other user immediately.