Content for  TS 23.402  Word version:  18.3.0

IP address is allocated to the UE when connectivity to new PDN is initiated. The IP address can be provided by either PDN-GW or external PDN. Access GW in trusted non-3GPP access system is responsible for delivering the IP address to the UE. Based on the signalling between the UE and the non-3GPP IP access system the UE should be able to know the connected PDN identity (APN). This enables the UE to uniquely associate each allocated IP address with the PDN from where it was allocated. The trusted non-3GPP Access shall support at least one of the following functionalities in order to successfully allocate IP address to the UE in the EPC:

• Support of DHCPv4 relay agent functionality for IPv4 parameter configuration and IP address allocation as specified in RFC 2131 and RFC 4039 and described in clause 4.7.1 for the Serving-GW. This functionality is used to support DHCPv4 based IPv4 address allocation mechanism in the UE. For this case the following applies:
  • At initial attach or handover attach, if the PDN type is IPv4 only, the trusted non-3GPP IP Access shall request IPv4 address in the Proxy Binding Update. The Protocol Configuration Options in the Proxy Binding Update includes the Address Allocation Preference to indicate that deferred IPv4 address allocation was requested by the UE. In the same way as it is defined in clause 4.7.1, the IPv4 address is assigned by the PDN-GW during the initial attach procedure and the IPv4 address is returned in the Proxy Binding Acknowledgement. The DHCPv4 Address Allocation Procedure Indication is included in the Proxy Binding Acknowledgement to indicate that IPv4 address allocation using DHCPv4 is allowed. The MAG shall not deliver the assigned IPv4 address to the UE before the DHCPv4 address allocation. After the PMIPv6 tunnel is set up between the trusted non-3GPP Access and the PDN-GW, the trusted non-3GPP Access may relay the DHCPv4 messages between the UE and the PDN-GW for IPv4 parameter configuration and IPv4 address allocation as specified for the Serving-GW in Figure 4.7.1-1.
  • At initial attach and handover attach, if the PDN type is IPv4v6 and deferred IPv4 address allocation is used, the trusted non-3GPP IP Access shall request both IPv6 network prefix and IPv4 address in the Proxy Binding Update. The Protocol Configuration Options in the Proxy Binding Update includes the Address Allocation Preference to indicate that deferred IPv4 address allocation was requested by the UE. In the same way as it is defined in clause 4.7.1, if deferred IPv4 address allocation is allowed, no IPv4 address is assigned by the PDN-GW during the initial attach procedure, only IPv6 network prefix is returned in the Proxy Binding Acknowledgement. The DHCPv4 Address Allocation Procedure Indication is included in the Proxy Binding Acknowledgement to indicate that IPv4 address allocation using DHCPv4 is allowed. After the PMIPv6 tunnel is set up between the Trusted Non-3GPP IP Access and the PDN-GW, when the UE requests the IPv4 address via DHCPv4, the trusted non-3GPP Access and PDN-GW perform steps 2 and 3 in Figure 4.7.1-1, and then the non-3GPP Access may relay the DHCPv4 messages between the UE and the PDN-GW for IPv4 parameter configuration and IPv4 address allocation as specified in Figure 4.7.1-1.
  • Any time after the UE releases the IPv4 address using DHCPv4 or IPv4 address lease time expires, and if the PDN Type is IPv4, the PDN-GW initiates "PDN-GW-initiated PDN-disconnection" procedure for the given PDN connection. The same IPv4 address shall not be allocated to another UE immediately.
  • Any time after the UE releases the IPv4 address using DHCPv4 or IPv4 address lease time expires, and if the PDN Type is IPv4v6, the PDN-GW initiates the "PDN-GW initiated IPv4 address Delete Procedure" procedure to delete the IPv4 address from the PDN connection and from bearer contexts. The same IP address shall not be allocated to another UE immediately.
• Support of DHCPv4 server functionality for IPv4 parameter configuration and IP address allocation as specified in RFC 2131 and RFC 4039. This functionality is used to support DHCPv4 based IPv4 address allocation mechanism in the UE. For this case the following applies:
  • At initial attach and handover attach, if the PDN type is IPv4v6 and deferred IPv4 address allocation is used, the trusted non-3GPP IP Access shall request both IPv6 network prefix and IPv4 address in the Proxy Binding Update. The Protocol Configuration Options in the Proxy Binding Update includes the Address Allocation Preference to indicate that deferred IPv4 address allocation was requested by the UE. In the same way as it is defined in clause 4.7.1, if deferred IPv4 address allocation is allowed, no IPv4 address is assigned by the PDN-GW during the initial attach procedure, only IPv6 network prefix and the DHCPv4 Address Allocation Procedure Indication are returned in the Proxy Binding Acknowledgement. After the PMIPv6 tunnel is set up between the Trusted Non-3GPP IP Access and the PDN-GW, when the UE requests the IPv4 address via DHCPv4, the MAG in Trusted Non-3GPP IP Access requests the IPv4 address for the UE from the PDN-GW via PMIPv6 signalling as it is described in Figure 4.7.2-1.
  • Any time after the UE releases the IPv4 address using DHCPv4 or IPv4 address lease time expires, and if the PDN Type is IPv4, the trusted non-3GPP access system will initiate "Trusted Non-3GPP IP Access requested PDN Disconnection Procedure with PMIPv6" procedure for the given PDN connection. The same IP address shall not be allocated to another UE immediately.
  • Any time after the UE releases the IPv4 address using DHCPv4 or IPv4 address lease time expires, and if the PDN Type is IPv4v6, the non-3GPP access may initiate "Non-3GPP access initiated IPv4 address Delete Procedure" procedure to delete the IPv4 address from the PDN connection and bearer contexts. The same IP address shall not be allocated to another UE immediately.
• Support of DHCPv6 (relay agent or server) functionality for IPv6 parameter configuration as specified in RFC 3736. This functionality is required to support DHCPv6 based parameter configuration mechanism in the UE.
• Support of prefix advertisement for IPv6 prefix received from PDN-GW in PMIPv6 Proxy Binding Acknowledgement.
• Support for IPv4 Address allocation that is received from PDN-GW from PMIPv6 Proxy Binding Acknowledgement using access specific mechanisms.
• Support of static IP address allocation. The non-3GPP access may receive a static IP address (i.e. a static IPv4 address and/or a static IPv6 prefix) from HSS/AAA during access authentication and authorization procedure. Then the non-3GPP access should forward the static IP address to the PDN-GW.

When an Untrusted Non-3GPP IP access is used two types of IP address are allocated to the UE:

• An IP address, which is used by the UE within the Untrusted Non-3GPP IP Access Network to get IP connectivity towards the ePDG.
• One or more IP address(es), which is used by the UE towards the external PDNs via the allocated PDN-GW(s).

The IP address that is allocated by the Untrusted Non-3GPP IP Access Network is used as the end point of the IPSec SAs between the UE and the ePDG. The allocation of this IP address is out of the scope of this specification. The IP address(es) that are allocated by the PDN-GW(s) are allocated to the UE when connectivity to a new PDN is initiated. The IP address(es) can be provided by either PDN-GW or external PDN as it is specified in clause 5.3.1.1 of TS 23.401. The ePDG receives the allocated IP address(es) within the PMIP Proxy Binding Acknowledgement or GTP Create Session Response and the ePDG is responsible for delivering the IP address(es) to the UE. The ePDG shall provide the UE with connected PDN information (APN), so that the UE can uniquely associate each allocated IP address with the PDN from where it was allocated. The ePDG may receive a static IP address (i.e. a static IPv4 address and/or a static IPv6 prefix) from HSS/AAA during IKEv2 tunnel establishment procedure. Then the ePDG should forward the static IP address to the PDN-GW.

Prior the use of S2c an IP address which will be used as a care-of address shall be allocated to the UE. When a Trusted Non-3GPP Access Network is used one or more IP addresses are allocated to the UE by the Trusted Non-3GPP Access Network. One of these IP addresses is used by the UE as care-of address within DSMIPv6. The allocation of these IP addresses is out of the scope this specification. When an Untrusted Non-3GPP Access Network is used one or more IP addresses are allocated to the UE by the Untrusted Non-3GPP Access Network. The allocation of these IP addresses is out of the scope of 3GPP. One of these IP addresses is used by the UE as the IP address towards the ePDG when IPSec SAs are established. During the IPSec SA establishment the ePDG allocates and delivers an IP address to the UE, which IP address is used by the UE as care-of address within DSMIPv6. This IP address is allocated by the ePDG either by using an internal address pool or using an external server, such as DHCP. The allocation of this IP address is implementation specific. When a UE is connecting to a PDN via S2c, address allocation for that PDN takes place as follows. During IKEv2 exchange for bootstrapping the DSMIPv6 security association (see clause 6.3) the following parameters can be negotiated between the UE and the PDN-GW/HA:

• The IPv6 prefix to which the IPv6 Home Address belongs, also called the "Home Network Prefix" and the PDN associated with the IPv6 prefix (PDN is indicated with APN);
• The UE's IPv6 Home Address;
• The DNS server address for that PDN.

The UE may request additional configuration parameters by running stateless DHCP as defined in RFC 4039 and RFC 3736 over the DSMIPv6 tunnel. The UE may also request an IPv4 home address using DSMIPv6 signalling, as defined in RFC 5555. The PDN-GW/HA may receive a static IP address (i.e. a static IPv4 address and/or a static IPv6 prefix) from HSS/AAA during the authentication and authorization procedure. Then the PDN-GW/HA shall assign the static IP address to the UE, as indicated above.

Optionally a single network prefix shorter than a /64 prefix may be assigned to a PDN connection (TS 23.401). When S2c is used to access a PDN, the UE acting as a Mobile Router may request delegation of one or more IPv6 prefix(es) via DHCPv6 Prefix Delegation signalling as described in RFC 6276. The UE does not need to explicitly register these additional prefixes using S2c signaling as implicit mode registration is used.

Optionally a single network prefix shorter than the default /64 prefix may be assigned to a PDN connection as specified in TS 23.401. When PMIP-based S5/S8 is used, the UE may request delegation of one or more IPv6 prefix(es) via DHCPv6 Prefix Delegation signalling as described in RFC 7148. In this case, the Serving-GW shall support DHCPv6 relay agent functionality for intercept the related DHCPv6 message. The UE uses DHCPv6 to request additional IPv6 prefixes (i.e. prefixes in addition to the default prefix) from the PDN-GW after completing stateless IPv6 address autoconfiguration procedures as specified in Figure 4.7.6-1.