16.1.5 IP address allocation

23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

16.1.5.1 General

In this Release of the specification, deferred IPv4 address allocation is not supported.

When using Single-connection mode and Multi-connection mode, the UE sees the PDN Connection as a point-to-point link similar to how it is in 3GPP access. Shared link parameters such as netmask and default router IP address are not used.

In Transparent Single-connection Mode, TWAG shall act as DHCPv4/v6 server for the UE.

In Single-connection mode and Multi-connection mode, the link model is described below:

– To support IPv4 connectivity, the IPv4 address shall be allocated and sent to the UE during PDN connection establishment.

– To support IPv6 connectivity, the PGW handles the RS/RA messages in GTP-based S2a scenario, while the TWAG handles the RS/RA messages in PMIP-based S2a scenario.

– To support IPv6 parameter configuration UE may use stateless DHCPv6. The PGW acts as DHCPv6 server. With PMIP-based S2a the TWAG may act as DHCPv6 relay.

16.1.5.2 IP address allocation in Transparent Single-Connection Mode

In order to enable IPv4 connectivity the TWAN shall support DHCPv4 server functionality for IPv4 parameter configuration and IP address allocation as specified in RFC 2131 [28] and RFC 4039 [29]. For this case the following applies:

– If the PDN type in the user subscribtion data is IPv4 or IPv4v6, the TWAN requests IPv4 address in the Proxy Binding Update or GTP Create Session Request from the PDN GW. The IPv4 address is delivered to the TWAN during the PMIPv6 or GTP tunnel establishement. When the UE requests the IPv4 address via DHCPv4, the TWAN delivers the received IPv4 address to the UE within DHCPv4 signalling after the PMIPv6 or GTP tunnel is established between the TWAN and the PDN GW.

NOTE 1: As a consequence the PDN GW configuration for the default APN used via Trusted WLAN access cannot dictate the use of deferred IPv4 address allocation.

NOTE 2: After releasing the IPv4 address using DHCPv4 Release procedure, the UE may subsequently request an IPv4 address for the same PDN connection. If the PDN connection is not released at this point of time, a subsequent IPv4 address request by the UE will result in the allocation of the same IP address, as the IPv4 address assigned to the UE has not been released in the PDN GW and TWAN.

In order to enable IPv6 the TWAN shall support of prefix advertisement for IPv6 prefix received from PDN GW in PMIPv6 Proxy Binding Acknowledgement or in the GTP Create Session Response. Moreover the TWAN may support DHCPv6 server functionality for IPv6 parameter configuration as specified in RFC 3736 [30]. This functionality is required to support DHCPv6 based parameter configuration mechanism in the UE. The TWAN may also support IPv6 RA options for DNS configuration accorduing to RFC 6106 [68].

NOTE 3: Configuration parameters are received from the PDN GW within PMIPv6 PBA message or within GTP Create Session Response message.

After the PDN GW releases the IPv4 address and/or IPv6 prefix, the PDN GW should not assign the same IPv4 address and/or IPv6 prefix to another UE immediately.

In case of static IP address allocation, the TWAN 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 TWAN should forward the static IP address to the PDN GW during the tunnel establishment request (in PBU or in Create Session Request message).

16.1.5.3 IP address allocation in Single-Connection Mode

Similar mechanism as described in TS 23.401 [4] clause 5.3.1.1 is used to decide the PDN type, with the following exceptions:

– The UE indicates the requested PDN type during EAP authentication procedure.

– The TWAG selects the PDN type according to the subscription data in the same way as the MME selects it when 3GPP access is used, as described in TS 23.401 [4].

– If the requested PDN type is IPv4v6, and both IPv4 and IPv6 PDN types are allowed by subscription but not IPv4v6, the TWAG shall set the PDN type to IPv4 or IPv6 where the selection between IPv4 and IPv6 is implementation specific. Then the UE shall not initiate the UE requested PDN connectivity procedure to this APN in order to activate a second PDN connection with the other single address PDN type.

If the PDN Type associated with the PDN connection is IPv4:

– The PDN GW shall allocate and send the IPv4 address to the TWAG in the Create Session Response or Proxy Binding Acknowledgement message. The IPv4 address received from the PDN GW is provided to the UE during the EAP authentication procedure. The PDN GW also sends IPv4 configuration parameters to the UE via PCO.

If the PDN Type associated with the PDN connection is IPv6:

– With GTP-based S2a, the PDN GW shall allocate and send the IPv6 network prefix to the UE in RA message. Because any prefix that the PDN GW will advertise to the UE is unique, there is no need for the UE to perform Duplicate Address Detection for global uniqueness for any IPv6 address configured from the allocated IPv6 network prefix. However, the PDN GW shall respond with Neighbor Advertisement upon receiving Neighbor Solicitation messages from a given UE. For example, the UE may perform Neighbor Unreachability Detection towards the PGW, the PGW supports the DAD related functionality as described in TS 23.401 [4]. Moreover, to ensure that link-local address generated by the UE does not collide with the link-local address of the PGW, the PDN GW shall provide an interface identifier to the UE and the UE shall use this interface identifier to configure its link-local address.

– With PMIP-based S2a, the PDN GW shall allocate and send the IPv6 network prefix to the TWAG in the Proxy Binding Acknowledgement. The TWAG sends it to the UE in RA message. Because any prefix that the TWAG will advertise to the UE is unique, there is no need for the UE to perform Duplicate Address Detection for global uniqueness for any IPv6 address configured from the allocated IPv6 network prefix. However, TWAG shall respond with Neighbor Advertisement upon receiving Neighbor Solicitation messages from a given UE, similar to that supported by PGW in the case of GTP based S5/S8 described in TS 23.401 [4], clause 5.3.1.2.2. Otherwise the PGW has the same functions as it is defined in TS 23.401 [4], clause 5.3.1.2.2. Moreover, to ensure that link-local address generated by the UE does not collide with the link-local address of the TWAG, the PDN GW shall provide an interface identifier to the UE and the UE shall use this interface identifier to configure its link-local address. The PDN GW shall also provide a link-local address to the TWAG and the TWAG shall use the link-local address on the access link shared with the UE.

– The PGW may support DHCPv6 server functionality for IPv6 parameter configuration as specified in RFC 3736 [30]. When the UE requests IPv6 parameter configuration via DHCPv6 procedure, the TWAG delivers DHCPv6 signallings between the UE and the PGW as a DHCPv6 relay in PMIP-based S2a scenario.

If the PDN type associated with the PDN connection is IPv4v6:

– The TWAG shall request both IPv6 network prefix and IPv4 address in the Create Session Request or Proxy Binding Update message.

– The IPv4 address allocation and IPv4 parameter configuration are the same as for PDN type IPv4 defined in previous bullets.

– The IPv6 network prefix allocation via IPv6 Stateless Address auto-configuration procedure and IPv6 parameter configuration via Stateless DHCPv6 procedure are the same as for PDN type IPv6 defined in previous bullets.

After the PDN GW releases the IPv4 address and/or IPv6 prefix, the PDN GW should not assign the same IPv4 address and/or IPv6 prefix to another UE immediately.

In case of static IP address allocation, the TWAG 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 TWAG should forward the static IP address to the PDN GW during the tunnel establishment request (in PBU or in Create Session Request message).

16.1.5.4 IP address allocation in Multi-Connection Mode

Similar mechanism as described in TS 23.401 [4] clause 5.3.1.1 is used to decide the PDN type, with the following exceptions:

– The UE indicates the request PDN type in WLCP signalling.

– The TWAG selects the the PDN type according to the subscription data received from the HSS/AAA in the same way as the MME selects it when 3GPP access is used, as described in TS 23.401 [4].

If the PDN Type associated with the PDN connection is IPv4:

– The PDN GW shall allocate and send the IPv4 address to the TWAG in the Create Session Response or Proxy Binding Acknowledgement message. The TWAG shall send the IPv4 address received from the PDN GW to the UE in WLCP message. The PDN GW also sends IPv4 configuration parameters to the UE via PCO.

If the PDN Type associated with the PDN connection is IPv6:

– The same considerations as above for PDN type IPv6 in single connection mode apply.

If the PDN type associated with the PDN connection is IPv4v6:

– The TWAG shall request both IPv6 network prefix and IPv4 address in the Create Session Request or Proxy Binding Update message.

– The IPv4 address allocation and IPv4 parameter configuration are the same as for PDN type IPv4 defined in previous bullets.

After the PDN GW releases the IPv4 address and/or IPv6 prefix, the PDN GW should not assign the same IPv4 address and/or IPv6 prefix to another UE immediately.