Content for  TS 23.304  Word version:  18.4.0

For unicast mode of 5G ProSe direct communication, the following mechanism for IP address/prefix allocation may be used:

1. DHCP-based IPv4 address allocation with one of the two UEs acting as a DHCP server.
2. IPv6 Stateless Address auto configuration specified in RFC 4862 for assignment of IPv6 prefix, with one of the two UEs acting as IPv6 default router.
3. IPv6 link-local addresses as defined in RFC 4862 are formed by UEs locally. The IPv6 link-local addresses are exchanged during the establishment of a secure layer-2 link over PC5. The UEs shall disable duplicate address detection after the layer-2 link is established.

For broadcast and groupcast modes of 5G ProSe direct communication, the following source IP address management applies:

1. the UE configures a link local IPv4 address to be used as the source IP address, as defined in clause 4.5.3 of TS 23.303. If it is not configured with an address, it uses Dynamic Configuration of IPv4 Link-Local Addresses RFC 3927.
2. the UE configures a link local IPv6 address to be used as the source IP address, as defined in clause 4.5.3 of TS 23.303. The UE may use this IP address for direct communication without sending Neighbour Solicitation and Neighbour Advertisement message for Duplicate Address Detection.

For communication with a 5G ProSe Layer-3 UE-to-Network Relay, the following mechanism for IP address/prefix allocation applies:

• The PDU Session Type used for the relay traffic shall support the IP version used by the 5G ProSe Layer-3 Remote UE. If the 5G ProSe Layer-3 Remote UE initiates an allocation of IPv4 address or an IPv6 prefix when the requested IP version is not supported in the corresponding PDU Session then IP address/prefix allocation fails.
  1. When the 5G ProSe Layer-3 Remote UE uses IPv4 to access the external DN:
     1. The IPv4 address allocation and IPv4 parameter configuration via DHCPv4 are performed according to RFC 2131 and RFC 4039 procedures. The IPv4 address provided to the 5G ProSe Layer-3 Remote UE from the 5G ProSe Layer-3 UE-to-Network Relay by DHCPv4 procedure shall correspond to a local IPv4 address range configured in the 5G ProSe Layer-3 UE-to-Network Relay.
     2. The DHCPv4 request from the 5G ProSe Layer-3 Remote UE is always sent subsequent to the establishment of the one-to-one 5G ProSe Direct Communication between the 5G ProSe Layer-3 Remote UE and the 5G ProSe Layer-3 UE-to-Network Relay, see details for the IPv4 address allocation in clause 5.4.4.3 of TS 23.303 with the following difference:
        • The ProSe Relay UE ID of the ProSe UE-to-Network Relay is replaced by the source Layer-2 ID of the 5G ProSe UE-to-Network Relay for PC5 unicast communication.
  2. When the 5G ProSe Layer-3 Remote UE uses IPv6 to access the external DN:
     1. IPv6 network prefix allocation via IPv6 Stateless Address auto-configuration. Router solicitation from the 5G ProSe Layer-3 Remote UE is always sent subsequent to the establishment of the one-to-one ProSe Direct Communication between the 5G ProSe Layer-3 Remote UE and the 5G ProSe Layer-3 UE-to-Network Relay, see details for IPv6 prefix allocation in clause 5.4.4.2 of TS 23.303 with the following differences:
        • The 5G ProSe Layer-3 UE-to-Network Relay shall obtain the IPv6 prefix assigned to the 5G ProSe Layer-3 Remote UE via prefix delegation function from the network as defined in clause 5.5.2.
        • The ProSe Relay UE ID of the ProSe UE-to-Network Relay is replaced by the source Layer-2 ID of the 5G ProSe UE-to-Network Relay for PC5 unicast communication.
        • PDN connection is replaced by PDU Session.
     2. IPv6 parameter configuration via Stateless DHCPv6: The UE may use stateless DHCPv6 for additional parameter configuration.
     3. The 5G ProSe Layer-3 UE-to-Network Relay assigns IPv6 prefixes from IPv6 prefix range that have been assigned to the PDU Session used for the relay traffic via IPv6 prefix delegation.

For communication with a 5G ProSe Layer-3 UE-to-UE Relay, the following mechanism for IP address/prefix allocation applies:

• IP address allocation mechanisms of unicast mode of 5G ProSe direct communication as described in clause 5.5.1.1 can be reused on each hop between a 5G ProSe End UE and the 5G ProSe Layer-3 UE-to-UE Relay.
• The 5G ProSe Layer-3 UE-to-UE Relay may provide the IP address of the target 5G ProSe End UE to the source 5G ProSe End UE in the Direct Communication Accept message, if the target 5G ProSe End UE IP address is available at the time.
• The 5G ProSe End UE may obtain the IP address of other 5G ProSe End UEs via the 5G ProSe Layer-3 UE-to-UE Relay using DNS query.