Section: 11.2.1.6 Support for CUPS across SGi
Content: Control plane and user plane separation of PGW as PGW-C and PGW-U, has been introduced as described in 3GPP TS 23.214[ Architecture enhancements for control and user plane separation of EPC nodes ]  [117]. For UE IP address from the DN AAA server in the external PDN: If the AAA server in the external PDN is reachable only via the PGW-U, the PGW-U forward all the Diameter or RADIUS messages between the DN AAA server in the external PDN and the PGW-C, according to 3GPP TS 29.244[ Interface between the Control Plane and the User Plane nodes ]  [114]. For UE IP address from DHCPv4/v6 server in the external PDN: If the DHCPv4/v6 server in the external PDN is reachable only via the PGW-U, the PGW-U forward all the DHCPv4/v6 messages between the DHCPv4/v6 server in the external PDN and the PGW-C. according to 3GPP TS 29.244[ Interface between the Control Plane and the User Plane nodes ]  [114]. NOTE: If the DN AAA server or the DHCPv4/v6 server in the external PDN is reachable directly, then the PGW-C communicates with it directly, without involving the PGW-U.