AVP level since their inclusion in the 3GPP architecture in Release-7. Essential PCC interfaces like the Gx/Rx/S9-interfaces [78-81] include both dedicated IPv6 AVPs (such as the Framed-IPv6-Prefix) or the generic any IP version AVPs (such as the CoA-IP-Address or the UE-Local-IP-Address). The generic 'any IP address' AVPs makes use of the predefined Diameter type Address, which can convey both IPv4 and IPv6 addresses with varying prefix lengths. We have stated earlier that each PDN Connection is assigned a /64 IPv6 prefix and the prefix should be used to match traffic flows to and from the UE. Full /128 IPv6 addresses are not really supported within the 3GPP architecture. However, some interfaces like the PCC Rx-interface [80] still attempt to use full /128 IPv6 addresses. For example, the Framed-IPv6-Prefix AVP is encoded as an address by using the prefix length of /128. The PCC interface does not really make any difference between PDN Types. Whether the activated PDN Connection is IPv6-only or dual-stack can be derived from the IP address conveying AVPs. As noted earlier, IPv6 support cannot be guaranteed although the interface supports it at the AVP level, if PCEF or Policy and Charging Rules Function (PCRF) implementations just neglect IPv6 content. 4.2.3 Charging and Billing The 3GPP architecture has both multiple charging elements and protocols/interfaces. They do not always even coordinate too much. The charging architecture is described in [82] IPv6 in 3GPP Networks and specifically for the packet switched domain in [83]. The main charging interfaces of interest are: Gy - the online charging reference point between the PCEF and the Online Charging System (OCS). The Gy-interface is replaced by the Ro-interface. Gz - the offline charging reference point between the PCEF and the Charging Gateway Function (CGF)/Offline Charging System (OFCS). Gz-interface is replaced by Rf- interface. Ro - the online charging reference point between the packet core elements (i.e., SGSN, GGSN, PGW, SGW, and MME) and the OCS. 