. Third, the requested and the sub- scribed PDN Type(s) have to match. IPv6 on the user plane also has an impact on charging, specifically the support for IPv6 and dual-stack PDN Types and address information in Charging Data Records (CDRs). We discuss charging impacts later, in Section 4.2.3. An SGSN, for GPRS using Gn/Gp-interfaces, a S4-SGSN for EPC using S4-interface, and a SGW for EPC using S5/S8-interfaces have different support for PDN Types, espe- cially concerning the PDN Type IPv4v6, and the handling of an unknown PDN Type varies depending on the 3GPP release. We discuss various PDN Type handling combinations and fallback scenarios in detail in Section 4.5. In the past there were SGSNs that did not even understand the PDP Type IPv6 and just caused the PDP Context creation to fail. Such behavior can be regarded as a violation of 3GPP specifications, though. Table 4.2 summarizes the user plane IPv6 support and its impact on the packet core SGSN, SGW, and MME elements. The user plane IPv6 (IPv6-only or dual-stack) is natively supported on EPC from 3GPP Release-8 onwards in SGW, MME, S4-SGSN, and the related signaling interfaces. In the case of GPRS, the Gn/Gp/Gr-based SGSN has IPv6-only support in virtually any release. For the dual-stack, 3GPP Release-9 is required. Specifically, Release-9 introduces the PDP Type IPv4v6 to Gn/Gp-interfaces, and Ext- PDP-Type and Ext-PDP-Address information elements for the Gr-interface [53]. In actual vendor products many of these release-specific features require the purchase of appropriate licenses to be activated and operational. If MBMS [49] is supported within the operator core network, then the SGSN needs to have IPv6 multicast support, more specifically for SSM [50-52]. Table 4.2 SGSN, SGW, and MME support for user plane IPv6 Functionality Gn/Gp-SGSN SGW/S4-SGSN Remarks IPv6-only Release-99 Release-8 Release-8 Dual-stack Release-9 Release-8 Release-8 Release-9 Gr support also required in Gn/Gp-SGSN. IPv6 in 3GPP Networks GGSN and PGW From the user plane point of vi