not just a prefix. MBMS IP Multicast Distribution for GTPv2 The MBMS IP Multicast Distribution information element may appear in the MBMS Session Start Request GTPv2 message that is sent from the MBMS Gateway to the MME/S4-SGSN [3, 49]. The information element contains both the IPv4 or IPv6 multicast destination address and the source address (for SSM [50]). Figure 4.18 shows the format of the MBMS IP Multicast Distribution information element. 4.3.3 GTP User Plane IPv6 on the user plane has no impact on the GTP-U. The GTP-U is transparent to the IP version it carries. 4.3.4 PMIPv6 Since the PMIPv6 was originally designed and built around Mobile IPv6 (MIPv6) [102], IPv6 on the user plane has no impact to the PMIPv6, neither on the user plane nor on the control plane. However, if the transport plane remains in IPv4, then PMIPv6 has to be enhanced with support for IPv4 addressing and an IPv4 transport plane [7]. Octets Type = 0x4a Length n (4 for IPv4, 16 for IPv6) Spare Instance 5 to n+4 IPv4 or IPv6 address (full addresses) Figure 4.17 The GTPv2 IP Address information element carrying either IPv4 or IPv6 address. IPv6 in 3GPP Networks Octets Type = 0x8e Length= n Spare'0000' Instance Common Tunnel Endpoint Identifier v4 = 0, v6 = 1 Address Length (v4 = 4, V6 = 16) IP Multicast Distribution Address (IPv4 or IPv6); Multicast Address v4 = 0, v6 = 1 Address Length (v4 = 4, V6 = 16) (k+2)-m IP Multicast Source Address (full IPv4 or IPv6 address) MBMS Header Compression Indicator (0 = uncomp., 1 = comp.) (m+2)-n Figure 4.18 The MBMS IP Multicast Distribution information element carrying either IPv4 or IPv6 address. IP Address Assignment, Configuration, and Management 4.4.1 Addressing Assumptions 3GPP has defined multiple IP address assignment mechanisms. While our main focus is on IPv6, we briefly go through also IPv4 related address assignment and configura- tion aspects. After all, they are tightly linked to the behavior of a dual-stack (i.e., PDN Type IPv4v6) bearer. Table 4.4 lists all 'relevant' IPv4 and IPv6 addr