(PDCP) layer [39, 40] for Iu-based 3rd Generation (3G)/UMTS Terrestrial Radio Access Network (UTRAN) or Iu- based 2G/GERAN [41, 42], and finally at the PDCP layer for the S1-based Long Term Evolution (LTE)/Evolved UMTS Terrestrial Radio Access Network (E-UTRAN). The SNDCP layer is between the UE and the SGSN. The PDCP layer is between the UE and the RNC for the 3G/UTRAN or the Evolved Node B (eNodeB) for LTE/E-UTRAN. Should the header compression be supported, then the network has to have support for the required header compression algorithms on the network elements that terminates either SNDCP or PDCP. Table 4.1 lists the header compression algorithms that are supported by the 3GPP system, and their IPv6 support. Additionally, it is good to verify that needed IPv6 profiles of the header compression algorithms are actually implemented, since there are usually different profiles for IPv4 and IPv6. Table 4.1 Header compression support for IPv6 Algorithm IPv6 support SNDCP Remarks Van Jacobson [43] Obsolete IPHC [44] Release-99 Release-99 Not needed by Voice over LTE (VoLTE) [45] ROHC [46, 47, 48] Release-6 Release-4 Profiles 0x0001 and 0x0002 are required by VoLTE [45] Deploying IPv6 in 3GPP Networks If Multimedia Broadcast Multicast Service (MBMS) [49] is supported within the operator core network, then the RNC (for UTRAN) and eNodeB (for E-UTRAN) may need to have IPv6 multicast support, more specifically for Source-Specific Multicast (SSM) [50-52]. SGSN, SGW, and MME Both a SGSN and a SGW are supposed to be transparent to the user plane traffic, since they are not regarded as routers doing forwarding but rather bridging devices. The PDN Type has a critical role during the PDN Connection creation. First, the SGSN, or in the case of EPC the MME, has to understand the requested PDN Type coming from the UE. Second, the SGSN/MME also has to understand the PDN Type downloaded as a part of the subscription profile data (downloaded over Gr- or S6d-interfaces in the case of (S4-)SGSN, and S6a-interface in the case of MME)