eir decompositions to ease possible debugging of GTP traces. Deploying IPv6 in 3GPP Networks PDN Address Allocation Information Element Figures 4.14 and 4.15 illustrate the GTPv2 PDN Address Allocation (PAA) information element from a Create Session response, which contain the required IP addressing infor- mation. This information element is used, for example, during the PDN Connection establishment between the SGW and the PGW (S5/S8-interfaces), the S4-SGSN and the SGW (S4-interface), the MME and the SGW (S11-interface) to request and assign IP addresses and prefixes to the UE. The PDN Type numbering follows the 3GPP's own registry defined in [3]. Furthermore, only IP packets are now allowed over the GTP tunnels, SO there is no specific field organization type like GTPv1 had. Regarding the IPv6 addresses, they are full addresses containing both prefix and a 64- bit IID selected by the PGW. On GTPv2 signaling the prefix part of the IPv6 address has no meaning, other than being aligned with the practices of GTPv1. There is one significant change/improvement in GTPv2 over GTPv1, namely the IPv6 prefix length is now included as part of the signaling. This small addition will better the forward compatibility of the GTPv2 if/when there are changes, for example, in IPv6 address autoconfiguration [22]. PDN Type Information Element The PDN Type information element can only be found in the Create Session Request mes- sage during the E-UTRAN Initial Attach, UE requested PDN connectivity, or PDP Context Activation (S4 case). The information element is used only for indicating the requested PDP Type during the connection activation. Unlike in GTPv1, the requested PDN Type information is now separate from the addressing information the PDN Address Alloca- tion information element. Figure 4.16 shows the information element format. Octets Type = 0x4f Length (5 for IPv4, 18 for IPv6, 22 for IPv4v6) Spare Instance Spare v4=001, v6 = 010, v4v6 = 011 6 to n+4 PDP Address (IPv4, IPv6 prefixlen+IID or IPv6 prefixlen+IID followed by I