arts configured to them. The obvious problems are that these solutions are usually non-standard and thus, not unified across networks, and therefore also lack a well-specified fallback mechanism from the UE's point of view. 4.3 End User IPv6 Service Impact on GTP and PMIPv6 Protocols 4.3.1 GTP Control Plane Version 1 This section goes through most, if not all, GTPv1 messages and their information elements that contain user plane IPv6 addressing information. We provide a lot of information element figures and their decompositions to ease possible debugging of GTP traces. End User Address Information Element Figures 4.12 and 4.13 illustrate the GTPv1 End User Address information element from a Create PDP Context response, which contains the required IP addressing informa- tion. This information element is used during the PDP Context establishment between the SGSN and the GGSN to request and assign IP addresses and prefixes to the UE. From Release-9 onwards the information element can also contain two addresses at the same time [9]. Octets Type = 0x80 Length (6 for IPv4, 18 for IPv6, 22 for IPv4v6) Spare '1111' PDP Type Organization (1 for IETF) PDP Type Number (0x21 for IPv4, 0x57 for IPv6, 0x8D for IPv4v6) PDP Address (IPv4, IPv6 or IPv4 followed by IPv6) Figure 4.12 The definition of the End User Address information element carrying GTPv1 IP addressing information. Deploying IPv6 in 3GPP Networks User Datagram Protocol, Src Port: gtp-control (2123), Dst Port: gtp-control (2123) GPRS Tunneling Protocol Flags: 0x32 Message Type: Create PDP context response (0x11) Length: 143 TEID: 0x01000065 Sequence number: Ox00d5 N-PDU Number: 0x00 Next extension header type: No more extension headers (0x00) end of GTP header, beginning of extension headers ---] Cause: Request accepted (128) Reordering required: False TEID Data I: 0x9080006d TEID Control Plane: 0x720000a0 Charging ID: 0x730000ab D End user address (IETF/Unknown PDP Type) D Protocol configuration options D GSN address : 10.102.248.166 GSN address : 10.102.248.166 