IPv4v6 IPv4v6 Note 3 IPv4v6 IPv4v6 IPv4v6 IPv4, IPv6 IPv4 or IPv6 Note 4 IPv4v6 IPv4v6 unset IPv4v6 IPv4v6 Note 4 IPv4v6 IPv4v6 unset IPv4v6 IPv4v6 Note 4 IPv4v6 IPv4v6 IPv4v6 IPv4v6 IPv4v6 Deploying IPv6 in 3GPP Networks Req. stands for the PDN Type requested by the SGSN/MME after matching against the subscribed PDN Types has been done. The table does not include the majority of the redundant combinations such requesting a PDN Type that is not subscribed in an HLR/HSS or configured in a PGW. Neither does the table consider possible intentional restrictions on PDN Type handling such as could be the case for inbound and outbound roamers. Roaming restrictions were briefly discussed in Section 4.2.5. In Table 4.9 comma-separated lists of addressing types mean that these are the possible choices (i.e. 'or'). Note 1 A pre-Release-9 SGSN treats an unknown PDP Type (here IPv4v6) as IPv4. This might cause an immediate PDP Context creation failure in the SGSN or conversion to PDP Type IPv4. Furthermore, the UE does not receive any Release-9 error codes, which could instruct the UE to create an IPv6 type parallel PDP Context. Note 2 A UE will receive an (E)SM cause #50 'PDN/PDP Type IPv4 only allowed' [12, 13]. The UE must not attempt to establish a second parallel PDN Connection of a different PDN Type in order to mimic dual-stack behavior. Note 3 A UE will receive an (E)SM cause #51 'PDN/PDP Type IPv6 only allowed' [12, 13]. The UE must not attempt to establish a second parallel PDN Connection of a different PDN Type in order to mimic dual-stack behavior. Note 4 A UE will receive an (E)SM cause #52 'single address bearers only allowed' [12, 13]. The UE is allowed/should establish a second parallel PDP Context/PDN Connection of a different PDN Type in order to mimic dual-stack behavior. In addition to the Table 4.9 selection rules, the UEs may implement their vendor-specific additional logic. One example is the case where the attempt at PDN Types IPv4v6 fails and the UE falls back to PDN Type IPv6 and eventually to Type I