3 UE with tight integration (A), loose integration (B), and Split-UE (C) - in the split case the tethering is performed by the MT or the TE on the mobile phone. Deploying IPv6 in 3GPP Networks mobile phone that shares its cellular connectivity over WLAN to a laptop and a tablet device. As shown in the figure, the MT function resides in the device providing access to the 3GPP network. The TE function, on the other hand, not only resides inside the hand- set, but logically also on the other devices, such as on the illustrated laptop and tablet. A significant factor in the Split-UE case is that the other devices are not necessarily aware of the fact that they are utilizing 3GPP access and having the role of 'TE'. As in the case 'B', some issues may arise due to differences in link types between TEs and the MT and from the MT to the 3GPP network. As shown in the figure, the whole set of handset and tethered devices is considered as an abstract UE from the cellular network point of view - the network serves the set of devices as if it were one traditional UE. IP address wise the handset is often, but not necessarily, performing IPv4 NAT functions and some variation of IPv6 Neighbor Discovery Proxy (see more in Section 3.4.10). When the tethered devices' data passes through handset's IP stack pointed by interface Ie1, the tethering can be considered to be done by the TE on a handset and not by the MT (indicated by interface Ie2). When the tethering is performed via Ie2 the interface is often implemented in a dial-up fashion; that is, the data channel may present serial communications and the AT-command set may be in use. As is often the case with tricks doable inside 'black boxes', several different implementation variations of the tethering feature are possible. The way of sharing connectivity described above and specified in pre-Release-10 3GPP standards does not require, or provide, any explicit support from the 3GPP network. Nevertheless, sometimes the tethering is (dis)allowed via administrative means: by polic- i