P interface. However, in reality integrated devices may have any kind of interface. Typically, an integrated UE has a tailored 'cellular aware' TCP/IP stack and APIs for applications. In this case, the IPv6 readiness - from the previous list items from 1 to 5 - is usually entirely controlled by the UE vendor, with the exception being 3rd party applications. The AT-command set and the interface has to obviously support IPv6 in 3GPP Networks IPv6 extensions, and if the PPP is really used, it also has to explicitly support IPv6 and Internet Protocol version 6 Control Protocol (IPv6CP) [35]. An alternative way to implement a UE separates the end host with the IP stack (the Terminal Equipment (TE) part) and the radio modem (the Mobile Terminal (MT) part). This is a typical dialup model setup and is commonly referred as the Split-UE. The protocol between the TE and the MT has traditionally been PPP, as originally defined in 3GPP standards [25]. However, it is fairly common today to use Universal Serial Bus (USB) based connection between the TE and the MT [36, 37], and expose the cellular point-to-point link as an Ethernet interface. Also, the difference between an integrated and Split-UE has blurred, and many UEs that were considered as integrated are actually internally Split-UEs. In Section 4.7 we will go into details, describing UE specific IPv6 considerations. Radio Access Network The Radio Access Network (RAN) ought to be completely transparent to user plane IP addressing. However, if the IP header compression is enabled and used, it can make a difference. Unfortunately there are multiple combinations of header compression algo- rithms, depending on what kind of RAN and which 3GPP release of it is in use. A header compression algorithm typically has explicit support for compressing IPv6 pack- ets. The header compression takes place either on the Subnetwork Dependent Convergence Protocol (SNDCP) [38] for Gb-based 2nd Generation (2G)/GSM/Edge Radio Access Net- work (GERAN) or at the Packet Data Convergence Protocol 