over the network, to the closing of the connection. Deploying IPv6 in 3GPP Networks Getting Connected We described in Section 2.3.1 that in the EPS system the default EPS Bearer is activated as a part of the network attachment procedure. Therefore, after the network attachment the UE has a working network connection. Similarly to the GPRS, the IP stack configuration, and IP address allocation is done during the default EPS Bearer establishment. The UE is provided by the IP addresses - one IPv4 address, a range of IPv6 addresses, or both. As in GPRS, the UE indicates which kind of connectivity it wishes to have (IPv4, IPv6, or both), and it may also provide the APN. The MME may adjust the requested IP version and the APN according to the subscription information it obtains from the HSS. The PGW allocates the IP addresses and provides additional configuration information, for instance the DNS server information. After the UE has configured its IP stack with the address, and additional configuration information provided, the UE is ready to start communicating to the Internet. Packet Delivery Perhaps not unexpectedly, the journey of a packet through the EPS system is quite similar to the journey of a packet through GPRS. There is a slight difference between the GTP and PMIP EPS variants due a difference in the link model. However, the difference is explained in detail in Section 4.1.1. Starting from the UE, the IP packet with the UE's IP address in the source address field starts its journey off by being sent by the UE's LTE modem over the LTE radio interface. As there is no radio controller element in the EPS architecture, the eNodeB is responsible for header compression, and terminating all radio protocols. The eNodeB has a mapping from the radio bearers to the equivalent GTP tunnels. The packet gets encapsulated by the eNodeB and sent to the SGW. The MME is not involved in the user-plane forwarding. Similarly to the SGSN in GPRS, the SGW has a bearer table mapping the tunnels on the S1-U to the equivalent tunnels 