in the S5/S8-interface. Thus, the SGW decapsulates the packet, and then re-encapsulates the packet. As described previously, in the GTP variant the tunneling between the SGW and the PGW is, as already the name says, using GTP. In the PMIP variant, the tunneling is provided by GRE. The packet is sent of by the PGW to further into the Internet. In the opposite direction, the packet arrives at the PGW. The UE's address is allocated from the PGW's address space, and therefore the packet is delivered to the PGW by normal IP routing. The PGW looks up the IP packet's destination address in its bearer table, and forwards the packet downstream on the right GTP or GRE tunnel depending on the EPS variant. The packet is then forwarded to the SGW, which is selected based on the downstream GTP tunnel. The SGW decapsulates the packet coming downstream over the S5/S8-interface, and re-encapsulates the packet to the S1-U interface. The packet is transmitted over the S1-U interface to the eNodeB. The eNodeB selects the right radio bearer based on the tunnel identifier of the GTP tunnel on S1-U, and forwards the packet over the radio interface to the UE. The packet in the UE is received by the LTE modem and forwarded to the IP stack. The packet has arrived. Basics of the 3GPP Technologies Ending the Connection The EPS default EPS Bearer is always on. Hence, as long as the UE is connected to the network, it has a valid IP address, and a working connection to the network. The connection is only deactivated at phone power off, or when transferring the phone to an offline state, such as 'flight mode'. 2.9 Chapter Summary In this chapter, we have examined the packet switched 3GPP network architectures - GPRS and EPS. The purpose was to provide an overview for the reader of the 3GPP network architectures, and the network connectivity services they provide. This should provide an adequate basis of the 3GPP concepts for the reader to understand the rest of the book. There are two GPRS variants, the 2G-GPRS with GERAN radio interface, and t