irection, the packet destination is set to the IP address allocated to the UE. As the UE's IP address has been allocated from the address pool of the GGSN, the packet travels the networks of the Internet, and arrives at the GGSN. The GGSN has a context table - practically a forwarding table that maps an IP address to the GTP tunnel that makes the PDP Context. The GGSN encapsulates the IP packet going downstream towards the UE, and sends it to the SGSN serving the UE. As for the packets coming upstream, the SGSN decapsulates the packet and in 3G case re-encapsulates the packet into the GTP tunnel, which is between the GGSN and the RNC serving the UE. The RNC de-encapsulates the packet. The packet is then mapped by the RNC to the radio bearers and sent to the UE. Again, all these steps inside the GPRS network are completely transparent to the IP packet. The IP packet then arrives at the UE's IP stack. Ending the Connection Modern smartphones activate PDP Contexts automatically. The PDP Context is often activated all the time, unless a preferred alternative is available such as WLAN. Thus, the PDP Context is activated as the phone is turned on, and is deactivated when the mobile phone is turned off. The PDP Context may be deactivated if the phone finds a preferred WLAN network, and re-actives when the connection to the WLAN is lost. However, some mobile phones keep a PDP Context activated only when there is an application that needs the connection to be active. However, as described in Section 2.3.1, the PDP Context deactivation can be done independently of the network attachment. Thus, the PDP Context can be deactivated, and the UE can stay attached to the network. The network detachment is usually only done when a phone is switched off, or switched to offline state such as 'flight mode'. 2.8.2 EPS As with GPRS above, in this section we will go through the life cycle of the network connection. This section will first go through the network attachment with the default bearer establishment, over the IP communication 