 station and the SGW, and S5/S8-bearers (in case of GTP-based S5/S8-interfaces) between the SGW and the PGW. On the GPRS side, the equivalent concept to the EPS Bearer is the Packet Data Protocol (PDP) Context. It is common to refer to PDN Connection and PDP Context as equivalent concepts, although that is not exactly correct. On the GPRS side, there are several architectural differences from the EPC, as discussed in Section 2.2, thus mapping a PDP Context to an EPS Bearer is not straightforward when it comes to bearer behavior details, functional details across various packet core elements, and the protocols used on various interfaces. For example, the GTP-based Gn/Gp-interfaces between the SGSN and the GGSN, and in the case of direct tunneling [8] between the Radio Network Controller (RNC) and the GGSN, use the older GPRS Tunneling Protocol version 1 (GTPv1), [9, 4]. The generic bearer concept for EPS is illustrated in Figure 4.1, when using GTP-based S5/S8-interfaces and for PMIP-based S5/S8-interfaces in Figure 4.2. For simplicity and overall clarity we will use the term PDN Connection to refer also to the PDP Context, unless there is a specific feature or functional difference that does not apply to both, and in this case we will use the exact terminology. One EPS Bearer is immediately established when the UE powers on, attaches to a radio network, and connects to a PDN, and that remains established throughout the lifetime of the PDN Connection to provide the UE with an always-on IP connectivity to the PDN. This bearer is referred as the default bearer in EPS and historically as the Primary PDP Context in GPRS. Any additional PDP Context or EPS Bearer that is established for the same PDN Connection is referred to as a dedicated bearer in EPS and as a Secondary PDP Context in GPRS. The dedicated bearers share their fate with the default bearer (as a detail, the same does not hold for GPRS Primary and Secondary PDP Contexts). For simplicity we use the term dedicated bearer for both the GPRS Secondary PDP Conte