xt and the EPS dedicated beader. IPv6 in 3GPP Networks Application and service layer Uplink traffic Downlink traffic flow aggregates flow aggregates UL-TFT DL-TFT UL-PF > RAB-ID S1-TEID <-> DL-PF -> RAB-ID <-> S5/S8-TEID S5/S8 S1-TEID eNodeB Radio bearer S1 bearer S5/S8 bearer EPS bearer Legend: UL-TFT - Uplink Traffic Flow Template DL-TDT - Downlink Traffic Flow Template UL-PF - Uplink Packet Filter DL-PF - Downlink Packet Filter RAB-ID - Radio Access Bearer Identifier TEID - Tunnel Endpoint Identifier Figure 4.1 Simplified unicast EPS Bearer concept for GTP-based S5/S8-interface. The default bearer handling is different from the EPS to the GPRS. In the GPRS, the UE can be attached to the radio network but still not have established the PDN Connec- tion. Consequently, there is no IP address allocated to the UE and the PDN Connection either. This is a rather fundamental difference between the EPS and the GPRS regarding the consumption of IP numbering resources. A UE using EPS IP connectivity always con- sumes IP number resources when attached to the radio network; that is, the UE is always on IP connectivity wise. It is possible to delay the allocation of the IPv4 address for the default bearer, if the UE indicates its willingness to use Dynamic Host Configuration Protocol version 4 (DHCPv4) [10, 11] for address configuration. The address allocation for PDN Connections and the default bearer are discussed in detail in Section 4.4 There is a substantial difference between the default bearer and the dedicated bearer. Each time a new default bearer (and the founding PDN Connection) gets created, new IPv4 address and/or IPv6 prefix is allocated and assigned for the PDN Connection. However, when a dedicated bearer gets created, it shares the existing IPv4 address and/or IPv6 prefix allocated for the PDN Connection. Dedicated bearers are differentiated using a Traffic Flow Template (TFT). A TFT is essentially an IP flow filter, and identifies an IP flow that receives a specific QoS treatment between the UE and the PGW.