(GTP) is a group of IP-based communications protocols used to carry General Packet Radio Service (GPRS) within GSM and UMTS networks. 3GPP Evolved Packet System (EPS) Application/Service Layer UL Traffic Flow Aggregates DL Traffic Flow Aggregates UL-TFT DL-TFT UL-TFT RB-ID DL-TFT S5/S8-TEID RB-ID S1-TEID S1-TEID S5/S8-TEID eNodeB Serving GW PDN GW Radio Bearer S1 Bearer S5/S8 Bearer Figure 3.28 Two unicast EPS bearers (GTP-based S5/S8). Reproduced with permission from © 2009 3GPP [21] S5/S8, and by an EPS bearer concatenated with IP connectivity between Serving-GW and PDN-GW in case of PMIP¹6 -based S5/S8. 17 An EPS bearer uniquely identifies traffic flows that receive a common QoS treatment between a UE and a PDN-GW and between UE and S-GW [21]. An EPS bearer is established when the UE connects to a PDN, and that remains established throughout the lifetime of the PDN connection to provide the UE with always-on IP connectivity to the PDN. The EPS bearer traffic flow template (TFT) is the set of all packet filters associated with that EPS bearer. An UpLink Traffic Flow Template (UL TFT) is the set of uplink packet filters in a TFT. A DownLink Traffic Flow Template (DL TFT) is the set of downlink packet filters in a TFT. Every dedicated EPS bearer is associated with a TFT. The initial bearer level QoS parameter values of the default bearer are assigned by the network, based on subscription data. That bearer is referred to as the default bearer. Any additional EPS bearer that is established to the same PDN is referred to as a dedicated bearer. The decision to establish or modify a dedicated bearer can only be taken by the EPC, and the bearer level QoS parameter values are always assigned by the EPC [11, 14, 21, 22]. 3.9.1.1 The EPS Bearer with GTP-based S5/S8 Figure 3.28 shows the GTP-U based bearer based on the protocol being used on S5 and S8 interfaces. In this case, the GTP tunnel IDs over S5/S8a interfaces has a one-to-one mapping to S1 interface Tunnel IDs as well as to Radio Bearer IDs over the Radio Bearer. 