Section: 4.7.2.2 The EPS bearer with GTP-based S5/S8
Content: Figure 4.7.2.2-1: Two Unicast EPS bearers (GTP-based S5/S8) An EPS bearer is realized by the following elements: - In the UE, the UL TFT maps a traffic flow aggregate to an EPS bearer in the uplink direction; - In the PDN GW, the DL TFT maps a traffic flow aggregate to an EPS bearer in the downlink direction; - A radio bearer (defined in TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [5]) transports the packets of an EPS bearer between a UE and an eNodeB. If a radio bearer exists, there is a one-to-one mapping between an EPS bearer and this radio bearer; - An S1 bearer transports the packets of an EPS bearer between an eNodeB and a Serving GW; - An E-RAB (E-UTRAN Radio Access Bearer) refers to the concatenation of an S1 bearer and the corresponding radio bearer, as defined in TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [5]. - An S5/S8 bearer transports the packets of an EPS bearer between a Serving GW and a PDN GW; - A UE stores a mapping between an uplink packet filter and a radio bearer to create the mapping between a traffic flow aggregate and a radio bearer in the uplink; - A PDN GW stores a mapping between a downlink packet filter and an S5/S8 bearer to create the mapping between a traffic flow aggregate and an S5/S8 bearer in the downlink; - An eNodeB stores a one-to-one mapping between a radio bearer and an S1 Bearer to create the mapping between a radio bearer and an S1 bearer in both the uplink and downlink; - A Serving GW stores a one-to-one mapping between an S1 Bearer and an S5/S8 bearer to create the mapping between an S1 bearer and an S5/S8 bearer in both the uplink and downlink. The PDN GW routes downlink packets to the different EPS bearers based on the downlink packet filters in the TFTs assigned to the EPS bearers in the PDN connection. Upon reception of a downlink data packet, the PDN GW evaluates for a match, first the downlink packet filter that has the lowest evaluation precedence index and, if no match is found, proceeds with the evaluation of downlink packet filters in increasing order of their evaluation precedence index. This procedure shall be executed until a match is found, in which case the downlink data packet is tunnelled to the Serving GW on the EPS bearer that is associated with the TFT of the matching downlink packet filter. If no match is found, the downlink data packet shall be sent via the EPS bearer that does not have any TFT assigned. If all EPS bearers (including the default EPS bearer for that PDN) have been assigned a TFT, the PDN GW shall discard the downlink data packet.