m, among which LWA is the only scheme that has network architecture implications that will be discussed in this section. The LWA has been supported in 3GPP specs since Rel-13, wherein a UE in RRC_CONNECTED state is configured by the eNB to utilize radio resources of LTE and Wi-Fi. Two scenarios are sup- ported depending on the backhaul connection between LTE and Wi-Fi namely non-co- located LWA scenario for a non-ideal backhaul and co-located LWA scenario for an ideal/ internal backhaul. The overall architecture for the non-co-located LWA scenario is illus- trated in Fig. 8.28, where the Wi-Fi Termination (WT) terminates the Xw interface for Wi- In LWA, the radio protocol architecture that a particular bearer uses depends on the LWA backhaul scenario and the way the bearer is set up. The LWA supports two bearer types: (1) vEPC (MME/S-GW) ((p)) Figure 8.28 Non-co-located LWA architecture [5]. 892 Chapter 8 Split LWA Switched LWA Split LWA Switched LWA bearer bearer bearer bearer bearer bearer LWAAP LWAAP Figure 8.29 LWA radio protocol architecture for the colocated and non-co-located scenarios [5,7]. split LWA bearer and (2) switched LWA bearer. These two bearer types are depicted in Fig. 8.29 for the co-located and the non-co-located scenarios. In the non-co-located LWA sce- nario, the eNB is connected to one or more WTs via Xw interface. In the co-located LWA scenario, the interface between LTE and Wi-Fi is implementation specific. For LWA, the only required interfaces to the core network are S1-U and S1-MME which are terminated at the eNB. The Wi-Fi has no core network interface. In the downlink and for the PDUs that are sent over the Wi-Fi link, the LTE-Wi-Fi aggrega- tion adaptation protocol (LWAAP) entity generates an LWAAP PDU (i.e., a PDU with data radio bearer (DRB) ID generated by LWAAP entity for transmission over Wi-Fi) containing a DRB identity and the WT. An LWA UE determines that the received PDU belongs to an LWA bearer and uses the DRB identity to determine to which LWA bearer the PDU belongs to. 