A architecture, the S1-U terminates at the eNB and, if Xw-U user data bearers are associated with E-RABs for which the LWA bearer option is configured, the user-plane data is transferred from the eNB to the WT using the Xw- - U interface. Fig. 8.30 shows the user-plane connectivity of eNB and WT in LWA, where the S1-U terminates at the eNB and the eNB and the WT are interconnected via Xw-U. In the non-co-located LWA scenario, Xw control-plane interface (Xw-C) is defined between eNB and WT. The application layer signaling protocol is referred to as Xw appli- cation protocol (Xw-AP). The Xw-AP protocol supports the transfer of Wi-Fi metrics from WT to eNB; LWA for a UE in ECM-CONNECTED state; establishment, modifica- tion, and release of a UE context at the WT; control of user-plane tunnels between eNB and WT for a specific UE for LWA bearers; general Xw management and error handling func- tions including error indication, setting up Xw, resetting Xw, and updating the WT configu- ration data. The eNB-WT control-plane signaling for LWA is performed through Xw-C - interface. There is only one S1-MME connection per LWA UE between the eNB and the MME. The coordination between eNB and WT is performed via Xw interface signaling. vEPC (S-GW) vEPC (MME) S1-MME ((q)) ((9)) User-plane Control-plane Figure 8.30 User-plane and control-plane connectivity of eNB and WT for LWA [10]. 894 Chapter 8 Fig. 8.30 shows control-plane connectivity of eNB and WT, where the S1-MME is termi- nated at the eNB and eNB and the WT are interconnected via Xw-C. The Wi-Fi mobility set is a set of one or more Wi-Fi access points identified by their BSSID/ESSID/SSIDs (these identifiers are used to describe different sections of a Wi-Fi network), in which Wi-Fi mobility mechanisms apply while the UE is configured with LWA bearer(s), that is, the UE may perform mobility between Wi-Fi APs belonging to the mobility set without informing the eNB. The eNB provides the UE with a Wi-Fi mobility set. When the UE is configured with a Wi-Fi mobility set, it wi