TE-Uu Wi-Fi Figure 11.1. Functional architecture for LTE and Wi-Fi carrier aggregation The eNB entity is the anchor point for the data exchanged with the mobile, belonging to the user plane (the IP packets) and the control plane and connects to the EPC network: - at the level of the mobility management entity (MME), via the S1- MME interface, for the S1-AP signaling; - at the level of the serving gateway (SGW), via the S1-U interface, for the S1 bearer. 11.2. Protocol architecture 11.2.1. LWA At the radio interface LTE-Uu, between the mobile and the eNB entity, the traffic data correspond to IP packets and the signaling data relate to RRC (Radio Resource Control) messages exchanged between the mobile and the eNB entity and NAS (Non-Access Stratum) messages exchanged between the mobile and the MME entity. Carrier Aggregation The traffic and signaling data is encapsulated by the data link layer, broken down into three sub-layers: - packet data convergence protocol (PDCP); - radio link control (RLC); - medium access control (MAC). LWA (LTE/WLAN Aggregation) occurs at the PDCP layer. The entity eNB carries out a switching of the bearers between, on the one hand, the S1 bearers and, on the other hand (Figures 11.2 and 11.3): - the LTE bearer, for which the data transits only on the LTE access; - the shared LWA bearer, for which the data can pass on both LTE and Wi-Fi accesses; - the switched LWA bearer, for which the data only passes over the Wi-Fi access. The LWA bearer is controlled by the eNB entity from measurement reports transmitted by the mobile. The PDCP frames transmitted over the Wi-Fi access are encapsulated by an LWAAP (LWA Adaptation Protocol) header containing the logical channel identifier (LCID) of the radio bearer. Shared Switched bearer bearer bearer LWAAP MAC LTE LLC / MAC Wi-Fi PHY LTE PHY Wi-Fi LTE access Wi-Fi access Figure 11.2. Protocol architecture for LWA aggregation eNB and AP entities are collocated Wi-Fi Integration to the 4G Mobile Network Shared Switched bearer bearer bearer LWAAP LLC / 