entity for termination of Session Termination Request (STR) mobile session Session Termination Answer (STA) AAA server response to STR request AAA server request for termination of mobile Abort-Session-Request (ASR) session Abort-Session-Answer (ASA) Response of the ePDG entity to the ASR request Request of the ePDG entity used for the Diameter-EAP-Request (DER) EAP-AKA authentication procedure for the DSMIPv6 mechanism AAA server response used for the EAP-AKA Diameter-EAP-Answer (DEA) authentication procedure Table 1.4. DIAMETER messages on the SWm interface Wi-Fi Integration to the 4G Mobile Network 1.3.2. PCRF interfaces The DIAMETER protocol is also supported on the interfaces between, on the one hand, the PCRF entity and, on the other hand (Figure 1.18): - PGW entity via the Gx interface; - trusted Wi-Fi access via the Gxa interface; - ePDG entity via the Gxb interface. Trusted Wi-Fi Access Figure 1.18. PCRF interfaces using the DIAMETER protocol The Gx, Gxa and Gxb interfaces make it possible to request the PCRF entity to: - retrieve the rules to apply to the default bearer created by the EPS network; - inform the PCRF entity of the termination of the session on the EPS network. The Gx, Gxa and Gxb interfaces allow the PCRF entity to provide the rules to be applied for the dedicated bearer. Table 1.5 summarizes the DIAMETER messages exchanged on the Gx, Gxa and Gxb interfaces. Architecture Based on Wi-Fi Access Messages Comments Request from PGW, ePDG or trusted Wi-Fi Credit-Control-Request (CCR) entities to retrieve the mobile profile Credit-Control-Answer (CCA) PCRF response containing the mobile profile Request from the PCRF entity containing the Re-Auth-Request (RAR) mobile profile Response of PGW, ePDG or trusted Wi-Fi Re-Auth-Answer (RAA) access to the RAR request Table 1.5. DIAMETER messages on the Gx, Gxa and Gxb interfaces MAC Layer 2.1. Frame structure 2.1.1. Frame header The MAC (Medium Access Control) header, described in Figure 2.1, encapsulates an LLC (Logical Link Control) frame whose size is