e CCR DIAMETER message to obtain the default bearer characteristics. The PCRF entity can change the value of the APN-AMBR. 3) The PCRF entity responds to the PGW entity with the CCA DIAMETER message containing the rules to be applied to the default bearer (QoS parameters, filter parameter, charging mode). 4) The PGW entity sends the AAA server the AAR DIAMETER message to communicate its identity and the access point name for the connection. 5) The AAA server transmits to the HSS entity the SAR DIAMETER message to transfer the information received from the PGW entity. 6) The HSS entity responds to the AAA server with the SAA DIAMETER message. 7) The AAA server responds to the PGW entity with the AAA DIAMETER message. 158 Wi-Fi Integration to the 4G Mobile Network 8) The PGW entity responds to trusted Wi-Fi access with the GTPv2C message CREATE SESSION RESPONSE, containing the following fields: PGW Address, PGW TEID, PDN Type, PDN Address, EPS Bearer Identity, EPS Bearer QoS, APN-AMBR and Additional Parameters. The trusted Wi-Fi access completes the authentication procedure (EAP Success message) by providing the elements of its configuration contained in the Additional Parameters field. 8.2.2. Untrusted Wi-Fi access The GTP-U protocol constructs the S2b tunnel from a TEID provided by the ePDG entity for downstream traffic and a TEID provided by the PGW entity for upstream traffic. The procedure for setting the S2a bearer resumes that described for the PMIPv6 mechanism with the following modifications: The PBU message in step 1 is replaced by the CREATE SESSION REQUEST message containing the following fields: IMSI, APN, RAT type, TEID ePDG, PDN Type, PDN Address, Bearer Identity EPS, EPS QoS Bearer, ePDG Address, APN-AMBR and Additional Parameters. The PBA message in step 8 is replaced by the CREATE SESSION RESPONSE message containing the following fields: PDN GW Address, PDN GW TEID, PDN Type, PDN Address, Bearer Identity EPS, EPS Bearer QoS, APN-AMBR and Charging ID. 8.3. MIPv4 FA mechanism 8.3.1. Components of mo