nages the S2a or S2b tunnel and the GTP-U (User) protocol for building the S2a or S2b tunnel. 156 Wi-Fi Integration to the 4G Mobile Network The GTPv2-C protocol allows the establishment or closure of the mobile context and the bearers of the mobile streams (Table 8.1). Message type Request Response CREATE/DELETE SESSION CREATE/DELETE SESSION Context management REQUEST RESPONSE CREATE/MODIFY/DELETE CREATE/MODIFY/DELETE Bearer management BEARER REQUEST BEARER RESPONSE Table 8.1. GTPv2-C messages The messages CREATE SESSION REQUEST/RESPONSE allow the creation of the context and possibly the default bearer. The messages CREATE BEARER REQUEST/RESPONSE allow the creation of default and dedicated bearers. The context is a collection of mobile-related information including identifiers, location, security and bearer characteristics. The tunnel is identified by the Tunnel Endpoint Identifier (TEID) carried by the GTP-U protocol, tunnel end IP addresses and UDP port numbers. The entity receiving the traffic data determines the value of the TEID parameter that the sending entity is to use. 8.2.1. Trusted Wi-Fi access The GTP-U protocol constructs the S2a tunnel from a TEID provided by the trusted Wi-Fi access for the downstream traffic and a TEID provided by the PGW entity for the upstream traffic. S2a/S2b Tunnel Establishment Wi-Fi access server GTPv2-C CREATE SESSION REQUEST DIAMETER CCR DIAMETER CCA DIAMETER AAR DIAMETER SAR DIAMETER SAA GTPv2-C DIAMETER AAA CREATE SESSION RESPONSE Figure 8.6. S2a tunnel establishment using GTPv2 mechanism The S2a Tunneling procedure, shown in Figure 8.6, starts during the mutual authentication procedure for the mobile and AAA server detailed in Chapter 6. 1) The Wi-Fi access transmits to the PGW entity the GTPv2C message CREATE SESSION REQUEST containing the following fields: IMSI, APN, RAT type, PDN Type, PDN Address, Bearer Identity EPS, Default EPS QoS Bearer, AP Address, AP TEID, APN-AMBR, Charging Characteristics and Additional Parameters. 2) The PGW entity sends the PCRF entity th