After the EAP authentication completes as described in the section on authentication, the RADIUS proxy caches the authentication response, including any attributes related to GTP signaling. Subsequently DHCP is initiated from the UE. On receiving DHCP DISCOVER, the RADIUS proxy cache is matched to get the AAA parameters related to the UE from the original authentication response. If PGW/GGSN (mobile gateway) IP address is not present in cached authentication, DNS resolution as described in section 1.2 is initiated for the WLAN APN obtained from AAA (in the cache) or for locally configured APN in the service associated with the UE. The DNS resolution provides a set of IP addresses for the mobile gateways. The GTP tunnel setup is attempted to the selected mobile gateway. The IP address provided by PGW/GGSN in the GTP response is returned in DHCP offer to the UE. The WLAN-GW acts as a DHCP to GTP proxy. The WLAN-GW is the default-GW for the UE. Any packets from the UE are then GTP tunneled to the mobile gateway. If the UE requests an IP address (for which it may have an existing lease on one of its interface) via DHCP option 50 in the DHCP request, then WLAN-GW sets the ‟handover bit” in the GTP session create message, and indicates the requested address in the PDN Address Allocation (PAA) field. This allows the PGW to look for existing session corresponding to the signaled IMSI and APN (with potentially different RAT-Type) and return its existing IP address in session create response. The old session and bearer is deleted by the PGW. The signaling of ‟handover bit” is supported with S2a and S2b (Release 10.0 and beyond). The IP address cannot be preserved over the Gn interface. The call flow in Figure: Inter WLAN-GW mobility based on data-triggered authentication and subscriber creation shows basic GTP setup (with S2a), the output provided on Figure: Inter WLAN-GW mobility based on data-triggered authentication and subscriber creation shows IP address preservation across inter-access (WIFI <-> 4G) moves.
DHCP release or lease timeout on WLAN-GW results in deletion of the GTP tunnel corresponding to the UE. The session or PDP context deactivation from PGW/GGSN also results in removal of the GTP state for the UE and the corresponding ESM host on WLAN-GW. Only the default bearer (or primary PDP context) for single default APN is handled over WIFI. GTP path-management messages (echo request and reply) are supported. Mandatory IEs are supported in GTP signaling. Hard coded default values are signaled for QoS and charging related IEs. For GTPv2, the bearer is signaled as non-GBR bearer with QCI value of 8, and MBR/GBR values of 0. APN-AMBR default values signaled are 20 Mb/s / 10 Mb/s downstream/upstream. For GTPv1, reliability and priority classes default to ‟best-effort”, allocation/retention priority defaults to 1, and the default peak-rate corresponds to class 9 (bit-wise 1001) which is slightly over 2 Mb/s. Charging characteristics IE which contains a 16 bit flag defaults to 0. In the future, RADIUS returned values or locally configurable values is signaled in QoS and charging IEs.
The IP address is returned in the create PDP context response or Create session response. The DNS server addresses for the UE are returned in IP control protocol (IPCP) option in a PCO IE in the response. The default gateway address provided to the UE in DHCP is auto-generated algorithmically on the WLAN-GW from the IP address returned by the PGW/GGSN for the UE. The WIFI AP is required to provide a split-horizon function, where there is no local switching on the AP, and all communication to/from any AP is via WLAN-GW. The WLAN-GW implements proxy-ARP and forwards all received traffic from the UE into the GTP tunnel. In the future, the default-GW address to be returned to the UE could be obtained in a PCO from the PGW/GGSN. The GTP-U processing of data packets is done in the IOM.