P [8] There are two types of information provided by the ANDSF, that is, the inter-system mobility policy and the access network discovery functionality. The ANDSF may provide both types of information or only one of them, according to the operator requirements and according to the roaming agreements. The inter-system mobility policies and access network discovery information provided to the UE by the ANDSF take precedence on the inter-system mobility policies and access network discovery information pre-configured on the UE. The ANDSF is discovered through interaction with the Domain Name Service function or the DHCP Server function. The usage of ANDSF capabilities is intended for scenarios where access-network level solutions are not sufficient for the UE to perform Network Discovery and Selection of non-3GPP technologies according to operator policies. Figure 11.6 shows the utilization of ANDSF for both roaming and non-roaming scenarios. 11.5.1.2 Network Entry Initial network entry is a process where the newly arrived UE is required to access network services. In the first step the mobile device is required to synchronize itself with the BS and exchange basic capabilities, after which the authenticating is carried out. After successful authentication, security keys are exchanged over the air interface. Then, registration takes place and IP address is obtained. This in turn triggers a bearer establishment between the ASN-GW and the P-GW by means of Proxy Mobile IP (in the case of WiMAX). In the case of un-trusted non-3GPP access, only Tunnel authentication is used and is executed across a SWm reference point. Tunnel authentication refers to the procedure by which the UE and the ePDG perform mutual authentication during the IPsec tunnel establishment between the UE and the ePDG (SWu reference point) [7]. The material in [6] shows how EPC enables a WiMAX UE to attach to 3GPP core network resources. This becomes possible by means of an AAA server, a PMIP interface between the WiMAX ASN-GW and P-GW (called S2a), an