24.3023GPPAccess to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networksRelease 18Stage 3TS
Figure A1 below shows an inter-system change procedure between 3GPP access network and non-3GPP access network using information obtained from ANDSF.
In this example the UE uses DHCP query to obtain the IP address of the ANDSF.
In this example flow, the communication between the UE and ANDSF does not imply use of any specific protocol.
The steps involved in inter-system change between 3GPP access network and non-3GPP access network are as follows.
Figure A1. Procedure for Inter-system change between 3GPP access and non-3GPP using ANDSF
1. Initial connectivity
The UE is connected to 3GPP network. The current applications are supported over the 3GPP access network.
NOTE: The procedure remains the same if the UE is initially connected to non-3GPP access network and wants to change to 3GPP access network.
2. Pre-provisioned policies
The inter-system mobility policy is pre-provisioned on the UE. Based on pre-provisioned operator policies the UE has preference for different non-3GPP networks such as WLAN, and WiMAX. The UE can select these access networks when they are available.
3. ANDSF Discovery
ANDSF discovery is performed as described in clause 126.96.36.199.1. The UE can discover ANDSF using DHCP query options as specified in IETF RFC 6153 , where ANDSF may be identified with a specific sub-option code. Optionally, the home operator can use OMA-DM’s bootstrap mechanism as specified in OMA-ERELD-DM-V1_2  to provide ANDSF information and security parameters for application layer authentication. Transport security is ensured by establishing an https tunnel between the UE and ANDSF,
4. Policy Update based on Network Triggers
Based on network triggers the ANDSF sends an updated inter-system mobility policy to the UE. The inter-system mobility policy includes validity conditions, i.e. conditions indicating when the policy is valid. Such conditions can include time duration, location area, etc.
5. Evaluate which non-3GPP networks to discover
The inter-system mobility policies specify the access networks that the UE can select; the UE has both WLAN and WiMAX radios. In this case, the inter-system mobility policy provided by the operator allows the UE to select either WLAN or WiMAX networks under all conditions. The UE, taking into account of the UE’s local policy, e.g. user preference settings, access history, obtains information about availability of both WLAN and WiMAX access networks in its vicinity.
6. Access Network Information Request
The UE sends a request to ANDSF to get information about available access networks. The UE also includes its location information in the request. ANDSF can limit the information sent to UE based on internal settings.
7. Access Network Information Response
The ANDSF sends a response to the UE which includes the list of available access networks types (in order of operator preferences), access network identifier and PLMN identifier. In this case the ANDSF responds with availability of both WLAN and WiMAX network in the vicinity of the UE.
8. Evaluate candidate non-3GPP networks
Based on the received information and UE’s local policy, the UE evaluates if it is within the coverage area of the available access networks in the order of preferences. In this case,based on the history and radio quality of WiMAX, the UE prefers WiMAX over WLAN access type. The UE powers on the WiMAX radio and checks for the presence of WiMAX network. The UE can listen to WiMAX broadcast messages (uplink/downlink channel data messages) and determines the presence of WiMAX network. Since the WiMAX network is the preferred network and since the UE has verified the presence of WiMAX network, the UE does not check for presence of WLAN network.
9. Non-3GPP Network Selection
The UE selects the most preferred available access network for inter-system mobility. In this case the UE selects the WiMAX access network.
10. Inter-system change Procedure
The UE initiates inter-system change procedure to the selected non-3GPP access network. The details of the inter-system change procedure are described elsewhere, see 3GPP TS 23.402 .
Annex B (informative):
Assignment of Access Network Identities in 3GPP
This annex describes the recommended assignment procedure of Access Network Identities within 3GPP.