If PLMN selection specified in TS 23.122
is applicable (e.g., at switch-on, recovery from lack of 3GPP coverage, or user selection of applicable 3GPP access technology), the PLMN selection to select the highest priority PLMN according to these specifications is performed before any access network discovery.
In the access network discovery procedure, the UE can get ANDSP information on available access networks in its vicinity and can use this information when determining the presence of operator preferred access networks. Determination of the presence of access networks requires using radio access specific procedures, which are not further described here.
The UE may obtain WLAN Selection Policy (WLANSP) rules information by pre-configuration or by downloading the policy information from the PCF as specified in TS 23.503
. The policy contains the UE access network discovery and selection related policy information to help the UE in discovering and selecting a WLAN access network (see TS 24.526
The UE may receive multiple valid WLANSP rules. When the UE is in the home PLMN, the UE uses the valid WLANSP rules from the home PLMN to select an available WLAN. When the UE is roaming and the UE has valid rules from several of the home PLMN, a visited PLMN and a PLMN equivalent to the visited PLMN, the UE uses the WLANSP rules in the following order of decreasing priority:
the valid WLANSP rules from the visited PLMN;
the valid WLANSP rules from the equivalent PLMN in which the UE last received WLANSP; and
the valid WLANSP rules from the home PLMN.
A WLANSP rule is valid if it meets the validity conditions included in the WLANSP rule (if provided).
The UE may apply the techniques specific to the WLAN access technologies to discover available WLAN access networks. Such techniques will not be further described here.
In addition, the UE may obtain information on operator preferred WLAN access networks via ANDSP.