6.3.12a.2 Access Network Selection Procedure

The steps executed by a N5CW device for access network selection are specified below and are very similar with the corresponding steps executed by a UE that supports NAS; see clause 6.3.12.2.

Step 1: The N5CW device constructs a list of available PLMNs. This list contains the PLMNs included in the PLMN List-4 advertised by all discovered WLAN access networks.

a. The N5CW device discovers the PLMN List-4 advertised by all discovered WLAN access networks by sending an ANQP query to each discovered WLAN access network. The ANQP query shall request "3GPP Cellular Network" information. If a WLAN access network supports interworking with one or more PLMNs, the ANQP response received by the N5CW device includes a "3GPP Cellular Network" information element containing one or more of the following lists: PLMN List-1, PLMN List-2, PLMN List-3 and PLMN List-4. The PLMN List-1, PLMN List-2 and PLMN List-3 are defined in clause 6.3.12. The PLMN List-4 includes the PLMNs with which "5G connectivity-without-NAS" is supported.

Step 2: The N5CW device selects a PLMN that is included in the list of available PLMNs as follows.

a. If the N5CW device is connected to a PLMN via 3GPP access and this PLMN is included in the list of available PLMNs, then the N5CW device selects this PLMN.

b. Otherwise (the N5CW device is not connected to a PLMN via 3GPP access, or the N5CW device is connected to a PLMN via 3GPP access but this PLMN is not in the list of available PLMNs):

• If the N5CW device determines to be located in its home country, then:
• The N5CW device selects the HPLMN if the N5CW device has a USIM or is pre-configured with an HPLMN, if the HPLMN is included in the list of available PLMNs. Otherwise, the N5CW device selects an E-HPLMN (Equivalent HPLMN), if an E-HPLMN is included in the list of available PLMNs. If the list of available PLMNs does not include the HPLMN and does not include an E-HPLMN, the N5CW device stops the access network selection procedure.
• If the N5CW device determines to be located in its visited country, then:
• The N5CW device determines if it is mandatory to select a PLMN in the visited country, as follows:
• If the N5CW device has IP connectivity (e.g. it is connected via 3GPP access), the N5CW device sends a DNS query and receives a DNS response that indicates if a PLMN must be selected in the visited country. The DNS response includes a lifetime that denotes how long the DNS response can be cached.
• If the N5CW device has no IP connectivity (e.g. it is not connected via 3GPP access), then the N5CW device may use a cached DNS response that was received in the past, or may use local configuration that indicates which visited countries mandate a PLMN selection in the visited country.
• If the N5CW device determines that it is not mandatory to select a PLMN in the visited country and the HPLMN or an E-HPLMN is included in the list of available PLMNs, then the N5CW device selects the HPLMN or an E-HPLMN, whichever is included in the list of available PLMNs.
• Otherwise, the N5CW device selects a PLMN in the visited country as follows:
• If the N5CW device has a USIM, the UE selects a PLMN in the visited country by considering, in priority order, the PLMNs, first, in the User Controlled PLMN Selector list and, next, in the Operator Controlled PLMN Selector list (see TS 23.122 [17]).
• If the N5CW device does not have a USIM, the N5CW device selects the highest priority PLMN in a pre-configured list, which is also included in the list of available PLMNs.
• If the list of available PLMNs does not include a PLMN that is also included in the pre-configured list(s), the N5CW device either stops the access network selection procedure, or may select a PLMN based on its own implementation.

Step 3: Finally, the N5CW device selects a WLAN access network (e.g. an SSID) to connect to, following the procedure specified in clause 6.6.1.3 of TS 23.503 [45], "UE procedure for selecting a WLAN access based on WLANSP rules", or any other implementation specific means.

After the N5CW device completes the above access network selection procedure, the N5CW device initiates the "Initial Registration and PDU Session Establishment" procedure specified in clause 4.12b.2 of TS 23.502 [3].