5 Network selection

24.2343GPP3GPP system to Wireless Local Area Network (WLAN) interworkingRelease 12Stage 3TSWLAN User Equipment (WLAN UE) to network protocols

5.1 General

WLAN selection consists of two selection procedures: I-WLAN selection and PLMN selection. These procedures are applicable to initial network selection at WLAN UE switch on and following recovery from lack of WLAN radio coverage. In order to ensure that the result of network selection is the association with an I-WLAN that has direct connection to HPLMN, both procedures are linked to each other as specified in this clause.

Two 3GPP – WLAN interworking network selection modes are defined, automatic and manual. At switch on, if the WLAN UE provides the optional feature of user preferred PLMN selection operating mode then this operating mode shall be used. The support of additional network selection modes is implementation dependent.

For manual network selection procedures defined in subclause 5.2.3 the WLAN UE produces a list of available PLMNs. The list of PLMN shall be acquired by performing one of the following:

1) If the WLAN UE and WLAN supports IEEE Std 802.11u™-2011 [23] then ANQP shall be used each WSID;

2) If the WLAN UE and WLAN supports IEEE 802.1x authentication, the WLAN UE shall associate and perform EAP based network discovery with the available WSID using the Alternative NAI until every available WLAN has been associated with and EAP network discovery has been performed; or

3) If the WLAN does not support IEEE 802.1x authentication and the "HPLMN Direct Access Indicator" as specified in subclause 7.11 allows direct access and if the WLAN UE chooses to perform direct access to HPLMN, then the WLAN UE shall attempt to create a direct connection to the HPLMN using tunnel management procedures as defined in clause 8.

For automatic selection procedures defined in subclause 5.2.4.

As an alternative option to this, if the WLAN UE is in automatic network selection mode and it finds a WSID known to support connectivity to the HPLMN, the WLAN UE selects the HPLMN and does not return to the I-WLAN Last registered PLMN. The operator controls this by the "I-WLAN HPLMN Priority Indication" as specified in subclause 7.10 whether a WLAN UE that supports this option performs this alternative behaviour. If the HPLMN cannot be found, the WLAN UE returns to the I-WLAN last registered PLMN if available.

If there is no I-WLAN Last Registered PLMN, or if selection is not possible due to the PLMN being unavailable or selection failure, the WLAN UE shall use a WSID that has a direct connection to HPLMN. This is done by performing the procedures in 1) – 3) above with the available WSIDs until a WSID that has a direct connection to the HPLMN has been found. If a WSID that has direct connection to HPLMN is not found, then the WLAN UE attempts to select a WSID that has connection to one of the PLMNs in the preferred PLMNs lists. The order that the WLAN UE follows for association with the available WSIDs is determined by the "User Controlled WLAN Specific Identifier list", "Home I-WLAN Specific Identifier List" and "Operator Controlled WLAN Specific Identifier list", if available.

Network selection procedure is completely independent of the result of the PLMN selection under other radio access technologies that are specified in 3GPP TS 23.122 [1]. The signal quality shall not be used as a parameter for network selection.

To assist in selecting a PLMN a number of lists are defined: the"User Controlled PLMN Selector list for I-WLAN" and the "Operator Controlled PLMN Selector list for I-WLAN". If these lists are supported on the USIM then the WLAN UE shall read and use all the entries.

5.2 PLMN selection

5.2.1 WLAN UE I-WLAN selection procedure

The WLAN UE shall use scanning procedures as specified in subclause 4.3 in order to find the available WSIDs.

For the purpose of discovering the supported PLMNs:

1) If both the WLAN and WLAN UE supports IEEE Std 802.11u™-2011 [23] the WLAN UE shall use ANQP procedures sequentially with each WSID; and

2) The WLAN UE shall sequentially perform association with each WSID.

The above shall be performed using the list of available WSIDs in the following order:

a) If the "I-WLAN HPLMN Priority Indication" as specified in subclause 7.10 is available and is set then if the "Home I-WLAN Specific Identifier list" data file is available in the USIM, each WSID in the "Home I-WLAN Specific Identifier list" data file in the USIM (in priority order).

b) If the "User Controlled WLAN Specific Identifier list" data file is available in the USIM, each WSID in the "User Controlled WLAN Specific Identifier list" data file in the USIM (in priority order).

c) If the "Operator Controlled WLAN Specific Identifier list" data file is available in the USIM, each WSID in the "Operator Controlled WLAN Specific Identifier list" data file in the USIM (in priority order).

NOTE: Requirements for the presence of the "User Controlled WLAN Specific Identifier list" data file, "Home I-WLAN Specific Identifier list" and the "Operator Controlled WLAN Specific Identifier list" data file are defined in 3GPP TS 31.102 [13].

d) If neither "User Controlled WLAN Specific Identifier list", "Home I-WLAN Specific Identifier list" nor "Operator Controlled WLAN Specific Identifier list" data file is available in the USIM and the ME supports at least one of the optional "User Controlled WLAN Specific Identifier list", "Home I-WLAN Specific Identifier list" or "Operator Controlled WLAN Specific Identifier list" lists in the ME memory:

i) if the "I-WLAN HPLMN Priority Indication" as specified in subclause 7.10 is available and is set then each WSID in the "Home WLAN Specific Identifier list" data file in the ME (in priority order);

ii) each WSID in the "User Controlled WLAN Specific Identifier list" data file in the ME (in priority order);

iii) each WSID in the "Operator Controlled WLAN Specific Identifier list" data file in the ME (in priority order).

e) Other WSIDs supporting 3GPP – WLAN interworking in implementation specific order.

In the case of Automatic PLMN selection the WLAN UE shall stop performing association with other WLANs once a direct connection to the HPLMN has been found if there is:

1) no EHPLMN list present; or

2) the EHPLMN list is present but empty; or

3) the EHPLMN list has a single entry which is the PLMN derived from the IMSI.

In the case when the EHPLMN list is present and the list has:

1) a single entry that is not the PLMN derived from the IMSI then the WLAN UE shall stop performing association with other WLANs once a direct connection to the EHPLMN has been found; or

2) two or more entries, then the WLAN UE shall stop association with other WLANs when the highest priority EHPLMN has been found.

If no association with any I-WLAN is found, the WLAN UE behaviour is implementation dependent.

The PLMN identities thus found are used in the PLMN selection procedure.

5.2.2 Void

5.2.3 Manual PLMN selection mode procedure

In case of manual network selection mode, for WLANs that:

1) together with the WLAN UE support IEEE Std 802.11u™-2011 [23], the WLAN UE shall send an ANQP request to each WSID. If the WSID supports advertisement of PLMNS, it shall send back an ANQP response to the WLAN UE including the Supported PLMNs list for WLAN access. See Annex A. If the WLAN UE receives a ANQP response where the "Info ID" is not "3GPP Cellular Network information" the behaviour of the WLAN UE is outside the scope of this specification.

2) support IEEE 802.1x authentication, the WLAN UE shall request for a list of supported PLMNs by issuing an EAP-Response/Identity message to the WLAN including as identity the alternative NAI. See subclause 4.2.5.

3) do not support IEEE 802.1x authentication, if the "HPLMN Direct Access Indicator " as specified in subclause 7.11 allows direct access and if the WLAN UE chooses to perform direct access to HPLMN, then for HPLMN access the WLAN UE shall sequentially perform association and perform tunnel management procedures as specified in the clause 8 with each broadcast WSID that does not support IEEE 802.1x authentication.

NOTE: In case 3), if authentication is required to access the internet when accessing a WLAN that does not support IEEE 802.1x authentication then the procedures to do this are outside scope of this specification.

Based on the results of Items 1) – 3) above, the WLAN UE shall indicate to the user the PLMNs which are available. If more than one I-WLAN is capable of being used to establish a direct connection with a PLMN, the WLAN UE should indicate each of the candidate I-WLANs along with the PLMN to the user. If displayed, PLMNs from the Supported PLMNs list shall be presented in the following order:

a) HPLMN (if the EHPLMN list is not present, or is present and empty);

b) If one or more of the EHPLMNs are available then based on the optional "I-WLAN Equivalent HPLMN Presentation Indication" as specified in subclause 7.12 either the highest priority EHPLMN among those that are available is to be presented to the user or all available EHPLMNs are presented to the user in priority order;

c) If the "User Controlled PLMN Selector for I-WLAN access" data file is available, PLMNs in the "User Controlled PLMN Selector for I-WLAN access" data file in the USIM (in priority order).

d) If the "Operator Controlled PLMN Selector for I-WLAN access" data file is available, PLMNs in the "Operator Controlled PLMN Selector for I-WLAN access" data file in the USIM (in priority order).

e) If neither "User Controlled PLMN Selector for I-WLAN access" nor "Operator Controlled PLMN Selector for WLAN access" data file is available in the USIM or in case when SIM is inserted:

i) each PLMN in the "User Controlled PLMN Selector with Access Technology" data file, if available in the USIM/SIM (in priority order);

ii) each PLMN in the "Operator Controlled PLMN Selector with Access Technology" data file, if available in the USIM/SIM (in priority order).

f) If none of the PLMN selector lists in steps c, d and e is available and the ME supports at least one of the optional "User Controlled PLMN Selector for I-WLAN access" and "Operator Controlled PLMN Selector for I-WLAN access" lists in the ME:

i) each PLMN in the "User Controlled PLMN Selector for I-WLAN access" data file in the ME (in priority order);

ii) each PLMN in the "Operator Controlled PLMN Selector for I-WLAN access" data file in the ME (in priority order).

g) Any other PLMN in random order.

The HPLMN may provide on the USIM additional information on the available PLMNs. If this information is provided then the WLAN UE shall indicate it to the user. This information, provided as free text may include:

– preferred partner;

– roaming agreement status; and

– supported services.

Furthermore, the WLAN UE may indicate whether the available PLMNs are present on the EHPLMN list, the "User Controlled Selector for I-WLAN access" data file or the "Operator Controlled PLMN Selector for I-WLAN access" data file. The WLAN UE may also indicate that the PLMN is not present on any of these lists.

If a PLMN was selected before the procedure and if the user does not select a PLMN, the selected PLMN shall be the one that was selected before the PLMN selection procedure started.

If successful authentication is achieved, the WLAN UE shall indicate the selected PLMN. If the"I-WLAN Last Registered PLMN" data file is available in the USIM (see 3GPP TS 31.102 [13]) then the WLAN UE shall store the selected PLMN on the USIM else the WLAN UE shall store the selected PLMN on the ME.

If no PLMN is found, the WLAN UE behaviour is implementation dependent.

5.2.4 Automatic PLMN selection mode procedure

In case of automatic selection for WLANs that UE shall select and attempt to authenticate with an available and allowable PLMN. For WLANs that:

1) together with the WLAN UE support IEEE Std 802.11u™-2011 [23], the WLAN UE shall send an ANQP request to each WSID. If the WSID supports advertisement of PLMNS, it shall send back an ANQP response to the WLAN UE including the Supported PLMNs list for WLAN access. See Annex A. If the WLAN UE receives a ANQP response where the "Info ID" is not "3GPP Cellular Network information" the behaviour of the WLAN UE is outside the scope of this specification.

2) do not support IEEE 802.1x authentication, if the "HPLMN Direct Access Indicator" as specified in subclause 7.11 allows direct access and if the WLAN UE chooses to perform direct access to HPLMN, then the WLAN UE shall sequentially perform association and perform tunnel management procedures as specified in the clause 8 with each broadcast WSID that does not support IEEE 802.1x authentication.

3) support IEEE 802.1x authentication, the WLAN UE shall request for a list of supported PLMNs by issuing an EAP-Response/Identity message to the WLAN including as identity the alternative NAI. See subclause 4.2.5.

Based on the results of Items 1) – 3) above, the WLAN UE shall choose an available and allowable PLMN in the following order:

a) If the "I-WLAN HPLMN Priority Indication" as specified in subclause 7.10 is available and set to prioritise HPLMN, then:

i) HPLMN (if the EHPLMN list is not present, or is empty);

ii) if the EHPLMN list is present and contains at least one entry the highest EHPLMN that is available; and

iii) if the "I-WLAN Last Registered PLMN" data file is available in the USIM, the PLMN in the "I-WLAN Last Registered PLMN" in the USIM;

else if the "I-WLAN Last Registered PLMN" data file is not available in the USIM and the ME supports the "I-WLAN Last Registered PLMN", the PLMN in the "I-WLAN Last Registered PLMN" in the ME;

b) If "I-WLAN HPLMN Priority Indication" as specified in subclause 7.10 is available and is not set or is not present on the USIM:

i) if the "I-WLAN Last Registered PLMN" data file is available in the USIM, the PLMN in the "I-WLAN last Registered PLMN" in the USIM;

else if the "I-WLAN Last Registered PLMN" data file is not available in the USIM and the ME supports the "I-WLAN Last Registered PLMN" and the last registered PLMN for I-WLAN is available and set to prefer the last registered PLMN, then the PLMN in the "I-WLAN Last Registered PLMN" in the ME;

ii) HPLMN (if the EHPLMN list is not present, or exists but is empty); or

iii) if the EHPLMN list is present and contains at least one entry the highest EHPLMN that is available.

c) If the "User Controlled PLMN Selector for I-WLAN access" data file is available in the USIM, each PLMN in the "User Controlled PLMN Selector for I-WLAN access" data file in the USIM (in priority order) ;

d) If the "Operator Controlled PLMN Selector for I-WLAN access" data file is available in the USIM, each PLMN in the "Operator Controlled PLMN Selector for I-WLAN access" data file in the USIM (in priority order);

NOTE: Requirements for the presence of the "User Controlled PLMN Selector for I-WLAN access" data file and the "Operator Controlled PLMN Selector for I-WLAN access" data file are defined in 3GPP TS 31.102 [13].

e) If neither "User Controlled PLMN Selector for I-WLAN access" nor "Operator Controlled PLMN Selector for I‑WLAN access" data file is available in the USIM or in case when SIM is inserted:

i) each PLMN in the "User Controlled PLMN Selector with Access Technology" data file, if available in the USIM/SIM (in priority order);

ii) each PLMN in the "Operator Controlled PLMN Selector with Access Technology" data file, if available in the USIM/SIM (in priority order).

f) If none of the PLMN selector lists in steps b, c and d is available and the ME supports at least one of the optional "User Controlled PLMN Selector for I-WLAN access" or "Operator Controlled PLMN Selector for I-WLAN access" lists in the ME:

i) each PLMN in the "User Controlled PLMN Selector for I-WLAN access" data file in the ME (in priority order);

ii) each PLMN in the "Operator Controlled PLMN Selector for I-WLAN access" data file in the ME (in priority order).

g) Any other PLMN in random order.

If successful authentication is achieved, the WLAN UE shall indicate to the user the selected PLMN. If the "I-WLAN Last Registered PLMN" data file is available in the USIM, the WLAN UE shall store the selected PLMN on the USIM else the WLAN UE shall store the selected PLMN on the ME.

If no PLMN is selected, the WLAN UE behaviour is implementation dependent.

If the WLAN UE loses coverage with the associated access point, a new I-WLAN is discovered automatically using the I-WLAN association procedure in subclause 5.2.1.

5.2.5 Network selection for emergency case

5.2.5.1 General

For cases where the WLAN UE has already successfully performed I-WLAN network selection, authentication and authorization, the WLAN UE may reuse this connection for the purposes of performing IMS emergency calls if the selected VPLMN supports the emergency realm. Else the WLAN UE shall select another PLMN via the I-WLAN that supports the emergency realm.

5.2.5.2 Manual PLMN selection for emergency case

Manual PLMN selection shall take place as described in subclause 5.2.3. For those PLMNs that support the emergency specific service realm, the support for this emergency specific realm shall be listed as well as that of its parent PLMN.

5.2.5.3 Automatic PLMN selection mode procedure for emergency case

Automatic PLMN selection shall take place as described in subclause 5.2.4 however if the WLAN UE also supports any RAT defined by 3GPP (see 3GPP TR 21.905 [1C]), the WLAN UE shall ensure that the PLMN selected via I-WLAN, is in the same country as that discovered as the result of performing a wideband scan of RATs defined by 3GPP, i.e. the WLAN UE shall correlate the available PLMN country codes via RATs defined by 3GPP with those available via I-WLAN. If no networks are discovered as a result of performing the wideband scan of RATs defined by 3GPP, the WLAN UE shall select any PLMN supporting the emergency realm (see 3GPP TS 23.003 [1A]) in an implementation dependent way. For cases where no PLMN is advertised supporting the emergency realm, UE shall select any PLMN in an implementation dependent way.

5.2.5.4 Network selection in the case of a WLAN UE equipped with neither a valid SIM nor a valid USIM

For the case the WLAN UE is not equipped with a valid SIM or a valid USIM, when the WLAN UE also supports any RAT defined by 3GPP (see 3GPP TR 21.905 [1C]), the WLAN UE shall perform a wideband scan of RATs defined by 3GPP and shall store the available PLMN country codes. The WLAN UE shall then select any PLMN supporting the emergency realm (see 3GPP TS 23.003 [1A]) that is in the same country as any of the available PLMNs. In the following cases:

– no PLMNs via I-WLAN are in the same country as the available PLMNs via RATs defined by 3GPP;

– the WLAN UE does not support any RAT defined by 3GPP; or

– PLMNs from more than one country are available,

the WLAN UE shall select any PLMN supporting the emergency realm in an implementation dependent way.

For cases where no PLMN is advertised supporting the emergency realm, UE shall select any PLMN in an implementation dependent way.

5.3 Void

5.4 User reselection and steering of roaming

5.4.1 WLAN UE procedures

5.4.1.1 General

At any time the user or HPLMN via the steering of roaming feature can request the WLAN UE to initiate reselection onto a supported PLMN, according to the following procedures, dependent upon the PLMN selection mode (automatic or manual). In this case and in both PLMN selection modes, the WLAN UE shall:

– disassociate with the current associated WSID by initiating disassociation procedure as specified in IEEE 802.11 1999 [11];

– initiate association procedure as specified in IEEE 802.11 1999 [11], taking into account PLMN selection procedure as specified in subclause 5.2;

– depending on the PLMN selection mode (automatic or manual), perform a new PLMN selection as specified in subclauses 5.4.1.2 and 5.4.1.3.

5.4.1.2 Automatic network selection mode

The WLAN UE shall follow the automatic network selection mode procedure as specified in subclause 5.2.4 with the exception that the WLAN UE shall not chose the current mediating PLMN unless it is the only PLMN that is available.

5.4.1.3 Manual network selection mode

The WLAN UE shall follow the manual network selection mode procedure as specified in subclause 5.2.3

5.4.1.4 Steering of roaming

If the WLAN UE receives a USAT REFRESH command qualifier (see 3GPP TS 31.111 [22]) of type "Steering of Roaming for I-WLAN", and if the "Operator Controlled PLMN Selector for I-WLAN access" data file is available in the USIM the WLAN UE shall:

a) replace the highest priority entries in the "Operator Controlled PLMN Selector for I-WLAN access" list in the USIM and the ME, if available, with the list provided in the REFRESH command; and

b) attempt to obtain service on a different PLMN as specified in subclause 5.4.1.2

In order to avoid unnecessary signalling, repeateded using of steering of roaming of a particular WLAN UE should be avoided.

5.4.2 3GPP AAA server procedures

The WLAN UE may associate with a new access point and select a different PLMN than the current PLMN in which the WLAN UE has been authenticated. In this case the 3GPP AAA server may receive a new EAP authentication request from the same user but from a different PLMN (e.g. the new selected WLAN VPLMN will generate a new decorated NAI). The 3GPP AAA server shall proceed with the new EAP authentication request.

If the EAP authentication procedure triggered by the new EAP authentication request from the same user is successful, the 3GPP AAA server may either release the current stored authentication status information or keep both the current stored authentication status information and the new authentication status information obtained from the latest successful EAP authentication procedure.