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Content for  TS 23.122  Word version:  16.6.1

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4.5 Location registration process  4.6 Service indication (A/Gb mode only)  4.7 Pageability of the mobile subscriber  4.8 MM Restart Procedure  4.9 SNPN selection process 
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4.5  Location registration process

4.5.1  General

When the MS is switched on and capable of services requiring registration, the action taken by the location registration process is as follows:
  1. SIM present and no LR needed (because of the status of the stored registration area identity and "attach" flag): The MS is in the update state "Updated";
  2. SIM present and LR needed: A LR request is made;
  3. No SIM present: The MS enters the update state "Idle, No IMSI".
In case b) above, and subsequently whenever a LR request is made, the MS enters a state depending on the outcome of the LR request, as listed in subclause 4.3.3 above. In case c) the GPRS and the non-GPRS update state enters "Idle, No IMSI".
Whenever the MS goes to connected mode and then returns to idle mode again, the MS selects the appropriate state.
A multi mode MS that also supports 3GPP2 access technology may fall back to 3GPP2 mode if no SIM is inserted.
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4.5.2  Initiation of Location Registration

An LR request indicating Normal Updating is made when, in idle mode,
  • the MS changes cell while the update status is "NOT UPDATED"; (for MS capable of GPRS and non-GPRS services when at least one of both update statuses is "NOT UPDATED")
  • the MS detects that it has entered a new registration area, i.e., when the received registration area identity differs from the one stored in the MS, and the LAI, TAI or PLMN identity is not contained in any of the lists of "forbidden location areas for roaming", "forbidden tracking areas for roaming", "5GS forbidden tracking areas for roaming", "forbidden location areas for regional provision of service", "forbidden tracking areas for regional provision of service", "5GS forbidden tracking areas for regional provision of service", "forbidden PLMNs for GPRS service" or "forbidden PLMNs" respectively, while being in one of the following update statuses:
    • UPDATED;
    • NOT UPDATED;
    • ROAMING NOT ALLOWED.
  • the MS detects that it has entered a new registration area, i.e., when the received registration area identity differs from the one stored in the MS, and the MS is attached for access to RLOS;
  • the MS detects that it has entered a registration area that has the same identity as the one stored in the MS, while the update status is "ROAMING NOT ALLOWED", and the LAI, TAI or PLMN identity is not contained in any of the lists of "forbidden location areas for roaming", "forbidden tracking areas for roaming", "5GS forbidden tracking areas for roaming", "forbidden location areas for regional provision of service", "forbidden tracking areas for regional provision of service", "5GS forbidden tracking areas for regional provision of service", "forbidden PLMNs for GPRS service" or "forbidden PLMNs" respectively.
  • the Periodic Location Updating Timer expires while the non-GPRS update status is "NOT UPDATED" (triggers Location Updating);
  • the Periodic Routing Area Update timer expires while the GPRS update status is "NOT UPDATED" (triggers Routing Area Update);
  • the Periodic Tracking Area Update timer expires while the EPS update status is "NOT UPDATED" (triggers Tracking Area Update);
  • a manual network reselection has been performed, an acceptable cell of the selected PLMN or the selected SNPN is present, and the MS is not in the update status "UPDATED" on the selected PLMN or the selected SNPN; or
  • emergency bearer services over packet services are requested by upper layers.
An MS which is attached for PS services other than RLOS and enters a new PLMN shall perform a routeing area update or a tracking area update or an MS which is registered via NG-RAN and enters a new PLMN shall perform a registration update if the following conditions are fulfilled:
  • if the MS is in S1 mode or N1 mode and the currently stored TAI list does not contain the TAI of the current serving cell;
  • the LAI, TAI or PLMN identity of the current serving cell is not contained in any of the lists "forbidden location areas for roaming", "forbidden tracking areas for roaming", "5GS forbidden tracking areas for roaming", "forbidden location areas for regional provision of service", "forbidden tracking areas for regional provision of service", "5GS forbidden tracking areas for regional provision of service", "forbidden PLMNs for GPRS service" or "forbidden PLMNs", or the MS has a PDN connection for emergency bearer services, or the MS has a PDU session for emergency services;
  • the current update state is different from "Idle, No IMSI"; and
    • the MS is configured to perform the attach procedure with IMSI at PLMN change (see "AttachWithIMSI" leaf of the NAS configuration MO in TS 24.368 or USIM file NASCONFIG in TS 31.102) and the new PLMN is the registered PLMN or an equivalent PLMN; or
    • the MS is not configured to perform the attach procedure with IMSI at PLMN change.
An MS which is attached for access to RLOS and enters a new PLMN shall perform tracking area update if the following condition is fulfilled:
  • the currently stored TAI list does not contain the TAI of the current serving cell.
If the new PLMN the MS has entered is neither the registered PLMN nor an equivalent PLMN, an MS which is attached for PS services and configured to perform the attach procedure with IMSI at PLMN change (see "AttachWithIMSI" leaf of the NAS configuration MO in TS 24.368 or USIM file NASCONFIG in TS 31.102) shall perform an attach procedure using IMSI as mobile identity.
An LR request indicating Periodic Location Updating is made when, in idle mode, the Periodic Location Updating timer expires while the non-GPRS update status is "UPDATED".
An LR request indicating Periodic Routing Area Update is made when the Periodic Routing Area Update timer expires while the GPRS update status is "UPDATED", except when the MS is attached for emergency bearer services.
An LR request indicating Periodic Tracking Area Update is made when the Periodic Tracking Area Update timer expires while the EPS update status is "UPDATED", except when the MS is attached for emergency bearer services.
An LR request indicating Periodic Registration Updating is made when the periodic registration timer expires while the 5GS update status is "UPDATED", except when the MS is registered for emergency services.
An LR request indicating IMSI attach is made when the MS is activated in the same location area in which it was deactivated while the non-GPRS update status is "UPDATED", and the system information indicates that IMSI attach/detach shall be used.
A GPRS attach is made by a GPRS MS when activated and capable of services which require registration. A GPRS attach may only be performed if the selected PLMN is not contained in the list of "forbidden PLMNs for GPRS service". Depending on system information about GPRS network operation mode MSs operating in MS operation mode A or B perform combined or non-combined location registration procedures. When the combined routing area update or GPRS attach is accepted with indication "MSC not reachable" or is not answered the MS performs also the corresponding location updating procedure or falls back to a GPRS only MS. When the combined routing area update or GPRS attach is rejected with cause "GPRS not allowed" the GPRS update status is "ROAMING NOT ALLOWED" and the MS performs the corresponding location updating procedure.
Furthermore, an LR request indicating Normal Location Updating is also made when the response to an outgoing request shows that the MS is unknown in the VLR or SGSN, respectively.
Table 2 in clause 5 summarizes the events in each state that trigger a new LR request. The actions that may be taken while being in the various states are also outlined in table 2.
A GPRS MS which is both IMSI attached for GPRS and non-GPRS services and which is capable of simultaneous operation of GPRS and non-GPRS services shall perform Routing Area Update in connected mode when it has entered a new routing area which is not part of a LA contained in the list of "forbidden location areas for roaming" or "forbidden location areas for regional provision of service".
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4.5.3  Periodic Location Registration  Word‑p. 43
A Periodic Location Updating timer (for non-GPRS operation), a Periodic Routing Area Update timer (for GPRS operation), a Periodic Tracking Area Update timer (for EPS operation) and a Periodic Registration Update timer (for 5GS operation) with the following characteristics shall be implemented in the MS (MS shall implement all timers corresponding to supported operations):
  1. Upon switch on of the MS or when the system information indicates that periodic location registration shall be applied, and the timer is not running, the timer shall be loaded with a random value between 0 and the broadcast or signalled time-out value and started.
  2. The time-out value for the Periodic Location Updating timer shall be within the range of 1 deci-hour to 255 deci-hours with a granularity of 1 deci-hour.
  3. When the timer reaches its expiry value, it shall be initiated with respect to the relevant time-out value, and the MS shall initiate the Periodic Location Registration corresponding to the expired timer. If the MS is attached for emergency bearer services or the MS is registered for emergency services, the MS shall locally detach instead of performing Periodic Location Registration.
  4. The Periodic Location Updating timer shall be prevented from triggering Periodic Location Updating during connected mode. When the MS returns to idle mode, the Periodic Location Updating timer shall be initiated with respect to the broadcast time-out value, then started. Thereafter, the procedure in iii) shall be followed.
  5. The Periodic Routing Area Update timer shall be prevented from triggering the Periodic Routing Area Update during Ready state. At transition from Ready to Standby state the Periodic Routing Area Update timer shall be initiated with respect to its time-out value, then started. Thereafter, the procedure in iii) shall be followed.
  6. If the MS performs a successful combined Routing Area Update the Periodic Location Updating timer shall be prevented from triggering the Periodic Location Updating until the MS starts using Location Updating procedure, for example because of a changed network operation mode or the MS uses non-GPRS services only.
  7. When a change in the time-out value occurs (at a change of serving cell or a change in the broadcast time-out value or a change in the signalled time-out value), the related timer shall be reloaded so that the new time to expiry will be: "old time to expiry" modulo "new time-out value".
  8. The Periodic Tracking Area Update timer shall be prevented from triggering Periodic Tracking Area Updating during connected mode. When the MS returns to idle mode, the Periodic Tracking Area Update timer shall be initiated with respect to the signalled time-out value, then started. Thereafter, the procedure in iii) shall be followed.
  9. The Periodic Registration Update timer shall be prevented from triggering Periodic Registration Updating during connected mode. If periodic timer is not running due to Strictly periodic registration feature, when the MS returns to idle mode, the Periodic Registration Update timer shall be initiated with respect to the signalled time-out value, then started. Thereafter, the procedure in iii) shall be followed.
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4.5.4  IMSI attach/detach operation  Word‑p. 44
The system information will contain an indicator indicating whether or not IMSI attach/detach operation is mandatory to use in the cell. The MS shall operate in accordance with the received value of the indicator.
A GPRS MS shall perform GPRS attach/detach procedures independent of the value of the IMSI attach/detach indicator. When a GPRS MS has to perform IMSI attach/detach independent of GPRS procedures (for example GPRS network operation mode 2) the handling described in the clause above applies.
When IMSI attach/detach operation applies, a MS shall send the IMSI detach message to the network when the MS is powered down or the SIM is removed while the update status is "UPDATED". The IMSI detach message will not be acknowledged by the network.
When the MS returns to the active state, the MS shall perform an LR request indicating IMSI attach, provided that the MS still is in the same registration area. If the registration area has changed, an LR request indicating Normal Location Updating according to subclause 4.5.2 shall be performed.
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4.5.5  No Suitable Cells In Location Area

If during location registration the LR response "No Suitable Cells In Location Area" or "No Suitable Cells In Tracking Area" is received:
  • The MS shall attempt to find another LA or TA of the same PLMN, the same SNPN, an equivalent PLMN on which it received the LR response. If the MS is able to find another LA or TA it shall attempt registration. If the MS is unable to find an LA or TA, the PLMN Automatic or Manual Mode Selection Procedure of subclause 4.4.3.1 or the SNPN Automatic or Manual Mode Selection Procedure of subclause 4.9.3.1 shall be followed, depending on whether the MS is in automatic or manual mode and whether the MS operates in SNPN access mode.
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4.6  Service indication (A/Gb mode only)

This is an indication to the user that service or CTS service is available.
The service indication should be set if the following conditions are all satisfied:
  1. Cell Selection: Camped on a suitable cell and in updated state, or in connected mode having been camped on a suitable cell.
  2. Location registration: In updated state, for MSs capable of services requiring registration.
A specific CTS service indication should be set when the CTS MS is attached to a CTS FP.
However due to the fact that there may be some transitory changes of state, the service indication is permitted to continue to be set for up to 10 seconds after the above conditions cease to be met. Also the service indication is permitted to take up to 1 second to be set after the above conditions are met.
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4.7  Pageability of the mobile subscriber

An MS is required to listen to all paging messages that could address it (see TS 45.002), when the following conditions are all satisfied:
  • A SIM is inserted;
  • The MS is camped on a cell;
  • The MS is not in state "Idle, No IMSI"; and
  • The MS is not performing the task to search for available PLMNs or available SNPNs. (Whenever possible during this task, the MS should listen for paging.). However, when the MS is camped on a cell, is registered in a PLMN and is performing its regular search for a higher priority PLMN, as specified in TS 22.011, then it shall listen to all paging messages that could address it.
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4.8  MM Restart Procedure  Word‑p. 45
In some cases, e.g. on change of SIM data, there is a need for the MM to be restarted without the need for user intervention.
To perform the procedure the MS shall behave as if the SIM is removed and afterwards a new SIM is inserted.

4.9  SNPN selection process |R16|

4.9.1  General

The MS operating in SNPN access mode shall perform the SNPN selection process.
The MS not operating in SNPN access mode shall not perform the SNPN selection process.
There are two SNPN selection modes - automatic SNPN selection mode and manual SNPN selection mode.
In the SNPN selection process, the MS shall consider only the access networks of the NG-RAN access technology.

4.9.2  Registration on an SNPN

The MS shall perform registration on the SNPN if the MS is capable of services which require registration. In both automatic SNPN selection mode and manual SNPN selection mode, the concept of registration on an SNPN is used. An MS successfully registers on an SNPN if:
  1. the MS has found a suitable cell of the SNPN to camp on; and
  2. an LR request from the MS has been accepted in the registration area of the cell on which the MS is camped.

4.9.3  SNPN selection

4.9.3.0  General

The ME is configured with a "list of subscriber data" containing zero or more entries. Each entry of the "list of subscriber data" consists of:
  1. a subscriber identifier in the form of a SUPI containing a network-specific identifier or an IMSI except when the SNPN uses:
    1. the EAP based primary authentication and key agreement procedure using the EAP-AKA'; or
    2. the 5G AKA based primary authentication and key agreement procedure;
  2. credentials except when the SNPN uses:
    1. the EAP based primary authentication and key agreement procedure using the EAP-AKA'; or
    2. the 5G AKA based primary authentication and key agreement procedure;
  3. an SNPN identity; and
  4. optionally, the unified access control configuration indicating for which access identities (see TS 24.501) the ME is configured in the SNPN.
The MS shall maintain a list of "temporarily forbidden SNPNs" and a list of "permanently forbidden SNPNs" in the ME. Each entry of those lists consists of an SNPN identity.
The MS shall add an SNPN to the list of "temporarily forbidden SNPNs", if a message with cause value #74 "Temporarily not authorized for this SNPN" (see TS 24.501) is received by the MS in response to an LR request from the SNPN. In addition, if:
  • the message is integrity-protected; or
  • the message is not integrity-protected, and the value of the SNPN-specific attempt counter for that SNPN is equal to the MS implementation specific maximum value as defined in TS 24.501;
then the MS shall start an MS implementation specific timer not shorter than 60 minutes.The MS shall remove an SNPN from the list of "temporarily forbidden SNPNs", if:
  1. there is a successful LR after a subsequent manual selection of the SNPN;
  2. the MS implementation specific timer not shorter than 60 minutes expires;
  3. the timer T3247 expires and the value of the SNPN-specific attempt counter for that SNPN is less than the MS implementation specific maximum value as defined in TS 24.501;
  4. the MS is switched off; or
  5. an entry of the "list of subscriber data" with the SNPN identity of the SNPN is updated or the USIM is removed if:
    • EAP based primary authentication and key agreement procedure using EAP-AKA'; or
    • 5G AKA based primary authentication and key agreement procedure;
    was performed in the selected SNPN.
If an SNPN is removed from the list of "temporarily forbidden SNPNs" list, the MS shall stop the MS implementation specific timer not shorter than 60 minutes, if running.
The MS shall add an SNPN to the list of "permanently forbidden SNPNs", if a message with cause value #75 "Permanently not authorized for this SNPN" (see TS 24.501) is received by the MS in response to an LR request from the SNPN.
The MS shall remove an SNPN from the list of "permanently forbidden SNPNs", if:
  1. there is a successful LR after a subsequent manual selection of the SNPN;
  2. the timer T3247 expires and the value of the SNPN-specific attempt counter for that SNPN is less than the MS implementation specific maximum value as defined in TS 24.501 ; or
  3. an entry of the "list of subscriber data" with the SNPN identity of the SNPN is updated or the USIM is removed if:
    • EAP based primary authentication and key agreement procedure using EAP-AKA'; or
    • 5G AKA based primary authentication and key agreement procedure;
    was performed in the selected SNPN.
When the MS reselects to a cell in a shared network, and the cell is a suitable cell for multiple SNPN identities received in the broadcast information as specified in TS 38.331, the AS indicates these multiple SNPN identities to the NAS according to TS 38.304. The MS shall select one of these SNPNs. If the registered SNPN is available among these SNPNs, the MS shall not select a different SNPN.
The MS operating in SNPN access mode shall maintain one or more lists of "5GS forbidden tracking areas for roaming", each associated with an SNPN. The MS shall use the list of "5GS forbidden tracking areas for roaming" associated with the selected SNPN. If the MS selects a new SNPN, the MS shall keep the list of "5GS forbidden tracking areas for roaming" associated with the previously selected SNPN. If the number of the lists to be kept is higher than supported, the MS shall delete the oldest stored list of "5GS forbidden tracking areas for roaming". The MS shall delete all lists of "5GS forbidden tracking areas for roaming", when the MS is switched off and periodically (with period in the range 12 to 24 hours). The MS shall delete the list of "5GS forbidden tracking areas for roaming" associated with an SNPN, when the entry of the SNPN in the list of subscriber data" is updated or when the USIM is removed if:
  • the EAP based primary authentication and key agreement procedure using the EAP-AKA'; or
  • the 5G AKA based primary authentication and key agreement procedure;
was performed in the selected SNPN.
If a message with cause value #15 (see TS 24.501) is received by an MS operating in SNPN access mode, the TA is added to the list of "5GS forbidden tracking areas for roaming" of the selected SNPN. The MS shall then search for a suitable cell in the same SNPN but belonging to a TA which is not in the "5GS forbidden tracking areas for roaming" list of the selected SNPN.
The MS should maintain a list of SNPNs for which the N1 mode capability was disabled due to receipt of a reject from the network with 5GMM cause #27 "N1 mode not allowed". When the MS disables its N1 mode capability due to receipt of a reject from an SNPN with 5GMM cause #27 "N1 mode not allowed":
  • the MS should add the SNPN identity of the SNPN which sent a reject with 5GMM cause #27 "N1 mode not allowed" to the list of SNPNs for which the N1 mode capability was disabled and should start timer TG if timer TG is not already running. The number of SNPNs for which N1 mode was not allowed that the MS can store is implementation specific, but it shall be at least one. The value of timer TG is MS implementation specific;
  • in automatic SNPN selection, the MS shall not select an SNPN for which the N1 mode capability was disabled as SNPN selection candidates, unless no other SNPN is available; and
  • the MS shall delete stored information on SNPNs for which the N1 mode capability was disabled when the MS is switched off, the USIM is removed, the entries of the "list of subscriber data" for the SNPNs are updated, or timer TG expires.
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4.9.3.1  At switch-on or recovery from lack of coverage  Word‑p. 48
4.9.3.1.0  General
At switch on, or following recovery from lack of coverage, the MS selects the registered SNPN (if it is available) using NG-RAN access technology and if necessary (in the case of recovery from lack of coverage, see subclause 4.5.2) attempts to perform an LR.
If successful registration is achieved, the MS indicates the selected SNPN.
If there is no registered SNPN, or registration is not possible due to the SNPN being unavailable or registration failure, the MS follows the procedure in subclause 4.9.3.1.1 or subclause 4.9.3.1.2 depending on its SNPN selection mode. At switch on, the MS shall use the SNPN selection mode that was used before switching off.
If registration is not possible on recovery from lack of coverage due to the registered SNPN being unavailable, an MS may, optionally, continue looking for the registered SNPN for an implementation dependent time.
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4.9.3.1.1  Automatic SNPN selection mode procedure
The MS selects another SNPN, if available, allowable, and identified by an SNPN identity in an entry of the "list of subscriber data" in the ME. If more than one SNPN are available, allowable, and each of them is identified by an SNPN identity in an entry of the "list of subscriber data" in the ME, how the MS selects one of those SNPNs is MS implementation specific.
The MS shall limit its search for the SNPN to the NG-RAN access technology.
Once the MS selects the SNPN, the MS attempts registrations on the selected SNPN using the NG-RAN access technology, the subscriber identifier and the credentials from an entry of the "list of subscriber data" with the SNPN identity matching the selected SNPN.
If successful registration is achieved, the MS indicates the selected SNPN.
If registration cannot be achieved because no SNPNs are available, allowable, and identified by an SNPN identity in an entry of the "list of subscriber data" in the ME, the MS indicates "no service" to the user, waits until a new SNPN is available, allowable, and identified by an SNPN identity in an entry of the "list of subscriber data" in the ME and then repeats the procedure.
If there were one or more SNPNs which were available, allowable, and identified by an SNPN identity in an entry of the "list of subscriber data" in the ME but an LR failure made registration on those SNPNs unsuccessful, the MS selects one of those SNPNs again and enters a limited service state.
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4.9.3.1.2  Manual SNPN selection mode procedure
The MS indicates to the user one or more SNPNs, which are available and each of them is identified by an SNPN identity in an entry of the "list of subscriber data" in the ME. Additionally, for each of the indicated SNPNs, the MS may optionally display a human readable name for the SNPN. This includes SNPNs in the list of "permanently forbidden SNPNs", and the list of "temporarily forbidden SNPNs". The MS may indicate to the user whether the available SNPNs are present in the list of "temporarily forbidden SNPNs" or the list of "permanently forbidden SNPNs". The order in which those SNPNs are indicated is MS implementation specific.
Editor's note [Vertical_LAN; CR#0503]: Obtaining human-readable name for SNPN is FFS
The MS shall limit its search for the SNPN to the NG-RAN access technology.
The user may select his desired SNPN and the MS then initiates registration on this SNPN using the NG-RAN access technology, the subscriber identifier and the credentials from an entry of the "list of subscriber data", with the SNPN identity matching the selected SNPN (this may take place at any time during the presentation of SNPNs).
Once the MS has registered on an SNPN selected by the user, the MS shall not automatically register on a different SNPN unless the user selects automatic SNPN selection mode.
If the user does not select an SNPN, the selected SNPN shall be the one that was selected either automatically or manually before the SNPN selection procedure started. If no such SNPN was selected or that SNPN is no longer available, then the MS shall attempt to camp on any acceptable cell and enter the limited service state.
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4.9.3.2  User reselection  Word‑p. 49
4.9.3.2.0  General
At any time the user may request the MS to initiate reselection and registration onto an available SNPN, according to the following procedures, dependent upon the SNPN selection mode of the UE.
4.9.3.2.1  Automatic SNPN selection mode
The MS selects an SNPN, if available, allowable, and identified by an SNPN identity in an entry of the "list of subscriber data" in the ME in accordance with the following order:
  1. an SNPN, which is available and identified by an SNPN identity in an entry of the "list of subscriber data" in the ME, excluding the previously selected SNPN. If more than one SNPN different from the previously selected SNPN are available, allowable, and each of them is identified by an SNPN identity in an entry of the "list of subscriber data" in the ME, how the MS selects one of those SNPNs is MS implementation specific.
  2. the previously selected SNPN.
The MS shall limit its search for the SNPN to the NG-RAN access technology.
The previously selected SNPN is the SNPN which the MS has selected prior to the start of the user reselection procedure.
Once the MS selects an SNPN, if the selected SNPN is other than the previously selected SNPN, the MS attempts registrations on the selected SNPN using the NG-RAN access technology, the subscriber identifier and the credentials from an entry of the "list of subscriber data" with the SNPN identity matching the selected SNPN.
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4.9.3.2.2  Manual SNPN selection mode procedure
The manual SNPN selection mode procedure of subclause 4.9.3.1.2 is followed.

4.9.4  Abnormal cases

If:
  1. the "list of subscriber data" is empty; or
  2. for each entry of the "list of subscriber data", such that an SNPN with the SNPN identity of the entry is available:
    1. there has been an authentication failure for the subscriber identifier of the entry on the SNPN; or
    2. the MS has received an "illegal ME" or "illegal UE" response to an LR request for the subscriber identifier of entry on the SNPN;
then effectively there is no selected SNPN ("No SIM" state).
When in automatic SNPN selection mode and the MS is in the "not updated" state with one or more suitable cells to camp on; then after the maximum allowed unsuccessful LR requests (controlled by the specific attempt counters) the MS may continue (or start if it is not running) the user reselection procedure in subclause 4.9.3.2 1.
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