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Content for  TS 23.122  Word version:  16.6.1

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3  Requirements and technical solutionsWord‑p. 14

3.0  General |R16|

The following clauses list the main requirements of idle mode operation and give an outline of the technical solution.

3.1  PLMN selection and roamingWord‑p. 15
The MS normally operates on its home PLMN (HPLMN) or equivalent home PLMN (EHPLMN). However, a visited PLMN (VPLMN) may be selected, e.g., if the MS loses coverage. There are two modes for PLMN selection:
  1. Automatic mode - This mode utilizes a list of PLMN/access technology combinations in priority order. The highest priority PLMN/access technology combination which is available and allowable is selected.
  2. Manual mode - Here the MS indicates to the user which PLMNs are available. Only when the user makes a manual selection does the MS try to obtain normal service on the VPLMN.
To prevent repeated attempts to have roaming service on a not allowed area (i.e. LA or TA), when the MS is informed that an area is forbidden, the LA or TA is added to a list of "forbidden location areas for roaming" or "forbidden tracking areas for roaming" respectively which is stored in the MS. These lists, if existing, are deleted when the MS is switched off or when the SIM is removed, and periodically (with period in the range 12 to 24 hours). LA area restrictions are always valid for complete location areas independent of possible subdivision into GPRS routing areas. The structure of the routing area identifier (see TS 23.003) supports area restriction on LA basis.
If a message with cause value #15 (see TS 24.008, TS 24.301 and TS 24.501) is received by an MS, then the MS shall take the following actions depending on the access technology in which the message was received:
GSM, GSM COMPACT or UTRAN:
The location area is added to the list of "forbidden location areas for roaming" which is stored in the MS. The MS shall then search for a suitable cell in the same PLMN but belonging to an LA or TA which is not in the "forbidden location areas for roaming" or "forbidden tracking areas for roaming" list respectively.
E-UTRAN:
The tracking area is added to the list of "forbidden tracking areas for roaming" which is stored in the MS. The MS shall then search for a suitable cell in the same PLMN but belonging to a TA or LA which is not in the "forbidden tracking areas for roaming" or "forbidden location areas for roaming" list respectively
NG-RAN:
The tracking area is added to the list of "5GS forbidden tracking areas for roaming" which is stored in the MS. The MS shall then search for a suitable cell in the same PLMN but belonging to a tracking area which is not in the "5GS forbidden tracking areas for roaming" list.
A VPLMN is added to a list of "forbidden PLMNs" in the SIM and thereafter that VPLMN will not be accessed by the MS when in automatic mode if a message with cause value "PLMN not allowed" or "Requested service option not authorized in this PLMN" or "Serving network not authorized" is received by an MS in response to an LR request from that VPLMN and:
  • the MS is configured to use timer T3245 as defined in TS 24.008, TS 24.301, and TS 24.501;
  • the MS is not configured to use timer T3245 and the message is integrity-protected;
  • the MS is not configured to use timer T3245, the message is not integrity-protected and the MS does not maintain a list of PLMN-specific attempt counters; or
  • the MS is not configured to use timer T3245, the message is not integrity-protected, the MS maintains a list of PLMN-specific attempt counters and the value of the PLMN-specific attempt counter for that VPLMN is equal to the MS implementation specific maximum value as defined in TS 24.008, TS 24.301 and TS 24.501.
A PLMN is removed from the "forbidden PLMNs" list if, after a subsequent manual selection of that PLMN, there is a successful LR or upon expiry of timer T3245 if the MS is configured to use timer T3245. This list is retained when the MS is switched off or the SIM is removed. The HPLMN (if the EHPLMN list is not present or is empty) or an EHPLMN (if the EHPLMN list is present) shall not be stored on the list of "forbidden PLMNs".
In A/Gb mode, an ME not supporting SoLSA may consider a cell with the escape PLMN code (see 3GPP TS 23.073 []) to be a part of a PLMN belonging to the list of "forbidden PLMNs".
Optionally the ME may store in its memory an extension of the "forbidden PLMNs" list. The contents of the extension of the list shall be deleted when the MS is switched off or the SIM is removed.
A VPLMN may be stored in the extension of the "forbidden PLMNs" list if a message with cause value "PLMN not allowed" or "Requested service option not authorized in this PLMN" or "Serving network not authorized" is received by an MS in response to an LR request from that VPLMN, and the following is valid:
  • the MS is not configured to use timer T3245, the message is not integrity-protected, the MS maintains a list of PLMN-specific attempt counters and the value of the PLMN-specific attempt counter for that VPLMN is less than an MS implementation specific maximum value as defined in TS 24.008, TS 24.301 and TS 24.501.
If a message with cause value "GPRS services not allowed in this PLMN" or "EPS services not allowed in this PLMN" is received by an MS in response to an GPRS attach, routing area update, EPS attach or tracking area update request or received in a network initiated GPRS detach or EPS detach request (see TS 24.008 and TS 24.301) from a VPLMN, that VPLMN is added to a list of "forbidden PLMNs for GPRS service" which is stored in the MS and thereafter that VPLMN will not be accessed by the MS for GPRS service when in automatic mode. This list is deleted when the MS is switched off or when the SIM is removed. A PLMN is removed from the list of "forbidden PLMNs for GPRS service" if:
  • after a subsequent manual selection of that PLMN, there is a successful GPRS attach, Routing Area Update, EPS attach or Tracking Area Update;
  • the MS is configured to use timer T3245 and timer T3245 expires; or
  • the MS is not configured to use timer T3245, the MS maintains a list of PLMN-specific PS-attempt counters as specified in TS 24.008 and TS 24.301, the value of the PLMN-specific PS-attempt counter for that PLMN has a value greater than zero and less than the MS implementation-specific maximum value as defined in clause 5.3.7b in TS 24.301, and T3247 expires.
The maximum number of possible entries in this list is implementation dependant, but must be at least one entry. The HPLMN (if the EHPLMN list is not present or is empty) or an EHPLMN (if the EHPLMN list is present) shall not be stored on the list of "forbidden PLMNs for GPRS service".
An MS that is attaching for emergency bearer services or for access to RLOS, or is attached for emergency bearer services or for access to RLOS, may access PLMNs in the list of "forbidden PLMNs" or the list of "forbidden PLMNs for GPRS service". The MS shall not remove any entry from the list of "forbidden PLMNs" or the list of "forbidden PLMNs for GPRS service" as a result of such accesses.
A UE capable of S101 mode maintains a list "forbidden PLMNs for attach in S101 mode"; the properties and handling in NAS signalling is defined in subclause 5.3.3 of TS 24.301.
If the MS is in GAN mode and a "Location not allowed" message is received (see TS 44.318), then the MS may attempt to select another PLMN so that further GAN registrations may again be attempted. The selection of the PLMN either automatically or manually is implementation dependent.
If MS that has disabled its E-UTRA capability re-enables it when PLMN selection is performed, then:
  • the MS should, for duration of timer TD, memorize the PLMNs where E-UTRA capability was disabled as PLMNs where voice service was not possible in E-UTRAN. The number of PLMNs where voice service was not possible in E-UTRAN that the MS can store is implementation specific, but it shall be at least one. The value of timer TD is MS implementation specific, but shall not exceed the maximum possible value of background scanning timer T as specified in subclause 4.4.3.3.1.
  • in automatic PLMN selection the MS shall not consider PLMNs where voice service was not possible in E-UTRAN as PLMN selection candidates for E-UTRA access technology, unless no other PLMN is available. This does not prevent selection of such a PLMN if it is available in another RAT; and
  • the MS shall delete stored information on PLMNs where voice service was not possible in E-UTRAN when the MS is switched off, the USIM is removed, timer TD expires or MS voice domain configuration changes so that E-UTRA capability disabling is no longer necessary.
The MS may support "E-UTRA Disabling for EMM cause #15" as specified in TS 24.301. If the MS supports "E-UTRA Disabling for EMM cause #15" and the "E-UTRA Disabling Allowed for EMM cause #15" parameter as specified in TS 24.368 or TS 31.102 is present and set to enabled:
  • the MS shall maintain a list of "PLMNs with E-UTRAN not allowed";
  • when the MS disables its E-UTRA capability on a PLMN due to E-UTRAN not allowed, it shall add the PLMN to the "PLMNs with E-UTRAN not allowed" list, and start timer TE if timer TE is not already running;
  • the number of PLMNs that the MS can store in the "PLMNs with E-UTRAN not allowed" list is implementation specific, but it shall be at least one;
  • the value of timer TE is MS implementation specific, but it shall not exceed the maximum possible value of background scanning timer T (8 hours or 240 hours for MSs supporting EC-GSM-IoT, Category M1 or Category NB1 as defined in TS 36.306)) as specified in subclause 4.4.3.3.1;
  • in automatic PLMN selection the MS shall not consider PLMNs included in the "PLMNs with E-UTRAN not allowed" list as PLMN selection candidates for E-UTRAN access technology, unless no other PLMN is available. This does not prevent selection of such a PLMN if it is available in another RAT; and
  • the MS shall delete stored information in the "PLMNs with E-UTRAN not allowed" list when the MS is switched off, the USIM is removed or timer TE expires.
The MS should maintain a list of PLMNs where the N1 mode capability was disabled due to IMS voice not available and the MS's usage setting was "voice centric" as PLMNs where voice service was not possible in N1 mode. When the MS disables its N1 mode capability due to IMS voice not available and the MS's usage setting was "voice centric":
  • the MS should add the identity of the PLMN to the list of PLMNs where voice service was not possible in N1 mode and should start timer TF if timer TF is not already running. The number of PLMNs that the MS can store where voice services is not possible is implementation specific, but it shall be at least one. The value of timer TF is MS implementation specific, but shall not exceed the maximum possible value of background scanning timer T as specified in subclause 4.4.3.3.1;
  • in automatic PLMN selection the MS shall not consider PLMNs where voice service was not possible in N1 mode as PLMN selection candidates for NG-RAN access technology, unless no other PLMN is available. This does not prevent selection of such a PLMN if it is available in another RAT; and
  • the MS shall delete stored information on PLMNs where voice service was not possible in N1 mode when the MS is switched off, the USIM is removed, timer TF expires or the MS's usage setting changes so that N1 mode capability disabling is no longer necessary.
The MS should maintain a list of PLMNs where the N1 mode capability was disabled due to receipt of a reject from the network with 5GMM cause #27 "N1 mode not allowed", as PLMNs where N1 mode is not allowed for 3GPP access. When the MS disables its N1 mode capability due to receipt of a reject from the network with 5GMM cause #27 "N1 mode not allowed":
  • the MS should add the identity of the PLMN to the list of PLMNs where N1 mode is not allowed for 3GPP access and should start timer TG if timer TG is not already running. The number of PLMNs that the MS can store where N1 mode is not allowed for 3GPP access is implementation specific, but it shall be at least one. The value of timer TG is MS implementation specific, but shall not exceed the maximum possible value of background scanning timer T as specified in subclause 4.4.3.3.1;
  • in automatic PLMN selection the MS shall not consider PLMNs where N1 mode is not allowed for 3GPP access as PLMN selection candidates for NG-RAN access technology, unless no other PLMN is available. This does not prevent selection of such a PLMN if it is available in another RAT;
  • if the MS is not configured to use timer T3245, the MS maintains a list of PLMN-specific N1 mode attempt counters for 3GPP access as specified in TS 24.501 and T3247 expires, then the MS removes for each PLMN-specific N1 mode attempt counter for 3GPP access that has a value greater than zero and less than the MS implementation-specific maximum value the respective PLMN from the list of PLMNs where N1 mode is not allowed for 3GPP access, as specified in subclause 5.3.20.2 in TS 24.501; and
  • the MS shall delete stored information on PLMNs where N1 mode is not allowed for 3GPP access when the MS is switched off, the USIM is removed or timer TG expires.
The MS in NB-S1 mode may maintain a list of "PLMNs with NB-IoT not allowed" where the NB-IoT capability was disabled due to receipt of a reject from the network with EMM cause #15 "no suitable cells in tracking area" and an Extended EMM cause IE with value "NB-IoT not allowed", as PLMNs where NB-S1 mode is not allowed. When the MS disables its NB-IoT capability due to receipt of a reject from the network with EMM cause #15 "no suitable cells in tracking area" and an Extended EMM cause IE with value "NB-IoT not allowed":
  • the MS may add the identity of the PLMN to the list of "PLMNs with NB-IoT not allowed" and start timer TH if timer TH is not already running. The number of PLMNs that the MS can store in the "PLMNs with NB-IoT not allowed" list is implementation specific, but it shall be at least one. The value of timer TH is MS implementation specific, but shall not exceed the maximum possible value of background scanning timer T as specified in subclause 4.4.3.3.1;
  • in automatic PLMN selection the MS shall not consider PLMNs included in the "PLMNs with NB-IoT not allowed" list as PLMN selection candidates for NB-IoT access technology, unless no other PLMN is available. This does not prevent selection of such a PLMN if it is available in another RAT; and
  • the MS shall delete stored information in the "PLMNs with NB-IoT not allowed" list when the MS is switched off, the USIM is removed or timer TH expires.
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3.1A  CSG selection / restriction |R8|Word‑p. 18
If the MS supports CSG, it is provisioned with an Allowed CSG list and an Operator CSG list and associated PLMN identities. Both lists can be retrieved either from the USIM if the lists are available in the USIM, or as described in TS 24.285 if the lists are not available in the USIM. These lists have zero or more entries.
There are two modes of CSG selection:
  • Automatic mode: This mode utilizes the Allowed CSG list and the Operator CSG list. After a PLMN is selected, the MS camps on a cell in that PLMN only if the cell is either not a CSG cell or it is a CSG cell with a CSG identity that is in the Allowed CSG list or in the Operator CSG List. The idle mode procedures of NAS are not impacted by this mode. Upon switch on the MS is in automatic mode.
  • Manual mode: In this mode, the MS indicates to the user a list of available CSGs and the associated PLMNs. Based on configuration by the HPLMN, the list of CSGs provided to the user for a certain PLMN is either:
    • not restricted by the Allowed CSG list and the Operator CSG List stored in the MS; or
    • restricted to entries in the Operator CSG List only.
      After the user makes a selection, the MS camps on a cell with the selected CSG identity and may attempt to register with the associated PLMN (see TS 24.008 and TS 24.301).
The CSG whitelist is a combination of Operator CSG list and the Allowed CSG list. NAS shall provide the CSG whitelist to the AS. If the contents of the CSG whitelist have changed, NAS shall provide an updated CSG whitelist to the AS.
If an integrity protected message with cause value #25 (see TS 24.008 and TS 24.301) is received by an MS for a CSG ID and associated PLMN identity present in the Operator CSG list, then for an implementation dependent time which is not shorter than 60 minutes, or until the MS is switched off, or the SIM/USIM is removed, or the Operator CSG list is updated:
  1. The NAS shall not include this CSG ID and the associated PLMN identity in the CSG whitelist provided to the AS; and
  2. In CSG manual mode selection, the MS shall not indicate to the user that this CSG ID and the associated PLMN identity is in the Operator CSG List stored in the MS.
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3.1B  PLMN selection triggered by ProSe direct communication |R12|Word‑p. 19
If the MS supports ProSe direct communication and needs to perform PLMN selection for ProSe direct communication as specified in TS 24.334, then the MS shall proceed as follows:
i)
the MS shall store a duplicate value of the RPLMN and a duplicate of the PLMN selection mode that were in use before PLMN selection due to ProSe direct communication was initiated, unless this PLMN selection due to ProSe direct communication follows another PLMN selection due to ProSe direct communication or a manual CSG selection as specified in subclause 4.4.3.1.3.3;
ii)
the MS shall enter into Automatic mode of PLMN selection as specified in subclause 4.4 taking into account the additional requirements in items iii) to x) below;
iii)
Among the PLMNs advertised by the E-UTRA cell operating in the radio resources provisioned to the MS for ProSe direct communication as specified in TS 24.333 or TS 31.102, the MS shall choose one allowable PLMN which:
  1. provides radio resources for ProSe direct communication;
  2. is in the list of authorised PLMNs for ProSe direct communication as specified in TS 24.334; and
  3. is not in the list of "PLMNs with E-UTRAN not allowed" as specified in subclause 3.1;
if conditions 1) through 3) above are met then the MS shall attempt to register on that PLMN. If none of the PLMNs meet conditions 1) through 3) above, the MS shall return to the stored duplicate PLMN selection mode and use the stored duplicate value of RPLMN for further action;
iv)
if the registration fails due to "PLMN not allowed" or "EPS services not allowed" as specified in TS 24.334, then the MS shall update the appropriate list of forbidden PLMNs as specified in subclause 3.1, and shall either:
  1. if the PLMN provides common radio resources needed by the MS to do ProSe direct communication as specified in TS 36.331, perform ProSe direct communication on the selected PLMN in limited service state. In this case the MS shall not search for available and allowable PLMNs during the duration of ProSe direct communication;
  2. return to the stored duplicate PLMN selection mode and use the stored duplicate value of RPLMN for further action; or
  3. perform the action described in iii) again with the choice of PLMNs further excluding the PLMNs on which the MS has failed to register.
  4. Whether the MS performs A), B) or C) above is left up to MS implementation.
v)
if the registration fails due to causes other than "PLMN not allowed" or "EPS services not allowed", the MS shall:
  • if the handling of the failure requires updating a list of forbidden PLMNs, update the appropriate list (as specified in TS 24.301); and
  • if the handling of the failure does not require updating a list of forbidden PLMNs (as specified in TS 24.301), remember the PLMN as a PLMN on which the MS has failed to register;
and the MS shall either:
A1)
return to the stored duplicate PLMN selection mode and use the stored duplicate value of RPLMN for further action;
B1)
perform the action described in iii) again with the choice of PLMNs further excluding the PLMNs on which the MS has failed to register; or
C1)
perform ProSe direct communication in limited service state on a PLMN advertised by the cell operating in the radio resources provisioned to the MS for ProSe direct communication as specified in TS 24.333 or TS 31.102, if registration on this PLMN has previously failed due to "PLMN not allowed" or "EPS services not allowed" as specified in TS 24.334 and if this PLMN provides common radio resources needed by the MS to do ProSe direct communication as specified in TS 36.331. In this case the MS shall not search for available and allowable PLMNs during the duration of ProSe direct communication;
Whether the MS performs A1), B1) or C1) above is left up to MS implementation.
vi)
if the MS is no longer in the coverage of the selected PLMN, then the MS shall either:
A2)
perform ProSe direct communication procedures for MS to use provisioned radio resources as specified in TS 24.334; or
B2)
return to the stored duplicate PLMN selection mode and use the stored duplicate value of RPLMN for further action.
Whether the MS performs A2) or B2) above is left up to MS implementation.
vii)
if the MS is unable to find a suitable cell on the selected PLMN as specified in TS 24.334, then the MS shall either:
A3)
if the PLMN provides common radio resources needed by the MS to do ProSe direct communication as specified in TS 36.331, perform ProSe direct communication on the selected PLMN in limited service state. In this case the MS shall not search for available and allowable PLMNs during the duration of ProSe direct communication; or
B3)
return to the stored duplicate PLMN selection mode and use the stored duplicate value of RPLMN for further action.
Whether the MS performs A3) or B3) above is left up to MS implementation.
viii)
if the MS is switched off while on the selected PLMN and switched on again, the MS shall use the stored duplicate value of RPLMN as RPLMN and behave as specified in subclause 4.4.3.1;
ix)
if the user initiates a PLMN selection while on the selected cell, the MS shall delete the stored duplicate value of PLMN selection mode, use the stored duplicate value of RPLMN as RPLMN and follow the procedures (as specified for switch-on or recovery from lack of coverage) in subclause 4.4.3.1. The MS shall delete the stored duplicate value of RPLMN once the MS has successfully registered to the selected PLMN; and
x)
if the MS no longer needs to perform Prose direct communication, the MS shall return to the stored duplicate PLMN selection mode and use the stored duplicate value of RPLMN for further action.
If the PLMN selected for ProSe direct communication is a VPLMN, the MS shall not periodically scan for higher priority PLMNs during the duration of ProSe direct communication.
The solution to prevent potential ping-pong between the RPLMN and the PLMN selected for ProSe direct communication is MS implementation specific.
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3.1C  PLMN selection triggered by V2X communication over PC5 |R14|Word‑p. 20
If the MS supports V2X communication over PC5 and needs to perform PLMN selection for V2X communication over PC5 as specified in TS 24.386, then the MS shall proceed as follows:
i)
the MS shall store a duplicate value of the RPLMN and a duplicate of the PLMN selection mode that were in use before PLMN selection due to V2X communication over PC5 was initiated, unless this PLMN selection due to V2X communication over PC5 follows another PLMN selection due to V2X communication over PC5 or a manual CSG selection as specified in subclause 4.4.3.1.3.3;
ii)
the MS shall enter into Automatic mode of PLMN selection as specified in subclause 4.4 taking into account the additional requirements in items iii) to x) below;
iii)
Among the PLMNs advertised by the E-UTRA cell operating in the radio resources provisioned to the MS for V2X communication over PC5 as specified in TS 24.385 or TS 31.102, the MS shall choose one allowable PLMN which:
  1. provides radio resources for V2X communication over PC5;
  2. is in the list of authorised PLMNs for V2X communication over PC5 as specified in TS 24.386; and
  3. is not in the list of "PLMNs with E-UTRAN not allowed" as specified in subclause 3.1;
if conditions 1) through 3) above are met then the MS shall attempt to register on that PLMN. If none of the PLMNs meet conditions 1) through 3) above, the MS shall return to the stored duplicate PLMN selection mode and use the stored duplicate value of RPLMN for further action;
iv)
if the registration fails due to "PLMN not allowed" or "EPS services not allowed" as specified in TS 24.386, then the MS shall update the appropriate list of forbidden PLMNs as specified in subclause 3.1, and shall either:
  1. if the PLMN provides common radio resources needed by the MS to do V2X communication over PC5 as specified in TS 36.331, perform V2X communication over PC5 on the selected PLMN in limited service state. In this case the MS shall not search for available and allowable PLMNs during the duration of V2X communication over PC5;
  2. return to the stored duplicate PLMN selection mode and use the stored duplicate value of RPLMN for further action; or
  3. perform the action described in iii) again with the choice of PLMNs further excluding the PLMNs on which the MS has failed to register.
Whether the MS performs A), B) or C) above is left up to MS implementation.
v)
if the registration fails due to causes other than "PLMN not allowed" or "EPS services not allowed", the MS shall:
  • if the handling of the failure requires updating a list of forbidden PLMNs, update the appropriate list (as specified in TS 24.301); and
  • if the handling of the failure does not require updating a list of forbidden PLMNs (as specified in TS 24.301), remember the PLMN as a PLMN on which the MS has failed to register;
and the MS shall either:
A1)
return to the stored duplicate PLMN selection mode and use the stored duplicate value of RPLMN for further action;
B1)
perform the action described in iii) again with the choice of PLMNs further excluding the PLMNs on which the MS has failed to register; or
C1)
perform V2X communication over PC5 in limited service state on a PLMN advertised by the cell operating in the radio resources provisioned to the MS for V2X communication over PC5 as specified in TS 24.385 or TS 31.102, if registration on this PLMN has previously failed due to "PLMN not allowed" or "EPS services not allowed" as specified in TS 24.386 and if this PLMN provides common radio resources needed by the MS to do V2X communication over PC5 as specified in TS 36.331. In this case the MS shall not search for available and allowable PLMNs during the duration of V2X communication over PC5;
Whether the MS performs A1), B1) or C1) above is left up to MS implementation.
vi)
if the MS is no longer in the coverage of the selected PLMN, then the MS shall either:
A2) perform V2X communication over PC5 procedures for MS to use provisioned radio resources as specified in TS 24.386; or
B2) return to the stored duplicate PLMN selection mode and use the stored duplicate value of RPLMN for further action.
Whether the MS performs A2) or B2) above is left up to MS implementation.
vii)
if the MS is unable to find a suitable cell on the selected PLMN as specified in TS 24.386, then the MS shall either:
A3)
if the PLMN provides common radio resources needed by the MS to do V2X communication over PC5 as specified in TS 36.331, perform V2X communication over PC5 on the selected PLMN in limited service state. In this case the MS shall not search for available and allowable PLMNs during the duration of V2X communication over PC5; or
B3)
return to the stored duplicate PLMN selection mode and use the stored duplicate value of RPLMN for further action.
Whether the MS performs A3) or B3) above is left up to MS implementation.
viii)
if the MS is switched off while on the selected PLMN and switched on again, the MS shall use the stored duplicate value of RPLMN as RPLMN and behave as specified in subclause 4.4.3.1;
ix)
if the user initiates a PLMN selection while on the selected cell, the MS shall delete the stored duplicate value of PLMN selection mode, use the stored duplicate value of RPLMN as RPLMN and follow the procedures (as specified for switch-on or recovery from lack of coverage) in subclause 4.4.3.1. The MS shall delete the stored duplicate value of RPLMN once the MS has successfully registered to the selected PLMN; and
x)
if the MS no longer needs to perform V2X communication over PC5, the MS shall return to the stored duplicate PLMN selection mode and use the stored duplicate value of RPLMN for further action.
If the PLMN selected for V2X communication over PC5 is a VPLMN, the MS shall not periodically scan for higher priority PLMNs during the duration of V2X communication over PC5.
The solution to prevent potential ping-pong between the RPLMN and the PLMN selected for V2X communication over PC5 is MS implementation specific.
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3.2  Regional provision of serviceWord‑p. 22
An MS may have a "regionally restricted service" where it can only obtain service on certain areas (i.e. LAs or TAs). If such an MS attempts to camp on a cell of an area for which it does not have service entitlement, when it does an LR request, it will receive a message with cause value #12 (see TS 24.008, TS 24.301 and TS 24.501). In this case, the MS shall take the following actions depending on the access technology in which the message was received:
GSM, GSM COMPACT or UTRAN:
The MS stores the forbidden LA identity (LAI) in a list of "forbidden location areas for regional provision of service", to prevent repeated access attempts on a cell of the forbidden LA. This list is deleted when the MS is switched off or the SIM is removed. The MS enters the limited service state.
E-UTRAN:
The MS stores the forbidden TA identity (TAI) in a list of "forbidden tracking areas for regional provision of service", to prevent repeated access attempts on a cell of the forbidden TA. This list is deleted when the MS is switched off or the SIM is removed. The MS enters the limited service state.
NG-RAN:
The MS stores the forbidden TA identity (TAI) in a list of "5GS forbidden tracking areas for regional provision of service", to prevent repeated access attempts on a cell of the forbidden TA. This list is deleted when the MS is switched off or the SIM is removed. The MS enters the limited service state.
In A/Gb mode, a cell may be reserved for SoLSA exclusive access (see TS 24.008 and TS 44.060). An MS is only allowed to camp normally on such a cell if it has a Localised Service Area subscription to the cell. Other MS may enter the limited service state.
The MS operating in SNPN access mode shall maintain one or more lists of "5GS forbidden tracking areas for regional provision of service", each associated with an SNPN. The MS shall use the list of "5GS forbidden tracking areas for regional provision of service" associated with the selected SNPN. If the MS selects a new SNPN, the MS shall keep the list of "5GS forbidden tracking areas for regional provision of service" 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 regional provision of service". The MS shall delete all lists of "5GS forbidden tracking areas for regional provision of service", when the MS is switched off. The MS shall delete the list of "5GS forbidden tracking areas for regional provision of service" 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:
  • 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.
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3.3  Borders between registration areasWord‑p. 23
If the MS is moving in a border area between registration areas, it might repeatedly change between cells of different registration areas. Each change of registration area would require an LR, which would cause a heavy signalling load and increase the risk of a paging message being lost. The access stratum shall provide a mechanism to limit this effect.

3.4  Access control

3.4.1  Access control

Due to problems in certain areas, network operators may decide to restrict access from some MSs (e.g., in case of congestion), and for this reason, a mechanism for common access control is provided. In A/Gb mode and Iu mode a mechanism for domain specific access control is also provided (see TS 43.022, TS 44.018 and TS 25.304).
A mechanism to restrict access is provided via EAB. A network operator can restrict network access of those MSs that are configured for EAB in addition to common access control and domain specific access control.
The MS can be configured for EAB in the USIM (see TS 31.102) or in the ME (see TS 24.368). An MS that supports EAB shall follow the EAB mechanism (see TS 24.008, TS 24.301, TS 44.018, TS 25.331, TS 36.331) when configured for EAB.
The MS can be configured for ACDC in the USIM (see TS 31.102) or in the ME (see TS 24.105). An MS that supports ACDC shall follow the ACDC mechanism (see TS 24.008, TS 24.301, TS 25.331, TS 36.331) when configured for ACDC.
The MS can be configured in the USIM (see TS 31.102) or in the ME (see TS 24.368) to override EAB. An MS that supports overriding EAB shall follow the overriding EAB mechanism (see TS 24.008, TS 24.301) when configured to allow overriding EAB.
In the case that a network operator decides to restrict access they may as an option allow restricted MSs to respond to paging messages and/or to perform location registrations. Mechanisms to allow this optional access are provided (see TS 25.304).
A network operator can also restrict some MSs to access the network for location registration, although via common access class control or domain specific access class control the MSs are permitted to access the network for other purposes.
If the MS is accessing the network with a special access class (Access classes 11 to 15), then the MS shall ignore EAB and ACDC.
If an MS configured for EAB is initiating an emergency call, then the MS shall ignore EAB.
If an MS configured for EAB is responding to paging, then the MS shall ignore EAB.
If an MS configured for ACDC is responding to paging, then the MS shall ignore ACDC.
If an MS configured for ACDC is initiating an emergency call, then the MS shall ignore ACDC.
If an MS configured for ACDC and the MO MMTEL voice call is started, the MO MMTEL video call is started or the MO SMSoIP is started (see TS 24.008, TS 24.301), then the MS shall ignore ACDC.
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3.4.2  Forbidden LA or TA for regional provision of serviceWord‑p. 24
The MS is not allowed to initiate establishment of a CM connection except for an emergency call when camped on a cell of an LA or TA of which belongs to the list of "forbidden location areas for regional provision of service" or "forbidden tracking areas for regional provision of service". The MS may respond to paging.
The MS is not allowed to request GPRS services except for an emergency bearer services or for access to RLOS when camped on a cell of an LA or TA of which belongs to the list of "forbidden location areas for regional provision of service" or "forbidden tracking areas for regional provision of service".
The MS is not allowed to request 5GS services except emergency services when camped on a cell of a TA of which belongs to the list of "5GS forbidden tracking areas for regional provision of service".
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3.5  No suitable cell (limited service state)

There are a number of situations in which the MS is unable to obtain normal service from a PLMN or SNPN. These include:
  1. Failure to find a suitable cell of the selected PLMN or of the selected SNPN;
  2. No SIM in the MS or the "list of subscriber data" with no valid entry;
  3. A "PLMN not allowed", "Requested service option not authorized in this PLMN" or "Serving network not authorized" response in case of PLMN or a "Temporarily not authorized for this SNPN" or "Permanently not authorized for this SNPN" response in case of SNPN when an LR is received;
  4. An "illegal MS" or "illegal ME" response when an LR is received (Any SIM or the corresponding entry of the "list of subscriber data" in the ME is then considered "invalid");
  5. An "IMSI unknown in HLR" response when an LR is received (Any SIM in the ME is then considered "invalid" for non-GPRS services);
  6. A "GPRS services not allowed" response when an LR of a GPRS MS attached to GPRS services only is received (The cell selection state of GPRS MSs attached to GPRS and non-GPRS depends on the outcome of the location updating), or an "EPS services not allowed" response is received when an EPS attach, tracking area update or service request is performed, or a "5GS services not allowed" response is received when a registration or service request is performed;
  7. Power saving mode (PSM) is activated (see TS 23.682); or
  8. Mobile initiated connection only (MICO) mode is activated (see TS 23.501 and TS 23.502).
  9. MS supporting CAG is camped on a CAG cell belonging to a PLMN, the CAG-ID of the CAG cell is not manually selected by the user and none of the CAG-ID(s) of the CAG cell are present in the "Allowed CAG list" associated with that PLMN in the "CAG information list";
  10. MS supporting CAG is camped on a non-CAG cell belonging to a PLMN, the PLMN ID of the non-CAG cell without a CAG-ID is not manually selected by the user and the UE is configured with "indication that the MS is only allowed to access 5GS via CAG cells" for that PLMN in the "CAG information list"; and
  11. MS supporting CAG is camped on a CAG cell belonging to a PLMN, the CAG-ID of the CAG cell is not manually selected by the user and the "CAG information list" does not contain an entry for the PLMN (e.g. because the UE is not (pre-)configured with a "CAG information list").
(In automatic PLMN selection mode, items a, c and f would normally cause a new PLMN selection, but even in this case, the situation may arise when no PLMNs are available and allowable for use).
(In automatic SNPN selection mode, items a, c, d, and f would normally cause a new SNPN selection if there are two or more entries in the "list of subscriber data", but even in this case, the situation may arise when no SNPNs are available and allowable for use).
For the items a to f, if the MS does not operate in SNPN access mode, the MS attempts to camp on an acceptable cell, irrespective of its PLMN identity, so that emergency calls or access to RLOS can be made if necessary, with the exception that an MS operating in NB-S1 mode, shall never attempt to make emergency calls or to access RLOS. When in the limited service state with a valid SIM, the MS shall search for available and allowable PLMNs in the manner described in subclause 4.4.3.1 and when indicated in the SIM also as described in subclause 4.4.3.4. For an MS that is not in eCall only mode, with the exception of performing GPRS attach or EPS attach for emergency bearer services, performing an initial registration for emergency services, or performing EPS attach for access to RLOS, no LR requests are made until a valid SIM is present and either a suitable cell is found or a manual network reselection is performed. For an MS in eCall only mode, no LR requests are made except for performing EPS attach for emergency bearer services or an initial registration for emergency services. When performing GPRS attach or EPS attach for emergency bearer services, an initial registration for emergency services, or performing EPS attach for access to RLOS, the PLMN of the current serving cell is considered as the selected PLMN for the duration the MS is attached for emergency bearer services, registered for emergency services, or attached for access to RLOS. In the limited service state the presence of the MS need not be known to the PLMN on whose cell it has camped.
For the items a, c, d and f, if the MS operates in SNPN access mode and the UE has a valid entry in the "list of subscriber data", the MS shall search for available and allowable SNPNs in the manner described in subclause 4.9.3.1. For the item b, if the MS operates in SNPN access mode, the MS attempts to camp on an acceptable cell. When in the limited service state, no LR requests are made until a valid entry of the "list of subscriber data" is present and either a suitable cell is found or a manual network reselection is performed. In the limited service state the presence of the MS need not be known to the SNPN on whose cell it has camped.
There are also other conditions under which only emergency calls or access to RLOS may be made if the MS does not operate in SNPN access mode. These are shown in table 2 in clause 5. ProSe direct communication and ProSe direct discovery for public safety use can be initiated if necessary (see TS 24.334) when in the limited service state due to items a) or c) or f). V2X communication over PC5 can be initiated if necessary (see TS 24.386) when in the limited service state due to items a) or c) or f).
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3.6  CTS fixed part selection (A/Gb mode only)Word‑p. 25
In CTS mode only or in automatic mode with CTS preferred, the CTS MS normally operates on a CTS fixed part on which the mobile station is already enrolled. If the CTS MS loses CTS coverage in these modes, it shall attempt periodically to select again a CTS fixed part.
To select a CTS fixed part, the CTS MS shall listen to the CTSBCH frequencies of all the fixed parts on which the MS is currently enrolled.
If the CTS MS is moving in a border area between one area with CTS coverage and one without it, it might repeatedly require CTS attachments and LU on the PLMN. To prevent this, the criteria C1_CTS and C2_CTS (defined in TS 45.008 subclause 11.1) are used. To attach to a CTS FP, the C1_CTS criterion shall be greater than zero. When the C2_CTS criterion falls below zero, the CTS MS shall consider itself to be no more under CTS coverage.
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3.7  NAS behaviour configuration |R10|Word‑p. 26
NAS behaviour can be operator configurable using parameters in the USIM (see TS 31.102) or in the ME (see TS 24.368). For parameters available in both the USIM and the ME, precedence is specified in TS 31.102 subclause 5.2.29.

3.8  CAG selection (N1 mode only) |R16|

The MS may support CAG.
If the MS supports CAG, the MS can be provisioned with a "CAG information list", consisting of zero or more entries, each containing:
  1. a PLMN ID;
  2. an "Allowed CAG list". The "Allowed CAG list" contains zero or more CAG-IDs; and
  3. an optional "indication that the MS is only allowed to access 5GS via CAG cells".
The "CAG information list" is stored in the ME.
If the MS supports CAG and is provisioned with a non-empty "CAG information list" then CAG selection is performed as part of subclause 4.4.3.1.1 and subclause 4.4.3.1.2.
If a PLMN is selected as described in subclause 4.4.3.1.2, the manual CAG selection is achieved according to subclause 4.4.3.1.2.
The NAS shall provide the AS with a "CAG information list", if available. If the contents of the "CAG information list" have changed, the NAS shall provide an updated "CAG information list" to the AS.
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3.9  SNPN selection |R16|

An MS may be enabled for SNPN.
An MS enabled for SNPN may operate in SNPN access mode.
The MS operating in SNPN access mode selects an SNPN for which it is configured with a subscriber identifier and credentials. The MS can have several sets of subscriber identifiers, credentials, and SNPN identities. There are two modes for SNPN selection:
  1. Automatic SNPN selection mode.
  2. Manual SNPN selection mode.

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