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Content for  TS 22.011  Word version:  17.3.0

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3  Provisions for providing continuity of service

3.1  Location registration

PLMNs shall provide a location registration function with the main purpose of providing continuity of service to UEs over the whole system area. The location registration function shall be such as to allow:
  • Fixed subscribers to call a UE by only using the directory number of the UE irrespective of where the UE is located in the system area at the time of the call.
  • UEs to access the system irrespective of the location of the UE.
  • UEs to identify when a change in location area has taken place in order to initiate automatic location updating procedures.
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3.2  Network selection

3.2.1  General

The UE shall support both manual and automatic network selection mechanisms (modes). The UE shall select the last mode used, as the default mode, at every switch-on.
As an optional feature of the ME, the user shall be able to set a preference in the ME for the mode that shall be used at switch on. If set, then the ME shall select this preference rather than the default mode.
The user shall be given the opportunity to change mode at any time.
Except as defined below, the MMI shall be at the discretion of the UE manufacturer.
The UE shall contain display functions by which Available PLMNs and the Selected PLMN can be indicated.
In order not to confuse the user, the same definitions of PLMN names shall be applied consistently both in registered mode and in the list presented to the user when in manual mode.
In shared networks a radio access network can be part of more than one PLMN. This shall be transparent to the user, i.e. the UE shall be able to indicate those PLMNs to the user, and the UE shall support network selection among those PLMNs, as in non-shared networks.
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3.2.2  ProceduresWord‑p. 10

3.2.2.1  General

In the following procedures the UE selects and attempts registration on PLMNs.
In this TS, the term "PLMN Selection" defines a UE based procedure, whereby candidate PLMNs are chosen, one at a time, for attempted registration.
A User Controlled PLMN Selector data field exists on the USIM to allow the user to indicate a preference for network selection. It shall be possible for the user to update the User Controlled PLMN Selector data field, but it shall not be possible to update this data field over the radio interface, e.g. using SIM Application Toolkit.
It shall be possible to have an Operator Controlled PLMN Selector list and a User Controlled PLMN Selector list stored on the SIM/USIM card. Both PLMN Selector lists may contain a list of preferred PLMNs in priority order. It shall be possible to have an associated Access Technology identifier e.g., NG-RAN, satellite NG-RAN, E-UTRAN (WB-S1 mode), E-UTRAN (NB-S1 mode), UTRAN, GERAN or GERAN EC-GSM-IoT associated with each entry in the PLMN Selector lists.
The UE shall utilise all the information stored in the USIM related to network selection, e.g. HPLMN, Operator controlled PLMN Selector list, User Controlled PLMN Selector list, Forbidden PLMN list.
The UE shall ignore those PLMN + access technology entries in the User Controlled PLMN selector and Operator Controlled PLMN selector lists where the associated Access Technology is not supported by the UE. In the case that there are multiple associated Access Technology identifiers in an entry the UE shall not ignore the entry if it includes any associated Access Technology that is supported by the UE.
It shall be possible to handle cases where one network operator accepts access from access networks with different network IDs. It shall also be possible to indicate to the UE that a group of PLMNs are equivalent to the registered PLMN regarding PLMN selection, cell selection/re-selection and handover.
It shall be possible for the home network operator to identify alternative Network IDs as the HPLMN. It shall be possible for the home network operator to store in the USIM an indication to the UE that a group of PLMNs are treated as the HPLMN regarding PLMN selection. Any PLMN to be declared as an equivalent to the HPLMN shall be present within the EHPLMN list and is called an EHPLMN. The EHPLMN list replaces the HPLMN derived from the IMSI. When the EHPLMN list is present, any PLMN in this list shall be treated as the HPLMN in all the network and cell selection procedures.
If registration on a PLMN is successful, the UE shall indicate this PLMN (the "registered PLMN") and be capable of making and receiving calls on it. The identity of the registered PLMN shall be stored on the SIM/USIM. However, if registration is unsuccessful, the UE shall ensure that there is no registered PLMN stored in the SIM/USIM.
If a registration is unsuccessful because the IMSI is unknown in the home network, or the UE is illegal, then the UE shall not allow any further registration attempts on any network, until the UE is next powered-up or a SIM/USIM is inserted.
If the registration is unsuccessful due to the lack to service entitlement, specific behaviour by the UE may be required, see clause 3.2.2.4.
To avoid unnecessary registration attempts, lists of forbidden PLMNs, TAs and LAs are maintained in the UE, see clause 3.2.2.4 and TS 23.122.
Registration attempts shall not be made by UEs without a SIM/USIM inserted.
An UE/ME which has not successfully registered shall nevertheless be able to make emergency call attempts on an available PLMN (which supports the emergency call teleservice), without the need for the user to select a PLMN. An available PLMN is determined by radio characteristics (TS 23.122).
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3.2.2.2  At switch-on or recovery from lack of coverageWord‑p. 11
At switch on, when in coverage of the last registered PLMN as stored in the SIM/USIM, the UE will attach to that network.
As an option, in automatic selection mode, when no EHPLMN list is present, the UE may select the HPLMN. When the EHPLMN list is present, the UE may select the highest priority EHPLMN among the available EHPLMNs. The operator shall be able to control the UE behaviour by USIM configuration.
As an option, if the UE is in manual network selection mode at switch-on
  • if the last registered PLMN is unavailable and no equivalent PLMN is available,
  • and the UE finds it is in coverage of either the HPLMN or an EHPLMN
then the UE should register on the corresponding HPLMN or EHPLMN. The UE remains in manual mode.
If the UE returns to coverage of the PLMN on which it is already registered (as indicated by the registered PLMN stored in the SIM/USIM), the UE shall perform a location update to a new location area if necessary. As an alternative option to this, if the UE is in automatic network selection mode and it finds coverage of the HPLMN or any EHPLMN, the UE may register on the HPLMN (if the EHPLMN list is not present) or the highest priority EHPLMN of the available EHPLMNs (if the EHPLMN list is present) and not return to the last registered PLMN. If the EHPLMN list is present and not empty, it shall be used. The operator shall be able to control by USIM configuration whether an UE that supports this option shall follow this alternative behaviour.
The default behaviour for a UE is to select the last registered PLMN.
If there is no registered PLMN stored in the SIM/USIM, or if this PLMN is unavailable and no equivalent PLMN is available, or the attempted registration fails, the UE shall follow one of the following procedures for network selection:
A) Automatic network selection mode
The UE shall select and attempt registration on other PLMNs, if available and allowable, if the location area is not in the list of "forbidden LAs for roaming" and the tracking area is not in the list of "forbidden TAs for roaming" (see TS 23.122), in the following order:
  1. An EHPLMN if the EHPLMN list is present or the HPLMN (derived from the IMSI) if the EHPLMN list is not present for preferred access technologies in the order specified. In the case that there are multiple EHPLMNs present then the highest priority EHPLMN shall be selected. It shall be possible to configure a voice capable UE so that it shall not attempt registration on a PLMN if all cells identified as belonging to the PLMN do not support the corresponding voice service;
  2. each entry in the "User Controlled PLMN Selector with Access Technology" data field in the SIM/USIM (in priority order). It shall be possible to configure a voice capable UE so that it shall not attempt registration on a PLMN if all cells identified as belonging to the PLMN do not support the corresponding voice service;
  3. each entry in the "Operator Controlled PLMN Selector with Access Technology" data field in the SIM/USIM (in priority order). It shall be possible to configure a voice capable UE so that it shall not attempt registration on a PLMN if all cells identified as belonging to the PLMN do not support the corresponding voice service;
  4. other PLMN/access technology combinations with sufficient received signal quality (see TS 23.122) in random order. It shall be possible to configure a voice capable UE so that it shall not attempt registration on a PLMN if all cells identified as belonging to the PLMN do not support the corresponding voice service;
  5. all other PLMN/access technology combinations in order of decreasing signal quality. It shall be possible to configure a voice capable UE so that it shall not attempt registration on a PLMN if all cells identified as belonging to the PLMN do not support the corresponding voice service.
In the case of a UE operating in UE operation mode A or B, an allowable PLMN is one which is not in the "Forbidden PLMN" data field in the SIM/USIM. This data field may be extended in the ME memory (see clause 3.2.2.4). In the case of a UE operating in UE operation mode C, an allowable PLMN is one which is not in the "Forbidden PLMN" data field in the SIM/USIM or in the list of "forbidden PLMNs for GPRS service" in the ME. When there is no available PLMN except for PLMNs in the "Forbidden PLMN" data field in the SIM/USIM, and the available PLMNs indicate that Disaster Condition applies, this PLMN shall be considered allowable for registration to the UE while the Disaster Condition is applicable.
If successful registration is achieved, the UE shall indicate the selected PLMN.
If registration cannot be achieved on any PLMN and at least one PLMN offering restricted local operator services has been found, the UE shall obtain user consent for restricted local operator services and the UE may use a list of preferred PLMNs for restricted local operator services stored in the ME. If none of the preferred PLMNs for restricted local operator services is available, the UE shall select any available PLMN offering restricted local operator services. If one of these PLMNs for restricted local operator service is chosen, the UE shall indicate the choice. If none are selected, the UE shall wait until a new PLMN is detected, or new location areas or tracking areas of an allowed PLMN are found which are not in the forbidden LA or TA list(s), and then repeat the procedure.
If registration cannot be achieved on any PLMN and no PLMN offering restricted local operator services has been found, the UE shall indicate "no service" to the user, wait until a new PLMN is detected, or new location areas or tracking areas of an allowed PLMN are found which are not in the forbidden LA or TA list(s), and then repeat the procedure. When registration cannot be achieved, different (discontinuous) PLMN search schemes may be used in order to minimize the access time while maintaining battery life, e.g. by prioritising the search in favour of BCCH carriers which have a high probability of belonging to an available and allowable PLMN.
B) Manual network selection mode
The UE shall indicate PLMNs, including "Forbidden PLMNs", which are available. If there are none, this shall also be indicated. The HPLMN of the user may provide on the USIM additional information about the available PLMNs, if this is provided then the UE shall indicate that information to the user. This information, provided as free text may include:
  • Preferred partner,
  • roaming agreement status,
  • supported services
Furthermore, the UE may indicate whether the available PLMNs are present on one of the PLMN selector lists (e.g. EHPLMN, User Controlled, Operator Controlled or Forbidden) as well as not being present on any of the lists.
For the purpose of presenting the names of the available PLMNs to the user, the ME shall use the USIM defined names if available or other PLMN naming rules in priority order as defined in TS 22.101 (Country/PLMN indication).
Any available PLMNs shall be presented in the following order:
  1. HPLMN (if the EHPLMN list is not present); or if one or more of the EHPLMNs are available then based on an optional data field on the USIM either the highest priority available EHPLMN is to be presented to the user or all available EHPLMNs are presented to the user in priority order; if the data field is not present, then only the highest priority available EHPLMN is presented;
  2. PLMNs contained in the "User Controlled PLMN Selector" data field in the SIM/USIM (in priority order);
  3. PLMNs contained in the "Operator Controlled PLMN Selector" data field in the SIM/USIM (in priority order);
  4. other PLMN/access technology combinations with sufficient received signal level (see TS 23.122) in random order;
  5. all other PLMN/access technology combinations in order of decreasing signal strength.
If a PLMN does not support voice services, then this shall be indicated to the user.
The user may select the desired PLMN and the UE shall attempt registration on this PLMN. (This may take place at any time during the presentation of PLMNs.)
If registration cannot be achieved on any PLMN and at least one PLMN offering restricted local operator services has been found, the UE shall obtain user consent for restricted local operator services and offer the user to select one of these networks. If one of these networks is selected, the UE shall indicate the selected PLMN, wait until a new PLMN is detected, or new location areas or tracking areas of an allowed PLMN are found which are not in the forbidden LA or TA list(s), and then repeat the procedure.
If the registration cannot be achieved on any PLMN and no PLMN offering restricted local operator services is selected, the UE shall indicate "No Service". The user may then select and attempt to register on another or the same PLMN following the above procedure. The UE shall not attempt to register on a PLMN which has not been selected by the user.
Once the UE has registered on a PLMN selected by the user, the UE shall not automatically register on a different PLMN unless:
  1. The new PLMN is declared as an equivalent PLMN by the registered PLMN;
    or,
  2. The user selects automatic mode.
If a PLMN is selected but the UE cannot register on it because registration is rejected with the cause "PLMN not allowed", the UE shall add the PLMN to the "Forbidden PLMN" list (clause 3.2.2.4.1). The UE shall not re-attempt to register on that network unless the same PLMN is selected again by the user.
If a PLMN is selected but the UE cannot register for PS services on it because registration is rejected with the cause "GPRS services not allowed in this PLMN", the UE shall not re-attempt to register for E-UTRAN or UTRAN PS or GERAN PS on that network. The PLMN is added to the list "Forbidden PLMN's for GPRS services". The UE shall not re-attempt to register for E-UTRAN or UTRAN PS or GERAN PS on that network unless the same PLMN is selected again by the user. The reception of the cause "GPRS services not allowed in this PLMN", does not affect the CS service.
For requirements to restrict the access of a UE to one or several specific RATs see clause 7.1.
If a PLMN is selected but the UE cannot register on it for other reasons, the UE shall, upon detection of a new LA (not in a forbidden LA list) of the selected PLMN, attempt to register on the PLMN.
If the UE is registered on a PLMN but loses coverage, different (discontinuous) carrier search schemes may be used to minimize the time to find a new valid BCCH carrier and maintain battery life, e.g. by prioritizing the search in favour of BCCH carriers of the registered PLMN.
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3.2.2.3  User reselectionWord‑p. 13
At any time, the user may request the UE to initiate reselection and registration onto an alternative available PLMN, according to the following procedures, dependent upon the operating mode.
A) Automatic Network Selection Mode
The UE shall follow the procedure defined in clause 3.2.2.2 A) above.
B) Manual Network Selection Mode
The procedure of clause 3.2.2.2 B) is followed.
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3.2.2.4  Mobile Station reactions to indications of service restriction from the network

Different types of UE behaviour are required to support, for example, national roaming, regionally provided service and temporary international roaming restrictions. The behaviour to be followed by the UE is indicated by the network.
3.2.2.4.1  "Permanent" PLMN restrictionWord‑p. 14
When a registration attempt by the UE is rejected by a network with an indication of "permanent" PLMN restriction, the PLMN identity shall be written to a list of "Forbidden PLMNs" stored in a data field in the SIM/USIM.
If a successful registration is achieved on a PLMN in the "Forbidden PLMN" list, the PLMN shall be deleted from the list. However, if successful registration is achieved on a PLMN in the "Forbidden PLMN" list while Disaster Condition applies, the PLMN shall not be deleted from "Forbidden PLMN" list.
When in automatic mode, the UE may indicate any PLMNs which will not be selected due to their presence in the "Forbidden PLMN" list.
If a UE receives an equivalent PLMN list containing a PLMN which is included in the "Forbidden PLMN" list, this PLMN shall be removed from the equivalent PLMN list before this is stored by the UE.
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3.2.2.4.2  "Partial" and "temporary" PLMN restrictions
When a registration attempt by the UE is rejected by a network due to a "partial" or a "temporary" PLMN restriction, the UE shall perform one of the following procedures determined by the indication in the location update reject cause sent by the network (see TS 23.122):
  1. The UE shall store the tracking area identity or location area identity in the list of "5GS forbidden TA, forbidden TAs or forbidden LAs for regional provision of service" respectively and shall enter the limited service state. The UE shall remain in that state until it moves to a cell in a location area where service is allowed.
  2. The UE shall store the tracking area identity or the location area identity in the list of "5GS forbidden TA, forbidden TAs or forbidden LAs for roaming" respectively and shall use one of the following procedures according to the PLMN selection Mode:
    1. Automatic network selection mode:
      The procedure of clause 3.2.2.2 A).
    2. Manual network selection mode:
      The procedure of clause 3.2.2.2 B).
  3. The UE shall store the tracking area identity or location area identity in the list of "5GS forbidden TA, forbidden TAs or forbidden LAs for roaming" respectively and shall search for a suitable cell in the same PLMN.
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3.2.2.4.3  PLMN restrictions for PS services
When a registration attempt for PS services by the UE is rejected by the network with the cause "GPRS services not allowed in this PLMN", the PLMN identity shall be written to a list of "forbidden PLMNs for GPRS service" in the ME. This list is deleted when the UE is switched off or when the SIM/USIM is removed; the maximum number of possible entries in this list is implementation dependent, but must be at least one entry (see TS 23.122).
If a successful registration is achieved on a PLMN in the "forbidden PLMNs for GPRS service" list, the PLMN shall be deleted from the list.
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3.2.2.5  Periodic network selection attempts

A UE in Automatic Mode shall make periodic attempts to look for a higher priority PLMN including associated Access Technology of the same country as the currently received PLMN including associated Access Technology. For the ranking of PLMNs the UE shall use the order used in clause 3.2.2.2. In the case that there is no associated Access Technology identifier, the mobile shall assume that all Access Technologies provided by a PLMN are of equal priority. Moreover, periodic network selection shall not lead to change of access technology within the registered PLMN.
In the case that the UE has stored a list of equivalent PLMNs, the UE shall only select a PLMN if it has a higher priority than all the PLMNs, in the list of equivalent PLMNs, which are of the same country as the currently registered PLMN.
In the case that there are multiple EHPLMNs available, the UE shall not attempt to select a higher priority EHPLMN when an EHPLMN has already been selected. The priorities of EHPLMNs are only applicable when the UE is on a VPLMN and multiple EHPLMNs are available.
The UE shall only make reselection attempts while in idle mode. In case of GPRS terminals, the UE shall only make reselection attempts while in Idle or Stand-by mode. In case of terminals operating E-UTRA and/or NR, the UE shall only make reselection attempts while in Idle or RRC-Inactive mode.
In the case of a UE receiving an eMBMS transport service when in idle mode, the UE may postpone the higher priority PLMN search and any reselection attempt until the eMBMS transport service has finished or been stopped.
The interval between attempts shall be stored in the SIM/USIM.
Only the service provider shall be able to select for which of the previous situations, periodic network selection shall be attempted and to set the interval value.
For UEs supporting only Access Technologies other than the following: NB-IoT, GERAN EC-GSM-IoT and Category M1 [17] of E-UTRAN enhanced-MTC the UE shall interpret the interval value to be between 6 minutes and 8 hours, with a step size of 6 minutes.
For UEs only supporting any of the following, or a combination of, NB-IoT, GERAN EC-GSM-IoT [18], and Category M1 [13] of E-UTRAN enhanced-MTC, the UE shall interpret the interval value to be between 2 and 240 hours, with a step size of 2 hours between 2 and 80 hours and a step size of 4 hours between 80 and 240 hours.
For UEs supporting a combination of IoT and non-IoT Access Technologies the UE shall interpret the interval value to determine the timer value as above based on the Access Technology currently in use by the UE.
One interval value shall be designated to indicate that no periodic attempts shall be made.
In the absence of a permitted value in the SIM/USIM, or the SIM/USIM is phase 1 and therefore does not contain the datafield, then a default value of 60 minutes, shall be used by the UE except for those UEs only supporting any of the following, or a combination of: NB-IoT, GERAN EC-GSM-IoT [18], and Category M1 [17] of E-UTRAN enhanced-MTC. For those UEs a default value of 72 hours shall be used.
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3.2.2.6  Investigation PLMN ScanWord‑p. 15
The operator shall be able to control by SIM/USIM configuration whether a UE that is capable shall perform an investigation scan. This investigation scan shall be performed after each successful PLMN selection as well as during limited service state. The investigation scan shall search for a higher prioritised PLMN that does not offer CS voice service. If such a PLMN is available, the user shall be informed. This enables the user to switch to such a PLMN using manual selection if the user so prefers. The investigation scan shall not be performed when no SIM/USIM is inserted.
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3.2.2.7Void

3.2.2.8  Steering Of Roaming |R7|

Steering to a specific VPLMN
It shall be possible for the HPLMN at any time to direct a UE, that is in automatic mode, to search for a specific VPLMN and, if it is available, move to that VPLMN as soon as possible. This VPLMN shall then be regarded as the highest priority VPLMN as defined by the operator, though any EHPLMN or PLMN on the User Controlled PLMN list shall have higher priority. This process shall be done transparently and without inconvenience to the user.
If the UE is in manual mode, the steering request shall be ignored.
If the UE is registered on a VPLMN that is present on the User Controlled PLMN List, the steering request shall be ignored. PLMNs contained on the User Controlled PLMN List shall have priority over the steered-to-PLMN.
The UE shall attempt to register on the specified VPLMN even if the specified VPLMN is present on a Forbidden List.
This mechanism shall be available to the HPLMN even if the VPLMN the UE is registered on is compliant to an earlier release of the 3GPP specifications.
VPLMN Redirection
It shall be possible for the HPLMN to request a UE, that is in automatic mode, to find and register on a different VPLMN from the one it is currently using or trying to register on, if another VPLMN, that is not in a Forbidden List, is available. The original VPLMN shall then be treated as the lowest priority VPLMN and would not be selected by the UE unless it is the only one available to the UE or has been selected in manual mode. This process shall be done transparently and without inconvenience to the user.
If the UE is in manual mode, the redirection request shall be ignored.
If the UE is registered on a VPLMN that is present on the User Controlled PLMN List, the redirection request shall be ignored.
This mechanism shall be available to the HPLMN even if the VPLMN the UE is registered on is compliant to an earlier release of the 3GPP specifications.
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3.2.3  Network selection for Multi-mode terminals with 3GPP Capability |R7|Word‑p. 16
Different types of Multi-mode terminals combining different technologies and systems in one terminal can be produced. It is not possible to foresee all possible configurations and provide a detailed technical specification for network and system selection for all possible multi-mode terminal configurations. The following provides the generic requirements for network and system selection for Multi-mode terminals with 3GPP Capability. These requirements are mandatory for a 3GPP capable multi-mode terminal, unless otherwise is explicitly specified elsewhere in the 3GPP Technical Specifications.
  • a multi-mode terminal, when in 3GPP mode of operation shall be compliant to the 3GPP specifications, including PLMN selection, cell selection and re-selection, paging reception etc.,
    • As consequence, the multi-mode terminal when entering 3GPP mode of operation shall act as if it were a 3GPP only UE which had just been switched-on. Similarly, when leaving the 3GPP mode of operation the multimode terminal shall act as if it were a 3GPP only UE which had just been switched-off
When the multimode terminal is in 3GPP mode, the switching between modes in the multi-mode terminal is considered an overlay functionality selecting mode of operation. For the design of the overlay functionality the following requirements shall be fulfilled:
  • The overlay functionality shall include a mechanism to avoid ping-pong between systems, e.g., a timer or hysteresis function
  • The overlay functionality shall not include network priority mechanisms, which conflict with the network priority mechanisms specified in 3GPP specifications, e.g., the Periodic network selection attempts scanning within 3GPP based systems for PLMNs of higher priority than the current serving PLMN.
  • Any functionality in the overlay system, such as background scan of other systems, shall not impact the fulfilment of 3GPP protocol requirements (in particular in regard to paging, cell selection, cell re-selection and PLMN selection)
  • As specified in this technical specification, the 3GPP technical specification provides the capability for the user to set their own 3GPP PLMN selection preferences; as well as the user can manually select any 3GPP PLMN. This has been done to ensure a fair competition environment. These principles shall be maintained in the design of the overlay functionality.
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