Content for  TS 23.122  Word version:  18.1.0

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 clause 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.

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; and
• if the selected cell is a satellite NG-RAN cell or a satellite E-UTRAN cell, it does not fulfil the conditions related to the list of "PLMNs not allowed to operate at the present UE location" as defined in clause 3.1, i.e. it is considered as candidate for PLMN selection.
• 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);
• the periodic registration update timer expires while the 5GS update status is "NOT UPDATED" (triggers mobility and periodic registration update procedure);
• 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 routing area update or a tracking area update or an MS which is registered via NG-RAN and enters a new PLMN or SNPN shall perform a registration update if the following conditions are fulfilled: 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. An LR request indicating Disaster Roaming registration updating is made when the MS supporting MINT needs to register to the PLMN offering disaster roaming services for the first time. 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".

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.

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, an 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 clause 4.5.2 shall be performed.

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 or an equivalent SNPN, 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 clause 4.4.3.1 or the SNPN Automatic or Manual Mode Selection Procedure of clause 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.