Section: 5.5.3 Tracking area updating procedure (S1 mode only) 5.5.3.1 General
Content: The tracking area updating procedure is always initiated by the UE and is used for the following purposes: - normal tracking area updating to update the registration of the actual tracking area of a UE in the network; - combined tracking area updating to update the registration of the actual tracking area for a UE in CS/PS mode 1 or CS/PS mode 2 of operation; - periodic tracking area updating to periodically notify the availability of the UE to the network; - IMSI attach for non-EPS services when the UE is attached for EPS services. This procedure is used by a UE in CS/PS mode 1 or CS/PS mode 2 of operation; - in various cases of inter-system change from Iu mode to S1 mode or from A/Gb mode to S1 mode; - in various cases of inter-system change from N1 mode to S1 mode if the UE operates in single-registration mode and as described in 3GPP TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [54]; - S101 mode to S1 mode inter-system change; - MME load balancing; - to update certain UE specific parameters in the network; - recovery from certain error cases; - to indicate that the UE enters S1 mode after CS fallback or 1xCS fallback; - to indicate to the network that the UE has selected a CSG cell whose CSG identity and associated PLMN identity are not included in the UE's Allowed CSG list or in the UE's Operator CSG list; - to indicate the current radio access technology to the network for the support of terminating access domain selection for voice calls or voice sessions; - to indicate to the network that the UE has locally released EPS bearer context(s); - to indicate to the network that the MUSIM UE needs to use an IMSI Offset value as specified in 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [10] that is used for deriving the paging occasion as specified in 3GPP TS 36.304[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode ]  [21]; - to indicate to the network the unavailability information or a change in the unavailability information; and - to indicate to the network that the UE needs to come out of the unavailability period and resume normal services. Details on the conditions for the UE to initiate the tracking area updating procedure are specified in clause 5.5.3.2.2 and clause 5.5.3.3.2. If the MUSIM UE is attached for emergency bearer services and initiates a tracking area updating procedure, the network shall not indicate the support of: - the NAS signalling connection release; - the paging indication for voice services; - the reject paging request; - the paging restriction; or - the paging timing collision control; in the TRACKING AREA UPDATE ACCEPT message. While a UE has a PDN connection for emergency bearer services, the UE shall not perform manual CSG selection. If control plane CIoT EPS optimization is not used by the UE, a UE initiating the tracking area updating procedure in EMM-IDLE mode may request the network to re-establish the radio and S1 bearers for all active EPS bearer contexts during the procedure. If control plane CIoT EPS optimization is used by the UE, a UE initiating the tracking area updating procedure in EMM-IDLE mode may request the network to re-establish the radio and S1 bearers for all active EPS bearer contexts associated with PDN connections established without control plane only indication during the procedure. In a shared network, the UE shall choose one of the PLMN identities as specified in 3GPP TS 23.122[ Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode ]  [6]. The UE shall construct the TAI of the cell from this chosen PLMN identity and the TAC received for this PLMN identity on the broadcast system information. The chosen PLMN identity shall be indicated to the E-UTRAN (see 3GPP TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [22]). Whenever a TRACKING AREA UPDATE REJECT message with the EMM cause #11 "PLMN not allowed" is received by the UE, the chosen PLMN identity shall be stored in the "forbidden PLMN list" and if the UE is configured to use timer T3245 (see 3GPP TS 24.368[ Non-Access Stratum (NAS) configuration Management Object (MO) ]  [15A] or 3GPP TS 31.102[ Characteristics of the Universal Subscriber Identity Module (USIM) application ]  [17]) then the UE shall start timer T3245 and proceed as described in clause 5.3.7a. Whenever a TRACKING AREA UPDATE REJECT message with the EMM cause #14 "EPS services not allowed in this PLMN" is received by the UE, the chosen PLMN identity shall be stored in the "forbidden PLMNs for GPRS service". Whenever a TRACKING AREA UPDATE REJECT message is received by the UE with the EMM cause #12 "tracking area not allowed", #13 "roaming not allowed in this tracking area", or #15 "no suitable cells in tracking Area", the constructed TAI shall be stored in the suitable list. In a shared network, if TRACKING AREA UPDATE REJECT is received as a response to a tracking area updating procedure initiated in EMM-CONNECTED mode, the UE need not update forbidden lists. A tracking area updating attempt counter is used to limit the number of subsequently rejected tracking area update attempts. The tracking area updating attempt counter shall be incremented as specified in clause 5.5.3.2.6. Depending on the value of the tracking area updating attempt counter, specific actions shall be performed. The tracking area updating attempt counter shall be reset when: - a normal or periodic tracking area updating or a combined tracking area updating procedure is successfully completed; - a normal or periodic tracking area updating or a combined tracking area updating procedure is rejected with EMM cause #11, #12, #13, #14, #15, #25 or #35: - a combined attach procedure or a combined tracking area updating procedure is completed for EPS services only with cause #2 or #18; or - a new PLMN is selected. Additionally the tracking area updating attempt counter shall be reset when the UE is in substate EMM-REGISTERED.ATTEMPTING-TO-UPDATE or EMM-REGISTERED.ATTEMPTING-TO-UPDATE-MM, and: - a new tracking area is entered; - timer T3402 expires; or - timer T3346 is started.