5.1 Overview

24.3013GPPNon-Access-Stratum (NAS) protocol for Evolved Packet System (EPS)Release 18Stage 3TS

5.1.1 General

This clause describes the procedures used for mobility management for EPS services (EMM) at the radio interface (reference point "LTE-Uu").

The main function of the mobility management sublayer is to support the mobility of a user equipment, such as informing the network of its present location and providing user identity confidentiality.

A further function of the mobility management sublayer is to provide connection management services to the session management (SM) sublayer and the short message services (SMS) entity of the connection management (CM) sublayer.

All the EMM procedures described in this clause can only be performed if a NAS signalling connection has been established between the UE and the network. Else, the EMM sublayer has to initiate the establishment of a NAS signalling connection (see 3GPP TS 36.331 [22]).

NOTE: In a satellite E-UTRAN access, a GNSS fix time in lower layers can delay transmission of an initial UL NAS message by up to 100 seconds (GNSS cold state).

5.1.2 Types of EMM procedures

Depending on how they can be initiated, three types of EMM procedures can be distinguished:

1) EMM common procedures:

An EMM common procedure can always be initiated whilst a NAS signalling connection exists. The procedures belonging to this type are:

Initiated by the network:

– GUTI reallocation;

– authentication;

– security mode control;

– identification;

– EMM information.

2) EMM specific procedures:

At any time only one UE initiated EMM specific procedure can be running. The procedures belonging to this type are:

Initiated by the UE and used to attach the IMSI in the network for EPS services and/or non-EPS services, and to establish an EMM context and if requested by the UE, a default bearer:

– attach and combined attach.

Initiated by the UE and used to attach the IMSI or IMEI for emergency bearer services, and to establish an EMM context and a default bearer to a PDN that provides emergency bearer services:

– attach.

Initiated by the UE and used to attach the IMSI or IMEI for access to RLOS, and to establish an EMM context and a default bearer to a PDN connection for RLOS:

– attach.

Initiated by the UE or the network and used to detach the IMSI in the network for EPS services and/or non-EPS services and to release an EMM context and all bearers, if any:

– detach and combined detach.

Initiated by the UE and used to detach the IMSI in the network for EPS services or non-EPS services and to release an EMM context and all bearers, if any:

– eCall inactivity procedure.

Initiated by the UE when an EMM context has been established:

– normal tracking area updating and combined tracking area updating (S1 mode only);

– periodic tracking area updating (S1 mode only).

The tracking area updating procedure can be used to request also the resource reservation for sending data.

3) EMM connection management procedures (S1 mode only):

Initiated by the UE and used to establish a secure connection to the network or to request the resource reservation for sending data, or both:

– service request.

The service request procedure can only be initiated if no UE initiated EMM specific procedure is ongoing.

Initiated by the network and used to request the establishment of a NAS signalling connection or to prompt the UE to re-attach if necessary as a result of a network failure:

– paging procedure.

Initiated by the UE or the network and used to transport NAS messages:

– transport of NAS messages;

– generic transport of NAS messages.

The transport of NAS messages procedure and the generic transport of NAS messages procedure cannot be initiated while an EMM specific procedure or a service request procedure is ongoing.

5.1.3 EMM sublayer states

5.1.3.1 General

In the following clauses, the EMM protocol of the UE and the network is described by means of two different state machines. In clause 5.1.3.2, the states of the EMM entity in the UE are introduced. The behaviour of the UE depends on an EPS update status that is described in clause 5.1.3.3. The states for the MME side are described in clause 5.1.3.4.

5.1.3.2 EMM sublayer states in the UE

5.1.3.2.1 General

In the following clauses, the possible EMM states of an EMM entity in the UE are described. Clause 5.1.3.2.2 summarizes the main states of an EMM entity. The substates that have been defined are described in clause 5.1.3.2.3 and clause 5.1.3.2.4.

It should be noted, however, that this clause does not include a description of the detailed behaviour of the UE in the single states and does not cover abnormal cases. A detailed description of the behaviour of the UE is given in clause 5.2. For the behaviour of the UE in abnormal cases refer to the description of the elementary EMM procedures in clauses 5.4, 5.5, 5.6 and 5.7.

5.1.3.2.2 Main states

5.1.3.2.2.1 EMM-NULL

EPS services are disabled in the UE. No EPS mobility management function shall be performed in this state.

5.1.3.2.2.2 EMM-DEREGISTERED

In the state EMM-DEREGISTERED, no EMM context has been established and the UE location is unknown to an MME and hence it is unreachable by an MME. In order to establish an EMM context, the UE shall start the attach or combined attach procedure (see clause 5.5.1).

5.1.3.2.2.3 EMM-REGISTERED-INITIATED

A UE enters the state EMM-REGISTERED-INITIATED after it has started the attach or the combined attach procedure and is waiting for a response from the MME (see clause 5.5.1).

5.1.3.2.2.4 EMM-REGISTERED

In the state EMM-REGISTERED an EMM context has been established. Additionally a default EPS bearer context has been activated in the UE:

– if EMM-REGISTERED without PDN connection is not supported by the UE or the MME; or

– if EMM-REGISTERED without PDN connection is supported by the UE and the MME, the UE has requested connectivity to a PDN and a default EPS bearer context is successfully established.

When the UE is in EMM-IDLE mode, the UE location is known to the MME with an accuracy of a list of tracking areas containing a certain number of tracking areas. When the UE is in EMM-CONNECTED mode, the UE location is known to the MME with an accuracy of a serving eNodeB. The UE may initiate sending and receiving user data and signalling information and reply to paging. Additionally, tracking area updating or combined tracking area updating procedure is performed (see clause 5.5.3).

5.1.3.2.2.5 EMM-DEREGISTERED-INITIATED

A UE enters the state EMM-DEREGISTERED-INITIATED after it has requested release of the EMM context by starting the detach or combined detach procedure and is waiting for a response from the MME (see clause 5.5.2).

5.1.3.2.2.6 EMM-TRACKING-AREA-UPDATING-INITIATED

A UE enters the state EMM-TRACKING-AREA-UPDATING-INITIATED after it has started the tracking area updating or combined tracking area updating procedure and is waiting for a response from the MME (see clause 5.5.3).

5.1.3.2.2.7 EMM-SERVICE-REQUEST-INITIATED

A UE enters the state EMM-SERVICE-REQUEST-INITIATED after it has started the service request procedure and is waiting for a response from the MME (see clause 5.6.1).

NOTE: Not all possible transitions are shown in this figure.

Figure 5.1.3.2.2.7.1: EMM main states in the UE

5.1.3.2.3 Substates of state EMM-DEREGISTERED

5.1.3.2.3.1 General

The state EMM-DEREGISTERED is subdivided into a number of substates as described in this clause. Valid subscriber data are available for the UE before it enters the substates, except for the substate EMM-DEREGISTERED.NO-IMSI.

5.1.3.2.3.2 EMM-DEREGISTERED.NORMAL-SERVICE

The substate EMM-DEREGISTERED.NORMAL-SERVICE is chosen in the UE when a suitable cell has been found and the PLMN or tracking area is not in the forbidden list.

5.1.3.2.3.3 EMM-DEREGISTERED.LIMITED-SERVICE

The substate EMM-DEREGISTERED.LIMITED-SERVICE is chosen in the UE, when it is known that a selected cell is unable to provide normal service (e.g. the selected cell is in a forbidden PLMN, is in a forbidden tracking area or the selected cell is a CSG cell whose CSG ID and associated PLMN identity are not included in the UE’s Allowed CSG list or in the UE’s Operator CSG List).

5.1.3.2.3.4 EMM-DEREGISTERED.ATTEMPTING-TO-ATTACH

The substate EMM-DEREGISTERED.ATTEMPTING-TO-ATTACH is chosen in the UE if the attach or combined attach procedure failed due to a missing response from the network or due to the circumstances described in clauses 5.5.1.2.5, 5.5.1.2.6, 5.5.1.3.5 and 5.5.2.3.4.

5.1.3.2.3.5 EMM-DEREGISTERED.PLMN-SEARCH

The substate EMM-DEREGISTERED.PLMN-SEARCH is chosen in the UE, if the UE is searching for PLMNs. This substate is left either when a cell has been selected (the new substate is NORMAL-SERVICE or LIMITED-SERVICE) or when it has been concluded that no cell is available at the moment (the new substate is NO-CELL-AVAILABLE).

5.1.3.2.3.6 EMM-DEREGISTERED.NO-IMSI

The substate EMM-DEREGISTERED.NO-IMSI is chosen in the UE, if the UE has no valid subscriber data available (SIM/USIM not available, or the SIM/USIM is considered invalid by the UE) and a cell has been selected.

5.1.3.2.3.7 EMM-DEREGISTERED.ATTACH-NEEDED

Valid subscriber data are available for the UE and for some reason an attach must be performed as soon as possible. This substate can be entered if the access class is blocked due to access class control, or if the network rejects the NAS signalling connection establishment.

5.1.3.2.3.8 EMM-DEREGISTERED.NO-CELL-AVAILABLE

No E-UTRAN cell can be selected. This substate is entered after a first intensive search failed when in substate EMM-DEREGISTERED.PLMN-SEARCH. Cells are searched for at a low rhythm. No EPS services are offered.

5.1.3.2.3.9 EMM-DEREGISTERED.eCALL-INACTIVE

The substate EMM-DEREGISTERED.eCALL-INACTIVE is chosen in the UE when:

– the UE is configured for eCall only mode as specified in 3GPP TS 31.102 [17];

– timer T3444 and timer T3445 have expired or are not running;

– a PLMN has been selected as specified in 3GPP TS 23.122 [6];

– the UE does not need to perform an eCall over IMS; and

– the UE does not need to perform a call to a non-emergency MSISDN or URI for test or terminal reconfiguration service.

In this substate, the UE shall not initiate any signalling towards the network, except to originate an eCall over IMS, or a call to a non-emergency MSISDN or URI for test or terminal reconfiguration service.

5.1.3.2.4 Substates of state EMM-REGISTERED

5.1.3.2.4.1 General

The state EMM-REGISTERED is subdivided into a number of substates as described in this clause.

5.1.3.2.4.2 EMM-REGISTERED.NORMAL-SERVICE

The substate EMM-REGISTERED.NORMAL-SERVICE is chosen by the UE as the primary substate when the UE enters the state EMM-REGISTERED.

5.1.3.2.4.3 EMM-REGISTERED.ATTEMPTING-TO-UPDATE

The substate EMM-REGISTERED.ATTEMPTING-TO-UPDATE is chosen by the UE if the tracking area updating or combined tracking area updating procedure failed due to a missing response from the network or due to the circumstances described in clauses  5.3.9, 5.5.3.2.5, 5.5.3.2.6, 5.5.3.3.5, 5.6.1.5 and 5.6.1.6. No EMM procedure except the tracking area updating or combined tracking area updating procedure shall be initiated by the UE in this substate. No data shall be sent or received.

5.1.3.2.4.4 EMM-REGISTERED.LIMITED-SERVICE

The substate EMM-REGISTERED.LIMITED-SERVICE is chosen in the UE, if the cell the UE selected is known not to be able to provide normal service.

5.1.3.2.4.5 EMM-REGISTERED.PLMN-SEARCH

The substate EMM-REGISTERED.PLMN-SEARCH is chosen in the UE, while the UE is searching for PLMNs.

5.1.3.2.4.6 EMM-REGISTERED.UPDATE-NEEDED

The UE has to perform a tracking area updating or combined tracking area updating procedure, but access to the current cell is barred. This state can be entered if the access class is blocked due to access class control, or if the network rejects the NAS signalling connection establishment.

No EMM procedure except:

– tracking area updating;

– combined tracking area updating; or

– service request as a response to paging

shall be initiated by the UE in this substate.

5.1.3.2.4.7 EMM-REGISTERED.NO-CELL-AVAILABLE

E-UTRAN coverage has been lost or PSM is active in the UE. If PSM is active, the UE can deactivate PSM at any time by activating the AS layer when the UE needs to send mobile originated signalling or user data. Otherwise, the UE shall not initiate any EMM procedure except for cell and PLMN reselection.

5.1.3.2.4.8 EMM-REGISTERED.ATTEMPTING-TO-UPDATE-MM

A combined attach procedure or a combined tracking area updating procedure was successful for EPS services only. User data and signalling information may be sent and received.

5.1.3.2.4.9 EMM-REGISTERED.IMSI-DETACH-INITIATED

The UE performs a combined detach procedure for non-EPS services only (detach type "IMSI detach"). This substate is entered if the UE is attached for EPS and non-EPS services and wants to detach for non-EPS services only. User data and signalling information may be sent and received.

5.1.3.3 EPS update status

In order to describe the detailed UE behaviour, the EPS update (EU) status pertaining to a specific subscriber is defined.

The EPS update status is stored in a non-volatile memory in the USIM if the corresponding file is present in the USIM, else in the non-volatile memory in the ME, as described in annex C.

The EPS update status value is changed only after the execution of an attach or combined attach, network initiated detach, authentication, tracking area update or combined tracking area update, service request or paging for EPS services using IMSI procedure or due to change in TAI which is not part of TAI list while timer T3346 is running.

EU1: UPDATED

The last attach or tracking area updating attempt was successful.

EU2: NOT UPDATED

The last attach, service request or tracking area updating attempt failed procedurally, e.g. no response or reject message was received from the MME.

EU3: ROAMING NOT ALLOWED

The last attach, service request or tracking area updating attempt was correctly performed, but the answer from the MME was negative (because of roaming or subscription restrictions).

5.1.3.4 EMM sublayer states in the MME

5.1.3.4.1 EMM-DEREGISTERED

In the state EMM-DEREGISTERED, the MME has no EMM context or the EMM Context is marked as detached. The UE is detached. The MME may answer to an attach or a combined attach procedure initiated by the UE (see clause 5.5.1). The MME may also answer to a tracking area updating procedure or combined tracking area updating procedure initiated by a UE if the EMM context is marked as detached. The MME may also answer to a detach procedure initiated by the UE (see clause 5.5.1.2.7).

If ISR is not activated or ISR is deactivated during a routing area updating or combined routing area updating procedure or an inter-system handover to A/Gb mode or Iu mode, the MME enters the state EMM-DEREGISTERED after the successful completion of the procedure.

5.1.3.4.2 EMM-COMMON-PROCEDURE-INITIATED

The MME enters the state EMM-COMMON-PROCEDURE-INITIATED, after it has started a common EMM procedure (see clause 5.4) and is waiting for a response from the UE.

5.1.3.4.3 EMM-REGISTERED

In the state EMM-REGISTERED, an EMM context has been established. Additionally a default EPS bearer context has been activated in the MME:

– if EMM-REGISTERED without PDN connection is not supported by the UE or the MME; or

– if EMM-REGISTERED without PDN connection is supported by the UE and the MME, the UE has requested connectivity to a PDN and a default EPS bearer context is successfully established.

5.1.3.4.4 EMM-DEREGISTERED-INITIATED

The MME enters the state EMM-DEREGISTERED-INITIATED after it has started a detach procedure and is waiting for a response from the UE (see clause 5.5.2).

Figure 5.1.3.4.4.1: EMM main states in the MME

5.1.4 Coordination between EMM and GMM

If GMM and EMM are both enabled, a UE capable of S1 mode and A/Gb mode or Iu mode or both shall maintain one common registration for GMM and EMM indicating whether the UE is registered for packet services or not.

A UE that is not registered shall be in state GMM-DEREGISTERED and in state EMM-DEREGISTERED.

If the UE performs a successful attach or combined attach procedure in S1 mode, it shall enter substates GMM-REGISTERED.NO-CELL-AVAILABLE and EMM-REGISTERED.NORMAL-SERVICE. The UE resets the attach attempt counter and the GPRS attach attempt counter (see 3GPP TS 24.008 [13]).

If the UE performs a successful GPRS attach or combined GPRS attach procedure in A/Gb or Iu mode, it shall enter substates GMM-REGISTERED.NORMAL-SERVICE and EMM-REGISTERED.NO-CELL-AVAILABLE. The UE resets the attach attempt counter and the GPRS attach attempt counter (see 3GPP TS 24.008 [13]).

At intersystem change from A/Gb or Iu mode to S1 mode when no PDP context is active, if EMM-REGISTERED without PDN connection is not supported by the UE or the MME, the UE shall move to state EMM-DEREGISTERED and state GMM-DEREGISTERED and then initiate an attach procedure. If EMM-REGISTERED without PDN connection is supported by the UE and the MME, the UE shall enter substates EMM-REGISTERED.NORMAL-SERVICE and GMM-REGISTERED.NO-CELL-AVAILABLE and initiate a tracking area updating procedure.

After successful completion of routing area updating or combined routing area updating and tracking area updating or combined tracking area updating procedures in both S1 mode and A/Gb or Iu mode, if the network has indicated that ISR is activated, the UE shall maintain registration and related periodic update timers in both GMM and EMM.

NOTE: As specified in clause 5.5.3.2.4 of this document or clause 4.7.5.1.3 of 3GPP TS 24.008 [13], the UE does not activate the ISR even if the network has indicated that the ISR is activated e.g. in the tracking area updating procedure triggered due to a change in UE network capability. In these scenarios, the UE only maintains one registration and related periodic update timer in GMM or EMM.

5.1.5 Coordination between EMM and MM

UEs that operate in CS/PS mode 1 or CS/PS mode 2 of operation shall use the combined EPS/IMSI attach procedure in order to attach to both EPS and non-EPS services.

UEs that operate in CS/PS mode 1 or CS/PS mode 2 of operation and are already attached to both EPS and non-EPS services shall use the combined tracking area updating and periodic tracking area updating procedures.

UEs that operate in CS/PS mode 1 or CS/PS mode 2 of operation and are already attached to both EPS and non-EPS services shall perform a combined detach procedure in order to detach for non-EPS services.

UEs that operate in CS/PS mode 1 or CS/PS mode 2 of operation should not use any MM timers related to MM specific procedures (e.g. T3210, T3211, T3212, T3213) while camped on E-UTRAN, unless the re-activation of these timers is explicitly described. If the MM timers are already running, the UE should not react on the expiration of the timers.

If the UE is configured for eCall only mode as specified in 3GPP TS 31.102 [17] and moves from GERAN/UTRAN to E-UTRAN, the UE shall:

– if timer T3242 is running, start timer T3444 with the time left on T3242 and stop timer T3242;

– if timer T3243 is running, start timer T3445 with the time left on T3243 and stop timer T3243;

– if the UE is attached for both EPS services and non-EPS services and timer T3242 or timer T3243 is running, perform a combined tracking area updating procedure; and

NOTE 1: A UE configured for eCall only mode as specified in 3GPP TS 31.102 [17] being attached for both EPS services and non-EPS services upon moving from GERAN/UTRAN to E-UTRAN is only possible in the case when the UE has performed a combined attach in E-UTRAN, subsequently moved to GERAN/UTRAN and returned to E-UTRAN before timer T3242 or timer T3243 expires.

– if the UE is attached for non-EPS services only and timer T3242 or timer T3243 is running, perform a combined attach procedure.

NOTE 2: Timers T3242 and T3243 are specified in 3GPP TS 24.008 [13].