ETSI TS 138 304 V15.6.0 (2020-01)

ETSI TS 138 304 V15.6.0 (2020-01)






TECHNICAL SPECIFICATION
5G;
NR;
User Equipment (UE) procedures in idle mode
and in RRC Inactive state
(3GPP TS 38.304 version 15.6.0 Release 15)

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3GPP TS 38.304 version 15.6.0 Release 15 1 ETSI TS 138 304 V15.6.0 (2020-01)



Reference
RTS/TSGR-0238304vf60
Keywords
5G
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3GPP TS 38.304 version 15.6.0 Release 15 2 ETSI TS 138 304 V15.6.0 (2020-01)
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Legal Notice
This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
The present document may refer to technical specifications or reports using their 3GPP identities. These shall be
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"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
ETSI

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3GPP TS 38.304 version 15.6.0 Release 15 3 ETSI TS 138 304 V15.6.0 (2020-01)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 6
2 References . 6
3 Definitions, symbols and abbreviations . 7
3.1 Definitions . 7
3.2 Abbreviations . 7
4 General description of RRC_IDLE state and RRC_INACTIVE state . 8
4.1 Overview . 8
4.2 Functional division between AS and NAS in RRC_IDLE state and RRC_INACTIVE state . 9
4.3 Service types in RRC_IDLE state . 12
4.4 Service types in RRC_INACTIVE state . 12
4.5 Cell Categories . 12
5 Process and procedure descriptions . 13
5.1 PLMN selection . 13
5.1.1 Support for PLMN selection . 13
5.1.1.1 General . 13
5.1.1.2 NR case . 13
5.1.1.3 E-UTRA case . 13
5.2 Cell selection and reselection . 13
5.2.1 Introduction. 13
5.2.2 States and state transitions in RRC_IDLE state and RRC_INACTIVE state . 15
5.2.3 Cell Selection process . 16
5.2.3.1 Description . 16
5.2.3.2 Cell Selection Criterion . 16
5.2.3.3 E-UTRAN case in Cell Selection . 17
5.2.4 Cell Reselection evaluation process . 17
5.2.4.1 Reselection priorities handling . 17
5.2.4.2 Measurement rules for cell re-selection . 18
5.2.4.3 Mobility states of a UE . 19
5.2.4.3.0 Introduction . 19
5.2.4.3.1 Scaling rules . 19
5.2.4.4 Cells with cell reservations, access restrictions or unsuitable for normal camping. 20
5.2.4.5 NR Inter-frequency and inter-RAT Cell Reselection criteria . 20
5.2.4.6 Intra-frequency and equal priority inter-frequency Cell Reselection criteria . 21
5.2.4.7 Cell reselection parameters in system information broadcasts . 21
5.2.4.7.0 General reselection parameters . 21
5.2.4.7.1 Speed dependent reselection parameters . 23
5.2.4.8 Inter-RAT Cell reselection in RRC_INACTIVE state . 24
5.2.5 Camped Normally state . 24
5.2.6 Selection of cell at transition to RRC_IDLE or RRC_INACTIVE state . 24
5.2.7 Any Cell Selection state . 25
5.2.8 Camped on Any Cell state . 25
5.3 Cell Reservations and Access Restrictions . 25
5.3.0 Introduction. 25
5.3.1 Cell status and cell reservations . 25
5.3.2 Unified access control . 26
5.4 Tracking Area registration . 26
5.5 RAN Area registration . 27
6 Reception of broadcast information . 27
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3GPP TS 38.304 version 15.6.0 Release 15 4 ETSI TS 138 304 V15.6.0 (2020-01)
6.1 Reception of system information . 27
7 Paging . 27
7.1 Discontinuous Reception for paging . 27
Annex A (informative): Change history . 29
History . 31

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3GPP TS 38.304 version 15.6.0 Release 15 5 ETSI TS 138 304 V15.6.0 (2020-01)
Foreword
This Technical Specification has been produced by the 3rd Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
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3GPP TS 38.304 version 15.6.0 Release 15 6 ETSI TS 138 304 V15.6.0 (2020-01)
1 Scope
The present document specifies the Access Stratum (AS) part of the UE procedures in RRC_IDLE state (also called Idle
mode) and RRC_INACTIVE state. The non-access stratum (NAS) part of Idle mode procedures and processes is
specified in TS 23.122 [9].
The present document specifies the model for the functional division between the NAS and AS in a UE.
The present document applies to all UEs that support at least NR Radio Access, including multi-RAT UEs as described
in 3GPP specifications, in the following cases:
- When the UE is camped on a NR cell;
- When the UE is searching for a cell to camp on;
NOTE: When the UE is camped on or searching for a cell to camp on belonging to other RATs, the UE behaviour
is described in the specifications of the other RATs.
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 38.300: "NR Overall Description; Stage 2".
[3] 3GPP TS 38.331: "NR; Radio Resource Control (RRC) - Protocol Specification".
[4] 3GPP TS 38.213: "NR; Physical layer procedures for control ".
[5] Void
[6] 3GPP TS 36.331: "E-UTRA; Radio Resource Control (RRC) - Protocol Specification".
[7] 3GPP TS 36.304: "E-UTRA; User Equipment (UE) procedures in RRC_IDLE state ".
[8] 3GPP TS 38.133: "NR; Requirements for Support of Radio Resource Management".
[9] 3GPP TS 23.122: "NAS functions related to Mobile Station (MS) in RRC_IDLE state".
[10] 3GPP TS 23.501: "System Architecture for the 5G System; Stage 2".
[11] 3GPP TS 38.215: "NR; Physical layer measurements".
[12] 3GPP TS 22.261: "Service requirements for the 5G system".
[13] 3GPP TS 24.890: "5G System – Phase 1; CT WG1 Aspects".
[14] 3GPP TS 24.501: "Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3".
[15] 3GPP TS 38.101-1: "NR; User Equipment (UE) radio transmission and reception; Part 1: Range 1
Standalone".
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3GPP TS 38.304 version 15.6.0 Release 15 7 ETSI TS 138 304 V15.6.0 (2020-01)
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
Acceptable Cell: A cell that satisfies certain conditions as specified in 4.5.
Available PLMN(s): One or more PLMN(s) for which the UE has found at least one cell and read its PLMN
identity(ies).
Barred Cell: A cell a UE is not allowed to camp on.
Camped on a cell: UE has completed the cell selection/reselection process and has chosen a cell. The UE monitors
system information and (in most cases) paging information.
Camped on any cell: UE is in idle mode and has completed the cell selection/reselection process and has chosen a cell
irrespective of PLMN identity.
Commercial Mobile Alert System: Public Warning System that delivers Warning Notifications provided by Warning
Notification Providers to CMAS capable UEs.
EHPLMN: Any of the PLMN entries contained in the Equivalent HPLMN list TS 23.122 [9].
Equivalent PLMN list: List of PLMNs considered as equivalent by the UE for cell selection, cell reselection, and
handover according to the information provided by the NAS.
Home PLMN: A PLMN where the Mobile Country Code (MCC) and Mobile Network Code (MNC) of the PLMN
identity are the same as the MCC and MNC of the IMSI.
Process: A local action in the UE invoked by an RRC procedure or an RRC_IDLE or RRC_INACTIVE state
procedure.
Radio Access Technology: Type of technology used for radio access, for instance NR or E-UTRA.
Registration Area: (NAS) registration area is an area in which the UE may roam without a need to perform location
registration, which is a NAS procedure.
Registered PLMN: This is the PLMN on which certain Location Registration outcomes have occurred, as specified in
TS 23.122 [9].
Reserved Cell: A cell on which camping is not allowed, except for particular UEs, if so indicated in the system
information.
Selected PLMN: This is the PLMN that has been selected by the NAS, either manually or automatically.
Serving cell: The cell on which the UE is camped.
Strongest cell: The cell on a particular frequency that is considered strongest according to the layer 1 cell search
procedure (TS 38.213 [4], TS 38.215 [11]).
Suitable Cell: This is a cell on which a UE may camp. For NR cell, the criteria are defined in clause 4.5, for E-UTRA
cell in TS 36.304 [7].
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An
abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in
TR 21.905 [1].
AS Access Stratum
CMAS Commercial Mobile Alert System
CN Core Network
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DCI Downlink Control Information
ETWS Earthquake and Tsunami Warning System
E-UTRA Evolved UMTS Terrestrial Radio Access
E-UTRAN Evolved UMTS Terrestrial Radio Access Network
IMSI International Mobile Subscriber Identity
MCC Mobile Country Code
MICO Mobile Initiated Connection Only
NAS Non-Access Stratum
NR NR Radio Access
PLMN Public Land Mobile Network
RAT Radio Access Technology
RNA RAN-based Notification Area
RNAU RAN-based Notification Area Update
RRC Radio Resource Control
UAC Unified Access Control
UE User Equipment
UMTS Universal Mobile Telecommunications System
4 General description of RRC_IDLE state and
RRC_INACTIVE state
4.1 Overview
The RRC_IDLE state and RRC_INACTIVE state tasks can be subdivided into three processes:
- PLMN selection;
- Cell selection and reselection;
- Location registration and RNA update.
PLMN selection, cell reselection procedures, and location registration are common for both RRC_IDLE state and
RRC_INACTIVE state. RNA update is only applicable for RRC_INACTIVE state. When UE selects a new PLMN, UE
transitions from RRC_INACTIVE to RRC_IDLE, as specified in TS 24.501 [14].
When a UE is switched on, a public land mobile network (PLMN) is selected by NAS. For the selected PLMN,
associated RAT(s) may be set, as specified in TS 23.122 [9]. The NAS shall provide a list of equivalent PLMNs, if
available, that the AS shall use for cell selection and cell reselection.
With cell selection, the UE searches for a suitable cell of the selected PLMN, chooses that cell to provide available
services, and monitors its control channel. This procedure is defined as "camping on the cell".
The UE shall, if necessary, then register its presence, by means of a NAS registration procedure, in the tracking area of
the chosen cell. As an outcome of a successful Location Registration, the selected PLMN then becomes the registered
PLMN, as specified in TS 23.122 [9].
If the UE finds a more suitable cell, according to the cell reselection criteria, it reselects onto that cell and camps on it.
If the new cell does not belong to at least one tracking area to which the UE is registered, location registration is
performed. In RRC_INACTIVE state, if the new cell does not belong to the configured RNA, an RNA update
procedure is performed.
If necessary, the UE shall search for higher priority PLMNs at regular time intervals as described in TS 23.122 [9] and
search for a suitable cell if another PLMN has been selected by NAS.
If the UE loses coverage of the registered PLMN, either a new PLMN is selected automatically (automatic mode), or an
indication of available PLMNs is given to the user so that a manual selection can be performed (manual mode).
Registration is not performed by UEs only capable of services that need no registration.
The purpose of camping on a cell in RRC_IDLE state and RRC_INACTIVE state is fourfold:
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a) It enables the UE to receive system information from the PLMN.
b) When registered and if the UE wishes to establish an RRC connection or resume a suspended RRC connection, it
can do this by initially accessing the network on the control channel of the cell on which it is camped.
c) If the network needs to send a message or deliver data to the registered UE, it knows (in most cases) the set of
tracking areas (in RRC_IDLE state) or RNA (in RRC_INACTIVE state) in which the UE is camped. It can then
send a "paging" message for the UE on the control channels of all the cells in the corresponding set of areas. The
UE will then receive the paging message and can respond.
d) It enables the UE to receive ETWS and CMAS notifications.
When the UE is in RRC_IDLE state, upper layers may deactivate AS layer when MICO mode is activated as specified
in TS 24.501 [14]. When MICO mode is activated, the AS configuration (e.g. priorities provided by dedicated
signalling) is kept and all running timers continue to run but the UE need not perform any idle mode tasks. If a timer
expires while MICO mode is activated it is up to the UE implementation whether it performs the corresponding action
immediately or the latest when MICO mode is deactivated. When MICO mode is deactivated, the UE shall perform all
idle mode tasks.
4.2 Functional division between AS and NAS in RRC_IDLE
state and RRC_INACTIVE state
Table 4.2-1 presents the functional division between UE non-access stratum (NAS) and UE access stratum (AS) in
RRC_IDLE state and RRC_INACTIVE states. The NAS part is specified in TS 23.122 [9] and the AS part in the
present document.
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Table 4.2-1: Functional division between AS and NAS in RRC_IDLE state and RRC_INACTIVE state
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3GPP TS 38.304 version 15.6.0 Release 15 11 ETSI TS 138 304 V15.6.0 (2020-01)
RRC_IDLE and UE Non-Access Stratum UE Access Stratum
RRC_INACTIVE
state Process
PLMN Selection Maintain a list of PLMNs in priority order according Search for available PLMNs.
to TS 23.122 [9]. Select a PLMN using automatic
or manual mode as specified in TS 23.122 [9] and If associated RAT(s) is (are) set for the
request AS to select a cell belonging to this PLMN, search in this (these) RAT(s) and
PLMN. For each PLMN, associated RAT(s) may other RAT(s) for that PLMN as specified in
be set. TS 23.122 [9].

Evaluate reports of available PLMNs from AS for Perform measurements to support PLMN
PLMN selection. selection.

Maintain a list of equivalent PLMN identities. Synchronise to a broadcast channel to
identify found PLMNs.

Report available PLMNs with associated
RAT(s) to NAS on request from NAS or
autonomously.
Cell Control cell selection for example by indicating Perform measurements needed to support
Selection RAT(s) associated with the selected PLMN to be cell selection.
used initially in the search of a cell in the cell
selection. Detect and synchronise to a broadcast
channel. Receive and handle broadcast
Maintain a list of "Forbidden Tracking Areas" and information. Forward NAS system
provide the list to AS. information to NAS.

Search for a suitable cell. The cells
broadcast one or more 'PLMN identity' in
the system information. Respond to NAS
whether such cell is found or not.

If associated RATs is (are) set for the
PLMN, perform the search in this (these)
RAT(s) and other RATs for that PLMN as
specified in TS 23.122 [9].

If a cell is found which satisfies cell
selection criteria, camp on that cell.
Cell Maintain a list of equivalent PLMN identities and Perform measurements needed to support
Reselection provide the list to AS. cell reselection.

Maintain a list of "Forbidden Tracking Areas" and Detect and synchronise to a broadcast
provide the list to AS. channel. Receive and handle broadcast
information. Forward NAS system
information to NAS.

Change cell if a more suitable cell is found.
Location Register the UE as active after power on. Report registration area information to
registration NAS.
Register the UE's presence in a registration area,
for instance regularly or when entering a new
tracking area.

Deregister UE when shutting down.

Maintain a list of "Forbidden Tracking Areas".

RAN Notification Not applicable. Register the UE's presence in a RAN-
Area Update based notification area (RNA), periodically
or when entering a new RNA.

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4.3 Service types in RRC_IDLE state
This clause defines the level of service that may be provided by the network to a UE in RRC_IDLE state. The following
three levels of services are provided while a UE is in RRC_IDLE state:
- Limited service (emergency calls, ETWS and CMAS on an acceptable cell);
- Normal service (for public use on a suitable cell);
- Operator service (for operators only on a reserved cell).
4.4 Service types in RRC_INACTIVE state
This clause defines the level of service that may be provided by the network to a UE in RRC_INACTIVE state. The
following two levels of services are provided while a UE is in RRC_INACTIVE state:
- Normal service (for public use on a suitable cell);
- Operator service (for operators only on a reserved cell).
4.5 Cell Categories
The cells are categorised according to which services they offer:
acceptable cell:
An "acceptable cell" is a cell on which the UE may camp to obtain limited service (originate emergency calls and
receive ETWS and CMAS notifications). Such a cell shall fulfil the following requirements, which is the minimum set
of requirements to initiate an emergency call and to receive ETWS and CMAS notification in an NR network:
- The cell is not barred, see clause 5.3.1;
- The cell selection criteria are fulfilled, see clause 5.2.3.2.
suitable cell:
A cell is considered as suitable if the following conditions are fulfilled:
- The cell is part of either the selected PLMN or the registered PLMN or PLMN of the Equivalent PLMN list;
- The cell selection criteria are fulfilled, see clause 5.2.3.2.
According to the latest information provided by NAS:
- The cell is not barred, see clause 5.3.1;
- The cell is part of at least one TA that is not part of the list of "Forbidden Trac
...