5G NR RRC Inactive State

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NR RRC_CONNECTED

NR RRC_IDLE

NR RRC_INACTIVEEstablish / Release

Release

Resume / Release with Suspend

3GPP TS 38.331

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2G / 3G Mobile Network Architecture

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Circuit Switched (CS) Core

AirInterface

Packet Switched (PS) Core

Base Station Controller

Base Station Transmitter / Receiver

Data (IP)Network

Voice (PSTN)Network

Base Station

User Equipment (UE)

Base Station Controller

Backhaul

RadioAccess

Network(RAN)

CoreNetwork

(CN)

Core Network• Connects to voice and data networks• Provides Security and Authentication• Billing / Charging• Roaming

Backhaul• Connects access network with core

network• Example: Fiber, microwave, satellite,

mesh, etc.

Access Network• Connects devices over the air• Allows mobility and handovers

4G Mobile Network Architecture

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Circuit Switched (CS) Core

AirInterface

Packet Switched (PS) Core

Base Station Controller

Base Station Transmitter / Receiver

Data (IP)Network

Voice (PSTN)Network

Base Station

User Equipment (UE)

Base Station Controller

BackhaulEvolution

Evolved Packet Core (EPC)

Data (IP)Network

eNB

UE

EvolvedPacketSystem(EPS)

Long Term Evolution (LTE) of Radio Interface

System Architecture Evolution (SAE)

RadioAccess

Network(RAN)

CoreNetwork

(CN)

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5G Mobile Network Architecture

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AirInterface

New & Evolution

Evolved Packet Core (EPC)

Data (IP)Network

eNB

UE

EvolvedPacketSystem(EPS)

5G Core (5GC)

Data (IP)Network

gNB

UE

5G System(5GS)

New Radio or Next-Generation RAN (NG-RAN)

RadioAccess

Network(RAN)

CoreNetwork

(CN)

5G System is defined as 3GPP system consisting of 5G Access Network (AN), 5G Core Network and UE. The 5G System provides data connectivity and services.

3GPP TS 23.501: System Architecture for the 5G System; Stage 2

3GPP TS 23.502: Procedures for the 5G System; Stage 2

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4G EPC EMM State Machine

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❑ UE switched off / out of coverage

❑ No serving MME or S-GW

❑ No IP address

❑ No default EPS bearer

❑ UE registered with EPC

❑ Serving MME and S-GW allocated

❑ IP address allocated

❑ Default EPS bearer exists

EMM-DEREGISTERED EMM-REGISTERED

4G EPC ECM State Machine

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❑ UE on standby

❑ No S1 or radio bearers

❑ UE localized to tracking area

❑ Paging

Service requests

Tracking area updates

❑ UE active

❑ All bearers

❑ UE localized to serving eNB

❑ Any communications possible

ECM-IDLE ECM-CONNECTED

4G EPS Bearer Architecture

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UE eNB S-GW P-GW Peer

Entity

Radio S1 S5 / S8 Gi

E-UTRAN EPC Internet

End-to-End Service

EPS BearerExternal

Bearer

E-RAB S5/S8 Bearer

S1 BearerRadio Bearer

4G Default and Dedicated Bearers

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eNodeBUE

S1-U S5/S8

S5/S8

P-GW

S-GWUu P-GW

PDN

Default EPS bearer setup - registrationDefault EPS bearer setupDedicated EPS bearerIP Packet

4G EMM, ECM and RRC States

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DEREGISTERED REGISTERED

RRC

ECM

EMM

OFF ATTACHING IDLE / REGISTERDSERVICE REQUEST

ACTIVE

IDLE CONNECTED

IDLE CONNECTED IDLE CONNECTED

5GS Registration Management (RM) State Machine

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❑ UE switched off / out of coverage

❑ No serving AMF or SMF

❑ No IP address

❑ No PDU Session

❑ UE registered with 5GC

❑ Serving AMF and SMF allocated

❑ IP address allocated

❑ PDU Session Established

RM-DEREGISTERED RM-REGISTERED

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5GS Connection Management (CM) State Machine

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❑ UE on standby

❑ No NAS Signalling

❑ UE localized to tracking area

❑ Paging, Service requests, etc.

❑ UE active

❑ NAS signalling and QoS flows

❑ UE localized to serving NG-RAN

❑ Any communications possible

CM-IDLE CM-CONNECTED

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5GS State Model

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RM-DEREGISTEREDCM-IDLE

RRC_IDLE

RM-REGISTEREDCM-IDLE

RRC_IDLE

RM-REGISTEREDCM-CONNECTED

RRC_INACTIVE

RRC_CONNECTED

Original Picture Source: 5G NR: Architecture, Technology, Implementation, and Operation of 3GPP New Radio Standards by Dr. Sassan Ahmadi, Jun 2019 (link)

5GS State Model – RRC_IDLE

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RM-DEREGISTEREDCM-IDLE

RRC_IDLE

RM-REGISTEREDCM-IDLE

RRC_IDLE

RM-REGISTEREDCM-CONNECTED

RRC_INACTIVE

RRC_CONNECTED

Original Picture Source: 5G NR: Architecture, Technology, Implementation, and Operation of 3GPP New Radio Standards by Dr. Sassan Ahmadi, Jun 2019 (link)

RRC_IDLE:• PLMN selection;• Broadcast of system information;• Cell re-selection mobility;• Paging for mobile terminated

data is initiated by 5GC;• DRX for CN paging configured by

NAS.

5GS State Model – RRC_CONNECTED

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RM-DEREGISTEREDCM-IDLE

RRC_IDLE

RM-REGISTEREDCM-IDLE

RRC_IDLE

RM-REGISTEREDCM-CONNECTED

RRC_INACTIVE

RRC_CONNECTED

Original Picture Source: 5G NR: Architecture, Technology, Implementation, and Operation of 3GPP New Radio Standards by Dr. Sassan Ahmadi, Jun 2019 (link)

RRC_CONNECTED:• 5GC - NG-RAN connection (both

C/U-planes) is established for UE;• The UE AS context is stored in

NG-RAN and the UE;• NG-RAN knows the cell which the

UE belongs to;• Transfer of unicast data to/from

the UE;• Network controlled mobility

including measurements.

5GS State Model – RRC_INACTIVE

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RM-DEREGISTEREDCM-IDLE

RRC_IDLE

RM-REGISTEREDCM-IDLE

RRC_IDLE

RM-REGISTEREDCM-CONNECTED

RRC_INACTIVE

RRC_CONNECTED

Original Picture Source: 5G NR: Architecture, Technology, Implementation, and Operation of 3GPP New Radio Standards by Dr. Sassan Ahmadi, Jun 2019 (link)

RRC_INACTIVE:• PLMN selection;• Broadcast of system information;• Cell re-selection mobility;• Paging is initiated by NG-RAN (RAN

paging);• RAN-based notification area (RNA) is

managed by NG- RAN;• DRX for RAN paging configured by NG-

RAN;• 5GC - NG-RAN connection (both C/U-

planes) is established for UE;• The UE AS context is stored in NG-RAN

and the UE;• NG-RAN knows the RNA which the UE

belongs to.

RAN-initiated paging, RNA & RNAU

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RRC_INACTIVE is characterized by:• Use of RAN Notification Area (RNA)

• similar to CN tracking area for Idle

• RNA is configured per UE by gNB• 1 to N cells defined by a List of cells or list of

RAN Area ID or list of TA IDs

• UE is reachable within a configured RNA via a RAN-initiated paging• RAN-initiated paging uses a RAN configured

UE ID (I-RNTI)

• RNA Update (RNAU) triggered periodically and when moving outside of the configured RNA Source: Intel – see references

Inactive-RNTI (I-RNTI)

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• There are following two types of the I-RNTI:• Full I-RNTI: A full I-RNTI which has a length of 40 bits which can be included

within a 64 bit RRCResumeRequest1 message over Common Control Channel 1• Short I-RNTI: A short I-RNTI which has a length of 24 bits which can be included

within a 48 bit RRCResumeRequest message Common Control Channel• The I-RNTI is applicable to the RRC Inactive State. While comparing with other

RNTI, the I-RNTI is not used to scramble the CRC bits. Instead, the I-RNTI is used to address the UE within RRC signalling messages.

• An I-RNTI can be allocated to a UE within an RRC Release message when it is moving from RRC Connected to RRC Inactive as part of suspendConfig

Source: Techplayon – see references

5GS RM, CM and RRC State Transition

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DEREGISTERED REGISTERED

RRC

CM

RM

ATTACHING CONNECTED / INACTIVE CONNECTED / ACTIVE

CONNECTED

CONNECTED INACTIVE CONNECTED

OFF

-

-

Legacy Idle-to-connected transition

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UE LTE/NR RAN CN

Initial radio synchronization

RRC Connection Request

RRC Connection Setup

RRC Connection Setup Complete

(Service Request)Initial UE message

(Service Request)

UE Context Setup

(Keys, Bearers)RRC Security Setup

RRC Security Setup Complete

RRC Reconfiguration (Bearer Setup)

RRC Reconfiguration Complete

UE Context Setup Complete

[UL / DL user data]

New Inactive-to-connected transition

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UE NR RAN CN

Initial radio synchronization

RRC Resume Request

RRC Resume

RRC Resume Complete

[UL / DL user data]

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References

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• 3G4G: 3GPP 5G Specifications (link)• 5G NR: Architecture, Technology, Implementation, and Operation of 3GPP New Radio Standards by

Dr. Sassan Ahmadi, Jun 2019 (link)• Ericsson Technology Review: Inactive State in 5G NR, June 2019 (link)• The 3G4G Blog: A Look into 5G Virtual/Open RAN - Part 3: Connection Release and Suspend, April

2020 (link)• Wireless Moves: The 5G Core – Part 6 – Connection-, Registration- And Session Management, May

2018 (link)• Wireless Moves: The 5G Core – Part 7 – More About Session Management, June 2018 (link)• Techplayon: 5G System Connection Management: CM-Idle and CM-Connected, Oct 2019 (link)• Intel: Overview 5G NR Radio Protocols, Nov 2018 (link)• How LTE Stuff Works: 5G NR: UE RRC States and State Transitions, Sep 2019 (link)• Techplayon: 5G NR Inactive-RNTI (I-RNTI) for RRC_INACTIVE State, Jan 2020 (link)• The 3G4G Blog: RRC states in 5G, Nov 2017 (link)• Netmanias: LTE EMM and ECM States, Sep 2013 (link)

Thank You

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