The document discusses 5G NR RRC inactive state. It begins by introducing the NR RRC states of CONNECTED, IDLE, and INACTIVE. It then references 3GPP specifications that define the inactive state and its establishment and release.

1. 5G NR RRC Inactive State
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NR RRC_CONNECTED
NR RRC_IDLE
NR RRC_INACTIVE
Establish /
Release
Release
Resume / Release
with Suspend
3GPP TS 38.331

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3. 2G / 3G Mobile Network Architecture
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Circuit Switched
(CS) Core
Air
Interface
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
Radio
Access
Network
(RAN)
Core
Network
(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

4. 4G Mobile Network Architecture
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Circuit Switched
(CS) Core
Air
Interface
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
Evolution
Evolved Packet
Core (EPC)
Data (IP)
Network
eNB
UE
Evolved
Packet
System
(EPS)
Long Term Evolution
(LTE) of Radio Interface
System Architecture
Evolution (SAE)
Radio
Access
Network
(RAN)
Core
Network
(CN)

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7. 5G Mobile Network Architecture
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Air
Interface
New & Evolution
Evolved Packet
Core (EPC)
Data (IP)
Network
eNB
UE
Evolved
Packet
System
(EPS)
5G Core (5GC)
Data (IP)
Network
gNB
UE
5G System
(5GS)
New Radio or Next-
Generation RAN
(NG-RAN)
Radio
Access
Network
(RAN)
Core
Network
(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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11. 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

12. 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

13. 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 Bearer
External
Bearer
E-RAB S5/S8 Bearer
S1 BearerRadio Bearer

14. 4G Default and Dedicated Bearers
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eNodeBUE
S1-U S5/S8
S5/S8
P-GW
S-GW
Uu P-GW
PDN
Default EPS bearer setup - registration
Default EPS bearer setup
Dedicated EPS bearer
IP Packet

15. 4G EMM, ECM and RRC States
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DEREGISTERED REGISTERED
RRC
ECM
EMM
OFF ATTACHING IDLE / REGISTERD
SERVICE
REQUEST
ACTIVE
IDLE CONNECTED
IDLE CONNECTED IDLE CONNECTED

16. 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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18. 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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20. 5GS State Model
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RM-DEREGISTERED
CM-IDLE
RRC_IDLE
RM-REGISTERED
CM-IDLE
RRC_IDLE
RM-REGISTERED
CM-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)

21. 5GS State Model – RRC_IDLE
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RM-DEREGISTERED
CM-IDLE
RRC_IDLE
RM-REGISTERED
CM-IDLE
RRC_IDLE
RM-REGISTERED
CM-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.

22. 5GS State Model – RRC_CONNECTED
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RM-DEREGISTERED
CM-IDLE
RRC_IDLE
RM-REGISTERED
CM-IDLE
RRC_IDLE
RM-REGISTERED
CM-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.

23. 5GS State Model – RRC_INACTIVE
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RM-DEREGISTERED
CM-IDLE
RRC_IDLE
RM-REGISTERED
CM-IDLE
RRC_IDLE
RM-REGISTERED
CM-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.

24. 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

25. 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

26. 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
-
-

27. 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]

28. 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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31. 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)

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