The document provides a comprehensive overview of 5G technology, covering its architecture, operating modes, and protocols. It highlights the need for 5G to accommodate growing mobile data traffic and enhance connectivity for IoT devices while detailing the advantages of its non-standalone (NSA) and standalone (SA) implementations. Additionally, the document discusses frequency ranges, key performance indicators, and the protocol stack associated with 5G networks.

1. Composed by –AALEKH JAIN
5G/NR Overview Architecture
and Operating modes

2. Content Coverage
5G Introduction
• What is 5G?
• Why do we need
5G?
• Usage of 5G?
• NR Frequency
Ranges
• Comparison of LTE
and NR
• NR operations
5G Architecture
overview
• 5G System
Architecture
• 5G Architecture
KPI
• 5G Protocol Stack
5G/NR RRC
Overview
• RRC Overview
• RRC Functions
• NR RRC States
• Need for
RRC_Inactive
State?
• How will
RRC_Inactive state
work?
• NR RRC Interaction
with LTE RRC
• NR RRC with
UTRAN / GERAN
RRC
NR NSA (Non-
Standalone)
• NSA ENDC
• NSA Option 3a
• NSA Option 3x
• EN-DC Protocol
Architecture
• EN-DC Network
Interfaces
• ENDC SN Addition
Procedure
NR SA
(Standalone)
• 5G/NR SA
• NR SA Initial
Access
Registration
• Voice over 5G
• SMS in NR

3. What is 5G?
• 5G is the fifth generation technology standard for cellular networks
• 5G is also known as NR stands for New Radio
• New network will have greater bandwidth, giving faster download
speeds, eventually up to 10 gigabits per second (Gbps).
• 5G will use mmWave for high bandwidth signal.
• 5G will have two versions, namely, SA (Standalone 5G) and NSA (non-
standalone 5G)
• 5G standard are also known as IMT-2020 Standard as raised by the ITU-
R (International Telecommunication Union - Radiocommunication
Sector)

4. Why do we need 5G?
• Mobile data traffic is rising rapidly, mostly due to
video streaming.
• With multiple devices, each user has a growing
number of connections.
• Internet of Things will require networks that must
handle billions more devices.
• With a growing number of mobiles and increased
data traffic both mobiles and networks need to
increase energy efficiency.
• Network operators are under pressure to reduce
operational expenditure, as users get used to flat
rate tariffs and don't wish to pay more.
• The mobile communication technology can enable
new use cases (e.g. for ultra-low latency or high
reliability cases) and new applications for the
industry, opening up new revenue streams also for
operators.

5. Usage of 5G?
ITU-R has defined the following main usage
scenarios for IMT for 2020
• Enhanced Mobile Broadband (eMBB) to
deal with hugely increased data rates, high
user density and very high traffic capacity
for hotspot scenarios as well as seamless
coverage and high mobility scenarios with
still improved used data rates
• Massive Machine-type Communications
(mMTC) for the IoT, requiring low power
consumption and low data rates for very
large numbers of connected devices
• Ultra-reliable and Low Latency
Communications (URLLC) to cater for
safety-critical and mission critical
applications
5G

6. NR Frequency Ranges
In NR, there are roughly two large frequency range specified in 3GPP. One is sub 6 Ghz called as FR1 and the
other is millimeter wave called FR2.
• FR1 extends 4G LTE, from 450 MHz to 6,000 MHz. These bands are specified from 1 to 255.
• FR2 is at a much higher frequency 24,250 MHz (~24GHz) to 52,600 MHz (~52GHz). These bands are
specified from 257 to 511.
The frequency bands in FR1 utilize many of the same frequency bands as those used for 4GMid-band spectrum.
They can provides faster speeds and lower latency than LTE bands. Expect peak speeds up to 1Gbps on FR1-
band spectrum. FR1 sub-6GHz bands are extremely effective in providing coverage and have capacity for a wide
range of 5G use cases. That means faster, more uniform data rates both indoors and outdoors for more
customers, simultaneously. Another reason to use sub-6GHz over mmWave is that, this band can travel farther
and penetrate solid objects like buildings better than a higher frequency spectrum such as mmWave.

7. NR Frequency Ranges
FR2 is what delivers the highest performance for 5G, but with major weaknesses. FR2 spectrum can offer peak
speeds up to 10Gbps and has extremely low latency. The main drawback of high-band is that it has low
coverage area and building penetration is poor. That means that to create an effective high-band network,
you’ll need a ton of cells. mmWave have a coverage area about 1 mile (1.6 km).
Although massive MIMO and beam forming ensure that strict line of sight is not a requirement to make use of
millimeter wave. A mmWave signal may not be able to penetrate buildings, but it will bounce around them to
ensure a decent signal. Also mmWave signal strength will degrade somewhat when it rains, as water drops
blocks the high frequency waves.

8. NR Frequency Ranges
NR operating
band
Uplink (UL) operating band
BS receive / UE transmit
FUL_low – FUL_high
Downlink (DL) operating band
BS transmit / UE receive
FDL_low – FDL_high
Duplex
Mode
n1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz FDD
n2 1850 MHz – 1910 MHz 1930 MHz – 1990 MHz FDD
n3 1710 MHz – 1785 MHz 1805 MHz – 1880 MHz FDD
n5 824 MHz – 849 MHz 869 MHz – 894 MHz FDD
n7 2500 MHz – 2570 MHz 2620 MHz – 2690 MHz FDD
n8 880 MHz – 915 MHz 925 MHz – 960 MHz FDD
n12 699 MHz – 716 MHz 729 MHz – 746 MHz FDD
n20 832 MHz – 862 MHz 791 MHz – 821 MHz FDD
n25 1850 MHz – 1915 MHz 1930 MHz – 1995 MHz FDD
n28 703 MHz – 748 MHz 758 MHz – 803 MHz FDD
n34 2010 MHz – 2025 MHz 2010 MHz – 2025 MHz TDD
n38 2570 MHz – 2620 MHz 2570 MHz – 2620 MHz TDD
n39 1880 MHz – 1920 MHz 1880 MHz – 1920 MHz TDD
n40 2300 MHz – 2400 MHz 2300 MHz – 2400 MHz TDD
n41 2496 MHz – 2690 MHz 2496 MHz – 2690 MHz TDD
n50 1432 MHz – 1517 MHz 1432 MHz – 1517 MHz TDD1
n51 1427 MHz – 1432 MHz 1427 MHz – 1432 MHz TDD
n66 1710 MHz – 1780 MHz 2110 MHz – 2200 MHz FDD
n70 1695 MHz – 1710 MHz 1995 MHz – 2020 MHz FDD
n71 663 MHz – 698 MHz 617 MHz – 652 MHz FDD
n74 1427 MHz – 1470 MHz 1475 MHz – 1518 MHz FDD
n75 N/A 1432 MHz – 1517 MHz SDL
n76 N/A 1427 MHz – 1432 MHz SDL
n77 3300 MHz – 4200 MHz 3300 MHz – 4200 MHz TDD
n78 3300 MHz – 3800 MHz 3300 MHz – 3800 MHz TDD
n79 4400 MHz – 5000 MHz 4400 MHz – 5000 MHz TDD
n80 1710 MHz – 1785 MHz N/A SUL
n81 880 MHz – 915 MHz N/A SUL
n82 832 MHz – 862 MHz N/A SUL
n83 703 MHz – 748 MHz N/A SUL
n84 1920 MHz – 1980 MHz N/A SUL
n86 1710 MHz – 1780 MHz N/A SUL
Operati
ng
Band
Uplink (UL) operating
band
BS receive
UE transmit
Downlink (DL)
operating band
BS transmit
UE receive
Duple
x
Mode
FUL_low – FUL_high FDL_low – FDL_high
n257
26500
MHz
–
29500
MHz
26500
MHz
–
29500
MHz
TDD
n258
24250
MHz
–
27500
MHz
24250
MHz
–
27500
MHz
TDD
n260
37000
MHz
–
40000
MHz
37000
MHz
–
40000
MHz
TDD
n261
27500
MHz
–
28350
MHz
27500
MHz
–
28350
MHz
TDD
NR operating bands in FR2
NR operating bands in FR1

9. Comparison of LTE and NR
Speed: 4G LTE Advanced provides up to 1Gbps performance,
5G NR can provide a potential 1-40Gbps as well.
Latency: 5G can offer a much lower latency than 4G.
Technologies: 4G has grown to accommodate many different
technologies: for example, LWA (LTE-WLAN). 5G scope is
designed to be broad and applicable not just for high-
performance devices, but also down to ultra-low power,
long-life and always connected IoT devices too.
Machine Type Communications: 5G meet the different
requirements of MTC required by IoT applications. Whereas
IoT in the 4G era is a mix of adapted 2G and 4G technologies.
5G services are better equipped to handle these.
Architecture: Unlike 4G, 5G technologies are designed to
take advantage of cloud-based or virtual Radio Access
Networks.
Device Intelligence: Unlike 4G, 5G has the capability to
differentiate between fixed and mobile devices. It uses
cognitive radio techniques to identify each device and offer
the most appropriate delivery channel.

10. NR operations
According to the 3GPP Release 15 standard that covers 5G networking, the first wave of networks and devices
will be classed as Non-Standalone (NSA), i.e., 5G networks will be supported by existing 4G infrastructure. Here,
5G-enabled smartphones will connect to 5G frequencies for data-throughput improvements but will still use 4G
for non-data duties such as talking to the cell towers and servers.
The initial roll-out of 5G cellular infrastructure will focus on enhanced mobile broadband (eMBB) to provide
increased data-bandwidth and connection reliability via two new radio frequency ranges FR1 and FR2.
The 5G Standalone (SA) network and device standard is still under review and is expected to be signed-off by
3GPP by 2020. The advantage of Standalone is simplification and improved efficiency, which will lower cost, and
steadily improve performance in throughput up to the edge of the network, while also assisting development of
new cellular use cases such as ultra-reliable low latency communications (URLLC).

11. 5G System Architecture
Non-Roaming
5G System
Architecture in
reference point
representation

12. 5G System Architecture
AMF - The Access and Mobility Management function (AMF) includes the following functionality.
o NAS ciphering and integrity protection.
o Registration management.
o Connection management.
o Reachability management.
o Mobility Management.
o Access Authentication & Access Authorization.
o Provide transport for SMS messages between UE and SMSF.
o Location Services management for regulatory services.
o EPS Bearer ID allocation for interworking with EPS.
SMF - The Session Management function (SMF) includes the following functionality.
o Session Management.
o UE IP address allocation & management.
o DHCPv4 (server and client) and DHCPv6 (server and client) functions.
o Configures traffic steering at UPF to route traffic to proper destination.
o Termination of interfaces towards Policy control functions.
o Control and coordination of charging data collection at UPF.
o Roaming functionality:

13. 5G System Architecture
UPF - The User plane function (UPF) includes the following functionality.
o Anchor point for Intra-/Inter-RAT mobility.
o External PDU Session point of interconnect to Data Network.
o Packet routing & forwarding.
o Packet inspection.
o QoS handling for user plane.
o Functionality to respond to Address Resolution Protocol (ARP) requests.
PCF - The Policy Control Function (PCF) includes the following functionality:
o Supports unified policy framework to govern network behavior.
o Accesses subscription information relevant for policy decisions in a Unified Data Repository (UDR).
NEF - The Network Exposure Function (NEF) supports the following independent functionality:
o Exposure of capabilities and events.
o Secure provision of information from external application to 3GPP network.
o Translation of internal-external information.
o Receives information from other network functions and store the received information as structured data
to a Unified Data Repository (UDR).
AF - The Application Function (AF) interacts with the 3GPP Core Network in order to provide services.

14. 5G System Architecture
UDM - The Unified Data Management (UDM) includes support for the following functionality:
o Generation of 3GPP AKA Authentication Credentials.
o User Identification Handling.
o Access authorization based on subscription data (e.g. roaming restrictions).
o Support to service/session continuity e.g. by keeping SMF/DNN assignment of ongoing sessions.
o Subscription management.
o SMS management.
AUSF - The Authentication Server Function (AUSF) supports authentication for 3GPP access and untrusted
non-3GPP access.
UDR - The Unified Data Repository (UDR) supports the functionality of storage and retrieval of subscription
data by the UDM and policy data by the PCF.
NSSF - The Network Slice Selection Function (NSSF) supports the following functionality:
o Selecting the set of Network Slice instances serving the UE.
o Determining the AMF Set to be used to serve the UE.
CHF – SMF uses the Charging Function (CHF) to manage the charging for a PDU Session. SMSF uses CHF to
manage the charging for the SMS over NAS. PCF use it to manage the spending limits for a PDU Session.

15. 5G Architecture KPI
5G network architecture is much more service oriented than previous generations. Some Key introduction in 5G
architecture are as below:
Network Slicing
Perhaps the key ingredient enabling the full potential of 5G architecture is network slicing. A network slice is an
independent end-to-end logical network that runs on a shared physical infrastructure, capable of providing a
negotiated service quality. A network slice could span across multiple parts of the network. A network slice
comprises dedicated and/or shared resources, e.g. in terms of processing power, storage, and bandwidth and
has isolation from the other network slices. Operators can effectively manage diverse 5G use cases with
differing throughput, latency and availability demands by partitioning network resources to multiple users or
“tenants”.
Network slicing becomes extremely useful for
applications like the IoT where the number of users
may be extremely high, but the overall bandwidth
demand is low. Each 5G vertical will have its own
requirements. Costs, resource management and
flexibility of network configurations can all be
optimized with this level of customization.

16. 5G Architecture KPI
Beamforming
Another breakthrough technology integral to the success of 5G is beamforming. Conventional base stations
have transmitted signals in multiple directions without regard to the position of targeted users or devices.
Through the use of multiple-input, multiple-output (MIMO) arrays featuring dozens of small antennas
combined in a single formation, signal processing algorithms can be used to determine the most efficient
transmission path to each user while individual packets can be sent in multiple directions then choreographed
to reach the end user in a predetermined sequence.
With 5G data transmission occupying the millimeter wave, free space
propagation loss, proportional to the smaller antenna size, and diffraction loss,
inherent to higher frequencies and lack of wall penetration, are significantly
greater. On the other hand, the smaller antenna size also enables much larger
arrays to occupy the same physical space. With each of these smaller antennas
potentially reassigning beam direction several times per millisecond, massive
beamforming to support the challenges of 5G bandwidth becomes more
feasible. With a larger antenna density in the same physical space, narrower
beams can be achieved with massive MIMO, thereby providing a means to
achieve high throughput with more effective user tracking.

17. 5G Protocol Stack
5G NR User
Plane Protocol
Stack

18. 5G Protocol Stack
5G NR Control
Plane Protocol
Stack

19. 5G Protocol Stack
Physical Layer (PHY)
• On PDSCH and PUSCH, i.e. downlink and uplink shared channels , PHY layer performs all the actions
required to turn the transport block generated by the MAC layer into a physical signal on the air interface,
i.e.
o CRC attachment to transport block or code blocks
o Segmentation of transport block into code blocks
o Channel coding
o Processing of HARQ
o Rate matching and scrambling
o Mapping to assigned resources and antenna ports
o Signal modulation and waveform generation
• PDCCH and PUCCH, i.e. downlink and uplink control channels can be used to
o Schedule transmission in uplink and downlink
o Notify the UE about the utilized slot format
o Provide power control commands
o Perform RACH procedure
o Generate reference signal used for layer1 and layer3 measurement
o Send scheduling request to gNB

20. 5G Protocol Stack
Medium Access Control (MAC)
• Maps logical channel onto transport channels
• Multiplexes and DE multiplexes MAC SDUs into transport blocks
• Is used for scheduling information reporting
• Performs error correction using HARQ
• Handles priority between different types of data
• Adds padding bits
Radio Link Control (RLC)
RLC sub layer supports three transmission modes: Transport Mode (TM), Unacknowledged mode (UM), and
Acknowledged mode (AM). Services and functions of RLC depend on the utilized transmission mode :
• Sequence numbering independent of the one in PDCP
• Error Correction through ARQ
• Segmentation and re-segmentation
• Segmentation and re-segmentation of RLC SDUs
• Reassembly of SDU from segments
• RLC SDU discard
• RLC re-establishment

21. 5G Protocol Stack
Packet Data Convergence Protocol (PDCP)
Functions of PDCP sub-layer depend mainly on whether the processed data unit belongs to control plane or
user plane:
• Sequence numbering of PDCP PDUs (both UP and CP)
• Header compression and decompression using ROHC only (UP only)
• Reordering and Duplicate detection (both UP and CP)
• In-order delivery of PDCP SDUs to higher layers (both UP and CP)
• Retransmission of PDCP SDUs (UP only)
• Ciphering and Deciphering (both UP and CP)
• PDCP SDU discard (UP only)
• PDCP re-establishment and data recovery for RLC AM (UP only)
• Duplication of PDCP PDUs to enhance reliability of transmission
Service Data Adaptation Protocol (SDAP)
Only protocol not present in LTE and applied when base station is connected to 5GC. Main functions are
• Mapping between a QoS flow and a data radio bearer
• Marking QoS flow ID (QFI) in both DL and UL packets

22. 5G Protocol Stack
Radio Resource Control (RRC)
• Broadcast of System Information
• Controlling UE access to network
• Paging of the UE based on request from 5GC
• Management of RRC connection between UE and NG-RAN
• Security functions
• Management of SRBs and DRBs
• Mobility functions for UE
• Measurement reporting of UE
Non Access Stratum (NAS)
Its termination points are UE on one side and AMF on the other. Used to provide core network control :
• Managing mobility of UE including procedures for authentication and identification
• Session management for establishment and maintenance of data connectivity
• NAS transport procedure for support of transport messages related to applications such as, SMS, LPP, 5G
system session management

23. RRC Overview
RRC stands for Radio Resource Control. As UE and Network is communicating via radio channel, RRC is the
common language understood by both network and UE. RRC is the control mechanism used by parties to reach
agreement on common configurations.
Another central role of RRC within each communicating party is to work as a control center for all of the lower
layers within each system. The collection of all the lower layers within UE or base station is called 'Radio
Resource'. The major role of RRC is to control (configure) all the Radio Resources (PHY, MAC, RLC, PDCP) to make
it possible to communicate between UE and the base station.
Services provided to upper layers by RRC
• Broadcast of common control information;
• Notification of UEs in RRC_IDLE, e.g. about a mobile terminating call;
• Notification of UEs about ETWS and/or CMAS
• Transfer of dedicated signaling.
Services expected from lower layers
• Integrity protection, ciphering and loss-less in-sequence delivery of information without duplication;

24. RRC Functions
• Broadcast of system information
• RRC connection control:
 Paging;
 Establishment/modification/suspension/resumption/release of RRC connection;
 Access barring;
 Initial AS security activation;
 RRC connection mobility, associated AS security handling, specification of RRC context information;
 Establishment/modification/suspension/resumption/release of RBs carrying user data (DRBs);
 Radio configuration control;
 Cell management in case of DC and CA;
 QoS control
 Recovery from radio link failure.
• Inter-RAT mobility including e.g. AS security activation, transfer of RRC context information;
• Measurement configuration and reporting:
• Other functions including e.g. generic protocol error handling, transfer of dedicated NAS information,
transfer of UE radio access capability information.

25. NR RRC States
5G has three RRC states RRC CONNECTED, RRC IDLE and RRC
Inactive state. Unlike LTE, in NR there is a addition RRC states
between RRC Connected and Idle and Network/UE can optionally
stay in INACTIVE state without completely releasing the RRC
when there is no traffic and quickly switch back to CONNECTED
states when necessary.
A UE is either in RRC_CONNECTED state or in RRC_INACTIVE
state when an RRC connection has been established. If this is
not the case, the UE is in RRC_IDLE state.
When UE is power up it is in Disconnected mode/Idle mode, It
can move RRC connected with initial attach or with connection
establishment. If there is no activity from UE for a short time, It
can suspend its session by moving to RRC Inactive and can
resume its session moving to RRC connected mode.
A UE can move to RRC Idle mode from RRC connected or RRC
Inactive state.

26. NR RRC States
RRC_IDLE:
• A UE specific DRX may be configured by upper layers.
• UE controlled mobility based on network configuration;
• The UE:
a. Monitors Short Messages transmitted with P-RNTI over DCI;
b. Monitors a Paging channel for CN paging using 5G-S-TMSI;
c. Performs neighboring cell measurements and cell (re-)selection;
d. Acquires system information and can send SI request.
RRC_INACTIVE:
• Performs all operations of RRC IDLE state;
• UE controlled mobility based on network configuration;
• The UE stores the UE Inactive AS context;
• A RAN-based notification area is configured by RRC layer;
• The UE:
a. Performs RAN-based notification area updates periodically and when moving outside the configured
RAN-based notification area;
b. All UE operations of RRC IDLE mode

27. NR RRC States
RRC_CONNECTED:
• The UE stores the AS context;
• Transfer of unicast data to/from UE;
• At lower layers, the UE may be configured with a UE specific DRX;
• For UEs supporting CA, use of one or more SCells, aggregated with the SpCell, for increased bandwidth;
• For UEs supporting DC, use of one SCG, aggregated with the MCG, for increased bandwidth;
• Network controlled mobility within NR and to/from E-UTRA;
• The UE:
a. Monitors Short Messages transmitted with P-RNTI over DCI (see clause 6.5), if configured;
b. Monitors control channels associated with the shared data channel to determine if data is scheduled
for it;
c. Provides channel quality and feedback information;
d. Performs neighboring cell measurements and measurement reporting;
e. Acquires system information.

28. Need for RRC_Inactive State?
The idea behind this new state is to hide the radio connection state from the core network to reduce the
number of signaling and tunnel establishments and tear-downs between the radio network and the core
network.
The RRC Inactive State is a solution to the system access, power saving, and mobility optimization. 5G has to
support eMBB, URLLC, and Massive IoT services at same cost and energy dissipation per day per area. To meet
these different services characteristics it requires new RRC state model.
• To support URLLC services which transmits small packets that require ultra-low latency and/or high
reliability
• Massive IoT Devices wakes up seldom power saving mode to transmit and receive a small payload.
• Devices need to camp in low activity state, and sporadically transmits UL data and/or status reports with
small payload to the network.
• Devices need periodic and/or sporadic DL small packet transmission.
• Smartphones and consumer devices which eMBB UE have periodic and/or sporadic UL and/or DL small
packet transmission and extreme data rates.

29. How will RRC_Inactive state work?
The idea behind this new state is to reduce the number of signaling and tunnel establishments. Even when the
screen is turned-off, background applications continue to exchange data with the Internet to keep the TCP
connections alive on a frequent basis. For this, LTE always requires a new tunnel setup because the radio has
been put into RRC_Idle state to conserve energy.
The 5G radio network can instruct a mobile device to go to RRC_Inactive state with an RRC Release message
that contains a ‘suspendConfig’. The radio link is then taken down to conserve energy but the logical signaling
link to the AMF in the core network and the user data tunnel to the UPF remain in place. When new data arrives
from the network side, the core network just forwards it to the gNB to which the user data tunnel is connected
to. The gNB then organizes a RAN-based paging on all gNBs that are in same RAN notification area in which
the mobile device is free to roam without having to inform the network about its new location. If the mobile
device responds to the RAN based paging with an RRC Resume Request from a different gNB, the radio bearer
and signaling context has to be transferred to the other gNB, as well as the signaling link and user data tunnel.
In case the mobile device moves to a cell that is outside the configured RAN Notification Area (RNA) it has to
establish an RRC connection and send an RNA Update message. The gNB then contacts the previous gNB and
the user’s context is transferred to the new gNB. The RRC connection can then be set to RRC_Inactive again and
a new RAN notification area is configured in the mobile device in which it can roam freely without notifying the
network.

30. NR RRC Interaction with LTE RRC
• In CONNECTED mode, Handover can be performed between NR-cell to LTE-cell and LTE-cell to NR-cell
• In IDLE state, NR can reselect to LTE and LTE can reselect to NR
• In RRC INACTIVE state, NR can reselect LTE but LTE can not reselect to NR RRC INACTIVE state

31. NR RRC with UTRAN / GERAN RRC
• In IDLE state, NR can reselect to UMTS (UTRA) and UMTS (UTRA) can reselect to NR
• In NR INACTIVE state, NR can reselect the UMTS IDLE, but UMTS IDLE can not reselect the NR INACTIVE state
• NR can reselect the GSM (GERAN) while it is in IDLE state
• GSM can do CCO (Cell Change Order) to NR while they are in IDLE state

32. NSA EN-DC
5G can be deployed in two different options, where SA (standalone)
consist of only one generation of radio access technology and NSA
(non-standalone) consist of two generations of radio access
technologies (4G LTE and 5G).
Multi-Radio Dual Connectivity (MR-DC) is a generalization of the
Intra-E-UTRA Dual Connectivity (DC), where a multiple Rx/Tx capable
UE may be configured to utilize resources provided by two different
nodes. One node acts as the MN (Master Node) and the other as the
SN (Secondary node). The MN and SN are connected via a network
interface and at least the MN is connected to the core network.
E-UTRAN supports MR-DC via E-UTRA-NR Dual Connectivity (EN-DC),
in which UE is connected to one eNB that acts as a MN and one en-
gNB that acts as a SN. The eNB is connected to the EPC via the S1
interface and to the en-gNB via the X2 interface. The en-gNB might
also be connected to the EPC via the S1-U interface. UE is
communicating with both eNB abd gNB but all those (signaling and
data) are going through LTE core network.
ENDC Architecture

33. NSA EN-DC
For a successful deployment of EN-DC the 4G network needs to support dual connectivity between E-UTRAN
and NR. Typically the 4G radio will be used to carry control signalling while NR and/or LTE will be used for user
data.
The standardised NSA EPC networking architecture includes three variants of NSA,
• In the Option 3 networking mode, the X2 interface traffic between eNB and gNB has NSA user plane traffic.
• In the Option 3a networking mode, there is only control plane traffic in the X2 interface.
• In the Option 3x networking mode, there is a little LTE user plane traffic in the X2 interface.
3x variant has low impact on EPC and enables data to route directly to the NR gNB to avoid excessive user
plane load on the existing LTE eNB. From the perspective of the impact on the existing network, the Option 3x is
relatively small and has become the mainstream choice for NSA networking.

34. NSA Option 3a

35. NSA Option 3x

36. EN-DC Protocol Architecture
Control Plane
• RRC PDUs generated by the SN can be transported via the MN to the UE. The
MN always sends the initial SN RRC configuration via MCG (Master cell group)
SRB (SRB1), but subsequent reconfigurations may be transported via MN or SN.
• In EN-DC, at initial connection establishment SRB1 uses E-UTRA PDCP. After
initial connection establishment, MCG SRBs (SRB1 and SRB2) can be configured
by the network to use either E-UTRA PDCP or NR PDCP.
• If the SN is a gNB, the UE can be configured to establish a SRB with the SN
(SRB3) to enable RRC PDUs for the SN to be sent directly between the UE and
the SN. Measurement reporting for mobility within the SN can be done directly
from the UE to the SN if SRB3 is configured.
• Split SRB is supported for all MR-DC options, allowing duplication of RRC PDUs
generated by the MN, via the direct path and via the SN. Split SRB uses NR
PDCP.
• In EN-DC, the SCG configuration is kept in the UE during suspension. The UE
releases the SCG configuration (but not the radio bearer configuration) during
resumption initiation.
Uu
SgNB
NR RRC
Uu
X2-C
MeNB
RRC
UE
RRC
(MeNB
state)
S1

37. EN-DC Protocol Architecture
User Plane
• In MR-DC, from a UE perspective, three
bearer types exist: MCG bearer, SCG bearer
and split bearer.
• In EN-DC, the network can configure either
E-UTRA PDCP or NR PDCP for MN
terminated MCG bearers while NR PDCP is
always used for all other bearers.
• From a network perspective, each bearer
(MCG, SCG and split bearer) can be
terminated either in MN or in SN.
• In split bearer, NR PDCP is used both in LTE
Anchor and NR. Splitting of data stream is
done by PDCP.

38. EN-DC Network Interfaces
• In Control Plane in EN-DC, the MME is the core network entity
between the MN and the SN for control plane signalling and
coordination. For each UE, there is also one control plane connection
between the MN and a corresponding CN entity.
• The MN and the SN involved in EN-DC for a certain UE control their
radio resources and are primarily responsible for allocating radio
resources of their cells.
• S1-MME is terminated in MN and the MN and the SN are
interconnected via X2-C
• In User plane in EN-DC, SGW is the network interface for the eNB and
gNB.
• X2-U interface is the user plane interface between MN and SN, and S1-
U is the user plane interface between the MN, the SN or both and the
S-GW.

39. ENDC SN Addition Procedure
The Secondary Node Addition procedure is initiated by the MN and is used to establish a UE context at the SN to
provide resources from the SN to the UE.

40. ENDC SN Addition Procedure
1. MN (Master Node : LTE eNB) send SgNB Addition Request to SN (Secondary Node : NR gNB). LTE eNB
forward following informations to NR gNB.
• E-RAB Characteristics (E-RAB Parameters, TNL address information)
• The requested SCG configuration information including the entire UE capabilities and UE capability
coordination result
• The latest measurement result for SN to choose
• Securiy Information to enable SRB3
• In case of bearer option that requires X2-U between MN and SN, X2-U TNS address information
• In case of SN terminated split bearers, the maximum supportable QoS level
2. (If SN decided to accept the request), it sends SgNB Addition Request Acknowledge performing followings
• Allocate the necessary radio resources transport network resources
• decides Pscell and other SCG Scells and provide the new SCG radio resource configuration to MN
• In case of bearer options that requires X2-U between MN and SN, provides X2-U TNS address
information
• In case of SCG radio resources being requested, provide SCG radio resource configuration
3. If NR gNB accept the SN addition request and provides all the necessary information to LTE eNB, LTE eNB
generate RRC Connection Reconfiguration message carrying all the necessary information and send it to UE.
This message carries NR RRC Connection Configuration, so that UE can figure out the necessary
configuration for NR gNB.

41. ENDC SN Addition Procedure
4. After UE received RRCConnectionReconfiguration, it checks if all the configurations in the message is
doable in UE side, it sends RRCConnectionReconfigurationComplete message. This message includes NR
RRC Response as well.
5. Once MN (LTE eNB) received RRCConnectionReconfigurationComplete from UE, the MN informs SN(NR
gNB) that UE has completed the reconfiguration procedure by SgNB Reconfiguration Complete.
6. UE acquire all the information required for RACH procedure from RRC Connection Reconfiguration message
instead of SIB. If configured with bearers requiring SCG radio resources, the UE performs synchronisation
towards the PSCell of the SN.
7. If PDCP termination point is changed to the SN for bearers using RLC AM, and when RRC full configuration
is not used, the MN sends the SN Status Transfer.
8. For SN terminated bearers moved from the MN, dependent on the bearer characteristics of the respective
E-RAB, the MN may take actions to minimize service interruption due to activation of EN-DC (Data
forwarding).
9. If applicable, the update of the UP path towards the EPC is performed.

42. 5G/NR SA
• NR SA (Standalone) option is the option with 5G core.
• In 5G SA Option 2, New Radio (NR) access network consisting of gNBs connected to 5G Core (5GC).
• The user-plane and control-plane of SA Option 2 are using NR and are completely independent of Long Term
Evolution (LTE).
Possible Evolution Path from NSA option 3 to SA option 2

43. NR SA Initial Access Registration
UE gNB AMF SMF UPF AUSFPCF
5GC
Msg1 : Random Access Preamble
(PRACH)
Msg2 : Random Access Response
Msg3 : RRCSetupRequest
Msg3 : RRCSetup
RRC_Connected
Msg3 : RRCSetupComplete
Initial UE Message
NAS-PDU : Registration Request
NAS Identity Request
NAS Identity Response

44. NR SA Initial Access Registration
UE gNB AMF SMF UPF AUSFPCF
5GC
Nausf_UEAuthenticate_authenticate Request
Nausf_UEAuthenticate_authenticate Response
NAS Authentication Request
NAS Authentication Response
NAS Security Mode Command
NAS Security Mode Complete
Npcf_AMPolicyControl_Create Request
Npcf_AMPolicyControl_Create Response
Nsmf_PDUSession_UpdateSMContext Request
PFCP Session Modification Request

45. NR SA Initial Access Registration
UE gNB AMF SMF UPF AUSFPCF
5GC
PFCP Session Modification Response
Nsmf_PDUSession_UpdateSMContext Response
Initial Context Setup Request
NAS-PDU : Registration Accept
SecurityModeCommand
SecurityModeComplete
RRCReconfiguration
[Registration Accept]
RRCReconfigurationComplete]
NAS Registration Complete
Uplink Data
Downlink Data

46. Voice over 5G
• 3GPP has specified that 5G uses the 4G voice/video communication
architecture and still provides voice/ video communication services based on
the IMS known as Voice over NR (VoNR).
• In VoNR, UEs camp on the NR network, and voice/video communication and
data services are carried on the NR network with gNB.
• VoNR cannot represent all 5G voice/video communication solutions
implemented by the 5G core network (5GC). Vo5G is needed to summarize
all 5G voice/video communication solutions which includs VoNR, VoeLTE, EPS
FB, and RAT FB.
• The 5GC does not provide the CSFB solution to simplify the network and
accelerate the exit of the CS voice.
• According to 3GPP, EVS and H.265 are mandatory codec for voice and video
communication services in Vo5G. EVS and H.265 require fewer bandwidths
to provide better user experience.

47. VoNR
• In initial stage, the NR network does not provide voice/video communication services. If the UE camping on
the 5G NR network makes a call, the voice/video communication and data services fall back to the 4G
network. The gNB sends a redirection or inter-RAT handover request to the 5GC. Then, the UE handovers to
the LTE network, and the VoLTE service is provided. This is knows as EPS Fallback. The advantage of EPS FB
is that the UE or gNB only needs to support the IMS signaling channel.
• In VoeLTE, UEs camp on the eLTE network (5GC with evolved eNB), and voice/video communication and
data services are carried on the eLTE network.
• Similar to EPS FB, in this case, the gNB sends a redirection or inter-RAT handover request to the 5GC to fall
back to the eLTE network and use the VoeLTE service. This is known as RAT FB.

48. SMS in NR
• NR supports SMS over NAS and SMS over IP.
• Within 5G Core, SMS Function (SMSF) supports
SMS over NAS (SMSoNAS).
• Besides, SMSoIP can also be considered as IMS
based SMS solution under 5G network. SMSoIP
can be deployed simultaneously with voice service
over IMS to provide both voice and short message
service.
• It is recommended to use SMSoNAS solution if
voice services over IMS is not supported or for a
5G data card/Machine Type Communications
(MTC)/Non-IMS device without voice service.

49. References
3GPP TS references
1. 3GPP TS 23.501, V15.9.0, System architecture for the 5G System (5GS);
2. 3GPP TS 37.340, V15.8.0, Evolved Universal Terrestrial Radio Access (E-UTRA) and NR; Multi-connectivity;
3. 3GPP TS 38.101-1, V15.9.0, User Equipment (UE) radio transmission and reception; Part 1: Range 1
Standalone
4. 3GPP TS 38.101-2, V15.9.1, User Equipment (UE) radio transmission and reception; Part 2: Range 2
Standalone
5. 3GPP TS 38.300, V15.9.0, NR; NR and NG-RAN Overall Description
6. 3GPP TS 38.331, V15.9.0, NR; Radio Resource Control (RRC) protocol specification
URL References
1. http://www.sharetechnote.com/
2. http://www.eventhelix.com/
3. http://www.techplayon.com/
4. https://www.gsma.com/futurenetworks/wiki/5g-implementation-
guidelines/#eb7ab6a5ffdc39e6149fecbcf21794c1
5. https://www.huawei.com/en/industry-insights/technology/vo5g-technical-white-paper

50. THANKS