5G Basic PART I

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Hi guys, this is our first 5G basic part in which we touch upon the difference between gNB and ng-eNB and service based architecture.

What is gNB?

It is the node that provides NR Control Plane and User Plane protocol terminations towards the UE.

gNB is connected to the 5G Core Network through the NG Interface.

What is ng-eNB?

It is the node which provides E-UTRA/LTE Control Plane and User Plane protocol terminations towards the UE.

ng-eNB is connected to the 5G Core Network through the NG Interface.

What is NG-RAN Architecture?

NG-RAN is the representation of the newly defined Radio Access Network(RAN) for 5G.

It allows the UE(device) to get both NR and LTE radio access.

The below diagram shows the inter-relation of NG-RAN with the overall  5G Core Network system.

Xn interface:

An ng-eNB is connected with other ng-eNBs and gNBs through the Xn interface.

NG interface:

It is the interface which connects the ng-eNBs or gNBs with the 5G Core Network.

In the Control Plane, the AMF and ng-eNB/gNB are connected by NG-C interface and in the User Plane, the UPF and ng-eNB/gNB are connected by NG-U interface.

5G System Architecture:

The Network Function services of every Control Plane Function are exposed through the service-based interface:

It also known as 5G system SBA( service based architecture).

The main 5G NFs are the following: 

(Note:all functionalities of individual functions are not mentioned)

Network Function	Functional description(supports)
AMF (Access and Mobility Management function) (It can be said that AMF has part of MME functionality from legacy LTE EPC.)	Access authentication and authorization, Security context management, Mobility Management, Termination of NAS signaling, Registration Management, Connection management, NAS ciphering & integrity protection Provide transport for SMS messages between UE and SMSF (Security Anchor Functionality), Location Services Management for regulatory services, EPS Bearer ID allocation for inter-working with EPS, UE mobility event notification, It helps to transport SM messages between UE and SMF.
SMF (Session Management function) (It can be said that SMF has part of the MME and PGW functionality from legacy LTE EPC.)	UE IP address allocation & management, Session Establishment, modify and release, including tunnel maintain between UPF and AN node, DHCPv4 (server and client) and DHCPv6 (server and client) functions, Selection and control of UP function, Configures traffic steering at UPF to route traffic to proper destination, Termination of interfaces towards Policy control functions, Charging data collection and support of charging interfaces, Control and coordination of charging data collection at UPF, down-link Data Notification, Roaming functionality.
UPF (User plane function) (It can be said that UPF has part of the SGW & PGW functionality from legacy LTE EPC.)	Anchor point for Intra-/Inter-RAT mobility, External PDU Session point of interconnect to Data Network, Packet routing & forwarding, Packet inspection, User Plane part of policy rule enforcement, e.g. Gating, Redirection, Traffic steering, Lawful intercept (UP collection), Traffic usage reporting, QoS handling for user plane, Uplink Traffic verification (SDF to QoS Flow mapping), Transport level packet marking in the uplink and downlink, Downlink packet buffering and downlink data notification triggering, ARP proxying.
PCF (Policy Control Function) (It can be said that PCF has part of the PCRF functionality from legacy LTE EPC.)	Supports unified policy framework to govern network behavior, Provides policy rules to Control Plane function(s) to enforce them, Accesses subscription information relevant for policy decisions in a Unified Data Repository (UDR). NOTE: The PCF can access the UDR which is located in the same PLMN as the PCF.
NEF (Network Exposure Function)	It Exposes the capabilities and events, Securely provisions the information from external applications to 3GPP network, Translates internal-external information, It function is to store the received information in the form of structured data by using a Standardized interface to a Unified Data Repository (UDR) (interface is to be defined by 3GPP). The stored information can be accessed and "re-exposed" to other network functions and Application Functions by the NEF, and can be used for other purposes such as analytics.
NRF (Network Repository Function)	Maintains the NF profile of available NF instances and their supported services, NF instance ID,NF type, PLMN ID, Network Slice related Identifier(s) e.g. S-NSSAI, NSI ID. FQDN or IP address of NF,NF capacity information, NF Specific Service authorization information, Names of supported services, Endpoint Address(es) of instance(s) of each supported service, Identification of stored data/information. For more information please check 3GPP TS 23.501 version 15.2.0 Release 15 6.2.6.
UDM (Unified Data Management)	User identification handling, Support of de-concealment of privacy-protected subscription identifier, Access authorization based on subscription data, generation of Authentication and Key Agreement (AKA) credentials, Support to service/session continuity, Lawful Intercept Functionality, Subscription management.
AUSF (Authentication Server Function) (It can be said that it is a part of HSS functionality from legacy LTE EPC.)	Acts as an authentication server.
AF (Application Function)	It influences traffic routing, Accessing Network Exposure  in Application layer and interacts with the Policy framework for policy control.
NSSF (Network Slice Selection Function)	Selecting the set of Network Slice instances serving the UE, Determining the Allowed and Configured NSSAI and, if needed, the mapping to the Subscribed S-NSSAIs, Determining the AMF Set to be used to serve the UE, or  a list of candidate AMF(s) (based on configuration) possibly by querying the NRF.

References:
1) 3GPP TS 23.501 V15.0.0 system architecture for the 5G system ( stage 2).