[5g NR] 5g NR system architecture

5G Networking scheme selection

  5G Base station is 5G The core equipment of the network , Provide wireless coverage , Realize wireless signal transmission between wired communication network and wireless terminal . because 5G The frequency of the network is higher than 4G The network is much higher , The higher the frequency is. , The greater the attenuation in the process of signal propagation ,5G The coverage radius of the base station is relatively small 4G smaller , therefore 5G The base station density of the network will be higher than 4G high . High density brings high investment to operators , The pressure of short-term funds is great , Long investment return cycle , about 5G Promotion will make it more difficult , Slow down .   

In order to reduce this promotion resistance ,4G And 5G The integrated networking mode is taken into account , That is to say NSA Non independent networking scheme .NSA Networking mode is a compromise between technology and reality , The perfect networking scheme is SA Independent networking , That is, all core networks and base stations are 5G, In this case , Lower transmission delay , Higher transmission rates , Can play perfectly 5G relative 4G The advantages of .

5G System architecture

  5G System is the most common system architecture , It's using 5G Core network +4G Enhanced base station +5G The networking mode of the base station , by NSA networking . Getting rid of ng-eNB after , It's using 5G Core network +5G Base station networking mode , by SA networking .5G The system includes 5G Access networks and 5G Core network , among NG-RAN representative 5G  Access network ,5GC representative 5G Core network .

5G System architecture   

5GC It mainly includes AMF、UPF Two parts , Plus one. SMF modular . And LTE Compared with the core network of the system ,5G The control side and user side of the core network are further separated .4G The core network is divided into MME,SGW and PGW In the third part of ,MME Mainly responsible for the control surface ,SGW and PGW Mainly responsible for the user side , Although the three are separated, they still overlap in function .5G The control and forwarding functions of the user plane are reconstructed , The reconstructed control plane is divided into AMF and SMF Two logical nodes .AMF Mainly responsible for mobility management , amount to 4G Of MME,SMF Responsible for session management function . User plane UPF Instead of LTE Online SGW and PGW. in other words ,5G After refactoring , The concentration of control surface and user surface is improved , Clearer Architecture .   

NG-RAN from gNB and ng-eNB Two kinds of base stations .gNB yes 5G The base station ,ng-eNB It's direct to 4G Upgrade the software of the base station , Let the interface above support 5G The core network and Xn Interface , To ensure the LTE Some original base stations can still be well utilized .gNB Between 、ng-eNB Between , as well as gNB and ng-eNB adopt Xn Interface .5G The access network is connected with the core network through NG Interface ,gNB/ng-eNB and AMF Between NG-C Interface , and UPF Between NG-U Interface .   

NG The interface can implement AMF/UPF and NG-RAN Many to many connections , That is, a AMF/UPF Can connect multiple gNB/ng-eNB, One gNB/ng-eNB You can also connect multiple AMF/UPF. about UE Come on , In the same AMF/UPF Move between base stations under , When switching occurs , Can still reside in the same AMF/UPF On ,UE A new registration process is not required . When AMF/UPF And NG-RAN When the connection path between is long or new resource allocation is made , Can change and UE Connected AMF/UPF. here AMF The main function of is mobility control , and UPF Its main function is to route and forward packets .

Entity function

   The following figure describes gNB、ng-eNB、AMF、UPF、SMF Division of functions of functional entities .

5G Entity function division

gNB and ng-eNB The main function of

• Wireless resource management related functions ： Wireless bearer control , Wireless access control , Connect mobility control , In uplink and downlink UE Dynamic resource allocation
• Data IP Head compression , Encryption and integrity protection
• When the information provided by the user cannot be determined AFM When routing , For in UE Select... When attaching AMF route
• Route user plane data to UPF
• Provide control plane information to AMF The routing
• Connection setup and release
• Scheduling and transmission of paging messages
• Scheduling and transmission of broadcast messages
• Measurement and measurement report configuration for mobility and scheduling
• Transmission level packet marking in uplink
• session management
• QoS Mapping between traffic management and wireless data bearer
• Support in RRC_INACTIVE State of UE
• NAS Message distribution function
• Wireless access network sharing
• Dual connection
• Support NR and E-UTRA Connection between

5G Core network （5GC） function

5GC It consists of three parts ：  AMF： Mainly responsible for access and mobile management functions UPF： Used to support user plane functions   SMF： Responsible for session management functions

AMF The main function

• NAS Signaling termination
• NAS Signaling security
• AS safety control
• be used for 3GPP Mobility between access networks CN Inter node signaling
• In idle mode UE Accessibility （ Including controlling and performing paging retransmission ）
• Registration area management
• Support mobility within and between systems
• Access authentication 、 to grant authorization , Including checking roaming rights
• Mobile management control
• SMF（ Session management function ） choice

UPF The main function

• Mobility anchor points inside and outside the system
• An external network interconnected with a data network PDU Conversation point
• Packet routing and forwarding
• Packet check and policy rule implementation of user plane part
• Uplink classifier , Support routing traffic to the data network
• Branch points to support multi hosting PDU conversation
• User plane QoS Handle , for example , Packet filtering , gating ,UL / DL Rate execution
• Uplink traffic verification （SDF To QoS Traffic mapping ）
• Downlink packet buffering and downlink data notification triggering

SMF The main function

• session management
• UE IP Address assignment and management
• Selection and control UP function
• To configure UPF Transmission direction of , Route the transmission to the correct destination
• Control policy implementation and QoS Part of
• Downlink data notification