[5g NR] UE registration process

author ： No.7 Huazai
Personal home page ： Welcome to my home page
Personal creed ： Starlight does not ask passers-by , Time and tide live up to those who want to .
Personal direction ： Focus on 4G/5G field , At the same time, take into account other network protocols , Codec protocol ,C/C++,linux etc. , Interested friends can pay attention to me , Communicate together .

1. flow chart

UE Registration process

2. Detailed process analysis

1. RRC Setup Request

• name ：RRC Connection establishment request
• Direction ：UE->gNB
• analysis ：UE towards gNodeB send out RRCSetupRequest news （ In the beginning RA in ,Msg3 The transmission is RRCSetupRequest news ）,RRCSetupRequest Message carrying RRC Establish reasons and UE identification , Request to create RRC Connect . among UE The logo can be S-TMSI Or random numbers , If the upper layer provides S-TMSI, Then carry S-TMSI Information to the gNodeB; without S-TMSI Information , Then a random number is generated .

2.RRC Setup

• name ：RRC Set up
• Direction ：gNB->UE
• analysis ： Carry in the message SRB1 Details of resource configuration

3.RRC Setup Complete(Registration Request)

• name ：RRC Connection established
• Direction ：UE->gNB
• analysis ：UE according to RRCSetup The message indicates SRB1 Resource information , Configure wireless resources , And then send RRCSetupComplete A message to gNodeB, carry selectedPLMN-Identity、registeredAMF、s-nssai-list and NAS news ,NAS The message is UE Registration request （Registration Request）.

4.Initial UE Message(Registration Request)

• name ： initial UE news
• Direction ：gNB->AMF
• analysis ：gNB by UE Distribute UE-NGAP-ID, according to selectedPLMN-Identity、registeredAMF、s-nssai-list choice AMF node , And then RRCSetupComplete Carried in the message NAS adopt Initial UE Message Send to AMF, Trigger NG-C Connection is established

5.Downlink NAS Transport(Identity Request)

• name ： The downside NAS transmission （Identity Inquire about ）
• Direction ：AMF->gNB
• analysis ：AMF Send down Identity Request, requirement UE Send identity information to AMF

6.DL Information Transfer(Identity Request)

• name ： Downlink information transmission （Identity Inquire about ）
• Direction ：gNB->UE
• analysis ：gNB Conduct NGAP decode , Take out NAS Send the data to UE

7.UL Information Transfer(Identity Response)

• name ： Uplink information transmission （Identity Query reply ）
• Direction ：UE->gNB
• analysis ：UE Put identity information into Identity Response, Reply to AMF, The type of identity information depends on AMF Identity Request Request , In practice, it is basically SUCI

8.Uplink NAS Transport(Identity Response)

• name ： The upside NAS transmission （Identity Query reply ）
• Direction ：gNB->AMF
• analysis ：gNB Take out NAS news Identity Response, after NGAP Send it to AMF

9.Downlink NAS Transport(Authentication Request)

• name ： The downside NAS transmission （ authentication request ）
• Direction ：AMF->gNB
• analysis ：AMF Send down Authentication Request, The message contains a group of HSS Generated authentication parameters

10.DL Information Transfer(Authentication Request)

• name ： Downlink information transmission （ authentication request ）
• Direction ：gNB->UE
• analysis ：gNB Conduct NGAP decode , Take out NAS Send the data to UE

11.UL Information Transfer(Authentication Response)

• name ： Uplink information transmission （ Authentication reply ）
• Direction ：UE->gNB
• analysis ：UE After receiving the authentication parameters given by the network side UE It will trigger the authentication algorithm ,UE After triggering the algorithm, a set of parameters will be generated , The function of these parameters is to compare with AUTHENTICATION REQEUT Carry the authentication parameters for comparison , If the parameters are consistent UE It will be considered a legal network , complete UE Authentication of the network , After the comparison, the result will be replied to AMF

12.Uplink NAS Transport(Authentication Response)

• name ： The upside NAS transmission （ Authentication reply ）
• Direction ：gNB->AMF
• analysis ：gNB Take out NAS news Authentication Response, after NGAP Send it to AMF

13.Downlink NAS Transport(SecurityMode Command)

• name ： The downside NAS transmission （ Safe mode command ）
• Direction ：AMF->gNB
• analysis ：AMF Send down SecurityMode Command, Conduct NAS Message encryption and completion protection

14.DL Information Transfer(SecurityMode Command)

• name ： The downside NAS transmission （ Safe mode command ）
• Direction ：gNB->UE
• analysis ：gNB Conduct NGAP decode , Take out NAS Send the data to UE

15.UL Information Transfer(SecurityMode Complete)

• name ： Uplink information transmission （ Safe mode complete ）
• Direction ：UE->gNB
• analysis ：UE according to SecurityModeCommand The message indicates NAS Integrity protection and encryption algorithm , Derive the key , And then to gNB reply SecurityModeComplete news

16.Uplink NAS Transport(SecurityMode Complete)

• name ： The upside NAS transmission （ Safe mode complete ）
• Direction ：gNB->AMF
• analysis ：gNB Take out NAS news SecurityMode Complete, after NGAP Send it to AMF

17.Initial Context Setup Request

• name ： Initial context establishment request
• Direction ：AMF->gNB
• analysis ：AMF towards gNodeB send out INITIAL CONTEXT SETUP REQUEST news , Start the initial context establishment process

18.SecurityMode Command

• name ： Safe mode command
• Direction ：gNB->UE
• Content ：gNB towards UE send out SecurityModeCommand news , notice UE start-up RRC Integrity protection and encryption process .

19.SecurityMode Complete

• name ： The security mode is established
• Direction ：UE->gNB
• Content ：UE according to SecurityModeCommand The message indicates RRC Integrity protection and encryption algorithm , Derive the key , And then to gNB reply SecurityModeComplete news

20.RRC Reconfiguration

• name ：RRC Reconstitution
• Direction ：gNB->UE
• Content ：gNB towards UE Issue and carry srb-ToAddModList Cellular RRCReconfiguration news , instructions UE establish SRB2 and DRB.

21.RRC Reconfiguration Complete

• name ：RRC The reconfiguration is complete
• Direction ：UE->gNB
• Content ：UE received RRCReconfiguration After the news , establish SRB2 and DRB.UE According to the message instructions, establish the corresponding PDCP Entity and configure relevant security parameters , Set up and configure RLC Entity , Set up and configure DCCH channel .
  SRB2 and DRB After the establishment is successful ,UE towards gNodeB reply RRCReconfigurationComplete news .

22.Initial Context Setup Response

• name ：UE Initial upper and lower establishment completion response
• Direction ：gNB->AMF
• analysis ：UE The initial upper and lower settings are completed