In this previous chapter we learnt about 5G NR initial access process in brief.
In this chapter we shall see the important message contents.
1. RRCSetupRequest:
UE sends a setup request
IE: ue-Identity / establishmentCause
Channels: CCCH, SRB0
2. INITIAL UL RRC MESSAGE TRANSFER
gND-DU sends RRC Setup Request message to gNB-CU
gNB-DU UE F1AP ID
SUL Access Indication
C-RNTI
RAN UE ID
(UL-CCCH-Message: rrcSystemInfoRequest, RRC Request: Create/Restore/Release)
3. DL RRC MESSAGE TRANSFER:
gNB-CU sends RRCSetup message to gNB-DU
gNB-DU UE F1AP ID (DU lookup UE context)
Index to RAT/Frequency Selection Priority
Execute Duplication
RRC-Container (DL-CCCH-Message: RRC establishment/rejection)
4. RRCSetup:
gNB-CU sends SRB1 configuration to UE
IE: masterCellGroup radioBearerConfig CellReselectionPriorities
Channels: CCCH, SRB0
5. RRCSetupComplete:
UE sends RRCSetupComplete to network.
The unique temporary identity of 5G-S-TMSI (Temporary Mobile Subscriber Identity) UE in the core network TA
selectedPLMN-Identity
registeredAMF
Guami-Type
s-NSSAI-List (Single Network Slice Selection Assistance Information)
dedicatedNAS-Message
DCCH, SRB1
6. UL RRC MESSAGE TRANSFER
Send RRC establishment is completed to gNB-CU
New gNB-DU UE F1AP ID
Selected PLMN ID
RRC-Container (UL-DCCH-Message: RRC establishment/recovery/reconfiguration completion, measurement report, safe activation completion, UE capability information)
7. INITIAL UE MESSAGE:
Inform the core network that UE wants to enter the network.
RAN UE NGAP ID
NAS-PDU
UE Context Request
5G-S-TMSI
8. INITIAL CONTEXT SETUP REQUEST
AMF prepares UE context to send to gNB
AMF UE NGAP ID
RAN UE NGAP ID
PDU Session Resource Setup Request Transfer (QoS)
Security Key
Mobility Restriction List
UE Radio Capability
UE Security Capabilities
9. UE CONTEXT SETUP REQUEST:
(gNB-CU -> gNB-DU) Create SRB DRB
SRB To Be Setup List
DRB To Be Setup Lis
UE-CapabilityRAT-ContainerList
SCell To Be Setup List
DRX Cycle
CU to DU RRC Information (handover,resource configuration)
RRC-Container
QoS Flow Mapping Indication
Resource Coordination Transfer Information
10. SecurityModeCommand:
AS security activation
SecurityAlgorithmConfig(IntegrityProtAlgorithm / cipheringAlgorithm)
11. UE CONTEXT SETUP RESPONSE:
(gNB-DU -> gNB-CU) notify gNB-CU of the completion of RB establishment
DRB Setup List
DRB Failed to Setup List
SRB Setup List
SRB Failed to Setup List
C-RNTI
DU to CU RRC Information
12. SecurityModeComplete:
Notification of network-side security activation completed
rrc-TransactionIdentifier
CriticalExtensions
13. UL RRC MESSAGE TRANSFER
(gNB-DU -> gNB-CU) notify gNB-CU of AS security activation messages
New gNB-DU UE F1AP ID
Selected PLMN ID
RRC-Container (UL-DCCH-Message: RRC establishment/recovery/reconfiguration completion, measurement report, safe activation completion, UE capability information)
14. DL RRC MESSAGE TRANSFER:
Carry RRCReconfiguration to gNB-DU
gNB-DU UE F1AP ID (DU lookup UE context)
Index to RAT/Frequency Selection Priority
Execute Duplication
RRC-Container (DL-DCCH-Message: RRC Reconfiguration/release, UE capability query)
15. RRCReconfiguration:
Send the overmatch command to UE
Add, modify and release RB after AS security activation (radioBearerConfig)
Establishment, modification and release of measurements; (measConfig)
Add, modify and release SCG and SCell (secondaryCellGroup)
16. RRCReconfigurationComplete:
Notify the base station that RRC reconfiguration has been completed.
rrc-TransactionIdentifier
CriticalExtensions
17. UL RRC MESSAGE TRANSFER
gNB-DU will notify gNB-CU of the information about the reconfiguration.
New gNB-DU UE F1AP ID
Selected PLMN ID
RRC-Container (UL-DCCH-Message: RRC establishment/recovery/reconfiguration completion, measurement report, safe activation completion, UE capability information)
18. INITIAL CONTEXT SETUP RESPONSE
Notify AMF contextual establishment completed
AMF UE NGAP ID IE
RAN UE NGAP ID IE
PDU Session Resource Setup Response Transfer (QoS)
3GPP TS 38.331: “NR; Radio Resource Control (RRC) protocol specification”;
3GPP TS 38.413: “NG-RAN; NG Application Protocol (NGAP)”;
3GPP TS 38.473: “NG-RAN; F1 application protocol (F1AP)”;
