Applicable Versions
NetSim StandardNetSim Pro


Applicable Releases
v12.2



All gNBs broadcast MIB and SIB1 control packets at 80 ms and 160 ms (and continue broadcasting at the 80/160ms interval subsequently). Post this cell selection occurs as explained below


Initial decision on which is the serving gNB: 

  • The UE attaches itself initially to the gNB from which it receives the highest SNR
  • If SNR from multiple gNBs are equal, the UE will attach to the gNB with the lowest ID
  • The gNB to which the UE is connected by the user in NetSim GUI at the network design stage, is only for visual purposes. It plays no role in determining which gNB the UE will attach to

After cell selection

  • RRC Connection establishment involves the following control packets:
    • RRC_SI: Selected gNB will send system information to UE
    • RRC_SETUP_REQUEST: Setup request will be sent by UE to selected gNB.
    • RRC_SETUP: Selected gNB sends the setup to UE which contains RRCTransactionIdentifier, RRCResponsetype, PDCP Properties: UEID and GNBID, DiscardDelayTimer , T_Reordering, Hdr Type, SN=0, dcBit.
    • RRC_SETUP_COMPLETE: UE sends back the setup complete containing RRCTransactionIdentifier, SelectedPLMNIdentity, AMFIdentifier, Gaumi Type, Hdr Type, SN, dcBit.
  • UE will send the UE_MEASUREMENT_REPORT to the connected gNB.  The measurement report is sent by each UE to its serving gNB and it contains SINR from all gNBs
  • The flow of these packets can be seen in NetSim packet trace / packet animation


If the SNR from another gNB is offset greater than SNR from serving gNB, it leads to handover. After the handover procedure is completed RRC Reconfiguration would happen between target gNB and UE. The UE will then send the UE MEASUREMENT REPORT to this gNB.