What is the difference between TC-RNTI and C-RNTI in 5G?

5G NR
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24

The Random Access Procedure is performed for the following five events:

  1. Initial access from RRC_IDLE.
  2. RRC Connection Re-establishment procedure.
  3. Handover.
  4. DL data arrival during RRC_CONNECTED requiring random access procedure, when UL TA synchronisation status is “non-synchronised”.
  5. UL data arrival during RRC_CONNECTED requiring random access procedure, when UL TA synchronisation status is “non-synchronised”.

And takes two distinct forms:

  1. Contention based (applicable to all five events).
  2. Non-contention based (applicable to handover and DL data arrival).
25

Exactly this i said above. :wink:

26

Yes, but for 5G NSA after sgnb addition we need to start with contention based procedure.
Let’s try to figure out more difference from LTE.

27

Not necessarily.
We can start with non-contention based also.

RACH_Procedure_for_LTE_Interworking

28

I think it can be both.
There’s no reason for non contention based to not be there.

29

Yes. For connected mode UE, RACH with non-contention based is safest way of getting HO/UL Synch done.

30

There’s one more condition and it is called RLF during which UE performs RACH procedure.

Usually contention-based RACH is done in non-critical cases and contention-free is performed during critical cases such as HO etc.

31

Hi Guys,
I do not see any difference in Temporary C-RNTI, whether it is 5G or LTE,

Obviously both will be carried in MSG2 during Random Access Procedure, that too in contention based random access, because based on Temporary C-RNTI UE is identified via eNB or gNB for transmitting MSG3 and MSG4.

5G NSA case mostly use contention free (I assume all vendors follow this due to the NSA setup procedure requirements? Where RACH can’t be counted under SGNB addition success ) In contention free random access procedure case, no such temporary C-RNTI requirement…so we don’t see in 5G NSA access procedure.

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