T300 and contention Resolution timer

Hi Experts.

I’m trying to understand need for two timers starting and stopping with the same messages: t300 and contention Resolution timer.

First one is 1sec and the other is 64ms.

In case expiration either of those two, UE will start again from msg1, but RRCfailure is declaring after t300.

So my misunderstanding is what happenings in case msg4 Resolution timer expire:

  1. UE will go through msg1-msg3 again and again until t300 expiration [ In this case, why we cannot see RRCSetupReguests].
  2. UE will wait expiration of t300, decleara RRCSetupFailure and than start from beginning.

In some logs long ago I was able to see after msg3 RRC setup request, consecutive messages of contention.resolution timer expiration until t300 expiration, in that moment reason was bad UL RF and msg3 couldn’t be detected by gNB.

T300 guard the RRC procedure and other time guard the MAC procedure.

Thats why you don’t see RRC setup request untill t300 expire.

OK, so after msg4 timer expiration, UE will go through msg1-msg3 again but only on MAC level?

Yes, until t300 timer expired.

Thanks for confirmation!

That part was confusing me a lot because I couldn’t understand in repeated case after msg4 timer expiration, what is contained in msg3 as RRC part is not there.

Also check this: First HARQ Feeback - #33 by AbdurRehman87