What is the difference between the contention resolution timer and T300?

Hi All,
What is the difference between the contention resolution timer and T300?

T300 starts when UE starts RRC connection request/SR etc i.e. MSG1 in RACH.
Contention resolution timer starts when UE starts sending MSG3.
If UE is able to decode the ACK (MSG4), contention resolution is success and the timer will be stopped.
If UE doesnt receive/cant decode MSG4 by the expiry of CR timer, UE will restart the RACH from MSG1.

T300 is started after sending msg3, right?

T300 is basically to evaluate the lower layer failures.
What if MSG1 itself is not responded by NW?
In that case, for how long UE should retry MSG1 with increased powerlevels every time?
This duration is given by T300.

T300 is RRC timer and starts once the RRC layer generates the RRC request and sends it to lower layers.

Are you saying that T300 starts from RACH request (MSG1)?

Yes, that’s my understanding.

It’s called backoff timer.

From MSG3.

So what is the difference between these two?

We have harqmsg after msg3. If failed then it goes to RACh again till the number you have set, as max 8 can be set.

T300 defines the waiting time for the RRC Connection Setup message after transmitting the RRC Connection Request message, i.e. it corresponds to the waiting time for MSG4 after transmitting MSG3.

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That will be used if msg 3 crc nok.

Yes. What about then contention resolution timer?

The reliability of MSG4 can be modified using the harqMaxTrDl parameter in Nokia.
This parameter defines the maximum permitted number of transmissions (original transmission + re-transmissions).
It is generally applicable to the downlink and is not just applicable to MSG4.
Thus, modifying this parameter will impact the downlink throughput the lifetime of the connection.
The parameter has a default value of 5 (allowing up to 4 re-transmissions), and a range from 1 to 16.

It’s sf32 or sf64 generally.

Normally set as 64 ms.

Yes, 32 ms or 64 ms. What is the difference between these two?

The window between msg3 and harqmsg3.

T300 we keep on higher value, say 300 ms.

Contention resolution timer is to check if the eNB has sent the Contention Resolution Identity MAC CE in response to msg3 to complete the contention resolution procedure (for contention based mechanism).
If no such message from eNB during this timer, then the new RACH procedure happened.
It is sent over sib 2.

When the macContentionResolutionTimer is expire then tow think happened.
⦁ Discard the Temporary C-RNTI
⦁ Consider the Contention Resolution not successful.

Once Msg3 is transmitted, the MAC entity will start mac-ContentionResolutionTimer and restart mac-ContentionResolutionTimer at each HARQ retransmission.
Monitor the PDCCH until mac-ContentionResolutionTimer expires or is stopped.
If the MAC PDU is successfully decoded then mac-ContentionResolutionTimer stop.