UE RLC packet flow from SN1 to SN6

Dear Experts.
Let’s say UE RLC has sent packet from SN1 to SN6.
Let’s say SN5 has some issue.
UE has sent but eNB has not received the SN so it will send NACK.
So my question is:

  1. So if that SN is not able to ACK means RLC window will stall (will not move ahead)?
  2. Till how long UE will keep on sending SN5.
  3. What if SN5 is never received by eNB? Does that mean data is lost and no way to recover?

Max. Retx threshold.
It should re-transmit keeping E2=1

But in case your Pdu carrying P=1 fails then t-poll retx timer gets expired.

Max. Retx threshold. → where this parameter gets configured.
It should re-transmit keeping E2=1.
What does E2=1 means?

If you see Ack mode header from specs if E1=1 means status pdu containing atleast 1 more nack combination which is represented by E2, given as NACK_SN +E1 +E2.
In this case E2 is set to which means if any segment still failed to receive from re-tx’ed pdu.
Mean last pdu was 1500B and got failed then mac will ask for further fragments like 1000B, 500B which is represented by E2 bit.
It can be the case for any SN PDU failing.

In this question, let’s say eNB is not able to receive the SN5, after maximum retries, will it declare RLF here?

Are you talking about control plane or data plane, what will be the value of D/C field?

Data plane.

What I know RLC informs MAC wrt So start and So end, mean it clearly tells MAC layer what is the starting and ending part of data which is showing NACK and further RLC breaks it down into snall chunks representing same.
But still if mac/pdcp not able to decode then it can be radio link failure.

I am not having a clear answer wrt radio link failure, since RLC is not generating data it itself getting from another layer so RLF or may be poor coverage or any other issue should be at phy layer or Application layer
If max re tx threshold expires at RLC layer then re established would be triggered.

This parameter is sent by eNB during RRC connection setup under srbtoAddmod list-> RLC settings
Infact all PDCP /RLC/MAC layer setting comes inside this message under Radioresource config dedicated.
Which is also used inside RRC connection reconfiguration complete.
I means RRC connection reconfiguration which is sent by eNB.

Thanks! :wink:
Continuing from here.
Let’s assume UE has triggered RLF, will UE do RACH again or eNB will send RRC_Conn_re-establishment?

Note: thanks alot for patience. This was bit confusing, really sorry I am new to LTE, but trying to understand/learn.

RLF - itself is not enough, based upon single layer we can never tell that its radio link failure.

Let’s take an example
RLC has logical channels
Srb1, Srb2, Dcch1-2, Dtch-3-10.
They keep data in buffer and Mac layer always pick data based upon priority And resources allocated.
So RLC UE data is only read by RLC eNB.

Yes, but not in case of VoLTE call.
There you will hear breaks in voice.
There are some cases life file transfers 1gb text file which will be forwarded in chunks but if any part is missed then complete process will start again.

No repy here. :grinning:. All good. :slight_smile: