Many RRC Connection Reestablishment Reject

[BENRHOUMASALEM]

Hi Expert,

In our network, we have a lot of RRC Connection Reestablishment Reject message reassigned from the ENB imediatly after receiving RRC Connection Reestablishment request message.
Vendor : NSN

Note that not all the reestablishement messages are rejected.

Please help to root cause and give us your recommendations. What could be the reasons ?

Best regards

[marcengo]

Check if RLF Handover feature is enabled. Otherwise, when a UE drops the connection while doing a handover from Cell A to Cell B, and for some reason reestablishes at Cell C, the reestablishment will be rejected by Cell C. It will only work if done at either Cell A or Cell B.

With the feature, you will solve this issue.

[sak2e]

have you DT log result? if you have could you send it? probably it will easier to check the root cause.

[BENRHOUMASALEM]

Hi,

Many thanks for your replays. Find attached Emil trace.
@ marcengo : I checked the feature, It not activated in our network. But In the majority of the cases, UE not droped the connection while doing a handover.
Please advise.

39048

[DJ Download]

I have the same situation, but in ourcase RLF triggered HO is active. RRC Reestablishment success rate is only 50%.
Most failures are due to T301 expiry, we set this to default at 400ms.

Does anybody experience the same situation we face here?


Hi,

Many thanks for your replays. Find attached Emil trace.
@ marcengo : I checked the feature, It not activated in our network. But In the majority of the cases, UE not droped the connection while doing a handover.
Please advise.

39048

[yassanino]

start by checking your admission control params ,may be you have congestion there
also to verify you PUCCH parameters
than it's better to check also MSG4 reception
try to enlarge "T301" param and see the impact
BR

[BENRHOUMASALEM]

Hi yassanino,
What's the relation between this cause of failure and T301 ? As you see in the screen shot, the Rejection is sended directly after RRC restab request. So no problem in T301!
@Expert :please to send your recommendations

[amadeo]

It seems to Radio condition problem. If you do re-establishment but while doing so your RF sync it out due to RF condition, they will fail.
In Emil i believe you can see the RF status. Check what is the RF condition when they are doing this re-establishment.


Hi,

Many thanks for your replays. Find attached Emil trace.
@ marcengo : I checked the feature, It not activated in our network. But In the majority of the cases, UE not droped the connection while doing a handover.
Please advise.

39048

[hassan.attique]

Hi All,
In nokia equipment if you have RL60 or before software version you will have this issue. In RL70 the issue is solved usin feature. The problem is after Successful HO IF RLF occur the Ue can send request to any eNB it is not necessory that re-establishment is request from same target eNodeB. As other eNB dont have valid Ue context so they reject the re-establishment request considering it to be invalid request. In RL70 they introduced a feature that any eNodeB can query UE context from target eNB for Re-establishment on X2 interface if it exist.



Hi Expert,

In our network, we have a lot of RRC Connection Reestablishment Reject message reassigned from the ENB imediatly after receiving RRC Connection Reestablishment request message.
Vendor : NSN

Note that not all the reestablishement messages are rejected.

Please help to root cause and give us your recommendations. What could be the reasons ?

Best regards

[BENRHOUMASALEM]

Yes. We tried this sollution but normally the load in X2 will be very high if we do a generalization

[amadeo]

Bern, Did you find the solution yet?

[BENRHOUMASALEM]

Yes amadeo, is with RLF feature

[rabatcasa]

Hi, RLF happen then Enb detected the Radio link Failure First and asked CN to release the UE context, when the UE detects RLF it was too late, so ENB could not find the Ue context and rejected the reestablishement :
3 possible reasons :
1- the Harq Retransmssion or RLC AM parameters are not optimal ( can you list the Harq Retransmssion treshold, and RLC AM param ? )
2- RRC txxxtimers nxxx parameters for UE to trigger the Radio Link Failure are not set correctly ( can you list the Txxx,nxxx paramaters ?
3- the RLF feature is not activated in the BS :)

[BENRHOUMASALEM]

I speak about RLF handover in LTE not Radio Link failure :)