Reasons for ERAB_REL_S1_OUTAGE

Hi Gents,

Can anyone support to know the reasons for ERAB_REL_S1_OUTAGE counter M8006C313?

LTE Nokia


I would say that if S1 is broken during call then this counter would be incremented.

Please check TNL counters too for U-plane and C-plane of S1.

We have noticed this KPI degradation on cell levels.

The cell that are having high traffic, although there is not packet losses on Transmission NW.

MTU size is in TX NW is limited to 1410.

Do you have fiber for those cells or microwave?


First Hope is MW and then is MPLS.

And you say there is no limitation of bandwidth on transmission for those cells?

Let’s say for a enodeB with 3 sectors and 2 layers (so a total of 6 cells) how much MW bandwidth you have on MW?

Yes if the MW is congested then there should be packet losses.

We have 3 Cells for LTE and 3 for 2G under same Node.

One Giga.

But there is also admission control in MW: i.e. the eNodeB does not even attempt to transmit if S1 is congested.

So you would not see packet loss, just that the RAB is dropped due to S1 outage.

Usually this should happen just for non GBR bearers.

You can check MW utilization or RSL check (quality check).

Do you see flat line on transmission counters for throughput for entire site?

This is stable and as per link budget.

I have found only one counter related to TX like M8035C5 SCTP_S1_UNVLDUR triggered for one MME out of 5MME.

But this MME is pingable from eNB to MME without only losses with packet size 1410.

We have one clue that this MME is not ping-able with MTU-1500.

We have reduced MTU size in eNB to match with TX MTU but problem is not solved.

Do we have any parameters that can be changed to cope the issue?

Is this issue with one site only or more?

Yes, i think @RFSpecialist is correct, it’s cause of S1 outage.

You can check also when it start to happen, if when only happen at high traffic only, then there are transmission limitation there.

Multiple sites at random but all the time our observation is same.

Errors increment is relating with traffic.

Do we have any parameter to limit packet size from eNB?

We have deleted MME from eNB ans issue solved but we can remove this MME permanently.

I can’t answer this question. May be there are RAN expert here can help.

But my friend in RAN expert tell me about this parameter long time ago to optim transmission load.

  • boostGuardTime
  • dlMaxBoostBytes
  • dlMinBoostBytes
  • minTcpPacketSize
  • timeBetweenTcpPackets
  • timeNextBoostingRound
  • ulMaxBoostBytes
  • ulMinBoostBytes

But I don’t know exactly how he is doing the optimization in Transmission.

These are cell level parameters and already set as default values.

Update: Problem solved after fixing all all X2 links.

RCA is still unknown.

Was X2 Issue? Very interesting…

Some of X2 links for down that are fixed.

Immediate after errors became 0 but still it’s not clear the reason why issue solved.

Logically X2 should not relate with S1.

You need to find this RCA, dear.

It’s very interesting issue, seriously…

:pray::pray::pray: could happen somewhere else.