Hello Experts!
What are the possible reasons for low E-RAB success ratio if E-UTRAN has no issues?
What is the root cause? And what sub counter is higher?
And how you judge E-UTRAN have no issue?
What things you checked?
Since it is common for all eNB in the cluster.
Issue suspected in EPC.
What could be the possible issue with EPC?
One thing you can do is to enable a Radio End and Core End traces and check live scenario.
Where actually failure observed.
You have subcounters for each failure type.
Yes, like TNL, MME, Radio, other etc.
This is a nice video on LTE KPI Optimization - they talk about ERAB Setup Success Rate. Maybe it helps…
From there, a small question on ERAB Failed Establishment due to “MME”: When its caused by Radio Quality, is it due to both UL / DL or only UL ?
Answer: Usually DL failures are recorded by eNB so eNB will know that the UE has experienced an RLF and thus, it will release the context itself. But in UL, the eNB might not be aware that the UE has experienced RLF and thus, the MME tells the eNB about the RLF via context release.
So in short, failures due to MME are related to uplink issues or issues that the eNB might not be able to monitor.
Another query: How to separate bundling of RRC reconfiguration & security mode? Is it possible through parameter changes.or something need to do at MME end?
Answer: Yeah this is possible in some vendors with RAN parameter changes on eNB. However, it is not done as that increases access latency.
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Transmission issue in Hub site, External in interference.
for 2 neighbors sites with low ERAB i got strange case before, Faulty handset, after Reset that IMSI the issue resolved, and the ERAB failures was counted under MME 
There could be bad iot device or rogue UEs…Need to do IMSI check for possible bad device…