pmErabRelAbnormalEnbAct – ERAB Releases by ENB
pmErabRelAbnormalMMEAct – ERAB Releases by MME
pmErabRelAbnormalEnbActCdt - due to down time
pmErabRelAbnormalEnbActUeLost - due to UE lost
pmErabRelAbnormalEnbActHpr - due to HO prep stage
pmErabRelAbnormalEnbActHo - due to HO exe stage
pmErabRelAbnormalEnbActTnFail - due to S1, X2 down or transport unavailability
pmErabRelAbnormalEnbActPe - due to pre-emption
pmErabRelAbnormalEnbActUeLost is high? uplink issues
is the RRC connection Reestablishement feature activated ?
ICIC to spread interference activated
HO Osscilation minimisations activated
PUSCH nominal power optimised
Neighbour Cells optimization
In this optimization project, 2 parameters were tuned;
A3offset and a2TresholdRsrpPrim
-A3offset : change from 3 to 2 db
–a2TresholdRsrpPrim : change from 120 to 110 dbm
DataRadioBearer : dlMaxRetxThreshold / ulMaxRetxThreshold
8 to 32
SignalingRadioBearer
dlMaxRetxThreshold / ulMaxRetxThreshold
8 to 32
The second major KPI for LTE is the LTE ERAB Success Rate which is also part of the accessibility. After the
UE has completed the RRC Connection which has been explained in my previous article, LTE KPI
Optimization: RRC Success Rate, it needs to get a Bearer assigned to it to initiate services. The bearer can be
default (usually Data QCI9) or dedicated (VoLTE QCI1). During initial access, the default bearer is added and
that constitutes the major portion of the total ERABs.
Firstly, lets understand the definition and points where the ERAB KPI is pegged. After the UE sends the RRC
Setup Complete message to the eNB, the eNB sends a S1 Initial UE Message to the MME indicating the
purpose of the UE (Attach, TAU, CSFB, Service Request etc) and its credentials. Once the MME receives this
message and it decides that a bearer is required, it will send an Initial Context Setup Request to the eNB. This
message is considered as the ERAB Attempt as it contains the bearers to be added along with their QCI values.
The eNB receives this message and adds the DRB (Data Radio Bearer) based on the bearer profile in Initial
Context Setup Request. But before the eNB can add bearers, it needs to activate the security for the connection.
This is done by the Security Mode Command which carries the ciphering and integrity protection algorithms.
After this the eNB sends a RRC Connection Reconfiguration message to the UE which adds a DRB and it
includes the configuration for the DRB like bearer identity, PDCP & RLC configuration (AM/UM etc). SRB2 is
also added at this point with this message. The UE receives these messages and reconfigures the connection.
Then the UE responds with Security Mode complete and RRC Connection Reconfiguration Complete messages.
As the eNB receives these messages, it sends an Initial Context Setup Response to MME and this message is
Internal to Wipro
considered as the ERAB Success.
Common Failures In ERAB Setup Phase
Now let’s understand the common failures that usually cause a ERAB setup failure. Most of the times, the
ERAB setup failures can be divided into two broad categories
Ø Radio Induced ERAB Setup Failures
Ø MME Induced ERAB Setup Failures
Let’s have an in-depth look at both of them and find ways to tackle them
Radio Induced ERAB Setup Failures

Radio Link Failure
Consider a UE that receives Security Mode Command but fails to maintain radio connection afterwards. This
can happen in following two scenarios:
1. N310 consecutive out-of-sync events and T310 expiry
N310 indicates an interval of 200 consecutive PDCCH decoding failures. Simply put, if the UE fails to decode
PDCCH for 200ms, it will be considered one N310. However, from here onwards, it is a sliding window with
10ms granularity. So, if the N310 value is 2 then it means that if the UE fails to decode PDCCH for 210 ms, it
will have exceeded the configured N310 threshold. Once, N310 has been exceeded, the UE starts timer T310
and if the UE is unable to retain the connection (still unable to decode PDCCH) before T310 expires, the UE
Internal to Wipro
will initiate RRC ReEstablishment. Let’s understand with an example. Consider N310 of 11 and T310 of
500ms, then the UE will initiate RRC Connection ReEstablishment after 800 ms (N310 = (200 + (10*10)) =
300ms + T310 = 500ms).
2. Maximum RLC retransmission count exceeded
Consider that the UE receives both the Security Mode Command and the RRC Connection Reconfiguration
message. Now, it has to transmit the Security Mode Complete and RRC Connection Reconfiguration Complete
message in Uplink. However, if the eNB fails to decode these responses, it will send a NACK to the UE or the
eNB may not send anything if it completely fails to even receive these messages. The RLC layer in the UE is
configured to resend the message if the message is not acknowledged. So, the RLC layer will keep resending
until a valid acknowledgement is received. But the RLC cannot resend the same message indefinitely and it has
a upper limit of retransmissions. Once that limit is reached, the RLC will not retransmit again and the UE will
consider that the radio link is compromised. This will trigger a RRC ReEstablishment Request.
However, in both these cases, the RRC ReEstablishment Request will be rejected by the eNB since processing
this request requires to have a valid UE context at the eNB. But since the UE did not respond to Security Mode
Command, so the eNB does not consider the context to be active yet and rejects the RRC ReEstablishment
Request. At the same instance, the eNB will send Initial Context Setup Fail to MME indicating an ERAB Setup
Failure.

Optimization
Such issues can be reduced by increasing the N310 & T310 value. For instance, if the value of N310 is
increased from 2 to 6 and T310 is increased from 500ms to 1000ms, then the UE will wait longer and there is
more chance that N311 will be triggered. N311 is the In-Sync value and so it is the opposite of N310. T310
stops if N311 is triggered. If N311 is 1 then it means that UE needs 100ms of successful PDCCH decoding to
stop T310. So, there is a higher probability of triggering N311 if the value of N310 and T310 is big.
Internal to Wipro
Similarly, if the RLC retransmission count threshold is increased from 8 to 16, then the RLC will retransmit 16
times instead of 8 times which will increase the probability that the eNB might be able to decode the message
and prevent RLF.

No Response From UE
In this case, the UE receives the Security Mode Command and the RRC Connection Reconfiguration messages
in downlink but does not respond to these messages in uplink. This can result in the Inactivity Timer expiry and
the eNB will send a UE Context Release Request to the MME during ERAB setup phase which will cause the
ERAB setup failure. Let’s see why this scenario happens in live networks. Once a UE receives a downlink
message which needs a response, it will need an uplink allocation to send a response. In order to get an uplink
allocation, the UE requests the eNB by using a Scheduling Request Indicator or SRI. The UE sends a SRI based
on the SRI Configuration shared with it in the RRC Connection Setup Message. The SRI Configuration tells the
UE about the periodicity of the SRI and it determines the subframe where the UE will send the SRI. So, the
eNB will look for that UE’s SRI in that subframe only and based on that, the eNB allocates an uplink resource
to the UE by instructing the UE on the PDCCH. Now, the vendors have moved to adaptive SRI intervals which
can result in a new SRI configuration in the RRC Connection Reconfiguration message. There are UEs that do
not support this change of SRI configuration and they keep using the old SRI configuration. So, once they have
received the Security Mode Command and the RRC Connection Reconfiguration messages in downlink and
they want to respond in uplink, they will have to send a SRI first. The UE will be sending SRI according to the
old SRI Configuration shared in RRC Connection Setup message while the eNB will be looking for the UE’s
SRI in the subframe defined in SRI Configuration of RRC Connection Reconfiguration message. This will
result in a scenario where the eNB will consider that there is no response from UE and once the inactivity timer
is expired, the ERAB setup will fail.
This can also happen if the UE is in poor coverage or if the PUCCH has high interference. The UE will keep
sending SRIs in the correct location on PUCCH but the eNB might not be able to read them resulting in a
similar scenario as explained above.

Optimization
If such a scenario is observed consistently, it will be a good idea to shift from an adaptive SRI period to a fixed
SRI period. This will avoid reconfiguring the SRI periodicity and will prevent this issue.
Also, using PUCCH enhancements like IRC on PUCCH can help reduce the probability of such issues.

RLC Mode Issue
This is rarely seen in networks when a UM mode (Unacknowledged Mode of RLC) QCI is used for UEs which
do not support UM mode. A common example is the QCI7 which is a Non-GBR QCI defined for live streaming
or voice services and it usually works in UM Mode. But there are many UEs which do not support UM mode
and the eNB simply fails to add a bearer with UM mode for them. This issue can be seen from the counters as it
will show that ERAB failures on Radio interface are happening only on QCI7 or any other QCI which is set to
UM Mode.

Optimization
Simply changing the RLC mode for the QCI from UM to AM should solve this issue.

Security Mode Failure
Internal to Wipro
Another issue that is a bit rare is the Security Mode Failure issue. In this case, the UE receives the Security
Mode Command from the eNB but responds with a Security Mode Failure message. Consequently, eNB sends
Initial Context Setup Failure to the MME resulting in ERAB setup failure. This happens if the security
configuration on the eNB is not supported by the UE or sometimes it can happen if the UE cannot handle both
the Security Mode Command and the RRC Connection Reconfiguration together. In most of the cases, this turns
out to be the terminal issue.
MME Induced ERAB Setup Failures
Let’s have a look at the MME induced ERAB failures. This may come as a surprise but most of the MME
induced ERAB setup failures in commercial networks are actually caused by the radio interface and not the
MME. I know it is hard to understand but those of you who have delved themselves in RRC and S1 traces will
understand it more clearly once I explain this issue.
As explained in the section above, when the UE experiences a RLF after receiving the Security Mode
Command, it can try RRC ReEstablishment which actually tells the eNB that there was a RLF on the UE’s side.
Consider a UE experiencing a RLF before it receives the Security Mode Command. The UE can only send a
RRC ReEstablishment after security is activated but if the UE experiences a RLF before the Security Mode
Command has been received, it cannot send a RRC ReEstablishment Request.
Now, consider that the UE experiences RLF after RRC Setup Complete message and before Security Mode
Command, this UE will go to idle and retry a new RRC connection by sending another RRC Connection
Request. Let’s say that the UE sends a RRC Connection Request to another eNB (eNB2) and that eNB2 will
start processing it. The eNB2 does not know that the eNB1 already has a ERAB setup process going on for this
UE. The eNB2 will send a S1 Initial UE Message to MME for this UE and the MME will see that it already has
another ERAB setup process going on with eNB1. So, for MME to initiate the new ERAB setup process by
sending Initial Context Setup Request to eNB2, it needs to first stop the process on eNB1, as it cannot have
separate context of same UE on two different eNBs. As a result, the MME will send a UE Context Release
Command to eNB1 asking to abort the ERAB setup process. The eNB1 is trying to find the UE over the air
interface and once it receives the Context Release Command from MME, it will consider that the MME aborted
the ERAB setup and will peg it as a MME induced ERAB setup failure. eNB1 will send an Initial Context Setup
Failure to MME and the ERAB setup on eNB1 will be pegged under MME induced failure. However, this issue
was actually caused due to radio issue but the eNB1 was not able to find that out.
Internal to Wipro
This issue can also happen if the UE sends the second RRC Connection Request to the same eNB or even to the
same cell. At RRC level, the eNB does not check TMSI value and the UE is referenced by its CRNTI. So, if the
same UE sends another RRC Connection Request to the same eNB, it will allocate a new CRNTI and will
consider it a new connection. But when the eNB will send S1 Initial UE Message to MME, the MME will check
the TMSI and will send UE Context Release Command to the previous session resulting in ERAB setup failure
on the first process.
Another scenario that can cause a MME induced ERAB Setup failure is the Initial Context Setup Timer on the
MME. If that timer is set to small value and eNB is waiting for the UE to respond to Security Mode Command,
the MME will send UE Context Release Command due to timeout. This will also result in a MME induced
ERAB Setup Failure.

Optimization
There is no real optimization on the first scenario as it is purely a coverage issue and coverage enhancement by
physical or soft changes can be done to mitigate it. The second scenario can be minimized by increasing the
Initial Context Setup Timer on the MME.
In case of any queries or feedback, please drop a comment below and I would love to respond and help.
The following two tabs change content below.

Bio

Latest Posts
Ali Khalid
Internal to Wipro
5G NR | VoLTE | LTE-A | Massive MIMO | NB-IoT | NDO Network Specialist at Ericsson, Australia
Ali Khalid is a Senior LTE/VoLTE RNPO, NB-IoT and 5G Solution Architect who has successfully delivered
and led a number of projects in different regions across the globe including Pakistan, Bahrain, UAE, Qatar,
Nigeria, Turkey and Oman. He is currently working in Strategic Competence Unit (SCU), a highly experienced
global team at Ericsson, Australia. In case of any questions or feedback, please feel free to drop a comment
below or connect with him on LinkedIn.
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October 11, 2017 Ali KhalidTelecomERAB Success Rate, LTE KPI Optimization, Radio Link Failure
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104 thoughts on “KPI Optimization: LTE ERAB Success
Rate”
1.
Temesgen Ambaw says:
February 8, 2021 at 6:30 pm
Dear Ali,
Some what different, is there a possibility to know the number of blocked connections (users) due to
low RSRP (i.e. below threshold value in case of serving cell outage) in LTE network?
Here is the KPI
Block_Cov = Nblocked / Nmeasured.
where Nblocked is the number of blocked connections occurred in a cell and Nmeasured is the total
number of users that measured the cell as the strongest cell.
The Block_Cov for a certain cell is obtained by dividing the number of blocked connections due to a
lack of coverage among the total number of connections that measure that cell with the highest RSRP
value in the scenario.
Thank you.
REPLY
2.
shobhashree panda says:
January 10, 2021 at 12:24 pm
Very informative article.. Thanks for sharing..
REPLY
3.
Hakime says:
November 4, 2020 at 6:43 pm
Internal to Wipro
Great explanation. Thankyou
REPLY
4.
parthq says:
June 30, 2020 at 7:25 pm
Hi Khalid,
1.Can you give a example for Security Mode Failure?
2.What is the cause given for Context Release Command from MME ,when MME sees the two
contexts of the same UE.
BR
Partha
REPLY
1.
Ali Khalid says:
July 5, 2020 at 5:20 am
One example is that sometimes when the SMC and RRC Reconfig are bundled, some UEs fail the
SMC.
When the MME gets request from the same UE such that the context is already present, it will
release the first context. The cause code depends on MME vendor but it should not be a normal
release.
REPLY
5.
Rohit says:
May 17, 2020 at 9:04 pm
Hi Ali,
I have one doubt.
If RLF occurs before security mode command then either UE move to Idle state or it will send new
RRC Connection request to same or different EnodeB.
But If RLF occurs after SMC then it will send RRC ReEstablishment Request to EnodeB as per above
figure and Enode will reject RRC ReEstablishment because UE has not undergo Security Complete.So
my point is at what scenario EnodeB will send RRC ReEstablishment complete message to UE ?
Won’t EnodeB send RRC ReEstablishment complete before Context setup ?
Could you pl explain
REPLY
Internal to Wipro
1.
Ali Khalid says:
May 24, 2020 at 3:58 am
Under normal procedure, until SMC is completed, the eNB does not know that the context is active
so it rejects RRC Reestablishment. However, now vendors have introduced enhancements such that
is the eNB has sent SMC but have not received SMC Complete, it still allows RRC Reestablishment
assuming that the UE must have received SMC that is why it is sending Reestablishment. So, in
short, if that enhancement is available with the vendor then it is possible to have RRC
Reestablishment complete before context setup complete.
REPLY
6.
Partha says:
May 5, 2020 at 8:42 pm
Thanks a lot for your wonderful explanation Ali Khalid…….
I have few questions in mind:
In the 1st diagram above that you have mentioned (i am little confused with the message flow
sequence) :
UE ENB
security mode command
<——————————————
rrc connection reconfiguration
rrc connection reconfiguration complete
——————————————>
my question is once the ENB sends “security mode command” to ue then the UE should reply with
“security mode complete” or ENB will send both “security mode command” & “rrc connection
reconfiguration” and then UE will reply with “security mode complete” and “rrc connection
reconfiguration complete” as in the below diagram:
UE ENB
security mode command
rrc connection reconfiguration
Please tell me which should be the correct flow the 1st one or the 2nd one.
REPLY
1.
Ali Khalid says:
May 17, 2020 at 6:25 am
Internal to Wipro
Both options are available. In the beginning, the eNB used to complete Security Mode Command
process and then initiate RRC Reconfig but now there are options to carry them in parallel to reduce
access latency. So, both signaling flows are correct depending whether the original implementation
is being used or the enhanced implementation is being used.
REPLY
1.
partha says:
May 21, 2020 at 9:03 pm
Thanks a lot for the reply…..I really appreciate your neat and clean approach to make things
understand to people..
Keep it up…
REPLY
1.
Ali Khalid says:
May 24, 2020 at 3:55 am
You are welcome
REPLY
7.
Pratik says:
January 14, 2020 at 6:09 am
hi,
I think if N310 value is set to 10 or 20 in Sib 2 or reconfig corresponds to 10 or 20 subframe counts as I
have seen this in logs. That means when BLER is above 10% for all this 10 or 20 consecutive
subframe counts it will start T310 timer which is in ms. In that too it will check 1 or 2 in-sync condition
that is nothing but N311 count.
I am not sure about 200 pdcch decoding failure as you have mentioned above.
REPLY
8.
Saumyasri Panda says:
September 11, 2019 at 12:24 am
Hi,
Thanks for sharing such a clean concept on E-RAB SR. I have overall 2 doubts.
1. What is the advantage of “Adaptive SRI” settings in network
2. What is the advantage of “UM QCI” settings in network
Internal to Wipro
REPLY
1.
Ali Khalid says:
September 15, 2019 at 5:27 am
Adaptive SRI helps reduce SRI periods when load is low which can reduce overall latency and vice
versa. UM QCI is basically used for RTP/UDP services like VoLTE.
REPLY
9.
vikas says:
August 28, 2019 at 8:21 am
hI, How we can calculate E-RAB drop rate in Drive test KPI.
What are the messages need to consider for erab drop calculation.
REPLY
1.
Ali Khalid says:
September 15, 2019 at 5:30 am
Most of the tools show abnormal releases/ call drop events in DT and you may use that to calculate
drop rate.
REPLY
10.
Victor Lud says:
July 19, 2019 at 10:50 am
Ola Ali
I am having a flaws of L.E-RAB.FailEst.MME. How should I proceed to eliminate this failure?
REPLY
1.
Ali Khalid says:
July 24, 2019 at 3:53 pm
Usually, E-RAB failures due to MME are caused by uplink issues. So, check the uplink related
parameters or if the cells are overshooting that might also cause this issue.
REPLY
Internal to Wipro
11.
Farah says:
July 10, 2019 at 10:22 am
Thanks a lot brother
Statistically RF conditions seem ok, CQI and RTWP is fine no degradation in any other KPI. Meanwhile
I have asked for trace to NOC team.
You mean T310? if yes so it is set at 2000ms which is Max value. I can increase N310.
REPLY
1.
Ali Khalid says:
July 11, 2019 at 3:54 am
T310 at 2000ms is already pretty high. You can try increasing N310 or optimize the cells to improve
quality.
REPLY
12.
Farah says:
July 10, 2019 at 7:52 am
Thanks
I found only one switch “interEnbReestabSwch” and it is ON. If RRC reestablishment switch is
disabled, no rrc reestablishment attempt would have been pegged.
REPLY
1.
Ali Khalid says:
July 10, 2019 at 9:07 am
No, this one should be the switch that enables inter-eNB Reestablishments and context fetching. The
ERAB setup is not related to Inter-eNB as it is specific to the serving cell. The RRC Reestablishment
failure during ERAB setup happens because most of the vendors do not support reestablishment in
this phase (i.e. pre-context setup). So, if you do not have another switch that allows this then you will
have to work on why reestablishment is happening during ERAB setup phase and that usually comes
down to radio quality or you might be able to improve your KPI by increasing the rlf timers.
REPLY
13.
Internal to Wipro
Farah says:
July 9, 2019 at 11:21 am
Aoa,
Thank for sharing detailed information
I have a query that ERAB SR is degraded with the counter “ERAB failure due to RRC reestablishment
request” and ” RRC reconfiguration failure”. I have checked there is no rise in RLC retransmission, no
specific QCI release increase, no security mode failure, no UE context release by eNB due to inactivity.
I didn’t find any counter for T310 timer expiry as I am working on ZTE
What next should I check?
REPLY
1.
Farah says:
July 9, 2019 at 11:26 am
Furthermore no failure due to admission control
REPLY
2.
Ali Khalid says:
July 10, 2019 at 5:10 am
If the counters are showing that the failure is due to RRC Reestablishment during ERAB Setup then
it is typically a radio issue. Some vendors have enhanced switches that enabled RRC
Reestablishment during ERAB setup – check if you have that enhancement as that will resolve most
of the issue.
REPLY
14.
Saw Paul Lu says:
June 28, 2019 at 8:26 am
Dear Mr.Ali,
Could you share me a knowledge about LTE call setup success rate failure due to E-RAB.FailEst.MME
.What is the main reason for this issue and what shall I check?
REPLY
1.
Ali Khalid says:
June 28, 2019 at 12:25 pm
Consider a UE experiencing a RLF before it receives the Security Mode Command. The UE can only
send a RRC ReEstablishment after security is activated but if the UE experiences a RLF before the
Security Mode Command has been received, it cannot send a RRC ReEstablishment Request. If UE
Internal to Wipro
experiences RLF after RRC Setup Complete message and before Security Mode Command, this UE
will go to idle and retry a new RRC connection by sending another RRC Connection Request. This
will initiate a new S1 Initial UE message from eNb to MME for the same UE which will make the
MME send a UE Context release to the first ERAB attempt session resulting in ERAB Setup Failure
Due to MME.
REPLY
1.
Saw Paul Lu says:
July 12, 2019 at 10:13 am
Mr.Ali,
Thank for your knowledge sharing.
REPLY
1.
Ali Khalid says:
July 13, 2019 at 10:42 am
You are welcome
REPLY
15.
Bhuvneshwar says:
May 2, 2019 at 9:38 pm
Hi Khalid,
Please help me to find out the rca for initial erab setup failure at all new on aired sites in LTE while rrc
and s1 is ok in Ericsson L17Q2.00 VERSION
REPLY
1.
Ali Khalid says:
June 24, 2019 at 7:32 am
If you do not have any specific sub-counters that show the failures for E-RAB setup then you will
need to put a S1/RRC trace to root-cause the issue.
REPLY
16.
Internal to Wipro
Abhimanyu Tyagi says:
April 11, 2019 at 2:19 pm
Thanks for sharing..
REPLY
17.
UMAIR BAQAI says:
March 18, 2019 at 9:15 am
Great explanation! Please shed some light on below topics when you can:
1. VoLTE Optimization
2. Carrier Aggregation troubleshooting
3. Load Balancing+Inter-Layer working Strategy
REPLY
1.
Ali Khalid says:
April 5, 2019 at 1:22 pm
They are in the pipeline – stay tuned
REPLY
18.
Raghvendra says:
March 5, 2019 at 2:08 pm
Hi Khalid,
Can ypu pls share LTE MIMO in detail & throughput optimization through MIMO,that would be very
useful as MIMO is not covered anywhere in detail.
Thnx
REPLY
19.
Gowtham says:
March 1, 2019 at 10:40 am
Hi Khalid
could u please explain LTE Data Setup failure causes and counter
REPLY
Internal to Wipro
20.
Dheeraj says:
February 22, 2019 at 10:49 am
Hi ,
Well Explained .
thanks Khalid for sharing
REPLY
1.
Ali Khalid says:
February 27, 2019 at 4:18 pm
Thanks Dheeraj
REPLY
21.
Raghvendra Singh says:
February 10, 2019 at 7:20 pm
Thanks Khalid Excellent explanation. !!!
I have a case here for QCI-1 , After E-RAB Setup Request from MME, eNB Send RRC reconfiguration
to UE but after 10 ms, eNB sending E-RAB Setup Response Message to MME with Protocol ID
“ErabFailedToSetupListBearersUres (29) “and Failure Cause ” Failure-In-Radio-Interface-Procedure
(26)”.
I am unable to find reason that why eNB did not wait for RRC Reconfiguration Complete message
before sending E-RAB Setup Message Response.
RRC reconfiguration time is 8 Sec.
We are using variable SRI in our N/W, with UM.
I am unable to upload snapshot here, So writing timings of messages.
E-RAB Setup Request (MME-eNB)— RRC Reconfiguration (eNB-UE)–> (3 ms)
RRC Reconfiguration (eNB-UE) — E-RAB Setup Response (eNB-MME)–> (2 ms)
E-RAB Setup Response (eNB-MME)– UE Context Release Command (eNB-MME)- (0.3 ms).
Based on Trace This decision is totally taken by eNB here.
Suggest if you have any Idea over it.
Thanks
REPLY
Internal to Wipro
1.
Ali Khalid says:
February 27, 2019 at 4:28 pm
No I have not seen this issue so far. But since, the eNB is responding after a fixed time to MME
without waiting for the RRC Recfg from the UE so yeah you are right the issue is at the eNB. Can
you check if there is any license or resource limitation? Do share your findings!
REPLY
22.
Ahmad says:
January 10, 2019 at 12:46 pm
Hi sir
Please we have zero E-RAB attempt afew cells , what reason for that
Thank you for you effort dear
REPLY
1.
Ali Khalid says:
January 15, 2019 at 9:44 am
Check if you have zero RRC and S1 attempts as well. If you have attempts at RRC and S1 (lots of
attempts) and no ERAB attempts then verify if it is a TAC problem (if the cells have different TACs).
If you have no RRC attempts as well then better check it for sleeping cell.
REPLY
23.
SaHar says:
January 7, 2019 at 7:07 am
Dear Khalid,
Thanks a lot for this useful knowledge sharing. I also face one issue in our network about ERAB EST
degradation on one or 2 cells of different sites for a duration of time. I asked our customer to do trace
and for some cases they didn’t confirm that issue is related to UE behavior. N310 and T310 are set on
their max value in our network and i have increased upper limit of UL re-transmissions on site. Yet,
issue is not recovered and as previously site was working with same settings (even lower limit of retransmissions) and KPI was perfect I doubt issue can be due to this. Do you have any idea about this
issue and what should I do as an optimizer?
REPLY
1.
Ali Khalid says:
Internal to Wipro
January 15, 2019 at 9:54 am
Without a trace analysis, it is difficult to root-cause the issue. You will need to check whether it was a
radio drop during ERAB or a MME induced ERAB failure which can also be due to radio issue. Use
the call flows explained in the article as a guide for trace analysis.
REPLY
24.
SUNDRESH PREMIL says:
June 13, 2018 at 10:59 am
Hi All,
I am looking for the E-RAB Successful Attach time (Secs or Mins) KPI for Huawei LTE. What will be the
Counter for this in Huawei PRS or U2000 Performance Query
Thanks
REPLY
1.
Ali Khalid says:
July 28, 2018 at 8:49 am
The counter exists under ERAB in M2000
REPLY
25.
Im says:
June 10, 2018 at 11:49 am
When are you going start VOLTE KPI optimization here
REPLY
1.
Ali Khalid says:
July 28, 2018 at 8:50 am
VoLTE is definitely on the cards. Soon.
REPLY
1.
Ankit says:
May 24, 2020 at 5:52 pm
Internal to Wipro
Waiting eagerly for the VoLTE Optimization
REPLY
1.
Ali Khalid says:
June 28, 2020 at 12:30 pm
Coming soon
REPLY
26.
vijay varma says:
April 15, 2018 at 8:57 pm
So, if the N310 value is 2 then it means that if the UE fails to decode PDCCH for 210 ms, it will have
exceeded the configured N310 threshold. Once, N310 has been exceeded, the UE starts timer T310
and if the UE is unable to retain the connection (still unable to decode PDCCH) before T310 expires,
the UE will initiate RRC ReEstablishment. Let’s understand with an example. Consider N310 of 10 and
T310 of 500ms, then the UE will initiate RRC Connection ReEstablishment after 800 ms (N310 = (200
+ (10*10)) = 300ms + T310 = 500ms).
In above example if we took N310 as 10 than as per calculation it should be like
N310=200+(9*10)=290ms
My calculation is right?
REPLY
1.
Ali Khalid says:
April 24, 2018 at 8:07 pm
Yeah, your calculation is correct
REPLY
27.
Kranthi says:
April 14, 2018 at 3:57 pm
Dear Bro,
Excellent sharing & very clean and in details about the KPI & love the detail explanation regarding
MME induced fails because of Radio issues
REPLY
Internal to Wipro
28.
Suraj says:
March 31, 2018 at 10:32 am
HI Khalid,
Have u seen any cell that is having high Erab failures bur RRC and S1 is ok
What could be the reason for this?
Thanks
REPLY
1.
Ali Khalid says:
April 1, 2018 at 2:36 pm
Yeah it is possible. For instance, a case of RNL failure due to RLC mode issue or SMC problem can
cause this.
REPLY
1.
Akhilesh Kumar Pandey says:
April 17, 2018 at 10:11 pm
How can we fixed this issue ,which parameter needs to be tune in ERicsson system for such
issue?
REPLY
29.
Abhijeet says:
February 27, 2018 at 1:50 pm
Dear Khalid,
I am facing one issue in our network, few sites in LTE initial erab setup success is poor,the problem is
that failure is just in one cell and other two cells is 100%, what could be the possible reason for this.
Regards
Abhijeet
REPLY
1.
arslan says:
March 14, 2018 at 6:09 pm
Internal to Wipro
which type of rab failure you are observing???
REPLY
30.
Munzir Khalil says:
February 2, 2018 at 3:54 pm
“However, in both these cases, the RRC ReEstablishment Request will be rejected by the eNB since
processing this request requires to have a valid UE context at the eNB. But since the UE did not
respond to Security Mode Command, so the eNB does not consider the context to be active yet and
rejects the RRC ReEstablishment Request. At the same instance, the eNB will send Initial Context
Setup Fail to MME indicating an ERAB Setup Failure.”
“As explained in the section above, when the UE experiences a RLF after receiving the Security Mode
Command, it can try RRC ReEstablishment which actually tells the eNB that there was a RLF on the
UE’s side. Consider a UE experiencing a RLF before it receives the Security Mode Command. The UE
can only send a RRC ReEstablishment after security is activated but if the UE experiences a RLF
before the Security Mode Command has been received, it cannot send a RRC ReEstablishment
Request.”
In first paragraph you said that UE will send RRC Re-establishment request but it will be rejected and
in 2nd paragraph you said that it is unable to send RRC Re-establishment request
Can you clear this confusion
REPLY
1.
Ali Khalid says:
February 4, 2018 at 8:58 am
The difference is the stage at which the RLF occurs. If the RLC occurs before the UE gets the SMC,
then there will be no RRC ReEstablishment but if the RLF occurs after the UE gets the SMC, then
the UE will send a RRC ReEstablishment.
REPLY
31.
Im says:
January 23, 2018 at 9:55 am
RACH optimization KpIS please
REPLY
32.
Neha Sharma says:
January 16, 2018 at 7:54 pm
Internal to Wipro
Very Well Explained…
REPLY
1.
Ali Khalid says:
January 17, 2018 at 11:03 am
Thanks Neha
REPLY
33.
Sufyan Ali says:
November 29, 2017 at 10:09 pm
Excellent Ali bhai … keep posting the good ideas about optimization.
REPLY
34.
Umer Aftab says:
November 19, 2017 at 8:48 pm
Excellent stuff Ali .. Keep rocking.
REPLY
1.
Ali Khalid says:
November 22, 2017 at 11:46 am
Thanks Umer
REPLY
35.
shashi says:
November 12, 2017 at 5:11 am
Good sharing..
Can we discuss on topics for call muting & how can we overcome it. Thanks
REPLY
Internal to Wipro
1.
Ali Khalid says:
November 16, 2017 at 7:42 am
I will explain that in the VoLTE sessions
REPLY
36.
WAJID ALI SHAH says:
November 4, 2017 at 4:11 am
Excellent.
REPLY
37.
dhayanithi says:
November 2, 2017 at 8:10 am
In general at S1AP the ERAB setup can fail if the corresponding QCI is not supported at eNB as eNB is
developed to support only certain QCI only or due to QoS IE parameter encode issue or due to ERAB
ID clash issue, or Even as part of the RRM RBC the setup can fail due to restriction in QCI support
(resource crunch), but I strongly feel the mode failure is not an issue. The QCI is decided based on
service flow between the AF and the UE at application interface level and eNB decides the Mode.
RRC level – The bearer setup happens using RRC Reconfig and the UE uses the config send by eNB
RRC. The UE RRC uses the eNB RRC config to set up it’s corresponding layer. The UE RRC can
report config failure only due to ASN violation, Mandatory field missing or it can even initiate Reestablishment. There is no way for UE to report mode not supported.
Do you say even the QCI 1, QCI 2 all can be configured to AM mode instead of UM. If so then we end
up more jitter and more delay in voice packet which is not agreed for these service.
REPLY
1.
Ali Khalid says:
November 2, 2017 at 10:39 am
For the Mode issue, I have seen it in three networks. It was verified from the UE’s capability that it
does not support UM mode and then from the CHR as well that it is rejected due to the mode
support. So, I have no doubt on the issue itself.
Coming to the second thing about QCI1 – ofcourse it needs UM. The idea is not that we need to
change mode to AM but if QCI-7 is being used then enabling this enhancement resolves the ERAB
failures due to this issue. It is not applicable to QCI1 as that is only used in the network for VoLTE
and UEs supporting VoLTE also support UM.
Internal to Wipro
REPLY
1.
Orial says:
November 13, 2017 at 10:15 pm
You are right about this case, I also encounter the same issue on my network specially with
roaming users that mostly used QCI7 for some services and normally the eNb cfg will reject them.
Going in CHR analyze for this type of error will tell the same exact reason, and also the bit 7 in the
FGI will show 0. So phones that don’t support Volte and are LTE mostly have QCI 7 configured for
UM only mode. We cannot change the phone cfg but a work around is map QCI7 with AM and you
are set to go. And yes MME can solve this issue easily :).
Nice explanation keep up the good work.
REPLY
1.
Ali Khalid says:
November 16, 2017 at 7:40 am
Thanks Orial
REPLY
38.
dhayanithi says:
October 31, 2017 at 7:46 am
Hi Khalid,
Regarding RLC Mode issue you had suggested to go for AM instead of UM. It is costly as more
resource is consumed for AM mode than UM. The UE mode configuration is driven by eNB RRC . So
for sure the UE ERAB failure is not due to Mode support issue at UE side.
REPLY
1.
Ali Khalid says:
November 1, 2017 at 6:12 am
It is costly, that is why vendors have introduced enhancements on the RLC layer. If these
enhancements are activated, the eNB changes the RLC mode to AM for the UEs that do not support
a UM mode for their bearer. Coming to the second point – the QCI is sent by the core and if the core
sends a QCI to the eNB that requires a UM mode, the eNB will reject it since the the UE does not
support UM mode and consequently, the ERAB setup will fail.
REPLY
Internal to Wipro
39.
Vijyant says:
October 21, 2017 at 10:45 pm
Good one Khalid bhai…keep rockin
REPLY
1.
Ali Khalid says:
November 1, 2017 at 6:15 am
Thanks Vijyant
REPLY
40.
Keshav says:
October 19, 2017 at 9:02 am
Very nice explained.. RCA & Optimization
REPLY
1.
Ali Khalid says:
October 21, 2017 at 2:28 pm
Thanks for the support
REPLY
41.
Col O P Aurora says:
October 17, 2017 at 5:16 am
Thanks for such a useful & informative article
REPLY
1.
Ali Khalid says:
October 21, 2017 at 2:28 pm
Thanks
Internal to Wipro
REPLY
42.
Puspendu Chatterjee says:
October 16, 2017 at 6:38 pm
Excellent Content , Can you please share the optimisation plan for ‘E-RAB Drops due to UE lost’ cases
…..
REPLY
1.
Ali Khalid says:
October 16, 2017 at 7:02 pm
Thanks. The Drop Rate KPI is definitely going to be there. You can subscribe for the updates
REPLY
43.
Abu Yousef ElMasry says:
October 15, 2017 at 10:30 am
Salam Ali,
Thanks for this great & simple topic about ERAB.
Would you please clarify the L.E-RAB.FailEst.RNL & L.E-RAB.FailEst.RNL.other counters under
Huawei KPI’s,
and which of the above reasons will be counted for the L.E-RAB.FailEst.RNL.other counter?
REPLY
1.
Ali Khalid says:
October 16, 2017 at 6:58 pm
All Radio failures are covered under RNL while UE capability type issues are covered under other
failures.
REPLY
2.
Homa says:
August 25, 2019 at 9:55 am
Internal to Wipro
Hi Ali,
Could you please explain Drop-RNL-EPC & Drop User Perspective & CGI Offset?
These are the E-RAB Drop causes.
Of cpurse I’m not sure bout CGI Offset.
Thanks,
REPLY
44.
Abhi says:
October 11, 2017 at 10:20 pm
Hi Ali,
Can you please tell me where i can find Initial Context Setup Timer value on H*****i system
REPLY
1.
Ali Khalid says:
October 12, 2017 at 5:55 am
This timer is on the MME as the MME sends the Initial Context Setup Request and the eNB needs to
respond to it. So, the timer value can be checked with MME guys. However, if you put a trace on a
top site, you can parse the ERAB Setup Failures and look into the MME induced ERAB failures. Now
if you calculate the time delta between Initial Context Setup Request and UE Context Release
Command, there will be a value that will be higher than others. The timer induced setup failures will
have a the same time value but other type of failures will be random. This should give you an idea of
the timer settings on the MME.
Internal to Wipro