Volte trouble-shooting-in-ericsson-lte-rtt

1. VoLTE Trouble Shooting in Ericsson LTE RTT.
Beloware some samplesof usingRTT to troubleshootVoLTEfailures.
IMSI = 311480125562721 onDate = 10/29/2014.
1) Example ofhow a GoodVoLTE call will look inE/// RTT.
For a successful VoLTEcall there isnormallyatGood DedicatedBeareranda Good Context.
The Bearer isSS=19 and isthe lengthof the VoLTE call,whichis 426.733 secondsinthe screenshot
above.
The Good ContextisfromRRC Setupto ContextReleaseand normallystartsbefore the Bearerandends
afterthe Bearer.
If the GoodContextstartsright before the VoLTEBearer,youcan use thisto guestimate if the VoLTEcall
was a TerminationorOrigination.
2) This is an example of a VoLTE LC for a short VoLTE Call with UL RF Issues.
The VoLTE Bearer isstill listedasaVGoodCall,because the MME/SGW tearsdownthe call ina normal
manner.It doesnotindicate toECDS that the Bearerwas torn downdue to an RF Failure.
That type of message isnotprovidedandiswhythe Bearerisstill listedasa VoLTE Good.
The VLC occurs at roughlyexactlythe same time the VGoodandthe VLC isthe RF recordfrom ECDS.
Hoveringoverthe ContextRelease reasonsprovide thisdetail
UE Release Cause =11 = RadioConnectionwithUELost. Internal Cause = 14 = RRC Reconfiguration
Time out.
Both these simplyindicate thatthe RFconditionwasbad.WhenI right-clickedanddida Handoff Popup,
there wasno handoff forthiscall.
Whenyoulookat the nextfewGoodContextrecords,theyare all on173.443.2 at 0.63/0.78 milesaway.

2. If I lookat the Right-ClickUEData Popupfor some of the otherGood Contextafterthe VLC,I can see Avg
CQI = 4.7 and UL PowerRestrictedat100%.
I alsosee that UL Nak%= 29.6% and UL BLER% = 31.0% and UL kbps= 27.
Thisindicatestome that the mobile Uplinkwasina bad RF condition.
The last thingto note that tendstoindicate thiswasa bad VoLTE call is thatfor the VGood Dedicated
Bearerrecords,the SGW BytesRxedinthe UL is0.
I have seeninthe past onsome one-wayaudiothatI had,that the QCI=1 Bearerrecordhad eitherUL or
DL SGW Bytes= 0. Thisis nota 100% indicatorthata one way audiooccurred,but itis a goodsanity
check.

3. 4) A single VoLTE Call with multiple VLCin it.
In the above screenshot,the VoLTE Call startsat 16:54:01.6 and endsat 17:03:04.5 as seeninrow 145
VGoodBearerrecord.
We see one VLCat 16:59:36 (row147) and anotherat 17:03:05.2 (row 141). The VLC at 17:03:05.3 is
Release UECause = 11 = RadioConnectionwithUElostand Internal Reason=6 = RLC Failure on
SignalingBearer.
To me thisindicatesthatthe VoLTECall endedwithadrop, since the VLCis at the same time of the
BearerEnd Time.
The VLC that occurs at 16:59:36 is inthe middle of the VoLTEcall.This indicatestome thatthe RF
ContextwasReleased,butdidnotcause the VoLTE Bearerto be released.
Since thisVLCwas inthe middle of the VoLTEcall,itlikelycausedsome audioholeswhile the Radio
Contextwasreleasedand re-established.
Note:The SubscriberNumberisnotpopulatedinall the ECDSrecords.If you onlyhave the Subscriber,
searchthat firstand thenre-querywiththe IMSIto make sure youhave all the records.
5) VoLTE SetupFail (VSF) example.
RTT can only capture some of the VSFcalls.Inthe case below,there is anERAB SetupFail.If we scroll to
the right to the ERAB SetupDetails,we will see thatthe setupfaileddue toResults=2 = Failure inRadio
Procedure.

4. Thisindicatesthe ESFoccurred due to Radioissues.Italsoreportsa DedicatedBearerActivationFailure
(DBAF). Ialso see thata normal CD occurs shortlyafterthe ESF.
6) VLC in the middle ofa VGoodcall.
Thisis an example of aVLCthat occurs in the middle of aVGoodCall.
Thismeansthat the VoLTE DedicatedBearerdidnotdrop,but the RF Contextdidfail inthe middle of
the call whichlikelycausedanaudiohole forthe enduser.
The VLC happenedat8:07:42 and the VGoodhappenedfrom8:07:25.3 to 8:07:54.1 whichisonlya 28
secondVoLTE call.
WhenI right-clickonthe VLC,I see that the HO resultswere FailedTx2RelocationOverallExpired.This
simplymeansthe HOtimerexpiredafter5seconds.
Since thiswasa 5 secondtimerexpire,Iwouldthinkthe userwouldhave alarge audiohole thatwould
be noticeable. Icanalsosee that the ServingRSRPwas -117 for473.544.22 at a distance of 4.71 miles.
The NeighborRSRPis -108 for 473.347.22 as seeninthe PrepOut Handoff info.
You mustlookat the timestampsonthe HOinformationtomake sure theyare the same HO. Inthis
example the PrepIn/Execute Inisfromthe previousHO.
The nextG Ctxtstarts at 8:07:43.2 andwhenyouhoveroverthe VYes,youcan see that there wasQCI=1
inthe Initial ContextSetupevent.Sothisisthe 2nd
RF record forthisVoLTE Call.That iswhy ithad VYes
init.
The VLC occurred on473.544.22 at 4.71 milesandthenthe RF restartedonthe same eNB 473.544.22 at
4.76 miles.Notsure whyitdidnot restarton eNB= 473.347.22 since itsRSRP was -108.

5. 7) Creating a Distance Histogram for all the VLC and VSF and plotting themon a map.
The Distance Histogrampage can be usedjustto lookat the VLC and VSF. Thisisdone by onlychecking
VSFand VLC whenrunningthe query.
In the screenshotbelow,I queriedthe last8 daysof VLCand VSFand itonlytook 16 secondstorun for
7885 VLC andVSF thathad Distance information.(VoLTE_Catfieldisindexed).
I thensortedbyTotal Countand foundthat 457.59.12 had the most VLC/VSFat173. I thenright-clicked
on that rowof data and chose “ShowCall LocationsonMap Pop-up”.
The Distance Histogramfor the VSF/VLCare thenplottedonthe Map Pop. You can openmultipleMap
Popupsat a time,butright-clickingona new row of data.

6. 8) Plotting where the VLC and VSFare occurring withSimple Query page.

7. Since we are still inearlystagesof VoLTE,inmost marketsyoucan querythe last8 days of all VLC and
VSFin the Simple Querypage.
Thenyou can right-clickonthe resultstable andchoose “Show Call LocationonMap Popup”.
In LTE RTT, we onlygetthe Distance measurementforone Mkt.eNB.Cell_IDanddisplaythisasanarc on
the map. The count of records at that distance is displayedintextatthe centerazimuthof the sector.
In the screenshotbelow,Izoomedintoanarea of interestonthe map and changedthe Arc Properties.I
increasedthe Thicknessto50% andkeptit as a Heat Map.

9. In contrast,I can turn off the Heat Map optionandreduce the Thicknessto10%. Thismakeseach arc
drawnat 100% transparency.
Update: The Session Status=22 were removed from the VLC formula on 1/21/2015 to match
the ELPT VLC formula.
LTE RTT Release V6.5 1/21/2015 at 8:00pm Eastern Change Control = NCC000000471189

10. 3) VLC with SessionStatus = 22 = ERAB Release withData Lost.
Thisis a newVLC introducedinE///RTT October2014 withthe upgrade to ECDS 5.4.1. This wasadded
to match the ELPT VLC formulathisit:(pmErabRelAbnormalEnbQci +pmErabRelMmeActQci )
RTT alreadymeasuredthiswiththe VoLTE CD. pmErabRelAbnormalEnbQci ="The total
numberof E-RABsreleasedabnormallypercell perQCIforrequestsinitiatedbyeNB.”
RTT hadto add SS=22 inorder to measure thispeg.
pmErabRelMmeActQci ="The total numberof active E-RABsreleasedperQCI forrequestsinitiatedby
MME, exceptactive E-RABsreleaseddue tosuccessful HO.AnE-RABisconsideredtobe active when
there are data in the DL or UL queuesforthe E-RAB.”
Howeverthere issome controversyinthe marketsthatthese are reallycustomerimpactingVoLTELost
Call.Several MarketshasusedrunIRIS traces onthese IMSI anddo not see anySIPerrors or RTP errors.
I have forwardedall thisinformationtothe Service Performance Teamfortheiranalysis.Atthispoint,
theystill wanttokeepthe pmErabRelMmeActQci inthe ELPTVLC formula,sowe will still be counting
the SS=22 as a VLC.
The good newsisthat since the SS=22 have beenaddedtoRTT, we can now lookupthese IMSIin other
toolsto furthervalidate if these were customer impactingissues.Before we were notable todothat
withjustthe peg,since itis simplyacounter.
In the screenshotabove,the SS=22 will occurat roughlythe same endtime as the G DBearer,whichis
17:27:21 inthe screenshot above.
The SS=22 VLC indicatesthatthe DedicatedBearerreleasewastriggeredbythe MME and that there
was still Datainthe queue thatwasnot sent.
The G Ctxtthat occurs shortlyafterthe VLC wasthe RF recordfor thisVoLTE call.
BottomLine:The official corporate formulaindicatesthisisaVLC.However,manyof the marketshave
provideddatato Service Performance Teamthatindicatesthese maynotbe customerimpactingdrops.