lte access fault diagnsis

8/16/2019 LTE Access Fault Diagnsis

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LTE Access Fault Diagnosis

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After UE select a suitable cell it initials attach flow including the following procedures!


"andom access

""C connection setup #""C cause! $% signaling&

NAS authentication procedure

E'"A( setup #Acti)ate default EPS bearer&

Setup dedicated bearer #%ptional onl* for some Smart UE that support +oIP&

Abo)e figure shows the detailed procedure




If UE re,uest ser)ice again while in idle status it initials -Ser)ice "e,uest procedure


/he whole procedure are )er* similar as initial attach procedure e0cept!

/he cause of ""C connection is -$% 1ata

No authentication and UE capabilit* ,uer* procedure as UE conte0t alread* e0ists

in $$E




/AU procedure is a UE idle beha)ior ensure that UE location is 2nown b* $$E. /he


scenarios of /AU can be!

UE initial attach

UE mo)e to a new /A area

Periodic /A update




/here are fi)e "A preamble formats which are used for cells of different radii. 3/E 411


supports preamble formats 5'6 and 3/E /11 supports preamble formats 5'7. /he

preamble format can be set through the PreambleFmt parameter and the cell radius can

be set through the CellRadius parameter.

4ormat 7 is a special "ACH preamble for 3/E'/11 onl*.


PreambleFormat

Length TCP TSEQ FDD Cell Radius (R) TDD Cell Radius (R)

0 1ms 103.1 µs 800 µs R ≤ 14.5km 1.4 km < R ≤ 14.5 km

1 2ms 684.4 µs 800 µs 29.5 km < R ≤ 77.3 km 29 .5km < R ≤ 77.3 km

2 2ms 203.1 µs1,600µs

14 .5km < R ≤ 29.5 km 14.5 km < R ≤ 29.5 km

3 3ms 684.4 µs1,600µs

77 .3km < R ≤ 100 km 77 .3km < R ≤ 100 km

4167.9µs

14.58 µs133.33µs

Not involved. R ≤ 1.4 km



Upon recei)ing the UE preamble the eNode( transmits an "A response o)er 13'SCH.


/he UE monitors the Ph*sical 1edicated Control Channel #P1CCH& in the /ransmission /ime

Inter)al #//I& until it obtains the re,uired "A response.

/he response contains "A'Preamble Identifier /iming Alignment Information Initial U3

8rant and /emporar* C'"N/I.

If multiple'UE send the preamble with the same "A'"N/I then eNode( detects that the

conflict occurs. /his conflict will be handled in contention resolution procedure.

A message on the 13'SCH can carr* multiple "A responses to be transmitted to multiple

use.

4or the UE 9

If the recei)ed "A'Preamble Identifier is consistent with the identifier that the UE

pre)iousl* sent the UE infers that the response is successful. /hen the UE transmits

uplin2 scheduled data.

%therwise the response fails. In this case if the number of random access

attempts is smaller than the ma0imum the UE attempts random access again.

%therwise random access fails.




With the grant the UE transmits uplin2 scheduled data o)er the U3'SCH. /his message is


scrambled b* temporar* C'"N/I. In this message UE will carr* its uni,ue I1 for contention

resolution if random access conflict.

(ased on different random access scenarios the message could be

""C connection re,uest

""C reestablishment re,uest

""C reconfiguration complete #Hando)er confirmation&

%ther user data

In case of -""C connection re,uest message UE sends its UE I1 to identif* the different

UE. /his UE I1 could be!

If UE alread* get S'/$IS from $$E then use S'/$IS as UE I1

If UE initial attach UE generate a random number according to its I$SI as UE I1

In the other case UE at least send its C'"N/I to identif* the different UE




After the UE sends message 6the contention resolution timer starts. /he UE monitors the


P1CCH before the timer e0pires. In the following situations the UE infers that the

contention resolution is successful and it notifies the upper la*er and stops the !

/he UE obtains the C'"N/I when monitoring the P1CCH.

/emporar* C'"N/I is obtained when the UE monitors the P1CCH. In addition the$AC Pac2et 1ata Unit #$AC P1U& is successfull* decoded.

If the contention resolution timer e0pires the UE infers that the contention resolution fails.

/hen the UE performs "A again if the number of "A attempts is smaller than the

ma0imum number of attempts.




Purpose of ""C connection


Setup S"(:

Send NAS message to EPC

"ele)ant counters!

A! ""C connection attempts #3.""C.Conn"e,.Att&

(! ""C connection setup successful #3.""C.Conn"e,.Succ&




After UE succeed attach to $$E $$E initial the E"A( setup procedure to setup


dedicated S: control plane for UE. At the same time the default P1N connecti)it* and EPS

bearer will also be setup. After E"A( setup there is alread* IP connecti)it* between UE

and gatewa* which is called -Alwa*s on line function.

"ele)ant counters!

A! E"A( setup attempts #3.E'"A(.InitAttEst&

(! E"A( setup successful #3.E'"A(.InitSuccEst&




/race of UE capabilit*





After S"(; setup all the NAS message on UU interface in carried b* S"(; with the


message ""C<13<IN4%</"ANS4 or ""C<U3<IN4%</"ANS4




NAS procedure is coming after ""C complete including


Attach re,uest #default&

1efault EPS bearer acti)it* #default&

1edicate EPS bearer setup #optional&

Authentication #optional&

Identification #optional&

NAS procedure is associated with E"A( setup procedure for NAS deli)er* on UU interface

NAS can be combined in common ""C message as NAS P1U or directl* transferred as

-""C<13=U3<IN4%</"ANS4 message9 on S: interface NAS can be combined in common

S:AP message as NAS P1U or directl* transferred as -S:AP<13=U3<NAS</"ANS message




/he barred cell onl* impacts on initial UE access hando)er in is not affected.





/his failure is caused b* eNode( admission failure. If PUCCH or S"S resource is limited


eNode( should stop admit all ser)ices including ""C.




"ele)ant ""C failure counter!



Counter name Description

L.RRC.SetupFail.ResFail Number of RRC connection setup failures due to

resource allocation failures

L.RRC.SetupFail.NoReply Number of RRC connection setup failures due to no

responses from the UE

L.RRC.SetupFail.Rej Number of RRC Connection Reject messages sent to

the UE in a cell



/his failure refers the fault between -Initial conte0t setup re,uest message and -Initial


conte0t setup response message. If an* step occur fault then E"A( setup procedure fails.




Scneario! the 3.E'"A(.4ailEst.No"epl* counter is incremented each time the eNode(


recei)es no responses from the UE before the corresponding timer e0pires after sending an

""C signaling message to the UE during the initial UE conte0t setup procedure or the E'

"A( setup procedure

Possible cause!

Poor 13=U3 co)erage which cause message missing.

UE internal process error




/racing message





$essage tracing



lte access fault diagnsis

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