7.access failure analysis

8/12/2019 7.Access Failure Analysis

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Access Failure Analysis

lectuerauthor

ZTE corporation CDMA Network

Planning&Simulation Dept.

Mobile:

E-mail:

lectuerauthor

ZTE corporation CDMA Network

Planning&Simulation Dept.

Mobile:

E-mail:


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Course point

Understand and grasp the access attemptprocess

Understand and grasp the user originationcall process and milestone Understand and grasp the mainly causes ofthe access failure Understand and grasp the analysis methodsand troubleshooting workflow of accessprocess.


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syllabus

summarizesummarizesummarize

access attemptaccessaccess attemptattempt

origination floworigination floworigination flow

brief cause of access failurebrief cause of access failurebrief cause of access failure

cases analysis of access failurecases analysis of access failurecases analysis of access failure

troubleshooting workflowtroubleshooting workflowtroubleshooting workflow


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summarize Access is an attempt that the terminalconnect with system throuth a message

sended to BTS in the air, origination is

a important access type, including:

Mobile to LandMTOL

Land to MobileLTOM

This course only discuss the case of MTOL


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MTOL access failure definition

We define an origination as the case of a MS diala number.

MS cant complete access process in valied timewhen network have enough resource It is an accessfailure.

There are some correlative timer for originationprocess defined in IS-95 and cdma2000 protocol.Mswill give up the attempt of accessing the networkwhen it miss the message from the BTS in valiedtime.It is another type of access failure.


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access attempt 1)


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access attempt 2


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access attempt 3


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access attempt process1. MS send access probe sequence in access channel based on random

access protocol,waiting for the response from BTS.

2. If MS get BTS response in TA after sended the access probe,MS change to

next call phase;If MS cant get BTS response, Ms will increase PI power to

send access probe again after random RT frames.

3. With the up course,When Ms finish all the access probe(Num_Step,max.16)

included in access sequence,which parameters are setted in OMC,

(Max_Req_Seq and Max_Rsp_Seqindicate request access and response

access seperately,max.15),still can not receive the BTS response,so occoran access failure.


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relatived parameter with access attempt


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syllabus








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Origination flow(air interface


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Origination milestone time limit

Upward chart show the most time limit of every milestone ,system set

lost timer T40 and make it in active state all the time from access

attempt to M2 start.


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Origination process timer


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Typical access incident sequence

From detected MS Origination message to gotten Service Connection

Complete,all the access time will cost about 1.52s.


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syllabus








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Causes of access failureCauses of access failure


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M1 milestone have not been achieved reason


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M2 milestone have not been achieved


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When MS receive channel designate message,it should acquiredF-TCH(BS sent null frame).MS search null frame for T50m second,

It will give up seach if it hasnt lock channel.


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Ms wil l send preamble in R-FCH after having acquired F-FCH.after BTS

have obtained R-FCH,it wil l send response message in F-FCH.if MS

didnt received BTS response message in T51m, it wil l make reinit ialize.


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We will take the access failure as a drop call and use drop call

analysis flow When MS have not received TCH connection

message.The reason are the TCH have been set up in forward

and reverse channel at the same time,and closed loop power

control and hand off message have being in active state.

BS and MS can exchange message for traffic neogation or

only communicate for service connect message when it is in

the process of service set up.


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syllabus








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access question typeDifficult to be paged and even worse page no response;Normal attached subscriber be paged as the response:detached;Difficult to make a call even worse cant make a call;Access time too long ;Other questions.

wireless parameter question;system hardware and software question;repeater question;Router direction question;Terminal question.


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cases1 wireless parameter factorQuestion description

Many users feed back that MS cant response to any paging all the time

in the express way from location A to location B. Detail informantion: thesignal cover is ok,when the MS been paged on the express way,MSC often

clue to orignation you dial cant reach at a moment ,but after MS once

make a originate call,it can response any paging.

Question analysisBTS which is relately to the coverage of express way from location A to

location B belongs to city A,B,C,D respectively,but all BTS belongs to one BSC.

according to phenomena descript before,two detail informantion have to be

considerate first:

1good wireless circumstance in the question road;2Once user make an or iginate call,page question is inexistent;The two detail information indicate that the page question and wireless

coverage have no relation,the reason l ies in the terminal dont update its

register information in time or MSC make wrong paging group.


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cases1 wireless parameter factorQuestion analysis

Check-up wireless parameters in OMC,find all the BTS was separated 4

page area in the BSC.LAC code of area A,B,C,D are: 21072210732107421075.REG_ZONE of area A,B,C,D are: 1111.When one terminal moving from one location to another,if REG_ZONE dont

change,terminal will not update its register information in the database.when

MS is paged,swith send page message to register area and this lead to page fail.

Question deal with

REG_ZONE parameter of area A,B,C,D change to1234experience summarize

SID parameter register parameter timer access parameter frequency and authentication parameter and so on, all these wireless parameter

configuration error may lead to access question.


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cases2 system hardware and software factorQuestion description

CDMA network of city A upgrade software to new versions so as to support

more new function,but after complete versions upgrad,all the call setupsuccess rate reduce from 97 to 95.Question analysis

Through collecting the traffic stastics of all service area in OMC we find a

phenomena:all the access process getting the SVE resource from 6th shelf

failed at last,so it is the SVE fault make the call access fail.

Question deal with

Change this SVE,call setup success rate resume normal.

experience summarizeIf software and hardware of system are incomplete or have fault,It will

lead to access question.We should learn about the support capable of the

system software for the access first and if there are haredware fault before we

do troubleshooting.


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cases3 repeater factorQuestion description

sector a of BTS A have low call success rate.base on statistic data,there

are too many call attempt from 4 to 6 am,almost come from one user and all

failed.

Question analisis

From information given by operator,there is a fiber repeater in the maincoverage area of this sector, repeater get signal from other BTS.This repeater

was verified didn t work at all in the cell site.we conclude that the fault of

repeater was made by abnormal call attempt.

Low the transmit power of sector a of BTS A in OMC,make BTS B cover this

area. After half hour,the stastics indicate call success rate of BTS B descend

and BTS A became normal.


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Question deal with

Take off terminal module of this repeater,problem vanished.

experience summarize

repeater have been use in many area,but it impact network performance at a

certain extent.for example repeater module repeater work abnormal repeaterterminal module send abnormal call,all can lead to call fail.

For access question consist in repeater,we should start project from repeater.

cases3 repeater factor


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cases4 Router direction questionQuestion description

Terminal of CDMA make a call to PSTN of other city,waiting for a long timeand was informed later cant reach at a moment .probability is 50% through

long time traffic stastics.

Question analysis

Tit is verified that wireless network is normal because terminal can get the

cant reach at a moment which come from annouce board.It indicate that

problem maybe lies in gateway MSC. We make signal analysis in MSC and findcall assigned link to T1,MSC send IAI(initialization addrss indication)

message,no ACM message response from T1;no similar case happen in T2.

Conclusion:because T1 configration error,lead all calls to T1 fail.

Question deal withBlock the link of T1,and check parameter.

Experience summarizeRoute direction question can lead to a big scale of outcall failure.


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cases5 coverage questionQuestion description

An operater feed back appear many second dial question after add some

new BTS in downtown area.

Question analyse

At first we make CQT in the area heavily effected by second dial,so we get

the result:or igination call 618 times,fail 4,termination call 618 times,fail 10,total

call number is 1236,total fail number is 14, percent is 1.13%.page fail question

in these area is heavy.

Now we analyse one example about cant reach in a PN pollution area.In this

case,origination user get the information cant reach at a moment , indicate

origination user access process is normal.question lies in process of page.From the signal message can see MSC send page request through A port at

17:16:28:880,send page message through air port at 17:16:29:040.


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Terminal should received page message at 17:16:03(OMC message track and

CNT1 test clock discrepancy 26s) ,but from the debug message of CNT1,handset

make idle handoff at this t ime,from PN246 to PN249,lead to terminal not received

corresponding page message .

cases5 coverage question


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Because of page fail,MSC send the second page message at17:16:35:840:

Analyse layer 3 message by CNT1,terminal have received corresponding

the second page message at 17:16:11:704,but handset make idle handoff from

PN249 to PN78,terminal neglect page message just before,lead to page fail,

origination user hear cant reach at a moment,please dial again lateriforigination terminal make a call again,and the terminal doesnt makee idle

handoff,the termnal will respond page message and connect,this is the second

dial.



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After RF optimization,reduce PN pollution in this area, avoid terminal idle

handoff in this area,question heve been solved at a certain extent.

experience summarize

After RF optimization ,the PN pollution have been reduced,it can improve

call setup success rate and page success rate ,reduce access question.

Question deal with



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call setup success rate

1Query the alarm information in OMC,check-up if there are any alarmabout hardware;

2Confirm if sector reverse RSSI is normal,check-up if there is wirelessinterference;

3Confirm the two frequence have the same output power if the system isdouble frequence system;

4confirm if the wireless parameter configuration is right.5Analyse OMC data, varify if certain subscriber or certain hardware leadto terminal access failure.

6Contrast BTS circumstance picture in network plan phase with currentcircumstance picture,observe if wireless circumstance have change obviously;

7If these method cant f ix the problem,we do the DT and CQT ,and combineOMC data to locate the fault.


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Cant reach at a moment questionMany reason will lead terminal cant be

reached , familiar have three type:

network coverage;

idle handoff;

Performance of terminal.

Toward upwards several factor, we canuse below workflow to resolve the problem :


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Cases of terminal cant reach at a moment1Confirm the coverage: find the number of Turn on register more largerthan the number of shut down register in period of time;page response rate

should change regularly in a day.

2After check the network coverage,next step is suggested to be followthe analysis method described in previous chapter.

3

We should analysis if there are too many idle handoff exclude of theup two factor,Most cases of terminal cant reach at a moment in the good

network coverage have been lead by idle handoff.

4IF situation is as before,we can check the terminal performance. baseon many test result,some terminal make a worse performance on thecondition of not enough power.

5The last method of how to resolve the access fault is to make a CQT.


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7.access failure analysis

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