omf000405 case analysis congestion training 20031001 a 1.4

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OMF000405 Case StudyOMF000405 Case Study

-Congestion ISSUE1.4-Congestion ISSUE1.4

Wireless Training Department



TCH congestion

SDCCH congestion

Course Contents



TCH congestion

TCH congestion

Basic principle

Causes for high TCH congestion

Case study of TCH congestion



TCH congestion

Basic principle of TCH congestion

Definition of TCH congestion rate

Measurement point for TCH congestion and analysis



TCH congestion

Definition of TCH congestion rate

TCH congestion rate (excluding handover)

=(TCH seizure failures for call TCH seizure failures for very

early assignment) ! ("ttempted TCH seizures "ttempted TCH

seizures for very early assignment) #$%%&



TCH congestion

Definition of TCH Congestion rate

TCH congestion rate (including handover)

=(TCH seizure failures for call TCH seizure failures for very

early assignment TCH seizure failures for intra B'C incoming

cell handover (no radio resource) TCH seizure failures for inter

B'C incoming cell handover (no radio resource) ) ! ("ttempted

TCH seizures (all) "ttempted TCH seizures for very early

assignment "ttempted TCH seizures for intra B'C incoming

cell handover "ttempted TCH seizures for inter B'C incoming

cell handover)



TCH congestion

T r af f i cM e a s ur em en t

P oi n t of

T r af f i cM e a s ur em en t

P oi n t of

T C H C on g

e s t i onr a t e

T C H C on g

e s t i onr a t e

Channel"ctive

Channel"ctive"c

*MM+D*"T+ "''*,- C.MM"-D

BT' B'C M'CM'

Channel/e0

first '"BM+sta1lish*-D( CM 'ervice /e0)

C/(Completel2information)

CC

'etup

Call 3roceeding

"ssignment/e0

"''*,-M+-T C.MM"-D

first '"BM +sta1lish*-D

"''*,-M+-T CM3 "ssignmentCM3

"lerting

Connect

Connect "c

Communication

Disconnect

/elease

/elease Complete

ClearCMD

ClearCM3

CM 'ervice "ccepted

Channel"ctive

Channel"ctive"c

4"

'DCCH

'DCCH

'"CCH(TCH)

'"CCH(TCH)

M' call flo5 as the caller



TCH congestion

"ttempted TCH seizures measurement point

"ttempted TCH seizures for call

/eceive the M'C assignment re0uest message

"ttempted TCH seizures for very early assignment

6hen there is no resource for 'DCCH allocation and very early

assignment is permitted

6hen channel re0uired is received and channel type is TCH

"ttempted TCH seizures for intraB'C incoming cell handover

6hen intraB'C incoming cell handover re0uest message is

received (non7'DCCH handover re0uest)8

"ttempted TCH seizures for interB'C incoming cell handover

6hen interB'C incoming handover re0uest message is received

(handover type is non7'DCCH)



TCH seizure failures9

TCH seizure failures for call:

TCH seizure failures for very early assignment:

TCH seizure failures for interB'C incoming cell handover:

TCH seizure failures for intraB'C incoming cell handover:

TCH seizure failures for intracell handover8

TCH congestion



TCH seizure failures for call measurement point9

($)C.--;"*< message is received in process of assignment8

()C<+"/CMD is received in process of outgoing B'C

handover8 The cause of handover is direct retry8

(2)C<+"/CMD is received in process of assignment

(>)//"B./T/+? is received in process of outgoing B'C

handover and the cause of handover is direct retry8

(@)//"B./T/+? is received in process of assignment8 (A)M',H./+?/+ is received in process of outgoing B'C

handover (direct retry)8

TCH congestion



TCH seizure failures for call measurement point9

() H.;"*< is received in outgoing B'C handover (direct retry)

() +//*-D is received in process of assignment8

(E) 6hen assignment failure message is sent8

($%)T-T (direct retry) timeout (outgoing B'C handover

re0uest)

($$)T-T (direct retry) timeout (outgoing B'C handover

complete)

TCH congestion



TCH seizure failures for very early assignment measurement

point9

($)CH"CT-"CF is received in the very early TCH assignment

process8 (CH"CT-"CF is received in 6"*T//+'T status in

satellite transmission BT')

()*n very early TCH assignment process: the returned cause is

(internal error) CG**-T+/-"<+// 5hen channel is 1eing

allocated8

(2)*n very early TCH assignment process: the returned cause is

(channel re0uest illegal) CG*-."CC+3T 5hen channel is 1eing

allocated8

(>)*n very early TCH assignment process: no channel is allocated8

(@)T-6"*TCH"CT timeout in very early TCH assignment

process8

TCH congestion



TCH congestion

TCH seizure failures for intraB'C incoming cell handover

measurement point9

TCH channel allocation fails at intraB'C incoming cell handover

TCH seizure failure for interB'C incoming cell handovermeasurement point9

6hen interB'C incoming cell handover failure message is sent

1ecause there is no TCH channel



TCH congestion

TCH seizure failure for intracell handover measurement point9

*n the ne5 TCH activation procedure: this item is measured

5hen the serving cell receives the CH"--+< "CT*G"T*.-

-+,"T*G+ "CF-.6<+D,+ message from the BT'8

This item is measured if the implementation of intracell handoverprocedure fails 1ecause the encryption algorithm in *ntracell

Handover /e0uest message does not support8

-o response after the timer (internal timer: @ seconds) timeout

5hen the serving cell activates the ne5 TCH8 *n intracell handover procedure: 6hen TCH re0uested 1ut there

is no TCH availa1le in the serving cell: and this leads to the

handover failure8 *n this case: this item is measured8



TCH seizure failures due to "7interface failures measurement

point9

" interface

"fter M'C sends "ssignment/e0: if trun circuit at "7interface is

fault: B'C 5ill return "ssignment;ailure directly8

*n this case: the usually cause is incorrect C*C data configuration of

trun circuit8

TCH congestion



TCH seizure failures due to "1is interface and 4m interface

failures

"1is interface and 4m interface

$8 T/ 1oard is faulty or performance unsta1le

8 4n1alance of uplin!do5nlin level for BT'

28 3oor 0uality of uplin!do5nlin signal caused 1y interference

>8 'DCCH and TCH 1elong to different T/ 1oard 5hich have

different coverage8

TCH congestion



Causes for high TCH congestion

Troubleshooting for high TCH congestion

Causes for High TCH Congestion



Causes for High TCH Congestion

Causes of high TCH congestion rate

*ncorrect configuration of trun circuit data at " interface

Co7fre0uency and co7B'*C lead to TCH assignment failure in handover

Board fault or unsta1le performance causes the high congestion rate

BT' hard5are is not properly installed: 5hich causes uplin!do5nlin

signal level un1alance and TCH congestion8

The transmitting po5er of BCCH T/ is too much higher than that of

TCH T/ in the same cell8

*nterference causes the congestion TCH assignment failure due to isolated site and complicated topography

result in the high congestion rate



TCH Congestion

Ho5 to locate the causes of high TCH congestion rate

"nalyze the causes of congestion remotely

$8 Traffic statistics

8 "larm information

28 BT' remote maintenance on .MC

>8 "1is interface message analysis

Chec BT' on7site



TCH Congestion

/emote analysis $9 traffic statistics

*n ITCH Measurement ;unctionJ: chec the channels are all

1usy or not

*f yes: perform load handover or suggest capacity expansion8

*f not: chec interference 1ands $K@8 if the cause is interference:

the call drop rate of the cell 5ill also 1e high8

/egister I/eceiving <evel Measurement ;unctionJ

$8 Chec the result 1y o1Lect to see 5hether the num1ers of uplin

and do5nlin reports on the same T/ 1oard are 1alanced8 'o 5e

can no5 the uplin and do5nlin are 1alanced or not8

8 Chec the result 1y time to see 5hether T/ measurement

reports are excessive8 'o 5e can no5 the congestion is related to

T/ 1oard or not 8



/emote analysis 9 alarm information

Chec alarms of the site 5hich has high congestion rate8

Chec 5hether there is any a1normal alarm: such as voltage

standing 5ave rate alarm: 3CM out of frame alarm and uplin

data 1us alarm8 udge 5hether the congestion rate is associated

5ith alarms in traffic statistics 8

TCH Congestion



/emote analysis 29 BT' remote maintenance on .MC

.n the BT' remote maintenance console: 1loc TCH 1oard in

turn8 .1serve 5hether the congestion rate is related to the T/

1oard8

TCH Congestion



/emote analysis >9 "1is interface message analysis8

Trace "1is interface message of the congested BT': analyze

"ssignment CMD sent on 'DCCH

*f the assignment al5ays fails on a specific T/ 1oard: the cause

may 1e one of the follo5ing9

T/ 1oard faulty or performance unsta1le8

4plin!do5nlin un1alance: hard5are pro1lem in uplin or do5nlin8

Bad 0uality of uplin or do5nlin signal8 "nalyze T" value of M' to

locate interference8

*f the assignment fails on the 1oards of the 5hole cell randomly:

analyze the measurement reports8 The causes may 1e the

follo5ing9

The topography in the cell coverage is 0uite complicated8

There is interference in the 5hole cell: such as interference fromrepeater8

TCH Congestion



TCH Congestion



Chec BT' on7site

Chec antenna and feeder for any pro1lem of uplin or do5nlin8

Dial test at the same place to see 5hether the assignment

failure al5ays occurs in a certain T/ or in the cell randomly8

Mae driving test to see 5hether there is a1normal handover

relationship and do5nlin interference: so as to find the cause of

the congestion rate8

'earch the interference source 5ith a spectrum analyzer8

.1serve 5hether the topography in the cell coverage is

complex8

TCH Congestion



Case Study of TCH Congestion

Cases of TCH congestion Case $9 " interface data configuration mistae

Case 9 T/ 1oard fault

Case 29 4plin hard5are pro1lem

Case >9 Do5nlin hard5are pro1lem

Case @9 +ffect from repeater in the cell

Case A9 .ther data configuration mistae

Case 9 *solated site and complicated topography



Case $ fault description 9

There is one B'C in the local net5or8 ;rom one day: TCH

congestion rate (excluding handover) of the 5hole net5or

increase to >&: and most of cells are highly congested8

A-interface Data Configuration Mistake



Case $ analysis9

'ince the fre0uency had not 1een changed: 4m interface

pro1lem is excluded8

Congestion rate is a1normal for most BT'8 *n this case: 5e can

search in a smaller range to see 5hether the congestion

pro1lem is related to a certain module or data modification8

"nalyze the main cause of TCH seizure failure through traffic

statistic and finally locate the pro1lem caused 1y data or

hard5are8

A-interface Data Configuration Mistake



Case $ Trou1leshooting9

$8"nalyze traffic statistics8 The pro1lem occurs after B'C data

modified and reloaded8 May1e it is related to B'C reloading8

"nalyze traffic statistics and find that the highly congested cells are

all on module $ of B'C: so the pro1lem should related to module $8

Chec TCH seizure failures (re0uested terrestrial resource

unavaila1le): *t sho5s that unavaila1ility of terrestrial resource is the

main cause of high congestion rate in module $8

The cause of terrestrial resources unavaila1ility is mainly on "1isinterface or " interface8 *t is 0uite unliely that "1is interface is faulty

for many cells in module $ at the same time8 Therefore: the cause

should 1e the hard5are or data at " interface8




Case $ Trou1leshooting9

8Chec the hard5are of " interface and find that the hard5are

is normal8 " interface hard5are pro1lem is excluded8

28 Chec the data configuration of " interface trun circuit and

find that the C*C code of the first 2 timeslots of group %: module

$ is IA@@2@J8 But group % of module $ in the trun group ta1le

corresponds to the circuit from B'C to M'C8 .1viously this C*C

num1er is 5rong8 Change it to I%K2$J: and then the congestion

rate 1ecomes normal8




Case $ conclusion9

$8 *n trun circuit data configuration at " interface: C*C must 1e

correct: other5ise: TCH assignment 5ill fail and the congestion

rate 5ill 1e high8

8 *n the meantime: if the C*C of t5o ;TC 1oards (multiple trun

circuits) are the same: this pro1lem 5ill also happen8




Case fault description 9

The configuration of a BT' is 'A!>! and it had 1een on service

successfully8 .ne day: the result of traffic statistics sho5s that

TCH channel in cell $ (A T/) congestion rate comes to %&8

The traffic volume of the cell is very lo5: it is a1out %8+rl in 1usy

hour8

"t the same time: the times of ITCH seizure failures for call (no

radio resource)J is %8

.1serve the channel status in cell $: all of channels are I*dleJ8

TRX Board Fault



TRX Board Fault

Case analysis9

$8 -o data has 1een adLusted and there is no hopping in the cell

and A T/s use different fre0uencies: it is unliely that they are

su1Lect to external interference at the same time8 Therefore: it

can not 1e 4m interface interference or data pro1lem8

8 Chec hard5are specifically8 'ince the pro1lem only occurs

to cell $: 5e can 1loc T/ one 1y one to determine 5hich T/

causes the assignment failure8

28;ind 5hether there is hard5are fault in the T/ for

assignment failure8 Confirm the fault T/ 1y means of resetting

and replacing8



TRX Board Fault

Case trou1leshooting9

$8 Chec BT channel status on .MC and find that there is

possi1ility of TCH seizure failure in BT> of cell $8

8 Bloc T/>: there is no TCH congestion all the day8 *t

indicate pro1lem is on T/>8

28 4n1loc T/> and reset them: congestion appear again8

>8 ,o to BT' site and mae a dial test on T/>: TCH seizure

failure still occurs8 *nterchange the slots of T/> and T/@:

mae the dial test again on T/@8 The TCH seizure failure

persists8

@8 /eplace T/> and mae dial test: there is no TCH

congestion8



TRX Board Fault

Case conclusion9

$8;aulty TCH T/ 1oard causes TCH seizure failures and high

congestion rate8

8 4sually: the fault of T/ 1oard can not 1e found on the BT'

maintenance console8 The pro1lem can 1e confirmed 1y

1locing T/s in turn8



Case 2 fault description9

" certain BT' configuration is 'A!A!A: the congestion rate of the

2 cells are all high since the BT' on service8 Having checed

and confirmed that there is no interference8

Ulink Hard!are "ro#le$



Case 2 analysis9

There is no interference 1ut congestion al5ays exists after the

BT' on service in every cell8 Chec hard5are of the BT' first8

Hard5are fault9 communication is normal for every cell: so it is

unliely that there is fault in the hard5are of every cell8

Hard5are connection9 "nalyze the traffic statistics for uplin or

do5nlin and then chec the hard5are connection of uplin or

do5nlin8




Case 2 trou1leshooting9

/egister traffic statistics I/eceiving <evel Measurement

;unctionJ and 0uery the result 1y time8 *t is found that 5hen the

receiving level and 0uality of different T/ 1oards in the same

cell are the same: the num1er of do5nlin measurement reports

is e0uivalent: 1ut the num1er of uplin measurement reports is

not e0uivalent8

Chec hard5are and find that the connection of T/ and CD4

in the same cell is incorrect8 "fter correction: the pro1lem is

solved8




Case 3Case 3

14258222

16646294

293105655

501

303

702

Times of uplink

receiving level

rank 0 and

receiving

quality rank 0

Times of uplink

receiving level

rank 0 and

receiving quality

rank 1

Times of Uplink

receiving level rank

0 and receiving

quality rank 2

30 minutes starting from

11:00 18-3-2001

Module ! 1" #ell ! $"

T%& 'o( 12


T%& 'o( 13


T%& 'o( 1)


T%& 'o( 1$


T%& 'o( 1*


T%& 'o( 1+




Case 2 conclusion9

*ncorrect hard5are connection 5ill cause TCH seizure failure8

The pro1lem can 1e located accurately 1y analyzing traffic

statistics8 *n this case: uplin hard5are receiver pro1lem is

located through I/eceiving <evel Measurement ;unctionJ8




Case > analysis9

There is no parameter adLustment 1efore the fault: so 5e should

focus on the hard5are: to see 5hether there is any fault or alarm8

Do!nlink Hard!are "ro#le$



Case > trou1leshooting9

Trace "1is interface message of the BT' and analyze the

signaling and find that in process of TCH seizure failure: the

uplin signal in the measurement report from M' is good: after

B'C sends "''*,-M+-T CMD: the do5nlin channel can not

1e seized8 'o the signal levels of uplin and do5nlin are not

1alanced: then "''* ;"*<4/+ message is appeared8 *t is also

found that the failure related to the last T/ 1oard of the cell8

Bloc T/ 1oard and congestion rate of the cell is less than $&8

There is pro1lem in T/ 1oard of do5nlin hard5are8

Chec and find that the G'6/ of T antenna and feeder

connected 5ith this T/ 1oard is higher than 8@8 3rocess the

antennaN feeder G'6/ alarm: pro1lem solved8




Case > conclusion9

"ntenna G'6/ alarm results in larger loss: less coverage and

assignment failure8 6hen M' is in BCCH T/ coverage: signal

level is good enough: 1ut after assignment a TCH in the 1oard

5here G'6/ alarm occurs: M' TCH seizure fails and the

congestion rate is increased8




Case @ fault description9

6hen an . BT' is expanded to .>: high congestion rate

occurs8 The pea value of congestion rate is as high as >%&8

%ffect fro$ Reeater in the Cell



Case @ analysis9

'ince congestion rate is a1normal after expansion

Chec 5hether the congestion occurs to all T/8 *f yes: re7chec

the connection of ne5ly added hard5are of the BT' to see 5hether

there is any fault8

*f congestion occurs to one or a fe5 T/s: chec the hard5are of

these T/s8

6hen hard5are pro1lem is excluded: consider external causes8 ;or

example: the repeater is not expanded: 5hich results in assignment

failure8




Case @ trou1leshooting9

Bloc T/ of the last t5o ne5ly added T/ on .MC and find that the

congestion rate is lo5ered to normal status8 3erhaps: the pro1lem is

related to ne5ly added 1oards8

"nalyze "1is interface signaling: the assignment failure occurs on

the t5o ne5ly added T/s8 "nd 'DCCH measurement report

analysis sho5s that the level on 'DCCH is normal and T" value is

large8 Ho5ever: there is no measurement report on '"CCH (TCH)8

Because sometimes the assignment of the t5o T/s succeed: so it is

impossi1le that these to5 ne5ly added T/s are 1oth faulty8

.perator told that there is a repeater in the cell8 6hen expansion:

the repeater did not loc on the t5o ne5ly added T/s8 Confirm and

reconfigure repeater: pro1lem solved8




Case @ conclusion9

Because of the repeater: the actual coverage areas of the

existing t5o T/ and the expanded t5o T/ are different: 5hich

results in the assignment failure8




Case A fault description9

*n net5or optimization: the congestion rate (including handover)

on 1usy hours of the t5o cells is as high as $%&8 ITCH seizure

failures excluding handoverJ and ITCH seizure failures for call

(no radio resource)J are normal8 Here: ITCH seizure failures

(all)J is very high: E times and A$ times respectively: 1ut ITCH

seizure failures for M.CJ is %J8

The traffic volume is a little lo5er than that 1efore optimization8

The interference 1and is normal8

Congestion rate is normal 1efore optimization8

&ther Data Configuration Mistake



Case A analysis9

6hen the net5or parameters are modified: the congestion rate

of the t5o cells is higher and only the congestion rate (including

handover) is higher: therefore: radio interference or hard5are

fault can 1e excluded8 Mainly analyze 5hether the handover is

a1normal or not8




Case A trou1leshooting9

/egister I*ncoming *nter Cell Handover Measurement ;unctionJ

for $@ minutes: and find that all the handovers from cell "

(C,*=#########$A) to these t5o cells all fail: and the handover

failure cause is not congestion8

;ailures of all handovers mean that there is pro1lem 5ith the

handover data8 Chec the handover data of the t5o cells and

find that there is co7fre0uency and co7B'*C as supposed: the

t5o cells are adLacent cell of cell ": therefore the handover from

the cell " to the t5o cells 5ill fail8

Change the BCCH and B'*C of one cell: and then the handover

pro1lem disappears and congestion rate 1ecome normal8




Case A conclusion9

T5o cells (1oth adLacent to cell ") 5ith co7fre0uency and co7

B'*C 5ill result in result in lo5 incoming cell handover

successful rate: 1ut also high TCH congestion rate (including

handover)8

The case indicates that TCH congestion rate (including

handover) and TCH congestion rate (excluding handover) are

different8




Case fault description9

"n . site in a su1ur1an county has suffered from high

congestion rate (excluding handover): from 2& to $%& (in

proportion to traffic volume)8 But the ITCH seizure failures for

call (no radio resource)J is %&8

$8 Bloc T/ in turn: the congestion rate is serious as 1efore8

8 .ther indexes9 call drop rate is high (a1out @&)8 *nterference

1and is normal8

'solated Site and Co$licated Toograhy




Case analysis9

$8 'ince the congestion rate is not very high: the pro1lem may

not 1e on the data or hard5are8

8 The interference 1and is normal: so the interference at the

4m interface is unliely8

28 "nalyze the cause of assignment failure8 Tae call trop rate

into consideration and analyze the receiving performance of

uplin or do5nlin: including level and 0uality8




Chec ICall Drop MeasurementJ and find that T" value is large

5hen call drop: the distance is a1out @8AFmK2$8$Fm a5ay

from the BT'8

Gie5 I/eceiving <evel Measurement ;unctionJ and find that

there are many measurement reports of lo5 signal level8

"nalyze "1is signaling and find that the uplin level is very lo5

(a1out 7EdBm) 5hen the assignment fails8

Drive test on7site and find the site is isolated: 5ith large

coverage and complicated topography8 6hen the M' is more

than @ Fm a5ay from the BT': it can receive 7E%dBm do5nlin

signal8 But the uplin signal is not enough: so TCH assignment

fails8




Case conclusion9

3oor uplin coverage causes the high congestion rate8 "dding

BT' can help to o1tain a continuous coverage8 Change the omni

site into directional site or add TM" can improve uplin strength

and avoid over shooting of do5nlin8




TCH congestion

SDCCH congestion

Course Contents

S CC C i



SDCCH Congestion

SDCCH congestion

Basic principle

Causes for SDCCH congestion and solutions

Case study of SDCCH congestion

SDCCH C i



SDCCH Congestion

;ormula for 'DCCH congestion rate9

'DCCH congestion rate="ttempted 'DCCH seizures meeting a

'DCCH 1loced state !"ttempted 'DCCH seizures (all)

Causes of 'DCCH seizure9

'DCCH assignment for M.C

'DCCH assignment for MTC

<ocation update

'DCCH handover 'hort message

*M'* attach and detach

SDCCH C ti



SDCCH Congestion

MS BTS BSC MSC

B'C random access immediate assignment

Cell 'DCCH seizure re0uest times

Channel /e0uiredChannel /e0uest (/"CH)

Cell immediate assignment re0uest times

Cell 'DCCH seizure failure BT''%%%$@

"ttempted 'DCCH seizures meeting a 'DCCH 1loced state

(-o 'DCCH availa1le)

*mmediate "ssignment Command

*mmediate "ssignment /eLect

C f SDCCH C ti d S l ti



<ocation area 1order results in excessive location update and

'DCCH attempt

.ptimize for location area design

Modify C/H (Cell /eselect Hysteresis)

Modify T2$ for B'C period location update 'olve fre0uent handover pro1lem 1et5een dual71and net5or

+xcessive short messages

"dd 'DCCH channel

+na1le dynamic 'DCCH allocation function

Causes for SDCCH Congestion and Solutions

SDCCH C ti



*nsufficient system capacity: lac of 'DCCH channels

+xpansion for more TCH and 'DCCH channels

More 'DCCH should 1e added

*mproper configuration of system parameters: /"CH system

parameter8

*ncrease /"CH access threshold (overcoming interference)8

Decrease maximum re7transmitting times and increase extended

transmission timeslotsBoard (T/) fault and transmission fault result in 'DCCH

congestion

SDCCH Congestion

C St d f SDCCH C ti



Case Study of SDCCH Congestion

'DCCH congestion cases

Case $9 Too many times of location update

Case 9 Transmission e0uipment 1oard fault

Case 29 Transmission timeslot multiplexer pro1lem

T M Ti f ( ti U d t



Case $ fault description9

*n a net5or: the radio lin call setup successful rate is lo58

"nalyze the traffic statistics and find that 'DCCHs congest in a

fe5 sites8

Too Many Ti$es of (ocation Udate

T M Ti f ( ti U d t



Case $ analysis9 'ince only a fe5 BT' are congested: register I'DCCH

Measurement ;unctionJ and analyze the ratio of 'DCCH seizure

for different causes: then 5e can find the real reason for 'DCCH

congestion8


Too Man Ti$es of (ocation Udate



Case $ trou1leshooting 9

$8 /egister I'DCCH Measurement ;unctionJ *n congested cell: 'DCCH is attempted a1out 2%%7>%% times in a

certain hour8 The configuration are all '$!$!$8 +ach cell is

configured 5ith 'DCCH! channels8 -ormally: they are enough to

support 2%%7>%% times seizure: 1ut there are dozens of 'DCCH

congestion for each cell in 1usy hour8

*t is found that most of 'DCCH seizures are for location update8

"nalyze the cell locations and find that the congested BT' are at

the 1order of t5o location area crossed 1y rail5ay: most of location

update are in a specific @ minutes8 ?uery the train timeta1le andfind that > or @ trains pass there 5ithin this period8 6hen the trains

pass 1y: a large amount of location update re0uests from M'8

8 "dd 'DCCH or ena1le 'DCCH dynamic allocation function:

pro1lem solved8





Case $ conclusion9

;or 'DCCH congestion due to location update: chec 5hether it

is caused 1y improper setting of location area8 "dd 'DCCH

channel or ena1le dynamic allocation function to solve the

pro1lem8


Trans$ission %)ui$ent Board Fault



Case fault description9 "fter a ne5 BT'2% is on service: 'DCCH channels are all in

status I"J: TCH channels are in I*J or I"J8 6hen the call is

connected: the communication is normal8 .1serve the traffic

statistics and find that 'DCCH seizure failure times are morethan $%%% (in 1usy hour)8





Case analysis9

'ince 'DCCH is congested after BT' is on service: 1ut

communication is normal8

;irst chec data and hard5are8 Because the 5hole site suffers from

congestion pro1lem: interchange "1is lin 5ith another BT' (5hich

has the same site configuration) to confirm 5hether there is anydata or hard5are pro1lem in "1is interface8

*f there is no pro1lem 5ith data or hard5are: 5e should analyze the

"1is interface transmission system8






Chec alarm and find there are <"3D lin fault alarm and recovery

alarm (5ithin one second)8 The alarms appear once per ten minutes8

Chec the data and then interchange "1is lin 5ith another BT'

5hich is in the same configuration: the other site 5or normally8 Butpro1lem of this site persists8 'o data and B'C hard5are have no

pro1lem8

/eplace TM4 and T/ 1oard in the BT' and the pro1lem persists8

Measure the transmission and self7loop B*+: then *t is found that thereis high B+/ for transmission8 Test the line section 1y section and find

that one M transmission 1oard is faulty8 /eplace the 1oard and the

pro1lem is solved8





Case conclusion9

*n this case: due to transmission high B+/ there is too much

'DCCH assignment message 1ut missed: then 'DCCH

assignment message re7sent: these cause high congestion rate8


Trans$ission Ti$eslot Multile*er "ro#le$



Case 2 fault description9

Many complaints from su1scri1ers it is difficult to mae a call

through > sites ("BCD): 1ut there are no related alarm

information8

Chec the > sites: the 1oard status are all normal8 "lmost no TCH

channel is seized successfully8 'ometimes one TCH status is I"J:

1ut return to I*J 5ithin several seconds8

.perator engineer said that BT'7" 5as attached 5ith BT'7B: BT'7

C and BT'7D: these > BT's used a primary com1iner (a

transmission timeslot multiplexer) and shared one +* 8

Trans$ission Ti$eslot Multile*er "ro#le$




Case 2 analysis9

The locate information is helpful to Ludge that the pro1lem is on

the hard5are or the transmission8 But it is unliely that faults

occur to hard5are of the > BT's8 The transmission lines of the >

BT's are related: therefore: chec the transmission carefully8





Case 2 trou1leshooting9

$8 .1serve B*+: there is B+/ indication for transmission8 But there are no

a1normal indication in micro5ave and optical transceiver8

8 Chec "1is interface signaling and find there are a large num1er of

3",*-,CMD messages: 1ut only one /;/+'.4/C+*-D*C"T*.-

message appears occasionally8 There is no CH"-"CT*G:

CH"-"CT*G"CF or *MM+D*"T+"''*,-C.MM"-D message8 *t

indicates that 'DCCH channel is not activated8

28 Chec data .NM log: no data modified 5ithin a fe5 days8

>8 /eload and activate BT' soft5are: and find that system response is

slo5 even communication timeout8 'DCCH is still congested after

soft5are reloaded8





Case 2 trou1leshooting9 @8 /eset the primary com1iner and initialize the > BT's: 'DCCH

are all seized and TCH can 1e seized successfully8 Trace "1is

interface signaling: CH"-"CT*G: CH"-"CT*G"CF or

*MM+D*"T+"''*,-C.MM"-D message appears8 'DCCH

is no longer congested 1ecause M' can mae a call

successfully8

A8 To avoid the same pro1lem occurring again: it is suggested

that the operator remove the com1iner for transmission timeslots

multiplexer8





Case 2 conclusion9

The transmission pro1lem causes 'DCCH congestion 1y M'

channel re0uest repeatedly8 Transmission pro1lem can 1e

caused 1y different reasons8 *n this case: the fault on the

primary com1iner leads 'DCCH can not 1e activated: so all BT'

connected 5ith this transmission e0uipment have the same

pro1lem8 *n handling this type of pro1lems: try to find the

similarity of the pro1lem and finally locate the pro1lem 5ith the

exclusive method8


omf000405 case analysis congestion training 20031001 a 1.4

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