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8/9/2019 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
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TCH congestion
SDCCH congestion
Course Contents
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TCH congestion
TCH congestion
Basic principle
Causes for high TCH congestion
Case study of TCH congestion
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TCH congestion
Basic principle of TCH congestion
Definition of TCH congestion rate
Measurement point for TCH congestion and analysis
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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) #$%%&
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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)
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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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
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Causes for high TCH congestion
Troubleshooting for high TCH congestion
Causes for High TCH Congestion
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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
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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
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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
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/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
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/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
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/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
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TCH Congestion
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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
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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
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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
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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
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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 Study of TCH Congestion
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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 Study of TCH Congestion
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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 Study of TCH Congestion
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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
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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
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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
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TRX Board Fault
Case conclusion9
$8;aulty TCH T/ 1oard causes TCH seizure failures and high
congestion rate8
8 4sually: the fault of T/ 1oard can not 1e found on the BT'
maintenance console8 The pro1lem can 1e confirmed 1y
1locing T/s in turn8
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Case 2 fault description9
" certain BT' configuration is 'A!A!A: the congestion rate of the
2 cells are all high since the BT' on service8 Having checed
and confirmed that there is no interference8
Ulink Hard!are "ro#le$
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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
Ulink Hard!are "ro#le$
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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
Ulink Hard!are "ro#le$
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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
Module ! 1" #ell ! $"
T%& 'o( 13
Module ! 1" #ell ! $"
T%& 'o( 1)
Module ! 1" #ell ! $"
T%& 'o( 1$
Module ! 1" #ell ! $"
T%& 'o( 1*
Module ! 1" #ell ! $"
T%& 'o( 1+
Ulink Hard!are "ro#le$
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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
Ulink Hard!are "ro#le$
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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$
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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 $&8
There is pro1lem in T/ 1oard of do5nlin hard5are8
Chec and find that the G'6/ of T antenna and feeder
connected 5ith this T/ 1oard is higher than 8@8 3rocess the
antennaN feeder G'6/ alarm: pro1lem solved8
Do!nlink Hard!are "ro#le$
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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
Do!nlink Hard!are "ro#le$
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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
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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
%ffect fro$ Reeater in the Cell
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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
%ffect fro$ Reeater in the Cell
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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
%ffect fro$ Reeater in the Cell
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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
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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
&ther Data Configuration Mistake
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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
&ther Data Configuration Mistake
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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
&ther Data Configuration Mistake
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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
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'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
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Case trou1leshooting9
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
'solated Site and Co$licated Toograhy
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Case conclusion9
3oor uplin coverage causes the high congestion rate8 "dding
BT' can help to o1tain a continuous coverage8 Change the omni
site into directional site or add TM" can improve uplin strength
and avoid over shooting of do5nlin8
'solated Site and Co$licated Toograhy
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TCH congestion
SDCCH congestion
Course Contents
S CC C i
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SDCCH Congestion
SDCCH congestion
Basic principle
Causes for SDCCH congestion and solutions
Case study of SDCCH congestion
SDCCH C i
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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
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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''%%%$@
"ttempted 'DCCH seizures meeting a 'DCCH 1loced state
(-o 'DCCH availa1le)
*mmediate "ssignment Command
*mmediate "ssignment /eLect
C f SDCCH C ti d S l ti
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<ocation area 1order results in excessive location update and
'DCCH attempt
.ptimize for location area design
Modify C/H (Cell /eselect Hysteresis)
Modify T2$ 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
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*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
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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
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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
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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 Many Ti$es of (ocation Udate
Too Man Ti$es of (ocation Udate
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Case $ trou1leshooting 9
$8 /egister I'DCCH Measurement ;unctionJ *n congested cell: 'DCCH is attempted a1out 2%%7>%% times in a
certain hour8 The configuration are all '$!$!$8 +ach cell is
configured 5ith 'DCCH! channels8 -ormally: they are enough to
support 2%%7>%% times seizure: 1ut there are dozens of 'DCCH
congestion for each cell in 1usy hour8
*t is found that most of 'DCCH seizures are for location update8
"nalyze the cell locations and find that the congested BT' are at
the 1order of t5o location area crossed 1y rail5ay: most of location
update are in a specific @ minutes8 ?uery the train timeta1le andfind that > or @ trains pass there 5ithin this period8 6hen the trains
pass 1y: a large amount of location update re0uests from M'8
8 "dd 'DCCH or ena1le 'DCCH dynamic allocation function:
pro1lem solved8
Too Many Ti$es of (ocation Udate
Too Many Ti$es of (ocation Udate
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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
Too Many Ti$es of (ocation Udate
Trans$ission %)ui$ent Board Fault
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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 $%%% (in 1usy hour)8
Trans$ission %)ui$ent Board Fault
Trans$ission %)ui$ent Board Fault
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Case analysis9
'ince 'DCCH is congested after BT' is on service: 1ut
communication is normal8
;irst chec data and hard5are8 Because the 5hole site suffers from
congestion pro1lem: interchange "1is lin 5ith another BT' (5hich
has the same site configuration) to confirm 5hether there is anydata or hard5are pro1lem in "1is interface8
*f there is no pro1lem 5ith data or hard5are: 5e should analyze the
"1is interface transmission system8
Trans$ission %)ui$ent Board Fault
Trans$ission %)ui$ent Board Fault
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Case trou1leshooting9
Chec alarm and find there are <"3D lin fault alarm and recovery
alarm (5ithin one second)8 The alarms appear once per ten minutes8
Chec the data and then interchange "1is lin 5ith another BT'
5hich is in the same configuration: the other site 5or normally8 Butpro1lem of this site persists8 'o data and B'C hard5are have no
pro1lem8
/eplace TM4 and T/ 1oard in the BT' and the pro1lem persists8
Measure the transmission and self7loop B*+: then *t is found that thereis high B+/ for transmission8 Test the line section 1y section and find
that one M transmission 1oard is faulty8 /eplace the 1oard and the
pro1lem is solved8
Trans$ission %)ui$ent Board Fault
Trans$ission %)ui$ent Board Fault
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Case conclusion9
*n this case: due to transmission high B+/ there is too much
'DCCH assignment message 1ut missed: then 'DCCH
assignment message re7sent: these cause high congestion rate8
Trans$ission %)ui$ent Board Fault
Trans$ission Ti$eslot Multile*er "ro#le$
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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 Study of SDCCH Congestion
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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 Study of SDCCH Congestion
Case Study of SDCCH Congestion
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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 Study of SDCCH Congestion
Case Study of SDCCH Congestion
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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 Study of SDCCH Congestion
Case Study of SDCCH Congestion
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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
Case Study of SDCCH Congestion
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