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RACCH
Due to the fact that the NECI(network element configuration
information) bit is always set to 1 in Alcatel-
Lucent BSS, Establishment causes can be divided into 2
categories:
Valid causes: 5 (6 if GPRS)
000: Location Update (Normal, Periodic, IMSI Attach)
100: Terminating call101: Emergency call
110: Call Re-establishment
111: Originating call (not emergency)011: if GPRS is implemented
in the cell
Invalid causes: 3 (2 if GPRS)
001:010:
011: if GPRS is not implemented in the cell
SD BLOCKING
Lack of sufficient SDCCH resources in a cell when a MS makes an
attempt for access is SDblocking1st Check SD traffic
utilization
if less than given channel then pblm in TS. Reset or shift the
TRX or time slot.
After that enable Dynamic SD.
Check Trend of Blocking any event LAC fail. Overshooting, TCH
DROP Increase so find the exact reasonresolve the problem
If all the things ok then Increase SD Time slot.SDCCH congestion
can be too high because of the subscribers' traffic demand in terms
of calls / LUs.Solution = add a TRX or site / redesign the LA
plan
High SDCCH congestion can be observed at peculiar period of the
day due to a peak of LU requests generby a big group of subscribers
entering a new LA at the same time (bus, train, plane).
Solution = redesign the LA plan or play on radio parameters
(CELL_RESELECT_HYSTERESIS, WI_OP
High SDCCH congestion can be abnormally observed without real MS
traffic in case a high level of noise
the proximity of a non-GSM radio transmitter.Solution = change
the BCCH frequency or put an RX filter
High SDCCH congestion can also be abnormally observed in a cell
in case one of its neighboring cell is
barred.Solution = Remove the barring
Board (TRX) fault and transmission fault result in SDCCH
congestion
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SD DROP
The SDCCH resource allocation is performed by the BSC. Once
allocated, the SDCCH channel is activatedby the BTS on BSC
request.T3101 is the guard timer for the SDCCH access from the MS.
The Default val
is 3 seconds.
Interference main cause. Check idle mode interference
report.
Co-BCCH,BSIC
Time slot faulty
OvershootingCSSR fail
Hardware
Main causes > SDCCH RF failures
Unbalanced cell power budget
Bad coverage (for example a moving car)
Interference (for example downlink)
Channel request received but not sent: 3 causes
1) Noise decoding due to Phantom RACCH
2) Reception of channel request sent to a neighboring cell
3) Reception of HO_ACCESS sent to a neighboring cell (During HO,
the first message sent
the target cell is HO Access.This message is an Access Burst
like Channel Request.Ifreceived on BCCH (in case TCH is identical
to or adjacent to BCCH), can be understood as
Channel Request (RACH).A new case of "Phantom RACH 2 origins of
SDCCH drop:
Radio problems when connected on SDCCH
BSS problems
TCH Blocking
The TCH Blocking Rate is defined as the proportion of TCH
requests from origination andhand-in calls that fail due to there
being insufficient TCH resources to carry the callTime slot faulty
reset the TRXLoad sharing (New Nbr Creatition)
Enable DRT
Increase queuing lengthInterference
Change HO margin load distribution. Enable traffic HO
Hardware problem
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TCH DROP
All the same reasons as that of SD Drop.
In addition to those following are other causes.
Poor downlink level (If drop at boundary then increase site,if
within boundary then repeater, power increasPoor downlink quality
(Rx good but poor quality then interference, co adjacent etc
frequency plan)
Poor uplink level (TMA increases sensitivity of BTS)
Poor uplink quality (PC and DTX)
Faulty transcoder or bad quality on abisHandover failure
Preemption
Missing NBR
HO FAIL (Increase capacity of congested cell)AMR Parameter
HRI
DAC (Crystal Frequency Shift) No synch between BSC & BTSCall
drops in GSM network can be caused by the following:
i) Equipment: GSM radios/Combiners can be a cause of this,
solution to this is replacement of the unit. AMobile Station(phone)
can also be a cause.
ii) VSWR (voltage wave standing ratio): VSWR caused by poor
connections on feeders, water penetration
fault on antenna etc
iii) Transmission problem: If transmission is not perfect, high
B.E.R (Bit error ratio) or other factors causin
inaccuracy of transmission.
iv) Interference: when there's frequency interfere (either
co-channel or adjacent interference).
v) Hand-over: if hand-over between two sectors is not well
defined.
Handover failures
Bad handover parameters settings
Hardware fault (TRX board fault)
Congestion
Interference
Coverage
Clock or timer mismatching
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Data Discrepancy
Interference
Co-BCCH BSIC in the NBRBSC not defined in MSC
Missing NBR
Blocking in cellBTS Load high
Interference in NBR Cell
NBR Cell overloaded
OvershootingSynch problem with neighbor cells
DAC Value Shifted
TCH ASSIGNMENT Success rate
3 main reasons
Hardware,Interference Co-BCCH BSIC and Overshooting
Tch congestion. When there is no TCH to make call or handoff
