Top10 dropped call

Nov. 2001 Henrik Centerham ERA/GG/NI TIM/NPOC/O
TOP 10 WORST CELLSTOP 10 WORST CELLS
OPTIMIZATIONOPTIMIZATION

AGENDA
• Basic Idea of TOP 10 Optimization
• Introduction to statistics
• Configuration
• SDCCH and TCH drop Analysis
• Congestion Analysis

Objective
THREE MAIN OBJECTIVES
• To keep track of the Network Performance
• To improve the Network Performance
• To achieve KPI purpose

GOAL
• To spread knowledge of how to optimize a
GSM network with help from statistics
• Share experience from other projects

BASIC IDEA TOP 10 OPTIMIZING
KPI
Top 10 optimizing
Procedures
TCH/SDCCH
DROP
Hand-overCongestion Random
Access
Paging (MSC)

TOP 10 Optimization
KPI - Key performance indicator
1) Paging
2) TCH Drop Rate
3) SDCCH Drop
4) Congestion
5) Service denied
6) Random Access

BASIC IDEA
• Improve the worst 10 performing cells
Improving the worst 10 cells will give the biggest
improvement on BSC and Network level
As many subscriber as possible will benefit from a
better network.
The 10 worst cells will be different depending on what
is decided to optimize.
TOP 10 Optimization

Resources
• Optimization per BSC, 1 region with 3-4 BSC per team
Team: 3 optimizer and 1 Cell-planner with support from
a pool of Filed Maintenance personnel and one expert.
• Location?
From a technical perspective preferably in regions with
local knowledge.
From an organizational perspective, Mexico City
TOP 10 Optimization
Decision need to be taken by management.

Resources
First and second BSC, one owner / BSC
TOP 10 Optimization
BSC 1
BSC 2
TEAM A
1 optimizer
1 cell-planner
TEAM B
1 optimizer
1 cell-planner

Analyzing statistical data
NWS
DATABASE
GSM NETWORK
WEB I
REPORTS
ANALYZE
• LOCATE PROBLEM
• SUGGESTIONS FOR
IMPORVMENT
• Change
request
• Trouble
report

Introduction to statistics.
WEB
NWS ANALYSER
Business Objects
STS DATA FILEOMS DATA FILES
TCP/IP
X25
AXE
1st Open Interface
Raw Interface
2nd Open Interface
- SQL Interfaces for other
applications or systems.
- Release Independent
Interfaces, e.g. GSM 12.04
PSA
LOADING
FM
External eventsBSDCSD
SDM
SDM FILE X FILE
External systems
SGwSMIA
X formatSDM format
STS Y DataOMS - Parsers
- Formatters

TOOLS
NWS
• Based on Business objects
• Possibility to create different reports and graphs.
• Direct access to SDM database where STS date are stored.
• Today SDM database is on Telcel LAN.

TOOLS
WEB I
• Tool to look at NWS reports bye using WEB browser
• No possibility to create different reports and graphs, only
look at predefined reports ant graphs.
• Possibility to down load data to excel
• Possibility change time period for statistic data
• No sort and filter in WEB I

• With statistics, performance of the network can be
measured
DROPPED CALLS
0,00
20,00
40,00
60,00
80,00
100,00
120,00
00151
00153
00182
00231
00233
00242
00351
00353
00402
00411CELL NAME
Nr.Dropp
0,00
1,00
2,00
3,00
4,00
5,00
6,00
Droperate
TFNDROP
T_DR-S

• With statistics problem-cells can easily be
identified.
DROPPED CALLS
0,00
20,00
40,00
60,00
80,00
100,00
120,00
00151
00152
00153
00181
00182
00183
00231
00411
00233
00241
00242
00351
00353
00403
CELL NAME
Nr.Dropp
TFNDROP

Data Reliability
• 24 Hours Statistic data must complete or at least 95% of
Statistic data must be used in Analyzing process.
• Lack of complete Statistic data can lead to wrong
analysis result.
• In case of losing statistics data at night, we might still
analyze the data. But if we lost statistics data during day
time, we should reject the data for analysis process.

Statistics are built up from counters that steps for different events,
counters are put into formulas.
Example - Counter
TFNDROP - Steps when a call is dropped
TFNDROPSUB - Steps when a call is dropped in OL subcell
Example - Formulas
TCH DROP RATE TFNDROP + TFNDROPSUB * 100 [%]
TFCASSALL + TFCASSALLSUB

Formula name
• The formula name is build of short abbreviations.
• IN WEB I the formula is describes with a short sentence.
Example
Formula: S_DR_BQ_OU
SDCCH DROP BAD QUALITY OVERLAID/UNDERLAID

Formula name
Formula:
S_DR_BQ_OU
Description:
Dropped SDCCH Connections due to Bad quality of Total
Number of Dropped SDCCH Connections
WEB I Description:
SDCCH Drop Reason, BQ %

Formula name
• Naming conversion
Name given in Webi STS formula
name
Description
TCH Drop, BQ % OU U.link TF_DRBQULOU
Dropped TCH/F Connection at Bad Quality uplink of Total Number of Dropped
TCH/F Connections
TCH Drop, BQ % OU D.link TF_DRBQDLOU
Dropped TCH/F Connection at Bad Quality downlink of Total Number of
Dropped TCH/F Connections
TCH Drop, BQ % OU B.link TF_DRBQBLOU
Dropped TCH/F Connection at Bad Quality both links of Total Number of
Dropped TCH/F Connections
TCH Drop, Sudden % OU TF_DR_SUDOU
Suddenly lost TCH/F Connections of Total Number of Dropped TCH/F
Connections

Ericsson provide many counters and standard formulas.
References
STS_formulas_PA10 - Formulas that will be used in Telcel project
NWSnamedefinitions - Conversion between formula name,
description and WEB I description.
R8 STS Formula - Standard Ericsson formula document

CONFIGURATION OL/UL - SUBCEL
Mexico Telcel
TCH
Frequencies
OL = HOP 1/1 over 6 -12 f
UL = NO HOP, 12-18 BCCH f
f
BCCH
TCH CHG1
CHG0
HOP
1/1
BCCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
UL
OL
SDCCH8SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH

CONFIGURATION TCH DROP
OL / UL STATISTICS
• Possible to get separate statistic for UL/OL Subell.
• Possibility to limit a suspected interference problem to
UL or OL frequency band.
• CHALLOC set to 1, CHAP set to 5, most traffic on UL
Subcel.

Preparation and Tools
• NWS WEB intelligent reports with correct formulas.
• There are standard report created for each statistics
analysis purpose.
• General Statistic daily and hourly reports for 24
hours statistic data per BSC. (All formulas needed
according to STS useful document TIM/TND-2001:
0023)

Preparation and Tools
• Maps with cell positions and antenna directions.
Use TCP or MapInfo. The map should show antenna
directions and BCCH, BISC.
• OSS
RNO and CNA.
In case of no access to OSS, dump file for each BSC
needed. (All parameters related, All neighbors
relation)

TOP 10 DROPPED CALL

TCH and SDCCH DROP
TCH - Traffic channel
SDCCH - Stand Alone Dedicated Control Channel
• Improvement on TCH drop will lead to improvement on
SDCCH drop
• Recommendation is to start with TCH drop
• The worst drop from a subscriber point of view is TCH
drop.

TCH DROP
Definition
• TCH Drop is an abnormal disconnection
Affects
• Subscribers will drop the call in conversation state
Objective
• Minimize dropped calls and thereby improve
retainability performance

TOP 10 Optimization - Dropped call
Different way to measure:
• TF_DR_TOTOU = Total number of Dropped TCH/F
Connections in UL and OL subcell
• TF_DR-S_OU [%]=Dropped TCH/F Connections of
Total Number of TCH/F
Connections
• TF_DR_ERLMOU=Erlang Minutes per Dropped TCH/F
Connection

CELL TF_DR_TOTOU TF_DR-S_OU TF_DR_ERLMOU
05522 59,00 5,71 20,61
05061 35,00 5,49 21,18
05503 30,00 4,41 29,65
08442 44,00 4,38 19,64
02001 159,00 4,30 27,26
06592 24,00 3,27 34,20
00402 101,00 3,25 32,05

CELL TF_DR_TOTOU TF_DR-S_OU TF_DR_ERLMOU
05522 59,00 5,71 20,61
05061 35,00 5,49 21,18
05503 30,00 4,41 29,65
08442 44,00 4,38 19,64
02001 159,00 4,30 27,26
06592 24,00 3,27 34,20
00402 101,00 3,25 32,05
WHY?
Cell 2001 affect most subscribers.

TCH DROP - WORK FLOW
UL SUBCEL
DROP REASSONS
OL UL
Yes
No
OUTPUT
REPORT
IS A CHANGE
REQUEST
NESSECARY?
ISSUE CR IN
REMEDY
ANALYSEANALYSEANALYSEANALYSEANALYSE
HIGH TA LOW SS
BAD
QUALITY
SUDDEN
LOST
OTHER
IDLE MESSUERMENT&
HANDOVER
REPORT
MRR, FAS, NCS,
MapInfo
What drop
reason have
higest %
drop?
What drop
reason have
higest %
drop?
OL SUBCEL DROP
REASSONS
Which subcel
OL or UL
have most
drops?
Dropped call
report
STS REPORTS
TOOS & STS REPORTS
1) SORT
& FILTER
PRE DEFINED
REPORT
TOP10 Droped
Calls
STS DATA
GSM
NETWORK

TCH DROP - Find the worst cells
Sorting process
• TF_DR_TOTOU, Descending
• Exclude drops with TF_DR-S_OU < 1,5% (Limit could
change)
• Cells with low drop rate in [%] can be hard to do
anything about.
• Some drops are normal.

TCH DROP - Find the worst cells
Sorting process
• What subcel have most number of drops?
• Overlaid subcel (OL)
• Underlaid subcel (UL)
BCCH
TCH CHG1
CHG0
HOP
1/1
BCCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
UL
OL
SDCCH8
TCH

TCH DROP REASON
Priority In following order:
• Drop due to TA
• Drop due to Signal Strength UL/DL or Both
• Drop due to Bad Quality UL/DL or Both
• Drop due to Sudden lost
• Drop due to Other reason
Understanding of how
a dropped call will be
categorized

TCH DROP REASON
Measurements and Filtering
• Not only one measurement report is used to determine
type of urgency condition.
• An average is made up of the last 6 measurements
reports ( number of measurement reports that will be
used can be set with parameters).
• Parameters
SS -- SSLENSI,SSLENSD
QL -- QLENSI,QLENSID

TCH DROP REASON
Parameters- Drop due to TA
MAXTA = Maximum timing advance a MS can use in a cell
If the measured and averaged timing advance value for an
ongoing call is equal or greater than MAXTA, the call is released.
Recommended value = 63
TALIM = Determines the maximum timing advance that the MS
is recommended to use in the cell.
If the measured and averaged timing advance value for an
ongoing call is equal or greater than TALIM the cell must be
abandoned urgently
Recommended value = 61

TCH DROP REASON
Parameters- Drop due to SS
LOWSSDL= Low signal strength limit for urgency
condition, downlink.
Recommended value =104dBm
LOWSSUL= Low signal strength limit for urgency
condition, uplink.
Recommended value =104dBm

TCH DROP REASON
Drop due to SS
SS
SS DL SS UL SS BOTH
=
TF_DRSSDLOU
20%
=
TF_DRSSULOU
10%
=
TF_DRSSBLOU
10%
= TF_DRSS_OU 40%

TCH DROP REASON
Parameters- Drop due to Bad Quality
BADQDL= Bad quality limit for urgency condition, downlink
Recommended value =55dtqu
BADQUL= Bad quality limit for urgency condition, uplink.
Recommended value =55dtqu
55dtqu = 5.5 RxQual

TCH DROP REASON
Drop due to BQ
BQ
BQ DL BQ UL BQ BOTH
=
TF_DRBQDLOU
20%
=
TF_DRBQULOU
10%
=
TF_DRBQBLOU
20%
= TF_DRBQ_OU 50%

TCH DROP REASON
Parameters- Drop due to Sudden lost
Sudden loss of connection is valid if none of the first three types
of urgency state are indicated (that is excessive TA, low signal
strength or bad quality) and the locating procedure indicates
missing measurement results from the MS.
TFSUDLOS is stepped according to above conditions

TCH DROP REASON
Parameters - Drop due to Other
If a connection is dropped and there in no abnormal conditions and
no indications that measurements reports are missing.
Drops due to Other = All drops - drops due to TA,SS,QL,SUD
TF_DR_OTHOU=
TFNDROP + TFNDROPSUB - (TFDISSDL + TFDISSDLSUB + TFDISSUL + TFDISSULSUB +
TFDISSBL + TFDISSBLSUB + TFDISQADL + TFDISQADLSUB + TFDISQAUL + TFDISQAULSUB
+ TFDISQABL + TFDISQABLSUB + TFDISTA + TFSUDLOS + TFSUDLOSSUB) * 100 [%]
TFNDROP + TFNDROPSUB

TCH DROP REASON
Problem indication - Drop due to TA
Ex1.
• Subscriber is far away from serving cell
• Possible missing neighbor
• If necessary plan for new site.
MS
35 KM
New site?
Missing Neighbor?

TCH DROP REASON
Ex2.
• Possible Dragon site
MS
35 KM
Down-tilt, lower antenna or change antenna type

TCH DROP REASON
Problem indication - Drop due to SS
• Missing neighbor
• Missing site (planned but not built)
• Lack of indoor coverage
• Site location
• Installation problem
Shopping mall
with many
subscribers Low
indoor SS.
Missing
Neighbor
Missing
SITE

TCH DROP REASON
• If many drops on UPLINK due to SS:
Could indicate installation problems such as lose feeders
hidden antennas.
• If many drops on DOWNLINK due to SS:
Could indicate wrong output power or lack of indoor
coverage.

TCH DROP REASON
Problem indication- Drop due to Bad Quality
• Interference, Co- or adjacent Interference
Change frequency
MS
BCCH 590
BCCH 590

TCH DROP REASON
• Interference - Co- or adjacent Interference
Down-tilt interferrer
BCCH 590
BCCH 590
High site

TCH DROP REASON
• UPLINK Interference - Check Idle Channel measurement
Change frequency or find source of interferrer
• How are the ICM over time? Regularly or from time to time?
• Parameters
LIMIT1=4
LIMIT2=8
LIMIT3=15
LIMIT4= 25
Interferance band Interferance level Messured Rxlev
1 I <=-106dBm 0 to 4
2 -106dBm<I<=-102dBm 5 to 8
3 -102dBm<I<=-95dBm 9 to 15
4 -95dBm<I<=-85dBm 16 to 25
5 -85dBm<I 26 to 63

TCH DROP REASON
• UPLINK Interference - Check Idle Channel measurement
Cellname ICH1 ICH2 ICH3 ICH4 ICH5
DF9999 0 0 10 30 60
DF5555 90 10 0 0 0
DF4444 100 0 0 0 0
This means that 10% of the time the measured
interference on idle TCH has SS according to
ICH BAND 2 -106dBm<I<=-102dBm

TCH DROP REASON
Problem indication- Drop due to Sudden lost
• Measurement reports from MS is missing.
• Last report had good RxQual and Rxlev.
Rapid decrease of signal strength
Hand-over lost
Battery pulled out by subscriber
TUNNEL
MS

TCH DROP REASON
Problem indication - Drop due to Other
• Since there is no urgent conditions but the call is still
dropped its hard to find the reason.
• Request NOM to Check for BTS error log
• Generally
• NOT a radio related problem
• Transmission problems
• TRU hardware problems
• Wrong definitions of cell in MSC & BSC
• Wrong LAC definition in MSC

TCH DROP Investigation report in NWS
BASIC IDEA
• Easy overview of problem cells
• Pre defined reports
Top 10 DROP CALL
TCH DROP
SDCCH DROP
ICH Measurement
Handover performance
All STS data hourly

SDCCH DROP
Definition
• SDCCH Drop is an abnormal disconnection of SDCCH
Affects
• Subscribers will not able to set up a call. The
subscriber will try again,
• A radio link time-out on the SDCCH will occupy an
SDCCH sub-channel for (RLINKUP+RLINKT)/2 second
and increase the risk for SDCCH congestion
Objective
• Minimize dropped calls and thereby improve
retainability & accessibility performance

SDCCH DROP
Counter: CNDROP
CNDROP steps for following cases:
• Error indication and Channel release, abnormal release.
– Low SS, high BER
• Radio link time out.
– Low SS, high interference
• No assignment command
– Congestion or No measurement report received
• Unsuccessful assignment command
– Low SS high interference

SDCCH DROP
• SDCCH IN UNDERLAID CELL
TCH• Interference problem on SDCCH can be limited to
BCCH FREQ
BCCH
TCH CHG1
CHG0
HOP
1/1
BCCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
UL
OL
SDCCH8SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH
SDCCH

SDCCH DROP
Formula:
S_DRCNTCOU = Dropped SDCCH Connections of Total Number of
SDCCH Connections when no TCH congestion
CNDROP - CNRELCONG * 100 [%]
CMSESTAB

SDCCH DROP - Find the worst cells
Sorting process
• S_DR_TOT-C, Descending
• Exclude drops with S_DRCNTCOU < 1,5% (Limit could
change)
• Cells with low drop rate [%] can be hard to do anything
about.
• Some drops are normal.

SDCCH DROP REASON
Priority In following order:
• Drop due to TA
• Drop due to Signal Strength
• Drop due to Bad Quality
• Drop due to Other reason

SDCCH DROP REASON
• Possible missing neighbor
• If necessary plan for new site.
MS
35 KM
New site?

SDCCH DROP REASON
• MS Battery run out
• Missing site (planned but not built)
• Lack of indoor coverage
• Site location
• Installation problem Shopping mall
with many
subscribers Low
indoor SS.
Missing
Neighbor
Missing
SITE

SDCCH DROP REASON
• Change frequency
MS
BCCH 590
BCCH 590

SDCCH DROP REASON
Down-tilt interferrer
BCCH 590
BCCH 590
High site

SDCCH DROP REASON
Problem indication - Drop due to Other
• Since there is no urgent conations but the call is still
dropped its hard to find the reason.
• Generally drops due to other reasons indicate a non RF
problem.
• Transmission problems
• TRU hardware problems
• Wrong definitions of call in MSC BSC
• Wrong LAC definition in MSC

THANKS FOR YOUR ATTENTION

Top10 dropped call

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