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Optimisation and Performance Measurement of GSM/GPRS networks
Telemanagement World ConferenceLas Vegas, 29th-31st October 2002
SANDEEP RAINAGSM & GPRS Consultant
TELSIM,TURKEYsandeep.raina@telsim.com.tr
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Telsim - GSM 900 operator in Turkey
GSM network operations since 1994
First GPRS network in Turkey in 2000
Third GPRS network in World in 2000
GSM world award winner (community category), 2000
41 % market share
Telsim
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Content
Issues in GSM and GPRS performance data collection Performance Indicators for GSM - Coverage, Capacity, Quality
How Performance Indicators for GPRS are different KPIs for GPRS Benchmarking GPRS KPIs Optimising GPRS - Coverage, Capacity, Quality
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Issues in collecting performance data
• Lack of standardisation on many interfaces ( PSTN, IN...)• A-bis (Source of Level, Quality and Interference analysis) is customised• A-interface(Source of LU, Call Setup, Handovers) has no details of radio link info. , measurements from BTS or Mobiles
• Multi-vendor environment increases volume of performance data• Matching multi-vendor info. for the simplest analysis• OMC, the main contributor, is a vendor specific device
• Establishing relationship between network elements for a fault (Contribution of each network element in providing fault info.)• Establishing correlation between faults - Symptoms, After-effects
Bad Performance could be due to Inherent / Genetic defect
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• Validity of extracted data / statistics• Sufficiency of extracted data / statistics• OMC-G does not tap Gb or Gn•Tool unavailable for MS to IP layer monitoring•Drive test is still a snapshot , not the complete picture
•Ascertaining the intensity of problem ; Irregular or no Customer feedback
• How to set a threshold ?…not enough documentation, standards• Hundreds of indicators available...how to make a choice ? Operator experience is not shared• Inflexibility of setting thresholds of operator-interest on Abis, Gn, Gb
• Too many configuration parameters • Missing link between field changes and planning specs.• One-stop controller of configurations not available
Issues in collecting performance data
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Key Performance Indicators
Set up time
Call drop rateCell
congestion
Cell interference
Handover
RxLevel
Call success rate
The operator concentrates on many varied performance indicatorsThe operator concentrates on many varied performance indicatorsassigning assumed / theoretical priorities...assigning assumed / theoretical priorities...
PRIORITY ASSIGNED TO PERFORMANCE ISSUES : OPERATOR VIEWPOINT
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Key Performance Indicators
Call Drops
Speech Quality
Coverage(Indoor)
No connection
Coverage(outdoor)
Call set up time
...while the subscriber judges the network on the basis of ...while the subscriber judges the network on the basis of a few basic indicators of performancea few basic indicators of performance
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Key Performance Indicators
It is very important to align our KPI definitionIt is very important to align our KPI definitionaccording to according to
what quality and performance means to what quality and performance means to
The SubscriberThe Subscriber
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Performance Indicators for GSM : Coverage
• Signal Strength - outdoors• In building, In-Car penetration signal levels• Uplink Voice Quality• Downlink Voice Quality• Call Drops • Cell Power control
Start from the gross issues....
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Performance Indicators for GSM : Capacity
• Erlangs per Cell • TCH success • TCH assignment failures• TCH Drop calls • TCH Blocking • Cell congestion• Congestion Relief Usage• BHCA against rated MSC limit• mErl/subs. against rated MSC limit• SMS/subs. Against MSC limit• MM values(HO,LU,Paging) against limits• Overload : Voice/Signalling/Processor
...to more detailed...
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• RxLev• Handovers• Call Drops• Call Success Rate• Call set up success rate• Call completion rate• Call set up time • Voice quality(MOS)• RxQual• Echo
• TCH success• TCH assignment failures• TCH Drop calls• SDCCH traffic blocking• SDCCH drop calls• SDCCH Success rates• Location Area Paging• Paging per MSC• PSTN availability and quality
...and finally micro fine-tuning of the network
Performance Indicators for GSM :Quality
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Why GPRS benchmarking is different
• Multi QoS introduces layered approach to setting benchmarks• Multi handset classes makes the situation a bit more complex• Low Transmission rates on Air Interface• High Radio Link Error on Air Interface
• WWW is low volumes of data and frequent transmissions
• Sequencing of Data is a new concept
• Data Queuing is a new concept
• Blocking probability not easy to define• Different throughput requirements for different applications
• FTP is high data volume and infrequent transmissions
• IP layer performance also influences GPRS performance• TCP layer performance influences GPRS performance
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How GPRS Benchmarking is different
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GPRS vs GSM - Shift in importance of common indicators
GPRSGSM
Importance level
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KPI sources
KPI Sources in GSM
KPI Sources in GPRS
Air Interface
Air Interface
Switching network
Core Network
PSTN
IP network
Performance should be measured end to end, element by element
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KPIs for GPRS
GPRS KPIs can be tapped from :
AIR INTERFACE• Voice Quality• Interference• BLER• RACH Load• UL/DL PDTCH Blocking Rate• Retransmissions on TCP layer ( http, ftp, smtp, pop, wap...)• Network Congestion• Data Compression rate• GPRS contenders per Cell • Cell UL/DL throughput
SESSION STATISTICS• Session Set up success Rate• Session Completion Rate• Dropped packets• Cell Reselections• Processor Loads• Data Traffic transferred• Data blocks erroneously decoded• Data blocks retransmitted
Can be measured
Should be measured
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CORE COMPLEX• SS7 links congestion• D/L TBF set up success• U/L TBF releases• U/L D/L TBF set up time• Throughput on UL /DL• Data Compression Rates• PDP Context activations • RA updates (subscriber mobility)• Timeslot usage UL and DL
KPIs for GPRS
IP NETWORK• Internet Congestion (Beyond Gi)• Internet Delay (Gi and beyond)• IP traffic per APN• IP traffic on different services• End to end application delays• Round Trip Time• Delays due to Routers and Switches
Can be measured
Should be measured
GPRS KPIs can be tapped from :
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Tools to collect GPRS KPIs ?
• Collect info. from L2 and L3 layers : RR, MM, MAC, RLC, LLC, GMM, SM, SNDCP• Pick up relevant indicators• Analyse causes and reasons for below-standard performance
• Graphical ,tabular interpretation• Combinations of indicators• Cross-relationship between GPRS indicators• Relationship between GSM and GPRS indicators
C-Value variance vs RLC DL Throughput(non-hopping)
-100
-90
-80
-70
-60
-50
0 10000 20000 30000 40000
Throughput (bps)
Mea
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FTP throughput over Rx level
020406080
100
1 3 5 7 9
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Test Number
Rx le
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FTP
thro
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Rx level FTP Throuhput
Delay over Rx level
020406080
100
1 3 5 7 9
11 13 15 17 19 21 23
Test number
Rx le
vel,
dela
y in
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Rx level Delay in dsec
• Drive Test measurements, RTT measurements
• K1205 Gb protocol tester
Tools to collect GPRS KPIs ?
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How to use GPRS KPIs ?Some calculations derived from basic KPIs
• What is available ? U/L and D/L bandwidth (CS1 and CS2) available per cell
• What is consumed ? U/L and D/L Channel Loading Factor - Percentage of the available bandwidth in use
Air Interface Data blocks / Total Available air bandwidth GPRS Channel Occupancy - Total data transmit time of GPRS channels of cell/ Total time a channel can be used No. of PDP context activations / subs. - Calculated from GGSN statistics
U/L and D/L Radio Bandwidth - Cell throughput indicator
• What is the frequency of access ? GPRS Access per AGCH - Assignment messages sent on the AGCH of a cell,calculated at OMCR
GPRS Access per PCH - Paging Request messages sent on the PCH of a cell, calculated at OMCR
GPRS Access per RACH - Channel Request messages sent on the RACH of a cell, calculated at OMCR
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• What is the external influence ? Network IP traffic figure at GTP layer - Directly related to the IP traffic per SGSN/GGSN
Application Overhead Factor - IP Data size in Bytes / IP data actually sent in bytes
Application Throughput - IP Throughput * Application Overhead Factor
• What is the rejection ? PDP activation reject rate - Calculated from stats at GGSN
GPRS Attach reject rate - Calculated from stats at SGSN Total no. of lost packets in the network - Calculated from statistics at SGSN and GGSN
• What is the usage pattern? U/L and D/L RLC Throughput - Total RLC data transmitted / time the GPRS channels were used
Coding Scheme Usage Ratio - Percentage of coding scheme usage per cell (RLC CS1 / RLC CS2)
How to use GPRS KPIs ?Some calculations derived from basic KPIs
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GPRS Benchmarking
• RxQual (CS2) 0.5 uM• C/I for CS1 9 dB uM• C/I for CS2 12 dB uM • BLER (CS2) 10 % uM• UL PDTCH Blocking Rate < 2% uM• DL PDTCH Blocking Rate <2% uM• TCP Retransmissions <10% uM• RLC/MAC Retransmissions <10% uM• Network Congestion <2% uM• GPRS users per cell(4 ts, CS2) 4 uM• Data Compression Rate 50 % uM• Session set up time 900ms. uM,Core
GPRS BENCHMARK VALUE SOURCE
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• Session set up success rate 98 % uM,Core (PDP context activation success)• Session drop rate 2 % uM, Core • SS7 link congestion 0.1%Core• DL set up success rate 98 % Core• UL TBF release 2 % Core • UL TBF set-up time 200 ms uM • DL TBF set-up time 400 ms uM • UL throughput (1 ts,CS2) 9 kbps uM• DL throughput (4 ts,CS2) 40 kbps uM• RA updates per subscriber network design value PCU,Core• GPRS pages per subscriber network design value Core• Dropped packets 2% uM,Core,IP
GPRS BENCHMARK VALUE SOURCE
GPRS Benchmarking
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• Cell reselections Core• Data blocks retransmitted uM• Internet (ISP) Congestion < 3% IP• Internet (ISP) delay < 25 ms(local),<400ms(ext.) IP
• Peak data traffic per subscriber network design value (100 KB/hr.) uM,SGSN• End to end application delay• Round trip latency 900 ms
uM,Core,IP • Router/switch delays < 5 ms Core,IP
GPRS BENCHMARK VALUE SOURCE
GPRS Benchmarking
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GPRS Optimisation-Capacity
Radio channel capacityGSM channel utilisationGPRS Channel utilisation
Staggered peaks of GSM and GPRS traffic
7:30
TR
AFFI
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2400 1200 2300 hours GSM + GPRS channel utilisation
Free Channel Capacity
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GPRS Optimisation-Capacity
23:0
022
:00
Radio channel capacityGSM channel utilisationGPRS Channel utilisation
Concurrent peaks of GSM and GPRS trafficTR
AFFI
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2400 1200 2300 GSM + GPRS channel utilisation
Free Channel Capacity
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Accelerator Softwares : Reduction in Data Volume
Application Type
1. Email (SMTP) 2. Text file transfers
3. Zip file transfers 4. JPEGs,GIFs transfers
5. Heavily animated webpages 6. Normal HTML webpages
GPRS Optimisation-Capacity
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1 2 3 4 5 6
WithoutAccelerationWithAcceleration
Data in
bytes
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GPRS OptimisationThroughput
Accelerator softwares : Test results
Internet webpage downloads faster • msn.com : 2.2 times faster• nasa.com : 3 times faster• nytimes.com : 3.4 times faster• heavily animated pages : 10 times faster
FTP transfers faster• jpeg file transfer : 2.7 times faster• exe file transfer : 2.7 times faster• zip file transfer : 1.6 times faster
E-mail faster • Uplink Email : 2.3 times faster
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• Reduce Interference to support higher coding schemes
• Expand GPRS in areas that promise high traffic No need to reserve timeslots across the network for GPRS
• Introduce CS3 and CS4 coding schemes to conserve GSM/GPRS capacity
GPRS OptimisationGeneral
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2. OSS devices for GSM and specially GPRS need to be more analytic
1. In complex GSM/GPRS networks the role of OSS for management is key
Summary
3. GPRS network management and performance indicators require different treatment and analysis from those of GSM 4. Performance measurement / Optimisation of GPRS is a vital learning exercise for 3G network management
5. QoS is a big question mark for GPRS and therefore for 3G too
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And what will be the performance standards for
MMS, Audio/Video Streaming formats ?
Current Performance/Optimisation methods provide Best effort services
So, how shall we improve our methods
to provide Guaranteed performance ?
THAT’S THE REAL CHALLENGE NOW !
Challenge
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SANDEEP RAINAGSM & GPRS Consultant
TELSIMTURKEY
sandeep.raina@telsim.com.tr
THANK YOU
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