View
328
Download
3
Category
Tags:
Preview:
Citation preview
RNO TRAINING
ACCESSIBILITY
Accessibility – Time plan• Day 1:
– Objective– Key Performance Indicators – KPIs– Accessibility Definition– Accessibility KPIs– Paging– Location Area Update
Key Performance Indicators - KPIs
• Key Performance Indicators (KPIs) are used to categorize the Network elements such as MSCs and BSCs.
• The KPI values allow the operator to
visually compare their network with other networks, and also highlight areas that may require focusing for improvements.
Key Performance Indicators - KPIs
KPI TOP 25% TOP 50% Below TOP 50%Paging Succes Rate (1st+2nd page) > 95.10 >= 93.24 < 93.24Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
Accessibility
Retainability
Voice Quality
Accessibility Definition• “The ability of a service to be obtained,
within specified tolerances and other given conditions, when requested by the user.”
• Total number of successful calls set up/Total call accesses to the network
Accessibility DefinitionCall to an MS
9805024
BSC
MSC/VLR
TRC
BTS
BTS
1
2
4
5
2
2
2
3
1
4
356
1. MSC/VLR sends paging command to all BSCs belonging to the location area (LA) where MS is located
2. BSC forwards the paging command to all BTSs in that LA, and the BTSs in their turn page the MS on the PCH
3. The MS responds to the BTS on the RACH and the BTS forwards the response to the BSC (forward to MSC)
4. The BSCs checks with the BTS if it has an SDCCH available and the BTS grants the MS an SDCCH by using
the AGCH
5. The MS and the BTS signal on the SDCCH, measurement reports sent on SACCH are forwarded from
the BTS to the BSC and once the signalling is done the BSC decides which TCH to use
6. TCH connection established between MS and BTS
Access ibi lit y
Accessibility KPIs
KPI TOP 25% TOP 50% Below TOP 50%Paging Succes Rate (1st+2nd page) > 95.10 >= 93.24 < 93.24Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
Paging
KPI TOP 25% TOP 50% Below TOP 50%Paging Succes Rate (1st+2nd page) > 95.10 >= 93.24 < 93.24Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
Paging – Overview
All BSC in the MSC
BSC wt cells using
specified LAC
MSC
local
global
Paging message Cells with specified LAC
Paging command
Paging command
Paging Request
Paging Request
Paging – Overview
• MS can be paged by IMSI or TMSI• Up to 4 Paging Requests per Paging block
• MS only listens for paging at particular PCH sub-channel corresponding to its Paging Group
IMSI IMSI T T TTorNote: T = TMSI
TTIMSIor
Paging - Overview
9702690
Listeningto PCH
Listeningto PCH
1 53 4207 2 3 4 57 0 16
Sleep mode
7 0 1
Sleep modeMeasuring on
neighbors
Listeningto PCH Measuring on
neighbors
TDMAframes
BSF S CFC FC S
Paging group
F (FCCH): Frequency Correction ChannelS (SCH):Synchronization ChannelB (BCCH):Broadcast Control ChannelC (CCCH):Common Control Channel;Paging Channel (PCH) or Access Grant Channel (AGCH)
BCCH + CCCH(downlink)
Paging - Overview
2nd page according to PAGREPGLOB
2nd page according to PAGREP1LA
Local Paging?
Paging in one LA. Wait for response:
PAGTIMEFRST1LA
Paging in MSC area. Wait for response:
PAGTIMEFRSTGLOB
yes no
VLR has an LAI (normal case) LAI is missing
Answer? Successful
Answer?Answer?
Paging in one LA. Wait for response: PAGTIMEREP1LA
Paging in MSC area. Wait for response:
PAGTIMEREPGLOB
Paging in MSC area. Wait for response:
PAGTIMEREPGLOBNo repeated
paging
Successful
unsuccessful
Either TMSI/IMSI
1 2 3 0IMSI used
Answer?
10
yes
yes yes
yes
no no
nono
Paging – Overview
• Upon receipt of a paging request message and if access to the network is allowed, the addressed MS shall initiate within 0.5 s the immediate assignment procedure. The establishment of the main signaling link is then initiated by use of an SABM with information field containing the PAGING RESPONSE message
• Upon receipt of the PAGING RESPONSE message the network stops timer PAGTIMERFRST1LA (PAGTIMEFRSTGLOB).
• If timer PAGTIMERFRST1LA (PAGTIMEFRSTGLOB) expires and a PAGING RESPONSE message has not been received, the network may repeat the paging request message and start timer PAGREP1LA (PAGREPGLOB).
Paging - Overview
1
2
PAGING
PAGING COMMANDPAGING REQUEST
MSC BSC BTS MS
A-interface
Processor Load too high?
Y N
Paging queue full?NY
Step NPAG1GLTOT or NPAG1LOTOT
Paging - OverviewMSMSC BSC BTS
Channel RequestChannel Required
Establish Indication (Paging Resp.)SCCP Conn. Req
(Paging Resp.)SCCP Conn. Conf.
SABM, Page Response
Channel Activation
Channel Activation Ack.
Immediate Assignment Command
Immediate Assignment
Paging Paging CommandPaging Request
UA
PCH
RACH
AGCH
SDCCHSDCCH
Random Access
Step NPAGE1RESUCC or NPAGE2RESUCC
Paging - Overview
BTS
BSC
MSC
LA 1
Paging
Paging
Paging
Removed due to overflow
Removed due to overflow
Removed due to time-out
Removed due to time-out
› Monitor and detect congestion on paging channel
Paging – Strategy• Recommended paging strategy is:
– First page as local page the MS by TMSI– Second page as global page the MS by IMSI
• Other strategies and constraints:– No second page: Less paging load, but risk more unsuccessful
paging– Second local page: Less paging load, risk more unsuccessful
paging– Second page by TMSI: Utilize less paging capacity, but some
pages maybe unsuccessful if TMSI of MS is wrong in VLR
Paging – BSC Capacity
• It is difficult to estimate BSC Paging Capacity• Rule of thumb: BSC can accommodate 8500 Paging
Commands/sec• To further optimize the BSC paging capacity, paging queue
overflow can be monitored with the following formula:
Where TOTCONPAG - step for every discarded paging message when paging queue is full
TOTPAG - paging messages received from MSC
%100TOTPAG
TOTCONPAGFAIL_PAG
Paging – BTS Capacity• CCCH consists of 2 sub-channels for DL: PCH & AGCH• AGCH used to allocate resource to MS during call setup• PCH used to send paging request to MS• Two types of Channel Configuration:
– Combined BCCH/SDCCH• 3 CCCH blocks
– Non combined BCCH/SDCCH• 9 CCCH blocks
• AGCH can have dedicated blocks or work by stealing mode
Paging – BTS Capacity
• Incoming paging command are buffered in a queue• One queue for each paging group• When paging blocks are available, BTS will send
these paging commands as paging requests over the air interface
• If queue is full, further incoming pages are discarded• If queue at BTS for too long time, the page may be
lost since MSC do not receive any page response after timer expired
Paging – Reducing Paging• IMSI attach/detach
– If ATT = ON, MS will send attach/detach information to MSC/VLR when it is powered on/off.
– Decrease unnecessary paging to MS not connected to network– Constraint is higher SDCCH utilization
• Periodic Registration– Avoid paging MS which lost coverage and not able to inform the
system that it is inactive– Timer T3212 specifies the period for periodic registration– Shorter T3212 leads to less paging, but higher utilization of
SDCCH
Paging Capacity Impacting Parameters
• BCCHTYPE: NCOMB or COMB– Non-combined BCCH will give higher paging capacity than
combined BCCH
• AGBLK: 0 – 1– AGBLK=0 gives higher paging capacity than AGBLK=1
• MFRMS: 2 – 9– The lower value for MFRMS, the higher paging capacity due to
trunking efficiency– MFRMS setting is a trade off between battery consumption and call
set up time
Paging – Optimization• Analyze the following issues that could be
possible reasons for poor Paging Performance:– Insufficient coverage– High interference– Non-optimum Paging Strategy– Non-optimum Paging parameter settings– Paging Congestion in MSc, BSC or BTS– De-activated or incorrect use of Paging features
Paging – OptimizationThe following actions can improve Paging Congestion:• MSC Paging Congestion
– Increase SAE• BSC/BTS Paging Congestion
– Check Paging Strategy– Increase number of Location Areas (This will increase SDCCH
load)– Set BCCHTYPE to NCOMB– Use TMSI paging requests– Ensure IMSI attach/detach is activated (ATT = yes)– Decrease T3212/BTDM (This will increase SDCCH load)
Paging – OptimizationLow Paging Success
N o TM SI A ttach / D e tach?
Activa te
W rong period ic loca tionupdating setting?
C orrect T3212 in BSC ,BTD M & G TD M in M SC
SD C C HC ongestion?
Increase SD C C H channe l Adaptive configura tion feature
P agingcongestion?
P lan m ore LA U se TM S I paging
TM S I pagingnot use?
Activate
a fte r no t pe riod icregis tra tion no t use? Activa te
EN D
Yes
No
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
Im p lic it detach
Paging - KPI
• Paging Success Rate is measured on MSc level and calculated with the following formula:
Paging Success Rate (1st+2nd page)
– Successful First and Second Pages of Total Number of First Pages
This is the End-User perceived Paging Success Rate, which is used as the Paging KPI.
[%]100*
1
NPAG1LOTOTNPAG1GLTOT
CNPAG2RESUCCNPAG1RESUC1
TOTALCELLS
TOTALCELLS
Paging – Additional indicators
• The following Paging indicator is useful when studying paging performance (MSc level):
Paging Success Rate (1st page)
Successful First of Total Number of First Pages
This is the formula showing the system behavior
[%]100*
1
NPAG1LOTOTNPAG1GLTOT
CNPAG1RESUC1
TOTALCELLS
TOTALCELLS
Paging – STS Counter Summary• Paging Success STS counters
– NPAG1GLTOT: The number of first global page attempts over A-Interface– NPAG1LOTOT: The number of first page attempts to a location area over
A-Interface– NPAG1RESUCC: The number of page responses to first page attempt on
A-interface– NPAGE2RESUCC: The number of page responses to repeated page over
A-interface
• Paging Congestion STS counters– TOTPAG: Number of paging messages received from the MSC – TOTCONGPAG: Number of Paging messages discarded due to
congestion– PAGPCHCONG: Number of discarded paging messages due to full
paging Queue. – PAGETOOOLD: Number of discarded paging messages due to old paging
messages. `
Paging – Parameter SummaryParameter Range Recommended Description
MFRMS 2-9 CCCH Multiframe
4 MF period between transmission of paging message to same paging group
AGBLK 0-7 0 Reserved CCCH blocks for AGCH
BCCHTYPE COMB, COMBC, NCOMB
- Channel configuration
T3212 0-255 40 Time between period registration
ATT YES, NO YES IMSI Attach/ detach allowed
CRH 0-14 (steps of 2) dB
4 Hysteresis used when MS in idle crosses a LA area
GPRSNWMODE 0-3 2 (No Gs-Interface & no MPDCH used)
Whether or not Gs-interface & MPDCH used
Paging – Parameter SummaryParameter Recommended Description
BTDM T3212 * 6 Implicit detach supervisionGTDM 6 min
Range: 0-255Extra guard time beforesubscriber set to detached
TDD OFF (default) Time inactive IMSI in VLRbefore it is removed
PAGTIMEFRST1LA 4sec (default)Range: 2-10sec
Time supervision for pageresponse for first page
PAGTIMEFRSTGLOB 4sec (default)Range: 2-10sec
Time supervision for pageresponse for first global page
PAGREP1LA 2 (recommend)Range: 0-3
How second page is sent
PAGEREPGLOB 0Range: 0-1
How global page is repeated
PAGTIMEREP1LA 7sec (default)Range: 2-10sec
Time supervision for pageresponse for second page
PAGTIMEREPGLOB 7sec (default)Range: 2-10sec
Time supervision for pageresponse for second globalpage
Paging – Parameter SummaryParameter Recommended Description
TMSIPAR 1 or 2 TMSI should be used or not TMSILAIMSC 0 (default)
Range: 0-1 New TMSI to be allocated at change or LAI within MSC/VLR
SECPAGEPATH 1 (recommend) Range: 0-2
Define which interface 2nd paging is sent
TIMPAGINGM 9 sec Range:2-20sec
Time supervision for 1st CS paging sent over Gs interface
SGSN Parameter
Parameter Recommended DescriptionT3133 5 sec
FixedTime supervision for PSPaging
Location Update
KPI TOP 25% TOP 50% Below TOP 50%
Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
KPI TOP 25% TOP 50% Below TOP 50%
Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
Location Update – Overview• In Idle Mode the MS is powered on but not allocated a
dedicated channel• The purpose of Idle Mode is for the MS to be able to
access the system and be reached by the system any time and anywhere
• Idle Mode behavior is managed by the MS• Idle Mode is controlled by the parameters which the MS
receives on BCCH.• Location Updates enable the to register its current
location to the network so that the network knows where to route incoming calls.
Location Update – Overview
Location Update – Overview
9702629
C21 = C1+CRO-TO* q(PT-T); PT=31C21 = C1-CRO PT=31
CRO - Cell reselection offset
TO - Temporary negativ offset
PT - Time for application of a temporary offset
T - Timer1 C2 is only supported by phase 2 mobiles
Cell reselection process
q(x) = 0, x <01, x 0
Location Update – Overview
9702630
• The serving cell becomes barred• Repeated unsuccessfull access attempts
(MAXRET)• Downlink signalling failure• C1<0 for serving cell more than 5s• C2neighbour>C2serving(+CRH) more than 5s
Cell reselection process
Location Update – Overview
Cell Reselection Hysteresis (CRH)• Receiving signal strength (RXLEV) hysteresis for required cell re-
selection over a location area border.• Each change of location area requires a location update to be
performed, which increases signaling load.• CRH is used in order to prevent ping-pong effects for cell selection
across location area borders• If the CRH value is set too low, the fluctuations in signal strength may
lead to a ping-pong effect for location updating.This will cause an undesired increase in the signaling load on the SDCCH
• If the parameter is set too high, the mobile may camp on the wrong cell (not the strongest one) for too long when entering a new location area.
Location Update – Overview
Location Update – Overview
9702631
• PLMN not allowed• No SIM card inserted• Illegal MS• IMSI unknown in HLR• .....
• Emergency calls only• Cell reselection as normal,
but CRH is ignored• No updating
Limited service state
Cell selection process
Location Update – Overview
9702632
• Normal - at change of Location area• Periodic - according to T3212• IMSI attach/detach, ATT
Location updating process
Location Update – Strategy• Location Area Code (LAC) is part of Cell Global Identity• Circuit Switched (CS) paging done based on LAC
• Larger LA – Higher paging load– Less LAC update, lower SDCCH utilization
• Smaller LA– Lower paging load– More LAC update, higher SDCCH utilization
Location Area – Strategy
Location Area (LA) dimensioning strategies:• Size of a LA must not exceed the maximum paging capacity for the BTS /
BSC• In a rural area, it is easy to find LA border cells. But there’s no reason to
have a smaller LA than required• General rule of thumb : 1 LAC per BSC• If a BSC covers a large area with high traffic, consider splitting the LA. This
will reduce the paging load in BTS and BSC• In larger cities, SDCCH load will be higher for LA border cells. If difficult is
experienced to find LA border cells and the BSC coverage area is small, several BSCs can share one LA
• Define LA border at cells with low subscriber density
• Good information is available in the Location Area Dimensioning Guideline
Location Update – Optimization• Analyze the following issues that could be possible
reasons for poor Location Update success rate:
– Insufficient coverage– High interference– Location Area borders not optimum– Low CRH Hysteresis– Short time for periodic registration (T3212)– Insufficient SAEs– SDCCH congestion
Location Update – OptimizationLow Location Updating
Success
borderce ll?
R eallocate to ano ther LA o r M SC Increase C R H
Low C R HHysteris is? Increase C R H
Bad LAD em ension ing? R e-d im ension ing LA
Short perod icreg is tra tion?
C heck T 3212 in BSC &BTD M in M SC
Interfe rence? C heck frequency p lan Activate rad io fea ture
Software F ileC ongestion?
C orrect se ttings for SAE 500 B lockM LU AP, M LC A P,M LVAP,M M M LR
SD C C HC ongestion?
Increase SD C C H channel Adaptive configura tion feature
Autom aticderegistra tion? Activa te au tom atic
de-reg is tra tion
EN D
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
Location Area Update - KPI• Location Area Update Success Rate is
calculated using the following formula:
Location Update Success Rate
– Successful Location Updates of Total Number of Location Updates
[%]100*1
NLOCNRGTOT NLOCOLDTOT
CNLOCNRGSUC CNLOCOLDSUC
1
TOTALCELLS
TOTALCELLS
Recommended