Day 1

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