cssr analysis

# How is the CSSR formula ?

CSSR_w/o_block = ImmAss SR x SSS Proc SR x Ass TCH SR

ImAss Phase

SSS Proc Phase

TCH Assignment Phase

ImmAss SR = NSUCCHPC(APSD,CRSD,ECSD,OCSD)-NSUCCHPC(SMTCSD) ATIMASCA(APSD,CRSD,ECSD,OCSD)-NSUCCHPC(SMTCSD)

SSS Proc SR = TASSAT (F,H) NSUCCHPC(APSD,CRSD,ECSD,OCSD)-NSUCCHPC(SMTCSD)

TCH Ass SR = TASSSUCC(F,H)+TASSFAIL(NRF,NRH)+SINTHINT(DR)+SUINBHDO(DR)+SUOISHDO(DR) TASSAT (F,H)

CSSR_w/o_block = ImmAss SR x SSS Proc SR x Ass TCH SR

ImmAss SR = NSUCCHPC(APSD,CRSD,ECSD,OCSD)-NSUCCHPC(SMTCSD) ATIMASCA(APSD,CRSD,ECSD,OCSD)-NSUCCHPC(SMTCSD)

SSS Proc SR = TASSAT (F,H) NSUCCHPC(APSD,CRSD,ECSD,OCSD)-NSUCCHPC(SMTCSD)

TCH Ass SR = TASSSUCC(F,H)+TASSFAIL(NRF,NRH)+SINTHINT(DR)+SUINBHDO(DR)+SUOISHDO(DR) TASSAT (F,H)

Analysis

# What factor can influence within this phase ? Phase I : ATIMASCA - SUIMASCALoss probability :a. No SDCCH available -> SDCCH attempt meeting blocked - High number of request - Lack of SDCCH resources - Over idle coverageb. Transmission problem - Abis interface -> messages loss (CHNAV, CHNAK) between BTS and BSC - flicker transmission - not LOS transmission (obstacle) -> wrong transmission planning - unnecessary cabling on DDF panel - problems on COBA/COSA modulec. HW problem & wrong installation on BTS -> bad processing/failure, un-received/sent of messages toward BTS/MS - high VSWR - broken module - untight connector - broken cable/feeder ; high loss - fabrication faulty : BTS mainboard, module slot - cell inversion : antenna, feeder, backplane, semirigid, wrong HW db creationd. Radio Interface problem -> messages loss between MS and BTS - frequency interference - unbalance UL & DL due to improper coverage (overshoot or lack of coverage), contour factor - unnecessary db setting

Phase II : SUIMASCA - NSUCCHPCLoss probability :a. Transmission problem - Abis interface -> messages loss (IMASS, ESTIN) between BTS and BSC - see point b on phase I explanationb. AGCH overload - see statistic meas : difference between TACCBPRO (2) - NACSUCPR(2) - if the differences > 0 means there are AGCH overloadc. Radio Interface problem -> messages (IMASS, SABM, CMSREQ) loss between MS and BTS ; no SABM sent to BTS by MS might be due to MS used 'phantom' RACH when send CHNREQ - see point d on phase I explanationd. HW problem & wrong installation on BTS -> bad processing/failure, un-received/sent of messages toward BTS/MS - see point c on phase I explanation

Analysis

Phase I : ATIMASCA - SUIMASCALoss probability :a. No SDCCH available -> SDCCH attempt meeting blocked - High number of request - Lack of SDCCH resources - Over idle coverageb. Transmission problem - Abis interface -> messages loss (CHNAV, CHNAK) between BTS and BSC - flicker transmission - not LOS transmission (obstacle) -> wrong transmission planning - unnecessary cabling on DDF panel - problems on COBA/COSA modulec. HW problem & wrong installation on BTS -> bad processing/failure, un-received/sent of messages toward BTS/MS - high VSWR - broken module - untight connector - broken cable/feeder ; high loss - fabrication faulty : BTS mainboard, module slot - cell inversion : antenna, feeder, backplane, semirigid, wrong HW db creationd. Radio Interface problem -> messages loss between MS and BTS - frequency interference - unbalance UL & DL due to improper coverage (overshoot or lack of coverage), contour factor - unnecessary db setting

Phase II : SUIMASCA - NSUCCHPCLoss probability :a. Transmission problem - Abis interface -> messages loss (IMASS, ESTIN) between BTS and BSC - see point b on phase I explanationb. AGCH overload - see statistic meas : difference between TACCBPRO (2) - NACSUCPR(2) - if the differences > 0 means there are AGCH overloadc. Radio Interface problem -> messages (IMASS, SABM, CMSREQ) loss between MS and BTS ; no SABM sent to BTS by MS might be due to MS used 'phantom' RACH when send CHNREQ - see point d on phase I explanationd. HW problem & wrong installation on BTS -> bad processing/failure, un-received/sent of messages toward BTS/MS - see point c on phase I explanation

Action

a. SDCCH capacity overhandling might be done by : - adding SDCCH TS within TRX - more selective on filtering MS for accessing network => only MS with good UL level can access the cell and get RACH (set RXLEVAMI, RACHBT) - reduce the (over) coverage by tilting adjustment b. Radio Interface quality improvement : - frequency retune - hopping optimization (hop mode, hop activation, HSN, maio, mall lists - check it all) - for dedicated mode - power control mechanism (threshold, step size) - for dedicated mode - no over coverage for preventing interfering with others => done by coverage adjustment - antenna optimization (ant type with proper beamwidth, ant height, azimuth, tilt)c. HW problem & wrong installation fixing : - changing any broken module/equipment - fix any wrong installationd. Transmission problem overhandling : - transmission replan by TNP (if no LOS) by antenna μw optimization (height), transmission re-route - fix any transmission cabling/connection problem and module failure

a. Solving AGCH overload by : - adding block AGCH reserved => set NBLKACGR, but must consider PCH reserved reducing impact by increasing this AGCH capacityb. Radio Interface quality improvement : - see point b on explanation abovec. HW problem & wrong installation fixing : - see point c on explanation aboved. Transmission problem overhandling : - see point d on explanation above

a. SDCCH capacity overhandling might be done by : - adding SDCCH TS within TRX - more selective on filtering MS for accessing network => only MS with good UL level can access the cell and get RACH (set RXLEVAMI, RACHBT) - reduce the (over) coverage by tilting adjustment b. Radio Interface quality improvement : - frequency retune - hopping optimization (hop mode, hop activation, HSN, maio, mall lists - check it all) - for dedicated mode - power control mechanism (threshold, step size) - for dedicated mode - no over coverage for preventing interfering with others => done by coverage adjustment - antenna optimization (ant type with proper beamwidth, ant height, azimuth, tilt)c. HW problem & wrong installation fixing : - changing any broken module/equipment - fix any wrong installationd. Transmission problem overhandling : - transmission replan by TNP (if no LOS) by antenna μw optimization (height), transmission re-route - fix any transmission cabling/connection problem and module failure

a. Solving AGCH overload by : - adding block AGCH reserved => set NBLKACGR, but must consider PCH reserved reducing impact by increasing this AGCH capacityb. Radio Interface quality improvement : - see point b on explanation abovec. HW problem & wrong installation fixing : - see point c on explanation aboved. Transmission problem overhandling : - see point d on explanation above

# What kind of process (procedures) occurred within this phase ?

# How can the SDCCH connection become drop ?

- SSS Procedure Phase start from CMS REQ message sent from BSC towards MSC, and stop after receipt of ASS REQ.- SDCCH are already seized within this phase.- Many SSS procedure events are performed during this phase, that are authentication, ciphering, IMEI check, TMSI re-allocation, setup message, and digit translation procedures.- From BSS point of view, loss analysis can be got from SDCCH drop counter (NRLFSDCC_1-9)

Authentication Process

Ciphering Process

Counter Sub Counter Description

NF

RLS

DC

C (

1,3)

1 T200 expired

2 unsolicited DM response, multi frame established state

3 sequence error

4 T_MSRFPCI expired

5 distance limit exceeded

6 handover access failure

7 radio link failure

8 remote transcoder failure

9 unspecified (others)

When BTS has sent layer 2 message in acknowledge mode (that is I frame message : ASS CMD) N200+1 times to the MS without receiving layer 2 acknowledgement from MS (reasons : any radio problems may exist) until T200 timer expired, then the connections are dropped.

What may be the most drop reason can be known from mesurement counter NRFLSDCC [1-9] :

Radio Problems (interference, coverage, HW&Installation)

TRACK/TRAU module failure, COBA/CU failure, wrong DB setting (TTRAU > T8 , TTRAU > T10, TTRAU = TSYNC => This setting is for ensuring that a signaling failure (T8 and T10) is detected before transcoder failure (TSYNC and TTRAU)

Failure on HO SDCCH-SDCCH ; Causes : Radio Problems (interference, coverage, HW&Installation)

MS has sent a Um layer 2 (LAPDm) message DM (Mode) to the BTS while the BTS-MS communication is in ’multiple frame stablished state’BTS has detected irregularities in the Um layer 2 (LAPDm) flow control functions (wrong message sequence) useds in’acknowledged mode’T_MSRFPCL is not adjustable on database

MS-BTS distance exceeds the threshold EXCDIST

- SSS Procedure Phase start from CMS REQ message sent from BSC towards MSC, and stop after receipt of ASS REQ.- SDCCH are already seized within this phase.- Many SSS procedure events are performed during this phase, that are authentication, ciphering, IMEI check, TMSI re-allocation, setup message, and digit translation procedures.- From BSS point of view, loss analysis can be got from SDCCH drop counter (NRLFSDCC_1-9)

Ciphering Process

IMEI Check & TMSI Reallocation Procedure

Setup Message & Digit Translation Procedure

When BTS has sent layer 2 message in acknowledge mode (that is I frame message : ASS CMD) N200+1 times to the MS without receiving layer 2 acknowledgement from MS (reasons : any radio problems may exist) until T200 timer expired, then the connections are dropped.

Radio Problems (interference, coverage, HW&Installation)


Failure on HO SDCCH-SDCCH ; Causes : Radio Problems (interference, coverage, HW&Installation)

MS has sent a Um layer 2 (LAPDm) message DM (Mode) to the BTS while the BTS-MS communication is in ’multiple frame stablished state’BTS has detected irregularities in the Um layer 2 (LAPDm) flow control functions (wrong message sequence) useds in’acknowledged mode’T_MSRFPCL is not adjustable on database

MS-BTS distance exceeds the threshold EXCDIST

# How is this phase ?

# TASSFAIL causes ?

CounterSub Counter for CHAN TYPE

DescriptionTCH/F TCH/H

6 11 Radio Interface Message Failure

7 12 Radio Interface Failure - reversion to old channel

8 13 No radio resource available

9 14 Directed Retry

10 15 Al Other CauseTA

SS

FA

IL

(1,3

0)

- TCH Assignment Phase start after receiving assignment request (ASS REQ) message on BSC from MSC, and stop after assignment complete (ASS COM) message sending- BSS Counter start from TASSATT and end by TASSSUCC- Actually TCH Blocking influence this phase, BUT on KPI Formula HCPT for CSSR, TCH blocking is excluded from TCH assignment failure, but counted as TCH Assignment Success -> see on sheet formula- There is still loss probability on SDCCH Drop with T200 expiry reason within this phase => check if any radio problem which cause loss of ASS CMD message- Any TCH Assignment Failure will increment TASSFAIL counter in BSC

TASSFAIL due to Radio Interface Message Failure

ASS CMD message is lost, may be caused by :- Radio Interface problem : Interference, Coverage, HW Failure / Wrong Installation- unnecessary T10 setting

Counted as TCH Assignment Success on KPI CSSR Formula HCPT -> see shet formula

TASSFAIL due to Radio Interface Failure - reversion to old channel

SABM message is lost while using FACCH, assignment TCH fail and back to SDCCH , may be caused by :- Radio Interface problem : Interference, Coverage, HW Failure / Wrong Installation- unnecessary T10 setting

Directed Retry HO ACCESS message is lost while using FACCH, assignment TCH fail and back to SDCCH on old cell , may be caused by :- Radio Interface problem : Interference, Coverage, HW Failure / Wrong Installation

TASSFAIL due to Directed Retry

When Directed Retry HO is performed, TASSFAIL(9) counter will be incremented


ASS CMD message is lost, may be caused by :- Radio Interface problem : Interference, Coverage, HW Failure / Wrong Installation- unnecessary T10 setting

Counted as TCH Assignment Success on KPI CSSR Formula HCPT -> see shet formula

SABM message is lost while using FACCH, assignment TCH fail and back to SDCCH , may be caused by :- Radio Interface problem : Interference, Coverage, HW Failure / Wrong Installation- unnecessary T10 setting

Directed Retry HO ACCESS message is lost while using FACCH, assignment TCH fail and back to SDCCH on old cell , may be caused by :- Radio Interface problem : Interference, Coverage, HW Failure / Wrong Installation

When Directed Retry HO is performed, TASSFAIL(9) counter will be incremented

DB Parameter Related

DB Parameter Object Description Value Setting Trade Off

RXLEVAMI BTS

RACHBT BTS Threshold for the signal level on RACH

NBLKACGR BTS

T200 BTS

IERCHOSDCC BTS

IRACHOSDCC BTS

EISDCCHHO BTS

TTRAU BTS

TSYNC

T10 BSC

Minimum received level at the MS required for access to the network

Increase => Idle coverage shrinking, less attempt SDCCH Decrease => Idle coverage enlargement, more attempt SDCCH

Increase => Low UL level can access RACH, more attempt SDCCH, less HO fail possibility due to FACCH rejected. Decrease => Only good UL level can access RACH, less attempt SDCCH, more HO fail possibility due to FACCH rejected.

Specifies the number of CCCH blocks to be reserved in CCCH TS for AGCH ; MAINBCCH provides 9 CCCH blocks (shared between PCH and AGCH)

Increase => Add CCCH blocks to be reserved for AGCH, decrease blockes to be reserved for PCH.Decrease => vica versa from statement above.

LAPDm timer 200 ; determines the waiting time for a layer 2 frameacknowledgement

Should be attended that this timer setting can much reduce drop call / signalling conection, but can also deliver non realistic image of the actual radio interface quality (less drop but poor quality). So need proper adjustment as trade off

To enable / disable intercell SDCCH HO

Set True => activate intercell SDCCH HO, more SDCCH usage, more possibility on SDCCH fail/drop.Set FALSE => disabling intercell SDCCH HO, less SDCCH usage, less possibility on SDCCH fail/drop

To enable / disable intracell SDCCH HO


To enable / disable interBSC SDCCH HO


Timer supervision start from sending UL TRAU frame and stop when first DL TRAU frame received by BTS

Must set to proper value ; Must follow the rule : TTRAU > T8, TTRAU > T10, TTRAU = TSYNC for ensuring signalling failure is detected before transcoder failure

BTS ; TRAU

Timer supervision start of TRAU frame handling. Start when 3 DL TRAU frame haven't correctly received, and reset when correct frame is received again.

Must be set to proper value ; Must follow the rule : TSYNC = TTRAU ; TSYNC setting in BTS object must be same with TSYNC setting in TRAU object

Time to return assignment complete (ASS CMP) message. Start from sending message ASS CMD and stop when ASS CMP received.

Must be set to proper value ; In the case of call setup, the setting must follow the rule : T10 < TTRAU

cssr analysis

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