GSM channel concept
Channel concepts:
There are two types of channel in GSM Network - Control channel and Traffic channel:
The traffic Channels: are used to transport encoded speech and data information. Full rate traffic channels TCH/F are defined using a group of 26 TDMA frames called a 26 frame multi-frame. The 26 frame multi-frame lasts 120ms and the traffic channels for the downlink and uplink are separated by three bursts. The TCH/F consists of one time slot in each TDMA frame i.e., one slot every 4.615ms.
The control Channels: are used for network management messages (call set up, control signaling etc.) and some channel maintenance tasks. These can be subdivided into BCH (Broadcast Channel), CCCH (Common Control Channel), and DCH (Dedicated Channel)
BCH: BCCH, FCCH, SCH / CCCH: RACH, AGCH, PCH / DCH: SDCCH, SACCH, FACCH, CBCH
BCCH (Broadcast channel): Its downlink channel is used for transmitting of system information unique BCCH define for entire cell and it is transmitted on Timeslot zero of BCCH carrier and Read only by idle mobile at least once every 30 secs
SCH (Synchronization Channel): It’s a Downlink channel and Carries information for frame synchronization and Contains TDMA frame number and BSIC.
FCCH (Frequency Correction Channel) it is a Downlink only and Enables MS to synchronize to the frequency and also helps mobiles of the ncells to locate TS 0 of BCCH carrier
RACH (Random Access Channel) It is Uplink only and Used by the MS to access the Network.
AGCH (Access Grant Channel) It is Downlink only and Used by the network to assign a signaling channel upon successful decoding of access bursts.
PCH (Paging Channel): Downlink only and Used by the Network to contact the MS.
SDCCH (Standalone Dedicated Control Channel): Its Uplink and Downlink and Used for call setup, location update and SMS.
SACCH (Slow Associated Control Channel): Used on Uplink and Downlink only in dedicated mode and Uplink SACCH messages - Measurement reports. Downlink SACCH messages - control info.
FACCH (Fast Associated Control Channel): Uplink and Downlink and Associated with TCH only and it are used to send fast messages like handover messages. Works by stealing traffic bursts
CBCH (Cell broadcast channel): It is used transmitting of broadcasting msg
TCH/f and TCH/H : gross rate 22.8kbps, speech 13kbps, data 9.6kbps (gross rate = 57*2*24/120ms = 22.8KBPS)
RCA for KPI in GSM Network
KPI (Key Performance Indicator)
TCH Drop: disconnect a unwanted call is known as TCH drop [TCH Drop = (TNDROP)/TCASSAL*100]
SDCCH Drop Rate = [(CNDROP-CNRELCONG)/ (CMSESTAB)]*100 %
SDCCH Blocking = (CCONGS)\(CCALLS)*100
TASR = (TCASSAL) / (TASSALL) *100
HOSR = (SUMOHSUCC+SUMEOHSUCC)/ (SUMOHOATT+SUMEOHATT)*100
Random Access Success Rate = (CNROCNT)/ (CNROCNT+RAACCFA) * 100
RAACCFA: Failed Random Access
CNROCNT: All accepted Random Access
TCH DROP
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HO FAIL
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DLQ
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Low Signal strength DL & UL
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Less, Many or Mismatch NBR
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BCCH & TCH Frequency Interference
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Bad Quality DL & UL
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TCH Cong at target cell
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Interference or error on E1
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High TA
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Low SS or Bad Qual on cell border
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Mismatch MAIO & HSN
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Bad Parameter regulation
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Mismatch HO algorithm
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Hardware Issue, faulty or Alarm
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High ICM, VSWR or path imbalance
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Mismatch HO parameter setting
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Antenna Faulty/ feeder
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E1 error & Transmission fault
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Sector swap
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Time-slot Issue
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Bad Parameter setting
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CO-BCCH / BSIC
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Poor Coverage and Spill
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Drop call due to Handover
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HO Delay
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High Utilization (>150%)
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Less, Many or Mismatch NBR or HO Delay
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uncorrected NBR planning
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Ater Issue or Ater Circuit Faulty
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Suddenly drop
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Interference or error on E1
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wrong combing
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Hardware fault ( Alarm & Swap)
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Bad Antenna installation
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Hardware fault ( Alarm & Swap)
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Low SACCH multiframe value
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TASR
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SD & TCH Congetion
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Low RLT value
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Poor coverage, Weak UL
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High utilization
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Low ACCMIN Value
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High utilization ( FR utilization)>150%
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less Half rate
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Low RACCH_access_min
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Hardware alarm or Trx Faulty
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HCS feature
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length of timer T3103 is low
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abis or A interface congestion or error
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length of timer T3109 is low
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length of timer T3111 is low
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Length of timer T305/T308 is set to great value.
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SD DROP
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PSR
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RACH
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Low SS, Bad Qual, and High TA
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Parameter of PSR is MFRMS and timer is T3113
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Poor BSIC Plan
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LAC Boundary
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incorrect cell parameter
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Poor BCCH Plan
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SW congestion
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excess paging discard
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Poor Coverage and Spill
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Due to TCH Congestion
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incorrect MSC parameter
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Phantom RACCH
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Hardware or TS faulty
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poor paging streagady
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Faulty antenna and cable
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Interference or error on E1
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SD congestion
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Poor ACCMIN and CRO
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drop call due to TCH congestion
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combined BCCH
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Mismatch MAXRET & TX
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uncorrected LAC dimension
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abis or A interface congestion or error
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decreasing signaling load on CCCH
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Ericsson GSM Parameter
MODE | PARAMETER |
IDLE MODE | ACCMIN CCHPWR CRH NCCPERM CBA Or CB CBQ CRO TO PT T3212 ATT MaxRet ACC BA List SIMSG |
PAGING | AGBLK MFRMS MaxRET |
RACH PARA | MaxRET TX |
LOCATION UPDATE | ATT BCCH TYPE T312 CRH |
Dynamic Full/ Half Rate Mode | DMQB DMQBAMR DMQBNAMR DMQG DMQGAMR DMQGNAMR DMTHAMR DMTHNAMR DHA DTHAMR DTHNAMR |
HCSBAND LAYER | LAYER LAYERTHR LAYERHYST PSSTEMP PTIMTEMP FASTMSREG CSYSTYPE MBCR |
CELL COMMON DATA | BSPWRB BSPWRT CGI BSIC BCCH NO. BCCH TPYE AGBLK FNOFFSET ECSC MSTXPWR TSC |
LOCATING URGENCY CELL DATA | TALIM PSSBQ PSSTA PTIMBQ PTIMTA PSSHF PTIMHF |
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