nortel gsm counters and metrics

GSM counters and metrics

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Copyright 2004 Nortel Networks, All Rights Reserved

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NORTEL CONFIDENTIAL

The information contained in this document is the property of Nortel Networks. Except as specifically authorized in writing by Nortel Networks, the holder of this document shall keep the information contained herein confidential and shall protect same in whole or in part from disclosure and dissemination to third parties and use same for evaluation, operation and maintenance purposes only.

The content of this document is provided for information purposes only and is subject to modification. It does not constitute any representation or warranty from Nortel Networks as to the content or accuracy of the information contained herein, including but not limited to the suitability and performances of the product or its intended application.

This is the Way. This is Nortel, Nortel, the Nortel logo, and the Globemark are trademarks of Nortel Networks. All other trademarks are the property of their owners.

without notice. Nortel Networks assumes no responsibility for errors that might appear in t.All other brand and


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PPP/DDD/CCC/NNNN 01.03 / EN Preliminary 30/JUN/2006 /38

CONTENTS

1 INTRODUCTION.......................................................................................................................4 1.1 OBJECT ..............................................................................................................................4

2 GENERALITIES ON GSM COUNTERS ....................................................................................5 2.1 COUNTER CATEGORIES ........................................................................................................5 2.2 COUNTERS LEVELS ...........................................................................................................5 2.3 COUNTER TYPES..................................................................................................................5 2.4 COUNTERS AND AMR...........................................................................................................6

3 RACH .......................................................................................................................................7 3.1 RACH COUNTERS ...............................................................................................................7 3.2 RACH METRICS...................................................................................................................8

4 PAGING .................................................................................................................................11 4.1 PAGING COUNTERS ............................................................................................................11 4.2 PAGING METRICS ...............................................................................................................12

5 SDCCH...................................................................................................................................13 5.1 SDCCH COUNTERS ...........................................................................................................13 5.2 SDCCH METRICS ..............................................................................................................13

6 TCH ASSIGNMENT AND ALLOCATION................................................................................14 6.1 TCH ASSIGNMENT AND ALLOCATION COUNTERS .....................................................................14 6.2 TCH ASSIGNMENT AND ALLOCATION METRICS.........................................................................15

7 AMR PENETRATION .............................................................................................................22 7.1 AMR PENETRATION COUNTERS ............................................................................................22 7.2 AMR PENETRATION METRICS ...............................................................................................22

8 TCH DROP .............................................................................................................................23 8.1 TCH DROP COUNTERS ........................................................................................................23 8.2 TCH DROP METRIC..............................................................................................................27

9 HANDOVERS.........................................................................................................................29 9.1 HANDOVER COUNTERS .......................................................................................................29 9.2 HANDOVERS METRICS ........................................................................................................32

10 AMR LINK ADAPTATION ......................................................................................................34 10.1 LINK ADAPTATION COUNTERS ..............................................................................................34


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10.2 LINK ADAPTATION METRICS .................................................................................................34

11 RADIO CONDITIONS .............................................................................................................35 11.1 RADIO CONDITIONS COUNTERS............................................................................................35 11.2 RADIO CONDITION METRICS .................................................................................................36


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1 INTRODUCTION

1.1 OBJECT

This document aims at providing all necessary knowledge for GSM counters, metrics, monitoring and troubleshooting. It will handle procedure by procedure, feature by feature all the most import counters and provide guidelines on expected values of strange behaviors


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2 GENERALITIES ON GSM COUNTERS Counters are incremented either at the BTS side (reception of a message from the Mobile Station) or at the BSC side (reception of a message from the BTS). They are then all stored on the BSC in files lasting 15 minutes prior to being sent to the OMC/SDO for hourly aggregation or kept as 15 minutes files.

2.1 COUNTER CATEGORIES

Counters are either - OFS: fast statistics - OGS: general statistics - ORT: real time

This document will only deal with OFS counters as they are the ones used for the monitoring by the operators.

2.2 COUNTERS LEVELS

Counters are retrieved at different levels:

- BSC level: load of boards, computation of various XXX - PCM level: level 1 or level 2 errors + pcm availability - Cell level: all GSM procedures - Transceiver zone level: to monitor dual band cells or dual zone cells each band or zone seperately - TDMA level: to investigate DRX HW issues

2.3 COUNTER TYPES

Counters are of different types according to what intends to be done with them:

CUMULATIVE COUNTER This counter offers the means of counting events. It can be used in threshold mode, but there is no minimum or maximum mode of operation. In addition to the header it contains a single field: CUMULATED VALUE Example: handover counters: C1138/x

VALUE COUNTER This counter offers the mean of measuring average and maximum values for the observed entities. It can be used in threshold mode. In addition to the header it contains three fields. The third field is used only if a maximum needs to be recorded. CUMULATED VALUE SAMPLES NUMBER MAXIMUM VALUE Example: counter of queuing duration, C1618

LOAD COUNTER This counter offers the means of sampling rapidly changing data, and obtaining an average and a minimum or maximum value of the sampled data. It can be used in threshold mode. In addition to the header it contains five fields. The fourth field is used only if a minimum or a maximum needs to be recorded. CUMULATED VALUE SAMPLES NUMBER MAXIMUM VALUE MIN/MAX FLAG CURRENT VALUE Example: TCH allocation counter C1611


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2.4 COUNTERS AND AMR

AMR was introduced in V14 version. AMR and EFR calls coexist in the same network and cell. Usage of AMR or EFR is only linked to the mobile performances: AMR capable or not To monitor AMR, some new counters specific to AMR were added. All counters prior to V14 were kept:

- some are incremented by AMR FR and HR - some are incremented by AMR FR only - some are incremented by AMR HR only - some are neither incremented by AMR HR nor AMR FR

The incrementation for AMR calls is based on the counter philosophy that can sometimes be guessed based on the counter name.

Complete table is available in PE/BSS/DD/018


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3 RACH

3.1 RACH COUNTERS

The RACH is emitted by the mobile and requests the BSC the allocation of a SDCCH channel.

C1026: gives the number of received RACH at the BTS side C1027: gives the number of decoded RACH at the BTS side C1033: gives the average strength of non decoded RACH. This value is usually around –115 dB. If this value were at higher value, for example –100dB, this would mean that much interference is present C1191/x: gives the repartition of the decoded RACH sent to the BSC for the several causes of RACH (location update, mobile originating call, answer to paging, emergency call…) C1192/x: each decoded rach requests the BSC for the allocation of a SDCCH channel. This counter gives the number of SDCCH channels allocated by the BSC for each cause (location update, mobile originating call, SMS …) C1161/x: if the BSC cannot or does not want to allocate SDCCH, it increases this counter. Possible causes: traffic with MSC is closed, lack of SDCCH resources, no response from BTS, timing advance of the RACH higher than 63, channel activate nack received from the BTS. In case of lack of SDCCH resources, the counter C1609/2 is incremented. (C1191-C1192=C1161) C1193/x: computes the number of allocated SDCCH effectively used by the mobiles. C1163/5: computes the number of allocated SDCCH that are not used by any mobiles. At the expiration of timer T3101 this counter is incremented. This counter is among others incremented in case of phantom RACH or bad radio conditions.

CAUTION: C1195 and C1196 are no more to be used. These counters are only incremented in case the Mobile release is Phase II. All mobiles with higher release version (example AMR Mobiles which are release 99) will not increment those counters.

RACH Channel required

Channel activation

Channel ack

Immediate assign command Immediate assign

Service request on SDCCH Establishment indication

C1026 C1027 C1033

C1191/x

C1192/x

C1193/x C1195 C1196

C1161/x

BSC BTS Mobile Station


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3.2 RACH METRICS

Difference between C1026 and C1027 is usually due to the number of GPRS RACH. The difference can be increased in case of RACH filtering by the BTS/BSC. Min level of non decoded RACH Average value of C1033: it gives the average strength of non decoded RACH (rach messages sent by MS, received by the BTS but that could not be decoded) This value is usually around –115 dB. If this value were at higher value, for example –100dB, this would mean that:

- much interference uplink is present - a cable UL is not correctly plugged in for the transceiver equipment

Check as well the “FH bus congestion” in the notification log. Check that no other neighbouring cell is using the same BCCH frequency. Network access failure Network is accessed in two steps 1/ BSC grants the SDCCH channel: C1192 / C1191 vs: SDCCH allocation issue 2/ MS tries to get on the granted SDCCH channel: C1192 vs C1193: SDCCH establishment issue

STEP 1: allocation

Check the difference between sum of C1191 and sum of C1192: Compute the metric: 1 - (SUM C1192/X) / (SUM C1191/X) Expected value: less than 1% Value showing a dimensioning issue: more than 5% If the result is 0 => no trouble of SDCCH allocation If the result is not 0: Check with the C1161/X counters why the SDCCH could not be granted by the BSC. Possible causes are:

- traffic with MSC is closed: check the A link - no response from BTS: check the Abis link - timing advance of the RACH higher than 63: there might be a power resurgence of another cell using

the same BCCH frequency and the same BSIC. - channel activate nack received from the BTS: check in what state is the BTS and eventually perform a

lock / unlock of the BTS - lack of SDCCH resources: go to the step SDCCH blocking and resource shortage

SDCCH resource shortage: Compute the SDCCH blocking ratio: C1608/(C1606+C1608) In case of SDCCH resource shortage, counter C1609/2 is incremented as TCH dynamically reconfigured are used for signaling. This ratio should not be higher than 0.01%. If the ratio is much higher than 0.01% it could be due to 3 reasons: - Radio trouble on the cell - Troubles on the Abis/BSC/A path -mere normal underdimensionning Radio trouble on the cell: Establishment success rate is very low so requests are triggered in a loop. Such troubles can be identified by looking at :

- assignment failure rate is high - C1033 which is lower than -110dB (-106 dB for example) - RxQual UL is very high - EFR tch mean holding time metric is low (less than 20 seconds)


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In such cases, the lack of SDCCH is very highly pegged along with an increase of C1163/5 Trouble on the Abis/BSC/A path Such troubles are very rare. - Abis congestion issue (1163/5 counter should highly pegg and SDCCH mean holding time should have reached higher values, location update requests represent more than 95% of the whole requests as they are requested in loop until the establishment is a success)=> reset the TMU board managing the cell to make the problem disappear - Trouble on SCCP link preventing the location update to correctly establish or issue with HLR/VLR (no success of the location update procedure: C1193/x = 0 at hourly level when C1192/ is highly pegged) In that case the lack of SDCCH is very highly pegged along with an increase of C1163/5 Mere under dimensioning: Too few SDCCH available. In that case, there is no high variation of C1163/5 Check if it is a new situation:

- Check how many SDCCH are configured (C1811 or display of all the channels with the GUI)and how many are up and running : C1701 average. It could be just due to the deconfiguration of a DRX (trap) leading to SDCCH channels deconfiguration. => lock and unlock of the troubled DRX, change of TDMA priority to give higher priority to the TDMA bearing the SDCCH channels, change of the impacted DRX

- Check if the lack of the cell or of neighbouring was changed. If yes then increase the number of SDCCH channels as cells at LAC boundaries require more SDCCH to be provisioned as they will do more location update procedure.

If it is not a new situation: increase the number of SDCCH channels Check the SDCCH traffic that is requested C1607 and compare it to the output (given by the erlang table at 0.01%) of the number of up and running SDCCH resources (C1701).

STEP 2: establishment Second step, if it seems that some mobile fail to get on the BSC successfully granted SDCCH, this is shown by C1163/5 counter. Check the difference between C1192 and C1193 (given also by C&163/5) and ratio: 1 - sum (C1193)/sum (C1192) Expected value: less than 3 % Value showing a problem to be looked at: more than 7% In case of problem: - Check if all cells or just one cell is affected. Easy check through an ordering of descending C1163/5 values at cell level - Check if all Rach causes encounter the issue or if only a certain type of request is hit by the difference. - Check establishment failure rate cause by cause: answer to paging, mobile originating call, location update - check if all hours are affected by an equal establishment failure or just some hours If only a specific establishment request is more heavily hit : example emergency call, then the network is probably facing a ghost RACH issue most usually due to frequency planning issues. RACH is such a tiny message that parasites can be identified as RACH: in that case a sdcch allocated for a ghost rach will never be used as there has been no mobile requesting it. In case of ghost rach, all requests causes are equally incremented of a few requests (for example 50 peggs per day): so it will be noticeable in priority for requestst with usually very few pegs as emergency calls, re-establishments…. Reconfiguration issue

- check with C1701 counter how many SDCCH are present in the cell


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- check with C1701 at hourly level before after if there as been any lock and unlock leading to the reconfiguration of the SDCCH on another DRX which is bad

- if there is more than one TDMA bearing SDCCH, check which one is causing the issue or if all of them is causing the issue (this can be checked thanks to C2141 and C2142 counters of assignment: if they are equal, there is no problem on the DRX, if there is a big difference, there is a problem on the DRX). It is to be kept in mind that DRXs belonging to a same cell can be desynchronized in case of quartz issue on the DRX itself or in case they get there synchronization on two different PCMs => check if 1 or several PCMs handling the site.

- check C1033: if lower than 108, there is an UL issue on the cell Ghost rach: allocation for emergency calls surges, no change in the establishment for emergency calls

- check for neighbouring cells using the same BCCH channels - check for local interferer - check with C2143 at hourly level the TEI mapping - check the whole path in the BTS for any cause of interfering noise (lightning protection, water in the

antennas cables) - change the rach max range for urban cells to a lower value (parameter : rndAccTimAdvThreshold) - check RxLevAccessMin: for Rxlev access min at -110dB it is expectable to reach higher SDCCH

establishment failure. In rural zones where maximum coverage is seeked, the value is usually at -110dB which is the sensibility limit of the BTS

Lapd congestion

- problem appears only at high traffic hours and disappears when the traffic decreases - very high increase of location update rach as in loop process until completion - 1161/3 no response to channel activate might increase when the problem is present Action: Reset all the MCA1 of the TMU, if no improvement then reset the TMU holding the cell group


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4 PAGING

4.1 PAGING COUNTERS

Paging messages are sent to all cells belonging to the location area where the mobile is.

On the air interface, for each paging command received from the MSC, 1+X repetitions will be sent no matter if the mobile has answered or not. X is defined by the BTS parameter NbOfRepeat. Paging messages are sent several times on the air interface as the air interface is not reliable. Paging counter are only incremented for each paging command from the MSC.

C1028: number of paging that has a free timeslot immediately and can be sent immediately on the air interface C1029: number of paging that had to wait once before finding a free timeslot. C1030: number of paging that had to wait twice before finding a free timeslot

MS

Pag cmd Pag cmd

Pag req 1MSC BSC BTS

2

3

4

Pag nowPag 1wPag 2wPag more

MSC BSC

BTS a

BTS a

BTS a

BTS a

BTS a

BTS a

BTS a

LAC 1

LAC 2

Paging cmd

Paging cmd

MSC BSC

BTS a

BTS a

BTS a

BTS a

BTS a

BTS a

BTS a

LAC 1

LAC 2

MSC BSC

BTS a

BTS a

BTS a

BTS a

BTS a

BTS a

BTS a

LAC 1

LAC 2

Paging cmd

Paging cmd


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C1031: number of paging that had to wait more than twice before finding a free timeslot C1604: average number of paging waiting to be transmitted C1605: after a certain time, if there is still no resource to transmit the paging on the air interface, the paging message is discarded. When counters C1031 and C1605 have high values, it traduces a lack of CCCH resources for the actual configuration of the Location Area. What can be done is: - change the BCCH combined channel in mainBCCH - reduce the number of cells in the Location Area - reduce the number of paging repetitions on the air interface

4.2 PAGING METRICS

Paging success rate can only be computed at the LAC level. Paging success rate at LAC level: expected value around 80%: if success rate is much lower

Check that paging are repeated at cell level (nbOfRepeat > 0) Check the rach counters to identify is any radio issue in some cells (if rach failure, there can be no

paging answer) Normally all the paging messages should be transmitted on the air interface without too much waiting for a paging block. If counter C1030, C1031 are pegged, check what the the average queue length for paging messages: C1604. Check as well that paging are not discarded C1605. If the paging have to wait too much or are even discarded, that could come from 1/ the provisioning 2/ the lac dimensioning Check the provisioning:

combined BCCH should only be used in cells with one or two DRXs. numberOfblocksforAccessGrant: set to 0, if gives more room for the paging messages. Check the lac dimensioning: if two many cells belong to the same lac, then the number of paging

messages to be sent on the air interface might become too high for the PCH channel whatever its configuration. The only solution is to reduce the lac size.


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5 SDCCH

5.1 SDCCH COUNTERS

C1606: Number of SDCCH allocations C1607: maximum and average value of SDCCH traffic C1608: allocation failure due to SDCCH lack C1609/2: allocation of a TCH to perform the signaling in case of SDCCH shortage Dimensioning of SDCCH is recommended at 0.1% of blocking. C1603: Duration of a SDCCH allocation. It enables to check is the SDCCH are correctly released. Usual SDCCH allocation duration mean value is less than 5 seconds. C1045: gives the number of allocation of SDCCH that lasted more than 25 seconds and the average duration of SDCCH allocation that lasted more than 25 seconds. C1060: Number of milliseconds during which all the SDCCH were allocated. It also gives the number of period during which all SDCCH were allocated. This counter enables to detect congestion. C1701: SDCCH resources configured and working. A comparison of the average and maximum value enables to detect if resources have been lost during the day C1163/x: repartition of the number of releases while the communication is in signalling phase on SDCCH. All C1163/x are drops of established SDCCH channels except for

C1163/5: sdcch establishment failure C1163/20: is a normal release

C1163/30: queueing expiry The first 4 screenings of 1163/X show an issue with the SS7 link: between BSC and NSS

Screening: 0 Receipt of a SCCP DISCONNECTION INDICATION message from the MSC. Screening: 1 Receipt of a RESET message from the MSC. Screening: 2 Receipt of a RESET CIRCUIT DOWNLINK message from the MSC. Screening: 3 Receipt of a SCCP DATA REFUSAL message from the MSC. Screening: 4

Screening 4 meaning there is an incorrect rach message => check what cell is affected and to what extend to identify incorrect rach messages Incorrect first L3 message (piggybacked in ESTABLISHMENT_INDICATION message): -not syntactically correct -not in the following list: CM SERVING REQUEST, PAGING RESPONSE, LOCATION UPDATING REQUEST, CM RE-ESTABLISHMENT REQUEST, IMSI DETACH.(a CLEAR REQUEST message is sent).

5.2 SDCCH METRICS

SDCCH blocking: C1608/0 / (C1608/0 + C1606) SDCCH drop metric: (C1163/x –C1163/20-C1163/5 –C1163/30)/ C1607 SDCCH holding time: average C1603


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6 TCH ASSIGNMENT AND ALLOCATION

6.1 TCH ASSIGNMENT AND ALLOCATION COUNTERS

C1049: TCH Assignment attempts for FR channel (EFR or AMR FR). Warning, in the assignment is included the intracell handovers C1050: TCH assignment success for FR channel (EFR or AMR FR) C1055: TCH assignment failure for FR channel (EFR or AMR FR) C1904/0: AMR FR assignment failure C1903/0: AMR FR assignment success C1904/1: AMR HR assignment failure C1903/1: AMR HR assignment success C1609: FR TCH allocation C1610: HR TCH allocation C1613: FR TCH allocation failure due to TCH lack C1614: HR TCH allocation failure due to TCH lack Dimensioning of TCH is recommended at 2% blocking at the busy hour C1616: length of the TCH queue C1600: connection duration on TCH. The average TCH duration is usually between 20 seconds and 60 seconds. C1057: gives the number of milliseconds during which all the TCH resources are used. It also gives the number of period during which all TCH resources are used. C1611/x: average number of TCH FR resources allocated. This counter enables to get the FR Erlang traffic C1612/x: HR erlang traffic C1700: TCH resources configured and working. A comparison of the average and maximum value enables to detect if resources have been lost during the day The difference between TCH assignment and TCH allocation is the following:

- allocation counters are incremented every time a traffic channel is allocated in a cell due to mobile originating calls, mobile terminating calls or handovers intercell and intracell.

- assignment counters are only allocated in a cell due to mobile originating calls, mobile terminating calls and handover intracell.

TDMA level At TDMA level, it is expectable to have TDMAs with lower traffic than other TDMAs because of the allocation strategy: Lowest TDMA id + higher TS value in the hopping tdmas. So the TDMAs with the lowest TDMAid will be allocated in priority and hence will handle more traffic than the other tdmas. It is only during higher traffic periods that the other TDMAs might be used. Regarding AMR HR, AMR Based on traffic enables handovers from AMR FR to AMR HR tdma per TDMA. Uneven AMR HR repartition on all the TDMA is therefore expectable TDMA counters 2141: EFR and AMR FR assignment request 2142: EFR and AMR FR assignment success 2118/0: AMR FR assignment request 2100/0: AMR FR assignment success 2118/1 AMR HR assignment request 2100/1: AMR HR assignment success 2102/0: AMR FR traffic in erlang C1828/0: AMR HR traffic in erlang C1824/0: EFR + AMR FR traffic in erlang C1825/0: TCH FR available


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6.2 TCH ASSIGNMENT AND ALLOCATION METRICS

TCH assignment failure: Assignment is a pure radio procedure. Reasons for failure might be: interference, bad DRX hardware, loss of GSM clock, loss of synchronization by the site manager. It is therefore interesting to look at the assignment failure at TDMA level. Assignment failure FR channels (AMR and EFR): (C1049-C1050)/C1049 The failure reason is purely to be seeked on the air interface. It is usually at a ratio below 1% In case of high assignment failure, the incoming handovers are impacted as well when the target DRX is the bad one. C1049-C1050 > C1055 : C1055 assignment failure counter only counts the assignment failure that succeeded to re-establish on the SDCCH to send the assignment failure message. Assignment failure AMR FR: C1904/0 / C1903/0 Assignment failure AMR HR: C1904/1 / C1903/1 Assignment failue at TDMA level: (C2142/0 - C2141/0) / C2141/0 In case of assignment failure on FR resources EFR or AMR FR:

- check with C1700 at hourly level before after if there as been any lock and unlock leading to the reconfiguration of the TCH on another DRX which is bad

- check thanks to C2141 and C2142 counters of assignment if the problem is on all tdmas or only a few of them: if they are equal, there is no problem on the DRX, if there is a big difference, there is a problem on the DRX.

- check with C2143 at hourly level the TEI mapping to identify the bad HW - It is to be kept in mind that DRXs belonging to a same cell can be desynchronized in case of quartz

issue on the DRX itself or in case they get there synchronization on two different PCMs => check if 1 or several PCMs handling the site.

In case of assignment failure on FR resources EFR or AMR FR: Very high values possible with bugged mobiles unable to perform AMR HR thus requesting through intracell handovers the assignment from AMR FR to AMR HR when load and radio quality conditions are met => issue appears only during specific hours at very high level. TCH blocking ratio TCH blocking ratio is a merely depends on the dimensioning of the resources at cell level: number of DRXs and number of TCH created. Global blocking: C1613 + C1614 / (C1610 + C1613 + C1614 + C1609) FR channels blocking (AMR FR and EFR): C1613/(C1609+C1613) TCH blocking should be lower than 2% at the busy hour. The reason is only a dimensioning issue. AMR HR blocking: C1614 /(C1610 + C1614) In case of intracell handovers activation (by default with AMR activation), the short blocking rate formula is no more valid. A user blocking rate formula is more appropriate: it is composed of blocked minus intracell handover selection failure: in case of intracell selection failure, there is no impact for the customer as the call is already on-going in the cell. User blocking rate:


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[C1613/0 + C1614/0+C1617/0 + C1617/1 –(1081-1082)- (C1069-C1071]-(C1070-C1072)] /(C1609_0+C1610_0+C1613+C1614+C1617_1+C1756_1+C1756_2+C1758_1+C1758_2+C1758_3+C1758_4+C1760_1+C1760_2+C1760_3+C1760_4+C1760_5-(C1069+C1070+C1081)) User blocking is the most interesting blocking formula as it removes blocking induced by intracell handover procedures and intercell handover procedures which are not impacting the end user as the call is already established. If traffic handover is activated, check for counter C1714 that gives the BTS overload duration If queueing is activated, check for the TCH queue length that gives an idea of how many additional TCH are requested: C1616/0 avg and the queueing duration C1618/0 average and C1618/1 average If GPRS is activated, check for counters C1814 and C1815 that gives the number of pre-emption success and failure when no more TCH are available. In case of high blocking, it is also necessary to monitor the duration in time when no resources are available at all for traffic: C1057 cum counter TCH blocking investigation: In case of TCH blocking, it is however interesting to check if the blocking issue comes from

- a mere underdimensiong, - TCH disconfiguration - TCH overflow - HW failure preventing the correct establishment of handovers leading to in loop incoming handovers or

ping pong handovers HW failure: check at TDMA level the incoming handovers execution success is good for every TDMA with C1844, C1845, C1846 and C1847: after a failure to execute an handover toward this cell, the handover is requested again and again in loop until correct completion which could create some blocking HW disconfiguration: check C1700 at hourly level to check if any glitch in the value, every single glitch means there has been a disconfiguration of the TDMA. If there was no HW failure and no HW disconfiguration, then it is a mere dimensioning problem


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TCH dimensioning issues no AMR activated Check the traffic C1611 carried by the cell at the busy hour and compare it with the 2% erlang table, that will give how many TCH should have been provisioned. Compare that value to the C1700 counter that gives the actual value of provisioned TCH and get the number of new TCH to be added to the cell.


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If AMR FR and HR is activated, there a possibilities to reduce the blocking rate without increasing the number of DRXs by increasing AMR HR penetration. One can achieve this with direct AMR HR allocation performed at a lesser RxLev or a fallback to AMR FR later in terms of C/I. Involved parameters are:

AMRDirectAllocRxLevUL AMRDirectAllocRxLevDL AMRHRToFRIntracellCodecModeThreshold

The table herbelow presents the traffic carried vs AMR HR penetration for a specific set of TCHs Check as well what are the AMR BoT parameters used HRcellLoadStart and HRCellLoadEnd to check that they are not too restrictive and provoking an HR on/off process less productive than with a correct setting.


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CAUTION: there is no queueing for AMR HR resources: the request will be changed to AMR FR. AMR HR is not possible on pre-empted PDTCH


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7 AMR PENETRATION

7.1 AMR PENETRATION COUNTERS

C1612/0 average: AMR HR traffic in erlang C1901/0 average: AMR HR traffic in erlang C1611 average: AMR FR and EFR traffic in erlang

7.2 AMR PENETRATION METRICS

EFR only traffic: C1611/0 – C1901/0 AMR penetration ratio on all traffic: (C1612 + C1901/0) / (C1612/0+C1611/0) This metric computes the percentage of traffic handled in AMR FR or HR as compared to the whole traffic. There is not target value to be reached, it just presents a picture of AMR mobile penetration in the network AMR HR penetration over all AMR traffic: C1612 / (C1612 + C1901/0) This metric computes the percentage of traffic handled in AMR HR as compared to the whole AMR traffic (AMR FR + AMR HR) Depending on parameters AMR Based on Traffic (HrCellLoadStart, HrCellLoadEnd); depending on the chosen adaptation table, AMRHRToFRIntracellCodecModeThreshold values and hrdirectallocthreshold, AMR HR penetration ratio can be much different from one network to the other one.


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8 TCH DROP

8.1 TCH DROP COUNTERS

There several screening for the release of TCH channels: 1164/x CAUTION: 1164/20 is not a drop call, all normally released calls increment this counter Drops related to the air interface are always the most heavily pegged : T200 drops, radio link time out. T3103 drops, This is a normal behavior because GSM is based on the air interface and if the signal strength or the quality gets low, then the call is bound to drop. 1164:TRAFFIC_RELEASE BTS LEVEL Meaning: number of releases while the communication is in “traffic” phase. Screening: 0 Receipt of a SCCP DISCONNECTION INDICATION message from the MSC. -> SCCP issues, see with MSC and check if no MSC board in charge of the SCCP is in failure. Screening: 1 Receipt of a RESET message from the MSC. -> check with MSC Screening: 2 Receipt of a RESET CIRCUIT DOWNLINK message from the MSC. -> check with MSC Screening: 3 Receipt of a SCCP DATA REFUSAL message from the MSC. -> SCCP issue, check with MSC Screening: 6 Expiration of T3107 timer before receipt of ESTABLISHMENT INDICATION -> this screening is only seen when intracell handovers are performed. When an intracell handover does not succeed and if the mobile fails to return to the old channel (the oneTCH it was on when the handover was triggered), then screening 6 is incremented. In case of AMR activation there will be an increase of this drop cause as AMR activation means intracell handovers from AMR HR to AMR FR channel or vice versa. The number of intracell will increase thus the number of drops due to intracell handovers follows. AMR Based on traffic feature enables to reduce the increase to acceptable values. Screening: 7 TS removal due to an O&M operation (associated cell put out of service...) -> maintenance operation performed Screening: 8 TS removal due to an equipment failure (PCM KO...) -> Calls are relayed by PCM timeslots to the BSC. A failure of a PCM will interrupt all the calls handled by it. Screening: 9 CIC removal due to an O&M operation (terrestrial circuit put out of service...) -> maintenance operation performed on terrestrial circuits on the A interface Screening: 10 CIC removal due to an equipment failure (PCM KO...). -> equipment failure on the A interface Screening: 11 Associated radio channel blocked due to an O&M action. -> a radio TCH channel on which a call was ongoing has been locked


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Screening: 12 Receipt of a CALL CLEARING request from the L1M following a call clearing distance threshold comparison. -> the BTS site manager has detected that the mobile currently on call was too far from the antenna. The call is then released. The usual value for this parameter is 35 km which is the maximum cell coverage of a cell. Screening: 13 Receipt of a CONNEXION FAILURE INDICATION message with Abis cause set to radio interface failure. -> issue on the air interface prevented the call to go on Screening: 14 Receipt of a CONNEXION FAILURE INDICATION message with Abis cause set to radio link time out RLT. -> the call is dropped because the BTS did not received many measurements reports from the mobile. The reason is that the radio for this call is so poor (low signal strength or bad quality) that the measurements reports send by the mobile cannot be decoded by the BTS. This cause is one of the most usual reasons for drop calls. Screening: 15 Receipt of a CONNEXION FAILURE INDICATION message with Abis cause set to O&M. -> O&M operation. Screening: 16 Receipt of a RELEASE INDICATION message from the BTS. this counter is pegged when the BSC receives a release indication message from the BTS. This counter is usually at low values. If this counter begins to get heavily pegged as compared to other days and if several cells show the same behaviour, then check if the SS7 TMUs are in good shape. This counter migh as well be slightly increased following AMR HR activation Screening: 17 Receipt of an ERROR INDICATION message: expiration of (N200 + 1) times of T200 timer. -> the call is dropped because the layer 2 connection between the mobile and the BTS is broken. The reason is that the radio for this call is so poor (low signal strength or bad quality) that layer 2 connection is lost. It is the layer counter part of the radio link time out (layer 3) Screening: 18 Receipt of an ERROR_INDICATION message: DM frame received in established multiframe state. Screening: 19 Receipt of an ERROR_INDICATION message: sequence error. Screening: 20 Receipt of a CLEAR_COMMAND message from the MSC. -> This is not a drop call. Every normal release of a call increments this screening. Screening: 21 Receipt of three RF RESOURCE INDICATION messages. -> this is a protective drop from the BSC: the BSC knows which TCH resources it has allocated to the BTS. The BTS, on the other hand, sends to the BSC messages telling which TCH it uses: RF resource indication. The two messages should match as the resources used at the BTS should be the one allocated by the BSC. If three messages in a row do not match, then the concerned TCH is released, and if there is a call on the TCH, it is released. Screening: 23 Two expirations of TmodMs timer (CHANNEL MODE MODIFY procedure). Screening: 24 Expiration of T3103 timer (handover procedure). -> this drop indicates that a call was dropped during the handover procedure. When a handover procedure fails (that means that the call was not handed over to the target cell), there are two possibilities: 1/ either the mobile succeeds in re-establishing on the originating cell in less that T3103 seconds, then the call is rescued and can go on. 2/ or the mobile does not succeed in re-establishing on the originating cell in the T3103 seconds allocated to this procedure, then the call is dropped and counter 1164/24 is pegged, drop after expiration of T3103. Screening: 25 Expiration of T8 timer (inter-BSC handover procedure).


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-> the inter BSC handover procedure was not finished when T8 expired, the call is dropped. Check if all cells belonging to the BSC are impacted and investigate on the MSC handling the handovers. Screening: 28 Others. -> it appears when there is a synchronization issue on the A or Ater interface. This counter is also incremented in following cases: - TRMs fault, - Lock of TRM, - PCM Ater fault, - Lock of PCM Ater. Screening: 31 SYS INFO procedure failure after a switchover. Screening: 32 Receipt of a CONNEXION FAILURE INDICATION message with Abis cause set to remote transcoder failure. -> it is the counter part of 1164/28 but on the ABIS interface. It has two possible causes 1 /there is a synchronization issue on the Abis PCM interface => try to switch PCM 2/ there is a blank call (for example if the BSC for any reason encounters a switching issue). Screening: 33 TDMA removal due to EDGE TDMA/TRX reconfiguration

1960/X: AMR FR drops

Screening: 0 Lapdm cause Screening: 1 radio cause Screening: 2 others causes

1961/X: AMR HR drops

Screening: 0 Lapdm cause Screening: 1 radio cause Screening: 2 others causes

Screening 0 Lapdm cause : this screening is the sum of following 1164screenings: Screening: 16 Receipt of a RELEASE INDICATION message from the BTS. Screening: 17 Receipt of an ERROR INDICATION message: expiration of (N200 + 1) times of T200 timer. Screening: 18 Receipt of an ERROR_INDICATION message: DM frame received in established multi-frame state. Screening: 19 Receipt of an ERROR_INDICATION message: sequence error. Screening 1 radio cause : this screening is the sum of following 1164 screenings : Screening: 6 Expiration of T3107 timer before receipt of ESTABLISHMENT INDICATION message, during an Dedicated Channel Assignment procedure or a handover Intracell on SDCCH procedure. Screening: 12 Receipt of a CALL CLEARING request from the L1M following a call clearing distance threshold comparison.Screening: 13 Receipt of a CONNEXION FAILURE INDICATION message with Abis cause set to radio interface failure. Screening: 14 Receipt of a CONNEXION FAILURE INDICATION message with Abis cause set to radio link failure. Screening: 23 Two expirations of TmodMs timer (CHANNEL MODE MODIFY procedure). Screening: 24 Expiration of T3103 timer (handover procedure). Screening: 25 Expiration of T8 timer (inter-BSC handover procedure). Screening 2 others causes :


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this screening is the sum of following 1164 screenings: Screening: 0 Receipt of a SCCP DISCONNECTION INDICATION message from the MSC. Screening: 1 Receipt of a RESET message from the MSC. Screening: 2 Receipt of a RESET CIRCUIT DOWNLINK message from the MSC. Screening: 3 Receipt of a SCCP DATA REFUSAL message from the MSC. Screening: 7 TS removal due to an O&M operation (associated cell put out of service...) Screening: 8 TS removal due to an equipment failure (PCM KO...) Screening: 9 CIC removal due to an O&M operation (terrestrial circuit put out of service...) Screening: 10 CIC removal due to an equipment failure (PCM KO...). Screening: 11 Associated radio channel blocked due to an O&M action. Screening: 28 Others. Screening: 31 SYS INFO procedure failure after a switchover. Screening: 32 Receipt of a CONNEXION FAILURE INDICATION message with Abis cause set to re-mote transcoder failure.

1174:TRAFFIC_RELEASE TDMA LEVEL only radio causes handled in particular because that are linked to tdma are shown so that a bad DRX could be identified Screening: 0 Expiration of T3107 timer before receipt of ESTABLISHMENT INDICATION message, during a Dedicated Channel Assignment procedure or a handover Intracell on SDCCH procedure. Screening: 1 Receipt of a CALL CLEARING request from the L1M following a call clearing distance threshold comparison. Screening: 2 Receipt of a CONNEXION FAILURE INDICATION message with Abis cause set to radio link failure. Screening: 3 Receipt of a RELEASE INDICATION message from the BTS. Screening: 4 Receipt of an ERROR INDICATION message: expiration of (N200 + 1) times of T200 timer. Screening: 5 Receipt of an ERROR_INDICATION message: DM frame received in established multiframe state. Screening: 6 Receipt of an ERROR_INDICATION message: sequence error. Screening: 7 Receipt of three RF RESOURCE INDICATION messages. Screening: 8 Two expirations of TmodMs timer (CHANNEL MODE MODIFY procedure). Screening: 9 Expiration of T3103 timer (handover procedure). Screening: 10 Updated on every (not only linked to radio problem) abnormal call release


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8.2 TCH DROP METRIC

Global TCH drop call per erlang: sum ((C1164/x)- C1164/20) / (1612/0 + C1611/0) 1164/20 corresponds to the normal releases EFR call drop per erlang: (C1164/X – C1164/20 – C1960/X – C1961/X) / (C1611/0 – c1901/0) AMR call drop per erlang: Sum(1960/x) + sum (1961/x) / (C1612/0 + C1901/0) These are the only metric that will enable to distinguish between AMR calls, EFR calls or to do the monitoring on all calls. Call drop per call was a metric once used but it has less meaning than the call drop per erlang of the MOU There is very little interest in monitoring the call drop AMR FR per erlang versus the call drop AMR HR per erlang as by default calls handled in AMR HR should be in better radio conditions than the majority of the calls handled in AMR FR. TCH drop metrics are expected to increase along with the load of the network: more load on the network means more interference hence degraded radio conditions that can impact the level of drops. Call drop repartition: Drops can be split into 3 main causes:

- radio - handover - system -

Repartition of the drop causes is also extremely important: - Rural zone: more RLT drops - Urban zone: more T200 drops Repartition of the TCH drops per TDMA is very important as well: C1174 counter. The traffic carried by each TDMA is also to be taken into consideration for a fair comparison between the TDMAs: TDMA with very little traffic will have very little drops => drop per erlang at TDMA level is of interest: C1174 / (FR + AMR HR traffic) Investigation: System drops 10% of system cause is the maximum accepted on a network. In case the system ratio is higher than 10%, investigations should be led to find out which the main system cause is and why the incrementation is high. Refer to part 8.1 for all the screenings meaning and explanation T3103 drop increase: check which cell has the highest drops. Check with C1200 and C1204 the relationship that presents the issue. If one relationship is identified, check on the neighbouring with C1844,C1845, C1846 and C1847 if all DRXs of the neighbouring cell are causing the issue or just 1. If all relationships are affected, then check with C1174 TDMA counter it any TDMA of the cell is more impacted by the drops If all DRXs, it could be an issue with the PCM of the neighbouring cell otherwise just a HW problem on a specific DRX or cabling (then check with C2143 which is the TEI) T3107 drop increase: HW or parameter setting Check if AMR or intracell handover has been suddenly activated, if yes then normal, reduction of T3107 can be obtained with AMR BoT activation starting from V15.1.1.. Check with C1174 which TDMA is responsible for the highest drops


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Check with C2141 and C2142 which TDMA is causing the issue or if all and check with C2143 which TEI is responsible for it. Radio link drop Check which cell is causing the highest drops. Check which TDMA of the cell is causing the highest drops: there could be a HW or cabling issue. Check with C1200 and C1204 if a handover relationship is no more present T200 increase Check which cell is causing the highest drops. Check which TDMA of the cell is causing the highest drops: there could be a HW or cabling issue.


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9 HANDOVERS

The handovers process is following 5 steps: 1: measurements of the radio conditions (done by the MS and by the BTS) 2: the measurements are then compared to the handover parameters inside the BTS to detect if a handover is needed. If yes, a handover request is sent by the BTS to the BSC: this message contains the type of the requested handover along with the list of suitable neighbouring cells 3: The BSC receives the handover request and checks if free resources are available in the list of suitable neighbouring cells. This is the handover selection process. If there is no free resource, the handover process is stopped and the process gets back to step 1, the handover selection phase has failed. 4: If a free resource is available, the handover command message can be send to the MS. This is the handover execution phase. 5 : The handover execution phase can succeed or fail. In case of failure there are two possibilities: either the call is dropped or the call manages to get back on the originating cell.

9.1 HANDOVER COUNTERS

C1138/x: handover repartition by cause UL level, quality, power budget, intracell… The handover cause repartition is important to identify any weak points of the cell in UL or in DL. Outgoing handovers: C1065: outgoing intra BSC handover execution attempts C1067: outgoing intra BSC handover execution success C1075: outgoing intra BSC handover requests C1135: the outgoing handover has failed but the mobile station was able to return on the old channel C1066: outgoing inter BSC handover execution attempts C1068: outgoing inter BSC handover execution success C1076: outgoing inter BSC handover request C1136: the outgoing handover has failed but the mobile station was able to return on the old channel.

SACCH: DL Measurement report

SACCH: DL Measurement report

measurement report UL

L1M computation

Handover indicationBSC

Handover command Handover command

Handover access

Handover completeHandover complete

SABM

UA


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Incoming handovers: C1069: incoming intra BSC handover requests C1071: incoming intra BSC handover execution attempts C1073: incoming intra BSC handover success C1070: incoming inter BSC handover execution requests C1072: incoming inter BSC handover execution attempts C1074: incoming inter BSC handover success Intracell handover C1081: intracell handover request C1082: intracell handover execution C1083: intracell handover succeeded Handover tiering: C1138/15 and C1138/16: number of tiering handover requests C1801: number of handover tiering failure due to lack of resources C1802: number of tiering handover success.

Neighboring cell counters C1202/0: handover execution from one cell to its neighbor C1204/x: handover failure from one cell to its neighbor split by cause: return to old channel, T3103 expiration, other this is particularly important to check in case of outgoing handover failure to check if one neighbouring relationship is more impacted than another one. In case one relationship is more impacted, one needs to check each TDMA of the neighboring cell for rxqual and assignment failure to identify whether one DRX could be faulty C1839/x: handover request per type toward a neighbouring cell (UL/DL, RxLev/Rxqual/Pbgt….) C1840/X: handover success per type Caution: no metric can be built from 1839 and 1840 as it sums selection failure and execution failure Investigation counters C1760:HO_FAILURE_INCOMING_INTER_BSS_TCH

Screening: 0 lack of radio resources: TCH resource failure Screening: 1 lack of terrestrial resources: underdimensionning of the A interface Screening: 2 incoming handover not allowed in the cell Screening: 3 receipt from the BTS of CHANNEL ACTIVATE NACK Screening: 4 expiration of TchnAck timer Screening: 5 Only on TCH. (CIC and speech coding algorithm incompatible /OR/ target cell and speech coding algorithm incompatible /OR/ CIC and channel mode incompatible /OR/ target cell and channel mode incompatible) AND no possible fall back. Incompatibility for CIC can be hardware or configuration Incompatibility for target cell can be hardware or configuration

C1764:HO_FAILURE_OUTGOING_INTER_BSS_TCH

Screening: 0 lack of radio resources: TCH resource failure Screening: 1 lack of terrestrial resources: underdimensionning of the A interface Screening: 2 incoming handover not allowed in the cell Screening: 3 T7 timer expiration Screening: 4 every other cases Screening: 5 only on TCH: (CIC and speech coding algorithm incompatible /OR/ target cell and speech coding algorithm incompatible /OR/ CIC and channel mode incompatible /OR/ target cell and channel mode incompatible) AND no possible fall back. Incompatibility for CIC can be hardware or configuration Incompatibility for target cell can be hardware or configuration

C1758:HO_FAILURE_INCOMING_INTRA_BSS_TCH

Screening: 0 lack of radio resources: TCH resource failure Screening: 1 incoming handover not allowed in the cell Screening: 2 receipt from the BTS of CHANNEL ACTIVATE NACK Screening: 3 expiration of TchnAck timer


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Screening: 4 only on TCH: (target cell and speech coding algorithm incompatible /OR/ target cell and channel mode incompatible) AND no possible fall back. Incompatibility for target cell can be hardware or configuration.

C1762:HO_FAILURE_OUTGOING_INTRA_BSS_TCH

Screening: 0 lack of radio resources: TCH resource failure Screening: 1 incoming handover not allowed in the cell Screening: 2 receipt from the BTS of CHANNEL ACTIVATE NACK Screening: 3 expiration of TchnAck timer Screening: 4 only on TCH: (target cell and speech coding algorithm incompatible /OR/ target cell and channel mode incompatible) AND no possible fall back. Incompatibility for target cell can be hardware or configuration.

AMR handovers C1953/X: amr intracell handover requests FR, FR to HR and HR to FR C1954/x: amr intracell handover execution FR, FR to HR and HR to FR C1955/X: amr intracell handover success FR, FR to HR and HR to FR C1956/x: Ncell handover execution for AMR HR channel C1958/x: Ncell handover failure for AMR HR channel C1957/x: Ncell handover execution for AMR FR channel C1959/x: Ncell handover failure for AMR FR channel TDMA incoming handover execution and failure counters C1844: tdma_ho_success_incoming_inter_bss_tch C1845: tdma_ho_success_incoming_intra_bss_tch C1846: tdma_ho_exec_incoming_intra_bss_tch C1847: tdma_ho_exec_incoming_inter_bss_tch


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9.2 HANDOVERS METRICS

Selection/Execution intercell Selection failure Execution failure Inc intra BSC HO (C1069 – C1071)/C1069 (C1071-C1073)/ C1071 Inc inter BSC HO (C1070 – C1072)/ C1070 (C1072 – C1074) / C1072 Out intra BSC HO (C1075 – C1065)/ C1075 (C1065 –C1067)/ C1065 Out inter BSC HO (C1076 – C1066) / C1076 (C1066 – C1068) / C1066 Selection/execution intracell Selection: 1 – C1082/C1081 Execution: 1-C1083/C1082 The intracell execution procedure is an assignment procedure, so in case of intracell handover failure check for the assignment failure ratio. Bad DRX is usually the root cause in case the ratio is above 10% especially for AMR intracell handovers (bad reception or emission, loss of GSM clock…) => check for C2141 and C2142 at TDMA level to identify the bad hardware or the bad frequency. Execution failure Neighbor per neighbor relationship: Neighbour by neighbour execution failure: Sum (C1204/X) / C1200 It is interesting to check the C1200 and C1204 values to identify the relationship which causes the issue : in that case, maybe the issue comes from the originating cell or site (check that intrasite is OK but intersite is KO) or from the target cell. Incoming execution failure per TDMA: TDMA_HO _INCOMING_INTRA_BSS_TCH_success ratio: (1845) / (1846) TDMA_HO _INCOMING_INTER_BSS_TCH_success ratio: (1844) / (1847) It is particularly interesting to check the incoming handovers failures on a tdma basis in case the incoming handover ratio is high to try to indentify a bad HW AMR handovers Most important AMR handovers are intracell handovers which are handled through (n,p) voting algorithm. AMR FR to HR intracell handover execution failure: 1-( C1955/1 )/ C1954/1 AMR HR to FR intracell handover execution failure: 1-( C1955/1 )/ C1954/1 AMR FR to FR intracell handover execution failure: 1-( C1955/0 )/ C1954/0 In case AMR L1M is used, it could be interesting to monitor if they are performing correctly otherwise a joint monitoring EFR and AMR is acceptable AMR HR handover execution failure: sum (C1958/X) /C1956/0 AMR HR handover execution failure: sum (C1959/X) /C1957/0 CAUTION: in case of isolated AMR cells (resp EFR cells) in an EFR zone (resp AMR Zone), inter BSC counters could be highly increased. Indeed when AMR is not activated on all the cells of the BSC, the handovers from EFR cells to AMR cells are handled in a specific way:

- call AMR in cell A BSC 1-> cell B BSC 1 with only EFR : this intercell intra BSC handovers is handled as inter BSC handovers: this is necessary because the coding scheme is handled by the TCU. The only way to request the TCU to change its coding scheme from AMR to EFR is to notify the BSC which can only be done by a fake inter BSC handover command. This enables to keep the call even if cell B has no AMR

- Call in EFR in cell B BSC 1 -> cell A with EFR / AMR : the call will be kept in EFR even if cell 1 supports AMR, so a normal intra BSC handover will be triggered. This behavior was specified so as to reduce the MSC load.


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Accordingly, intra BSC and inter BSC evolution and success rate will be analyzed for the partial AMR activation along with drop ratio for T3103 cause. Three periods will be displayed: EFR only, AMR partial activation, AMR full activation on the BSC.

How to investigate outgoing handover issues on one specific cell: 0/ check which cell is impacted with the handover execution outgoing failure and monitor for any strange reason with C1762 and C1764 1/Check if it has incoming handover execution failure or assignment failure and the resource availability (C1700) and get down to hourly level 2/ check point 1 at TDMA level 3/ check at neighbouring cell level if any relation ship is more impacted with C1200 and C1204 4/ check at neighbouring cell for any change of handover cause (C1839) 5/ check for the identified neighbouring cell whether it has incoming handover execution failure or assignment failure and the resource availability (C1700) and get down to hourly level 6/ check for the identified neighbouring cell the same metrics as in point 5 but at TDMA level Handovers problem are of various kinds: - loss of synchronization between DRXs or cells due to BSC or due to instable PCM - bad HW in the target cell or bad cabling - change of “synchronized” parameter in the adjacent cell handover object when the cells do not belong to the same site - blocking in the target cell delaying the handover execution and leading to T3103 drops - after DRX upgrade if one DRX is ciphered and the target DRX is not ciphered or change of the ciphering algorithm in the BSC or NSS - for inter BSCs handovers, bad cell referencing in the HLR/VLR mixing the paths between the 2 BSCs in case handover succeeds from BSC A to BSC B but not in the reversed direction - for inter BSC handovers, loss of synchronization between the two BSCs


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10 AMR LINK ADAPTATION

10.1 LINK ADAPTATION COUNTERS

Codec usage repartition: C1975/X: AMR FR UL codecs C1976 : AMR HR UL codecs C1977/x : AMR FR DL codecs C1978/x : AMR HR DL codecs C1979/x : bad speech frames AMR FR C1980/x: speech frames AMR FR C1981/x: bad speech frames AMR HR C1982/x: speech frames AMR HR

10.2 LINK ADAPTATION METRICS

Codec usage repartition: AMR FR UL codecs repartition: C1975/X / sum (C1975/X) AMR HR UL codecs: C1976/X / sum (C1976/x) AMR FR DL codecs : C1977/x / sum (C1977/x) AMR HR DL codecs : C1978/x / sum (C1978/x) One can look at the frame error rate codec per codec keeping in mind that strong values for 5,9 and 4,75 in AMR FR is expectable as in tunnels or strongly degrading conditions, these are the codecs that will be used before the drop. UL Frame error rate computation: AMR FR Global: sum (C1979/x) / (sum C1980/x) AMR FR Codec per codec: C1979/x / C1980/x AMR HR Global: sum (C1981/x) / (sum C1982/x) AMR HR Codec per codec: (C1981/x) / (C1982/x) AMR Link adaptation is dependant on the chosen adaptation table and also dependant on the level of C/I UL and downlink on the network. It is also strongly dependant on whether AMR BoT is activated or not One can look at the codec usage repartition


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11 RADIO CONDITIONS

11.1 RADIO CONDITIONS COUNTERS

EFR only: C1623/0: RxLev DL EFR C1624/0: RxLev UL EFR C1625/0: RxQual DL EFR C1626/0: RxQual UL EFR C1905/0: C/I UL EFR C1622: missing DL measurement EFR: counts all DL measurements performed by the mobiles and sent to the BTS but that were not received by the BTS (BTS expecting that each 480 or 470 a meas rep is to be received, if not received then +1 to lost measurements) AMR FR C1908/0: RxLev DL AMR FR C1909/0: RxLev UL AMR FR C1910/0: RxQual DL AMR FR C1911/0: RxQual UL AMR FR C1916/0: C/I AMR FR C1930/0: missing DL measurement AMR FR AMR HR C1920/0: RxLev DL AMR HR C1921/0: RxLev UL AMR HR

Stop meas ack sent to BSC at the end of call with the concatenated value of all UL and DL measurements

T0: MS measures RxLev, RxQual DL and sends the values in SACCH

T0+480ms: MS measures RxLev, RxQual DL and sends the values in SACCH

T0 +n480: MS measures RxLev, RxQual DL and sends the values in SACCH

SACCH 1

SACCH 2

SACCH n

T0: BS measures RxLev, RxQual and C/I UL and stores DL values received in SACCH

T0+480ms: BS measures RxLev, RxQual UL andC/I and stores DL values received in SACCH

T0+n480: BS measures RxLev, RxQual UL and C/I and stores DL values received in SACCH

Call end

Call start

Stop meas ack


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C1922/0: RxQual DL AMR HR C1923/0: RxQual UL AMR HR C1928/0: C/I AMR HR C1931/0: missing DL measurement AMR HR TDMA level: tdma_rxlev_downlink (2153) tdma_rxlev_uplink (2154) tdma_rxqual_downlink (2155) tdma_rxqual_uplink (2156) tdma_rxlev_downlink_amrfr (2104) tdma_rxlev_uplink_amrfr (2105) tdma_rxqual_downlink_amrfr (2106) tdma_rxqual_uplink_amrfr (2107) tdma_rxlev_downlink_amrhr (2108) tdma_rxlev_uplink_amrhr (2109) tdma_rxqual_downlink_amrhr (2110) tdma_rxqual_uplink_amrhr (2111) tdma_ms_lost_measurements_amrfr (2112) tdma_ms_lost_measurements_amrhr (2113) tdma_c/i_uplink_fr (2123) tdma_c/i_uplink_amrfr (2124) tdma_c/i_uplink_amrhr (2125)

11.2 RADIO CONDITION METRICS

All the above counters are managed by the BTS computed every 480 ms on TCH and every 470 ms on the SDCCH. At the end of the call, they are sent to the BSC in the stop meas ack message. To get the average value, one needs to divide the sum of the counters by the length of the total call duration TCH + SDCCH for the global and TCH AMR only for AMR. AMR impact: RxLev and RxQual: There is no reason why RxLev or RxQual should be different for AMR calls or EFR calls if the power control parameters used on the two types of call are the same. Between AMR FR and AMR HR, AMR HR calls are by conception of AMR necessarily in better radio conditions than AMR FR calls: thus AMR HR RxLev and RxQual is better than AMR FR RxLev and RxQual. There is therefore no reason to compare the RxLev and RxQual separately. It is the same explanation for C/I and timing advance. With AMR Based on Traffic activated, calls in very good radio conditions can be handled by AMR FR if the cell has not crossed the load threshold. Hence, AMR FR RQual and RxLev values are better than without AMR BoT Same for C/I and timing advance. Frame error rate AMR was designed so as to be more robust than EFR. The global AMR frame error rate will necessarily be lower than EFR frame error rate thanks to the link adaptation enabling to use more robust codecs in degraded radio conditions C/I Due to internal AMR coding with a cap at 23dB, AMR C/I will always be lower than EFR C/I. The difference between EFR and AMR will of course depend on the average C/I of the network: with a low average C/I, the difference will tiny, with a high C/I, the difference will be more important due to more sample at 23dB and higher


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RxLev UL Global: (C1624 + C1909 + C1921) / ([AVG_1603 * C1606 / 470] + [AVG_1600 * (C1609_0 - C1900) / 480] + [AVG_1902_0 * C1900 / 480] + [AVG_1902_1 * C1610_0 / 480]) EFR: (C1624)/ ([AVG_1603 * C1606 / 470] + [AVG_1600 * (C1609_0 - C1900) / 480]) AMR Global: (C1909 + C1921) / ( [AVG_1902_0 * C1900 / 480] + [AVG_1902_1 * C1610_0 / 480]) RxLev DL Global: (C1623 + C1908 + C1920) / ([AVG_1603 * C1606 / 470] + [AVG_1600 * (C1609_0 - C1900) / 480] + [AVG_1902_0 * C1900 / 480] + [AVG_1902_1 * C1610_0 / 480] - C1622 - C1930 - C1931) EFR: (C1623)/ ([AVG_1603 * C1606 / 470] + [AVG_1600 * (C1609_0 - C1900) / 480]-C1622) AMR Global: (C1908 + C1920) / ( [AVG_1902_0 * C1900 / 480] + [AVG_1902_1 * C1610_0 / 480] - C1930 - C1931) RxQual UL Global: (C1626 + C1911 + C1923) / ([AVG_1603 * C1606 / 470] + [AVG_1600 * (C1609_0 - C1900) / 480] + [AVG_1902_0 * C1900 / 480] + [AVG_1902_1 * C1610_0 / 480]) EFR: (C1626 ) / ([AVG_1603 * C1606 / 470] + [AVG_1600 * (C1609_0 - C1900) / 480]) AMR Global: (C1911 + C1923) / ( [AVG_1902_0 * C1900 / 480] + [AVG_1902_1 * C1610_0 / 480]) RxQual DL Global: (C1625 + C1910 + C1922) / ([AVG_1603 * C1606 / 470] + [AVG_1600 * (C1609_0 - C1900) / 480] + [AVG_1902_0 * C1900 / 480] + [AVG_1902_1 * C1610_0 / 480] - C1622 - C1930 - C1931) EFR: (C1625) / ([AVG_1603 * C1606 / 470] + [AVG_1600 * (C1609_0 - C1900) / 480] - C1622) AMR Global: (C1910 + C1922) / ([AVG_1603 * C1606 / 470] + [AVG_1600 * (C1609_0 - C1900) / 480] + [AVG_1902_0 * C1900 / 480] + [AVG_1902_1 * C1610_0 / 480] - C1930 - C1931) FER UL: Global EFR: 1721/0 erroneous frames 1720/0: good and bad frames AMR Global C/I Global: (C1905 + C1916 + C1928) /([AVG_1603 * C1606 / 470] + [AVG_1600 * (C1609_0 - C1900) / 480]+ AVG_1902_0 * C1900/480+(AVG_1902_1 * C1610_0/480)) EFR: C1905/([AVG_1603 * C1606 / 470] + [AVG_1600 * (C1609_0 - C1900) / 480]) AMR FR: C1916/(AVG_1902_0 * C1900/480) AMR HR: C1928/(AVG_1902_1 * C1610_0/480) Timing advance Global: (C1809_0 + C1917_0 + C1929_0) / (C1600 + C1902_0 + C1902_1) EFR: C1809_0 / C1600 AMR FR: C1917_0 / C1902_0 AMR HR: C1929_0 / C1902_1 TDMA level

Same metrics as at cell level can be built using the TDMA counters for the numerator and the denominator (connection duration on SDCCH C2151, TCH C2150, AMR FR TCH C2103/0 ,AMR HR TCH C2103/1). It should be carefully monitored that enough samples are present at TDMA level to decide whether the values are representative of the real quality.When getting down to the TDMA level, the aim is to monitor whether one TDMA (fixed frequency plan change) or one DRX is impacted by degraded values. There really no gain to monitor the rxqual for all the types of calls: the best is to monitor EFR if most of the traffic is handled in EFR or AMR Global is most of the traffic is handled by AMR. In parallel it is of the utmost importance to monitor the incoming handover failure rate and the assignment failure ratio on each of the tdma to get the confirmation of the issue raised by bad indicators on rxlev or rxqual.


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Bad TDMA if: Either any samples on the TDMA, bad values of,rxlev,rxqual and C/I Or few samples on the TDMA but assignment failure is very high along with incoming handover failure Additional information could be obtained through timing advance metric values Bad UL BCCH TDMA: C1033 average at a value lower than -109dB Investigation Check the cabling and HW: if the problem stays on the TEI or moves with the TDMAid - If the issue stays on the TEI, then it is a cabling or HW issue - If the issue moves with the TDMA, check with the network configuration if it is a fix frequency or on hopping:

- If fixed frequency, check in the neighborhood for reuse of the same frequency or interference - If hopping frequencies, check HSN/MAIO usage in the cell and in the neighbouring cells

TDMA to DRX TEI mapping: With counters C2143 and C2144, it is possible to know the mapping between a bad tdma and the DRX TEI which is the hardware identifier. 2143 gives the TEI value 2144 gives the information whether the TDMA was reconfigured or not during the period => value C2143 is valid if C2144 for that time is at 0

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