1. 3G TO 2G CELL RESELECTION PARAMETERS SPECIFICATION....

2. 3G TO 2G HANDOVER PARAMETERS SPECIFICATION......................

3. INTER-RAT HANDOVER FROM WCDMA TO GSM WITH

FORMULA AND ROUTE CAUSE ANALYSIS

1. 3G to 2G cell reselection parameters specification

Parameters Value Meaning

Qoffset1sn(U2GNCELL- QOFFSET1SN) 7 7dB

Min RX level(U2GNCELL- QRXLEVMIN) -50 -99dBm

Hysteresis 1(UCELLSELRESEL-IDLEQHYST1S) 2 4dB

Inter-RAT cell reselection

threshold(UCELLSELRESEL- SSEARCHRAT)2 4dB

Reselection delay time

(UCELLSELRESEL- TRESELECTIONS )1

1S*DRX

Cycle

Length

Min quality level(UCELLSELRESEL- QQUALMIN) -18 -18dB

Step 1: 3G measure Ec/Io < Inter-RAT cell reselection threshold(4dB) + Min quality level(-18dB) : =-14dB

Step 2: GSM Rxlev measurement value > Min RX level(-99dBm)

Step 3:

GSM Rxlev measurement value – Qoffset1sn (7dB) > 3G RSCP measurement value + Hysteresis1 (4dB)

Step 4: Reselection delay time

Step 5: Trigger 3G to 2G reselection

Parameters specification:

Step1: 3G measure Ec/Io < Inter-RAT cell reselection threshold + Min quality level

3G measure Ec/Io: the measurement Ec/Io value in 3G serving cell.

Inter-RAT cell reselection threshold: Threshold for inter-RAT cell reselection. When the quality (CPICH Ec/Io measured by UE) of the serving cell is lower than the threshold plus Min quality level of the cell, the inter-RAT cell reselection procedure will be started.

Value range: -16 ~ 10.

Physical value range: -32 ~ 20 ; step: 2.

Physical unit: dB.

Min quality level: Minimum required quality level corresponding to the CPICH Ec/Io. UE can camp on the cell only when the CPICH Ec/Io measured is larger than the value of this parameter; it will affect the call setup success rate.

Value range: -24 ~ 0.

Physical unit: dB.

Step 2: GSM Rxlev measurement value > Min RX level

GSM Rxlev measurement value: the measurement BCCH Rxlev value in GSM cell.

Min RX level: Minimum required Rxlev value of the GSM neighboring cell.

Value range: -58 ~ -13.

Physical value range: -115 ~ -25; step: 2.

Physical unit: dBm.

Step 3: GSM Rxlev measurement value – Qoffset1sn > 3G RSCP measurement value + Hysteresis1

GSM Rxlev measurement value: the measurement BCCH Rxlev value in GSM cell.

3G RSCP measurement value: the measurement RSCP value in 3G serving cell.

Qoffset1sn: Offset for GSM Rxlev measurement value. It is used for cell reselection process. The greater the value is, the less is the probability of reselecting the GSM neighboring cell

Value range: -50 ~ 50.

Physical unit: dB. Actual value = -115 + (58 + GUI value) * 2

Hysteresis 1: Hysteresis for 3G RSCP measurement value. It is used for cell reselection process. The

greater the value is, the less is the probability of reselecting the GSM neighboring cell

Value range: 0 ~ 20

Physical value range: 0 ~ 40; step: 2.

Physical unit: dB.

Step 4: Reselection delay time

Reselection delay time: If the signal quality of a GSM neighbor cell is better than the 3G serving cell (satisfied the step 3) during the specified time of this parameter, the UE will reselect the neighbor cell. It is used to avoid ping-pong reselection between different cells

Value range: 0 ~ 31

Physical unit: second.

The actual value of reselection delay time setting is depended on the DRX cycle length coefficient.

DRX cycle length coefficient: Used by UE to calculate the DRX cycle length of the CN domain.

Value range: 6 ~ 9.

Recommendation value: 8.

How to calculate the reselection delay time by DRX cycle length coefficient. Refer to 3GPP 25.133

Formula: DRX cycle length = 2n * 10ms

E.g. If DRX cycle length coefficient = 8 then

DRX cycle length = 28 * 10ms = 2560ms=2.56s

Then use table below to get the reselection time and number of DRX cycles (defined by 3GPP)

DRX cycle length [s] TmeasureGSM [s] (number of DRX cycles)

0.08 2.56 (32)

0.16 2.56 (16)

0.32 5.12 (16)

0.64 5.12 (8)

1.28 6.4 (5)

2.56 7.68 (3)

5.12 10.24 (2)

Step 5: Trigger 3G to 2G reselection

2. 3G to 2G-Handover parameters specification

Parameters Value Meaning

Cell individual offset(U2GNCELL- CIOOFFSET) 0 0

GSM RSSI threshold(UINTERRATHOCOV-

TARGETRATCSTHD)21 -90dB

Hysteresis(UINTERRATHOCOV- HYSTFORINTERRAT) 0 0dB

Inter-RAT handover trigger time (UINTERRATHOCOV-

TIMETOTRIGFORVERIFY)0 0S

Filter coefficient (UINTERRATHOCOV-

INTERRATFILTERCOEF )D3 3(No Unit)

Report interval (UINTERRATHOCOV-

INTERRATPERIODREPORTINTERVAL)D2000 2000ms

Inter-freq measure start RSCP threshold

(Event 2D)( UINTERRATHOCOV-

INTERRATCSTHD2DRSCP )-This is RNC wise ,it can be set

cell wise also

-100 -100dBm

Inter-freq measure end RSCP threshold

(Event 2F) ( UINTERRATHOCOV-

-97 -97dBm

INTERRATCSTHD2FRSCP )-This is RNC wise ,it can be set

cell wise also

2D Hysteresis(UINTERRATHOCOV -HYSTFOR2D) 4 2dB

2F Hysteresis(UINTERRATHOCOV -HYSTFOR2D) 4 2dB

2D trigger time(UINTERRATHOCOV -TRIGTIME2D) D320 320ms

2F trigger time(UINTERRATHOCOV -TRIGTIME2F) D1280 1280ms

Step 1:

3G RSCP measurement value=<Inter-freq measure start RSCP threshold(-100db)-2D Hysteresis(2db)/2 : = -101

Step 2: Filter coefficient(3)

Step 3: Report interval(D2000)

Step 4: GSM Rxlev measurement value + Cell individual offset (0) >= GSM RSSI threshold (-90)

+ Hysteresis(0)/2

Step 5: Inter-RAT handover trigger time

Step 6: Trigger Inter-RAT handover

Parameters specification:

Step1:

3G RSCP measurement value = < Inter-freq measure start RSCP threshold – 2D Hysteresis/2

3G RSCP measurement value: the measurement RSCP value in 3G serving cell.

Inter-freq measure start RSCP threshold: UE will report 2D event and then RNC will send signal to start CM and inter-frequency measurement when the measured value is lower than this threshold.

Value range: -115 ~ -25

Physical unit: dBm

2D Hysteresis: Hysteresis value of the 2D event. This parameter value is related to the slow fading characteristic. The greater this parameter is valued, the less ping-pong and misjudgment can be caused. However, in this case, the event cannot be triggered in time.

Value range: 0 ~ 29 Physical value range: 0 ~ 14.5 with the step size of 0.5 Physical unit: dB

2D event refer to 3GPP 25.331

Triggering condition Equation 1:

The variables in the formula are defined as follows:

QUsed is the quality estimate of the used frequency.

TUsed 2d is the absolute threshold that applies for the used frequency and event 2d.

H2d is the hysteresis parameter for the event 2d.

Leaving triggered state condition Equation 2:

The variables in the formula are defined as follows:

QUsed is the quality estimate of the used frequency.

TUsed 2d is the absolute threshold that applies for the used frequency and event 2d.

H2d is the hysteresis parameter for the event 2d.

2D trigger time: 2D event trigger delay time. This parameter value is related to the slow fading characteristic. The greater this parameter is valued, the less the misjudgment probability is. However, the response speed of the event to the measurement signal change becomes lower.

Value range: D0, D10, D20, D40, D60, D80, D100, D120, D160, D200, D240, D320, D640, D1280, D2560 and D5000

Physical value range: 0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320, 640, 1280, 2560 and 5000

Physical unit: ms

Inter-freq measure end RSCP threshold: UE will report 2F event and then RNC will send signal to stop CM and inter-frequency measurement when the measured value is higher than this threshold.

Value range: -115 ~ -25

Physical unit: dBm

2F Hysteresis: Hysteresis value of the 2F event. This parameter value is related to the slow fading characteristic. The greater this parameter is valued, the less ping-pong and misjudgment can be caused. However, in this case, the event cannot be triggered in time.

Value range: 0 ~ 29

Physical value range: 0 ~ 14.5 with the step size of 0.5 , Physical unit: dB

2F event refer to 3GPP 25.331

Triggering condition:

Equation 1:

The variables in the formula are defined as follows:

QUsed is the quality estimate of the used frequency.

TUsed 2f is the absolute threshold that applies for the used frequency and event 2f.

H2f is the hysteresis parameter for the event 2f.

Leaving triggered state condition:

Equation 2:

The variables in the formula are defined as follows:

QUsed is the quality estimate of the used frequency.

TUsed 2f is the absolute threshold that applies for the used frequency and event 2f.

H2f is the hysteresis parameter for the event 2f.

2F trigger time: 2F event trigger delay time. This parameter value is related to the slow fading characteristic. The greater this parameter is valued, the less the misjudgment probability is. However, the response speed of the event to the measurement signal change becomes lower.

Value range: D0, D10, D20, D40, D60, D80, D100, D120, D160, D200, D240, D320, D640, D1280, D2560 and D5000

Physical value range: 0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320, 640, 1280, 2560 and 5000 Physical unit: ms

Step 2: Filter coefficient

Filter coefficient: Inter-RAT measurement L3 filter coefficient, the greater this parameter is valued, the stronger smoothing effect can be caused to the signal and the greater anti-slow fading ability can be possessed. However, the signal change tracing ability becomes weaker.

Value range: D0, D1, D2, D3, D4, D5, D6, D7, D8, D9, D11, D13, D15, D17, D19.

Physical value range: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 13, 15, 17, 19.

Filter coefficient 0 1 2 3 4 5 6 7 8 9 11

Iterative report 1 2 3 5 7 10 15 21 30 42 85

Time

2D threshold

2D Hysteresis/2

2D Hysteresis/2

-100dBm

RSCP

-85dBm

Start 2D measurement

2D Trigger time Send 2D event to RNC

Stop 2D measurement

Start 2F measurement 2F Trigger time Send 2F event to RNC

Stop 2F measurement

2F threshold

2F Hysteresis/2

2F Hysteresis/2

Step 3: Report interval

Report interval: Time interval in which UE reports the inter-RAT measurement results to RNC periodically.

Value range: D250, D500, D1000, D2000, D3000, D4000, D6000, D8000, D12000, D16000, D20000, D24000, D28000, D32000, D64000. Physical value range: 250, 500, 1000, 2000, 3000, 4000, 6000, 8000, 12000, 16000, 20000, 24000, 28000, 32000, 64000. Physical unit: ms.

Step 4: GSM Rxlev measurement value + Cell individual offset >= GSM RSSI threshold

+ Hysteresis/2

GSM Rxlev measurement value: the measurement BCCH Rxlev value in GSM cell.

GSM RSSI threshold: Requirement for the BCCH Rxlev of GSM cell in the inter-RAT handover.

Cell individual offset: It is used in inter-RAT handover decision process. The greater the value is, the more is the probability of handover to the GSM cell.

Value range: -50 ~ 50.

Physical unit: dB.

Hysteresis: It decides whether to trigger the GSM handover decision together with the GSM RSSI threshold. The value can be decreased to some degree in areas with less shadow fading, and increased in areas with more shadow shading.

Value range: 0 ~ 15.

Physical value range: 0~7.5; step: 0.5.

Physical unit: dB.

Triggering conditions:

Equation 1:

The variables in the formula are defined as follows:

MOther RAT is the measurement quantity for the cell of the other system.

CIOOther RAT is the cell individual offset for the cell of the other system.

TOther RAT is the absolute threshold that applies for the other system in that measurement.

H is the hysteresis parameter for inter-RAT handover

Leaving triggered state conditions:

Equation 2:

The variables in the formula are defined as follows:

MOther RAT is the measurement quantity for the cell of the other system. MOther RAT is expressed in dBm.

CIOOther RAT is the cell individual offset for the cell of the other system.

TOther RAT is the absolute threshold that applies for the other system in that measurement.

H is the hysteresis parameter for inter-RAT handover

Step 5: Inter-RAT handover trigger time

Inter-RAT handover trigger time: The inter-RAT handover to GSM procedure will be started if the GSM BCCH Rxlev always satisfies the inter-RAT handover decision (step 4) during the specified period of this parameter.

Value range: 0 ~ 64000. Step: 1

Physical unit: ms

Step 6: Trigger Inter-RAT handover

Inter-RAT Handover from WCDMA to GSM (CS Domain)KPI Definition

Definition of the RNC-level indicators:

VS.SRELOC.SuccPrep.IRHOCS.Rate = VS.SRELOC.SuccPrep.IRHOCS / VS.SRELOC.AttPrep.IRHOCS

VS.IRATHO.SuccCSOut.RNC.Rate= VS.IRATHO.SuccCSOut.RNC / VS.IRATHO.AttCSOut.RNC

Definition of the cell-level indicators:

VS.IRATHO.SuccRelocPrepOutCS.Cell.Rate= <IRATHO.SuccRelocPrepOutCS> / <IRATHO.AttRelocPrepOutCS>

VS.IRATHO.SuccOutCS.Cell.Rate =<IRATHO.SuccOutCS> / <IRATHO.AttOutCS>

The handover process includes the following two processes:

Relocation preparation process

The SRNC sends the RELOCATION REQUEST message to the CN. The message contains such information as the relocation type, relocation reason, source PLMN, source LAC, source SAC, destination PLMN, and destination LAC.

The CN interacts with the GSM by forwarding the GSM MSC, and prepares the related resources.

After the GSM-related resources are prepared, the CN sends the RELOCATION COMMAND message to the SRNC. The message contains the layer 3 information element, and the element carries the information about the related resources allocated by the GSM.

If the allocation of all resources or some resources fails, the CN sends the RELOCATION PREPARATION FAILURE message to the SRNC.

Handover implementation process

The RNC delivers the HANDOVER FROM UTRAN COMMAND message to the UE. The message carries the RAB ID, activation time, GSM frequency, and the GSM message in the form of a bit string.

After the UE accesses the GSM, the CN sends the IU RELEASE COMMAND message continuously, instructing the RNC to release the resources of the UE in the WCDMA system.

Relocation preparation failure is mainly caused for the following reasons: The 2G equipment is abnormal or resources are not enough.

The CN parameters are not configured reasonably.

The configurations of GSM neighboring cells are not consistent with actual parameters.

Handover implementation failure is mainly caused for the following reasons: The parameters of 2G neighboring cells are not configured correctly.

The 2G encryption algorithm is not consistent with the 3G encryption algorithm.

There exists side-channel interference in 2G cells.

The handover threshold is not set reasonably.

Analysis Process

1. Discussing the Problem and Ascertaining the Problem Background

When the problem occurs, determine the key time at which the success rate is changed, and know the recent adjustment of the 2G access network, 3G access network, and CN. Analyze the impacts of the key actions performed at the corresponding time upon the KPIs.

2. Determining the Main Scenarios

Firstly, measure the relocation preparation success rate and handover implementation success rate of the RNC level and cell level respectively according to the performance data of the RNC. Determine which flow causes the descent of the inter-RAT handover-out success rate, and check whether the success rate of the entire network or the success rate of some cells decreases. If the problem only occurs in one or two cells, it indicates that the problem is related to the configuration of the GSM neighboring cells.

Secondly, analyze which cause leads to the descent of the inter-RAT handover-out success rate. Table lists the failure causes defined by the performance counter.

Table 1 Indicators related to CS inter-RAT handover-out failure

Indicator (Level1) Sub-indicator (Level2)

VS.SRELOC.FailPrep.IRATCSOut

(Relocation preparation failure)

VS.SRELOC.Fail.IRATCSOutNRpl

VS.SRELOC.Fail.IRATCSOutCanc

VS.SRELOC.Fail.IRATCSOutTexp

VS.SRELOC.Fail.IRATCSOutTfai

VS.SRELOC.Fail.IRATCSOutTOve

VS.IRATHO.PrepFailCSOut.UkwnRNC

VS.IRATHO.PrepFailCSOut.NoRsrc

VS.IRATHO.PrepFaiCSInTgtOveL

VS.IRATHO.PrepFailCSOutReqinfnotavai

VS.IRATHO.FailCSOut.RNC

(Handover implementation failure)

VS.IRATHO.FailCSOut.CfgUnRNC

VS.IRATHO.FailCSOut.PhyFaRNC

Analyzing the Causes Case by Case

VS.SRELOC.Fail.IRATCSOutNRpl/ VS.SRELOC.Fail.IRATCSOutTexp

After the SRNC sends the RELOCATION REQUIRED, the SRNC starts the timer to wait for the RELOCATION COMMAND message. If the RELOCATION COMMAND message is not received when the timer times out, the SRNC sends the RELOCATION CANCEL message and measures the indicator.

<Method of analysis>

− Check whether the RNC links and MSC links are normal.

− Check the CN configuration, especially the transmission parameters of the 2G MSC/VLR, for example, the data of the MTP layer, data of the SCCP layer, and inter-MSC trunk data.

− Query the CN configuration, and check whether inter-RAT handover is allowed.

− Trace and analyze the MSC/BSS signaling. Ask the CN personnel and 2G personnel to attend the analysis.

VS.SRELOC.Fail.IRATCSOutCanc

After requesting the handover preparations, the RNC receives the release command sent by the CN. It is usually caused as follows:

− The inter-RAT handover request is initiated during the signaling (for example, location update). Location update is complete before the flow is complete, so the CN initiates the release.

− The subscriber who sets up the call hangs up during the handover preparation, so the CN initiates the release.

Although handover is not complete, the two circumstances are normal flow embedment.

VS.SRELOC.Fail.IRATCSOutTfai

The relocation fails in the target CN/RNC or in the system. Usually, the cause is as follows:

− The CN configurations are not correct.

− The BSS does not support the relocation.

<Method of analysis>:

− Check the CN negotiation data.

− Check whether the BSS allows inter-RAT handover-in.

− Check whether the configurations of GSM neighboring cells are consistent with the actual parameters. The BTS may fail to find the target cell. If the problem occurs only to one or two cells, you can trace the IOS data, determine whether the relocation failure occurs only to one or two target cells, and check the parameters of the GSM neighboring cells of the target cells.

VS.IRATHO.PrepFailCSOut.UkwnRNC

The target RNC is unknown. The cause is the main cause of relocation failure. Usually, the reason is that the MSC cannot find the route leading to the 2G cells.

<Method of analysis>:

− Check the CN configuration. It is possible that the LAI of the 2G target cell is not configured on the MSC.

− Check the consistency of the parameters of GSM neighboring cells configured on the RNC.

VS.IRATHO.PrepFailCSOut.NoRsrc

No resources are available. Usually, the BSC has no resources available for the access of the UE or the 2G MSC has no information about the target cells.

<Method of analysis>:

− Check the resource utilization of the 2G BSS. It is possible that no channel is available because the channel is occupied by another subscriber.

− Check the status of the target cell. The target cell may be faulty.

− Check the mapping between the target cell and 2G MSC on the 3G MSC.

VS.IRATHO.FailCSOut.CfgUnRNC

The handover is not supported by the configuration. Usually, the UE does not receive the HANDOVER FROM UTRAN COMMAND message delivered by the RNC because of the incorrect RNC format, incompatibility of the UE, or incorrect configuration of the encryption parameters.

<Method of analysis>:

The encryption parameters are not set correctly

− Trace the IOS data of the top N cells, and query the encryption algorithm.

Check whether the parameter of the encryption algorithm on the BSC is consistent with that carried by the relocation command.

Note:In the 3G system, the encryption process is required. In the 2G system, the encryption process is optional. Therefore, the 2G system can send an encryption-related parameter optionally when the UE is handed over from the UMTS to the GSM.

If the 2G system does not send an encryption-related parameter, the MSOFTX3000 uses the default handover configuration to reestablish a Cipher Mode Setting parameter and sends the parameter to the RNC through the signalling message of Relocation command. When the 2G system sends an encryption parameter carrying the chosen encryption algorithm, the MSOFTX3000 uses the chosen encryption algorithm to establish the Cipher Mode Setting parameter and sends the parameter to the RNC through the signalling of Relocation command.

− If they are not consistent, further trace the CN signaling and query the encryption parameter received by the MSC.

Modify the handover parameter configuration of the 2G LAC, so that the encryption parameter carried by the CN to the RNC is consistent with the encryption parameter used by the 2G system.

UE compatibility

− Trace the IOS data of the top N cells, obtain the failure flow, and analyze whether there exists a typical scenario, for example, some flow interactions cause the UE to return the message of Unsupported Configuration.

− Obtain the IMSIs of the terminals through the CHR or PCHR log. If the problem mainly occurs in one or two terminals, it indicates that the problem is caused by the UE. Then, inquire the customer about the corresponding IMEI of the IMSI, and query the type of the failed terminal.

− If conditions permit, verify the problem in the HQ. Alternatively, ask the field personnel to conduct drive test.

Incorrect RNC signaling format

− Trace the IOS data of the top N cells, and capture the failed cells.

− Compare the HO_FROM_UTRAN_CMD_GSM generated at the failure time with the signaling generated at the time of normal handover. A usual problem is as follows: The handover command does not carry the encryption indication. If this problem occurs, you need to modify the handover parameter configuration of the 2G LAC on the MSC.

The ETSI GSM PHASE I protocol has a defect: The handover command does not carry the encryption information. The ETSI GSM PHASE II protocol has rectified the defect. However, the GSM devices of lots of vendors have not rectified the defect in accordance with the ETSI GSM PHASE II protocol. If the CN does not reestablish the encryption for the RNC, a format error occurs.

<Suggestions>:

If the 2G BSC does not send the Chosen Encryption Algorithm parameter, configure the handover parameter of the 2G LAC on the MSOFTX3000.

For other problems, directly collect the related information and feed back the information to the R&D department for analysis.

VS.IRATHO.FailCSOut.PhyFaRNC

Inter-RAT handover implementation failure is mainly caused as follows:

1) After receiving the Handover From Utran command, the UE attempts to access the system on the BTS.

2) The UE repeatedly sends the Handover Access message to the BTS through the FACCH, starts the T3124 timer (the default is 320 ms), and stops sending the message if receiving the PHY INFO message.

3) If the timer times out, the BTS returns the old Utran channel and replies the physical channel failure.

<Method of analysis>:

− Check the parameter configuration of the GSM neighboring cells. For example, if the BCCHARFCN is not configured correctly, the cell in the measurement report that reaches the handover threshold is not the actual cell accessed by the UE. As a result, the signal quality of the actual handover cell does not satisfy the handover requirements and thus the handover fails.

− Check whether the unreasonable setting of the handover threshold causes the easy handover but poor signal quality of the 2G cell.

− Check whether the handover failure is caused because the encryption algorithms are not consistent.

− If you still cannot solve the problem, ask the 2G personnel to attend the analysis.

IRAT Failures due to Configuration Issues

Data ConfigurationInter-RAT handover fails due to incomplete configuration data, so pay attention to the following dataconfiguration.

GSM neighbor configuration is complete on RNC. The configuration includes(RNC Dump UEXT2GCELL )− Mobile country code (MCC)− Mobile network code (MNC)− Location area code (LAC)− GSM cell identity (CELL ID)− Network color code (NCC)− Base station color code (BCC)− Frequency band indicator (FREQ_BAND)− Frequency number− Cell independent offset (CIO)Guarantee the correctness of the previous data and GSM network.Note : Check if Neighbour Definition is failed due to BCCH BSIC Clash .If Any clash found change the BCCH BSIC of GSM Cell .

Add data ofWCDMA neighbor cells on GSM BSS. The data includes: − Downlink frequency− Primary scramble− Main indicator− MCC− MISSING NEIGHBOR CELL− LAC− RNC ID− CELL IDAccording to the strategies of unilateral handover of inter-RAT handover, if the dataconfiguration is complete, the inter-RAT handover problems are due to delayed handover.Afrequently-used solution is increasing CIO, increasing the threshold for starting and stoppingcompression mode, increasing the threshold to hand over to GSM.

MISSING 3G-2G NEIGHBOR CELL

CausesThe causes to call drop due to 3G-2G inter-RAT handover are as below:After the 2G network modifies its configuration data, it does not inform the 3G networkof modification, so the data configured in two networks are inconsistent.Missing neighbor cell causes call drop.The signals fluctuate frequently so call drop occurs.Ping-pong reselect.Handset problems causes call drop. For example, the UE fails to hand over back or toreport inter-RAT measurement report.The best cell changes upon Physical channel reconfiguration.Improperly configured LAC causes call drop (solve it by checking data configuration).