GPRS Traffic

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Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

GPRS Traffic Statistics

Page 2Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page 2

Objectives

� GPRS traffic measurement indicates the basic performance of the

GPRS.

� Each traffic measurement item indicates the features of the

network.

� Traffic measurement helps to quickly handle the network problems.

� A complete performance measurement system is provided for the

network performance analysis, network optimization, and fault

location of the GPRS network.

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Contents

1. GPRS Traffic Structure

2. GPRS Traffic Analysis


GPRS Traffic Statistics Introduction� GPRS performance measurement involves the CPU performance, Um

interface performance, Pb interface performance, and PCU overall

performance. The GPRS performance measurement provides data

support for the GPRS performance familiarity, GPRS optimization, and

fault location.

� GPRS counters can be categorized into:

� Service model establishment

� Network performance optimization

� Troubleshooting

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There are 7 kinds of measure type :

� BSC Overall Performance Measurement

� BSSGP Performance Measurement

� CPU Performance Measurement

� G-Abis Interface Performance Measurement

� NS Performance Measurement

� Pb Interface Performance Measurement

� Cell Performance Measurement

GPRS Traffic Statistics Introduction


� The BSC overall performance analysis include:

� Traffic load model: Number of Uplink TBF Establishment Attempts and Number of Downlink TBF Establishment Attempts;

� GPRS output: Total Number of Uplink LLC_PDUs Sent, Total Bytes of Uplink LLC_PDUs Sent, Total Number of Downlink LLC_PDUsReceived and Total Bytes of Downlink LLC_PDUs Received;

� Paging load: Number of Circuit Paging Requests Sent and Number of Packet Paging Requests Sent;

� Packet channel resource: Mean Number of Available PDCHs and Mean Number of Occupied PDCHs.

BSC Overall Performance Measurement

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� The BSC overall performance analysis is to check the overall running state of the BSS. The results of the measurement are used to Analyze the QoS of GPRS BSS.

� If the measurement result exceeds the reference range, the radioenvironment, network parameter configuration, network resource configuration and network equipment should be optimized, such asNumber of Successful Uplink TBF Establishment, Number of Successful Downlink TBF Establishment, Number of Uplink TBF Normal Release and Number of Downlink TBF Normal Release.

BSC Overall Performance Measurement


� The object of the measurement is board, which includes POMU and RPPU.

� It measure the load of cpu

� the value of average CPU occupancy is too high: Check whether the operations such as FTP, performance measurement task register and file operating are being implemented.

CPU Performance Measurement

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� Cell Performance Measurement focus on RLC/MAC layer performance:

such as access performance, TBF establishment and release

measurement, PDCH resource measurement

Cell Performance Measurement


Uplink RLC Data Transmission Measurement

10

Downlink LLC Data Transmission Measurement

9

Uplink LLC Data Transmission Measurement

8

Downlink TBF Establishment/Release Measurement

7

Uplink TBF Establishment/Release Measurement

6

Paging Request Measurement5

Rate of Successful Packet Assignment4

Packet Access Performance Measurement on PACCH

3

Packet Access Performance Measurement on PCCCH

2

Packet Access Performance Measurement on CCCH

1

Measurement itemNo.

EGPRS 8PSK_MEAN_BEP Different Value Measurement

21

EGPRS GMSK_MEAN_BEP Different Value Measurement

20

Downlink EGPRS RLC Data Transmission Measurement

19

Uplink EGPRS RLC Data Transmission Measurement

18

Downlink EGPRS TBF Establishment/Release Measurement

17

Uplink EGPRS TBF Establishment/Release Measurement

16

PDCH Extreme Value Measurement15

PDCH Resource Performance Measurement 14

Resource Maintenance Performance Measurement

13

Cell Radio Channel Performance Measurement12

Downlink RLC Data Transmission Measurement11

Cell Performance Management

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� NS Performance Measurement:

� Analyze the traffic load of GPRS BSS.

� Monitor the service of NS layer of Gb interface

� BSSGP performance measurement The object of the measurement is cell The results of the measurement are used to create traffic model

� G-Abis Interface Performance Measurement indicate the performance of G-Abis transmission.

� Pb Interface Performance Measurement, The object of the measurement is LAPD. The initial items can be used to reflect the performance of Pbinterface, and they are also helpful for troubleshooting of the GPRS network. Please refer to the analysis and application part of each item for the detailed usage.

GPRS Traffic Statistics Introduction


Contents

1. GPRS Traffic Structure

2. GPRS Traffic Analysis

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GPRS Traffic Analysis ProcessStart

Regular analysis of traffic data

Whether the trafficdata is faulty? Locate the fault

Whether the trafficstatistical item is faulty?

BSC overall analysis

Traffic modelaccumulationand analysis

Whether the BSCitem is faulty?

Faulty occurs

Checklist

Analyze the BSC traffic data

Locate the abnormal cell

Analyze the cell traffic data

Analyzetransmission link

Analyzecongestion rate

Analyze cell-drop rate

Solve theequipment fault

Solve thetransmission

fault

optimize thenetwork

End

Yes

No

No

Yes

Yes

No


BSC Overall Performance Analysis

� In the current GPRS network, the cell handover is unavailable and the MS

reselects a cell totally by itself. If cell reselection is performed during

transmission, call drop occurs inevitably. However, the TBF transmission

time is short (2 to 3 seconds), the impact on services is relatively small

although the call drop rate in the GPRS system is higher than that in the

speech system.

� If the call drop rate is high, need to check the traffic measurement data of

cells in the suspicious period of time and find the cells with extremely high

call drop rate. Locate the faults (the common case is faulty cell channel

status and network optimization problems) and rectify them. For details,

refer to the check of the retain ability KPIs of cells.

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� Resource utilization KPIs are used to analyze the PDCH data to check

whether the system is overloaded.

� The PDCH is of two types: dynamic PDCH and static PDCH. One RPPU

of the PCU supports a maximum of 120 available PDCHs (if upgraded to

EDGE, the maximum number of available PDCHs decreases).

Resource Utilization Analysis


Pb Interface Link Analysis

� The Pb interface is the signaling interface between the PCU and the BSC.

� As a semi-dependent device, the PCU can connect multiple BSCs. The

communication between the PCU and the BSC is realized through

transmission devices or even long distance transmission devices.

� The LAPD traffic measurement data indicates the transmission quality of

the Pb interface and the basic conditions of high-layer data.

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� LAPD performance counters include the following:

� Number of SABM frames sent

� Number of message retransmissions

� You can determine the stability of links by checking the number of

message retransmissions.

Pb Interface Link Analysis


Cell-level Performance Analysis

� In the cell-level performance analysis, the KPIs of the following four

aspects should be checked:

� Transmission performance

� Access performance

� Resource utilization

� Retain ability

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Transmission Performance Analysis� The transmission path between the MS and the GPRS core

network is called the transmission link of the cell. It includes the

Um interface, G-Abis interface, Pb interface, and Gb interface.

� Um interface analysis

� Abnormality rate of N3101, N3103, and N3105 (talked together

with call drop later)

� Retransmission rate of RLC uplink and downlink data block and

the number of CS upgrade and demolition

� G-Abis interface analysis

� The TRAU Link Measurement in the G-Abis Interface Performance

Measurement is a cell-level measurement unit used for analysis of

transmission quality on the link layer.


� For the GPRS network, if the retransmission rate is too high, the setting of

the initial coding scheme may be inappropriate. The retransmission rate

can be excessively high if a high rate is adopted for data transmission.

� Another possibility is that the setting of the coding rate adjustment

threshold in the CSPARA parameter table is inappropriate, and thus the

MS and the network cannot use the optimal coding scheme for

transmission.

� For the EDGE network, check the setting of the initial coding scheme (the

rate adjustment threshold for the EDGE network is fixed).

� If the data configuration is correct, you need to check whether there is

interference on the Um interface.

Um Interface Analysis ---retransmission and CS upgrade

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G-Abis Interface Analysis� TRAU Link Measurement includes three important counters:

Number of Out-of-Synchronization Frames Received, Number of

Check Error Frames Received, and Number of Normal Burst frames

Received. The check error frames are the transmission link check

error after channel synchronization. They directly indicate the link

quality.

00050

numberframenormalreceivednumberframeeerrorcheckreceived

rateerrorframeAbisG .≤=−


Access Performance

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Assignment Success Rate

%100×=ABRateSuccessAssignmentUplink

A − Number of Uplink TBF Establishment Attempts

B − Number of Successful Uplink TBF Establishment

%100×=DCRateSuccessAssignmentDownlink

C − Number of Downlink TBF Establishment Attempts

D − Number of Successful Downlink TBF Establishment


Uplink TBF Establishment Attempts� The mobile station initiates stage-1 access procedure by sending of

CHANNEL REQUEST messages on RACH. When the PCU receives this

message from MS, one time of Uplink TBF Establishment Attempt is

counted.

MS

A

CHANNEL REQUEST

NETWORK

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� The mobile station initiates stage-2 access procedure by sending of

CHANNEL REQUEST messages on RACH.

� When the PCU receives PACKET RESOURCE REQUEST message for

establishing uplink TBF from the MS, one time of Uplink TBF Establishment

Attempt is counted.

M S Network

A

RESOURCE REQUEST

PACKET UPLINK ASSIGNMENT

UPLINK DATA BLOCK

Uplink TBF Establishment Attempts


� Uplink TBF establishment during a downlink TBF. The mobile station may

request establishment of an uplink transfer during a downlink TBF . A

Channel Request Description information element will be included in the

PACKET DOWNLINK ACK/NACK message.

� When the PCU receives the this message from the ACK/NACK from MS,

one time of Uplink TBF Establishment Attempt is counted.

Uplink TBF Establishment Attempts

M S Network


UPLINK DATA BLOCK

A

Packet Downlink Ack/Nack

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M S Network

A

CHANNEL REQUEST

IMMEDIATE ASSIGNMENT

UPLINK DATA BLOCK

Uplink TBF Establishment Success� Uplink TBF will be successfully established in stage-1 access if uplink

data blocks on the PDCH assigned are received by PCU after it sent

IMMEDIATE ASSIGNMENT.


M S Network

A

RESOURCE REQUEST


UPLINK DATA BLOCK

Uplink TBF Establishment Success

� Uplink TBF will be successfully established in stage-2 access if uplink

data blocks on the PDCH assigned are received by PCU after it sent

Packet Uplink Assignment.

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M S Network

A


UPLINK DATA BLOCK

Uplink TBF Establishment Success� Successful uplink TBF establishment on PACCH. Uplink TBF will be

successfully established on PACCH if uplink data blocks on the PDCH

assigned are received by PCU after it sent Packet Uplink Assignment.


Assignment Success Rate Analysis

� Due to the speech service preferred and the data service features, the

assignment success rate of the GPRS network is usually higher than that

of the GSM network.

� If the assignment success rate is low, you need to check the traffic

measurement data of cells in the suspicious period of time. Usually, you

can find the cells with extremely high congestion rate. Locate the faults

and rectify them. For details, refer to the check of the radio access KPIs

of cells.

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� Check the counter Number of uplink/downlink TBF establishment failures

due to no channel. If the congestion rate is high because of these two

counters, the possible causes are as follows:

� The user manually blocks the channel or cell, leading to MS access

difficulties. Check the Number of BSC-originated channel blocking,

Number of BSC-originated cell blocking, and Number of Gb-originated

cell blocking in the Resource Maintenance Capability Measurement to

determine whether channels are blocked in the statistic period.

Access Performance –no channel available


Access Performance –no channel available

� If no channels are blocked, the number of multiplexed packet channels

and MSs may reach the maximum value, leading to MS access

difficulties. Adjust MaxUlHighLd/MaxDlHighLd of the pdchpara table on

the PCU maintenance terminal to allow the cell to carry more PS

services.

� If you only adjust the maximum number of multiplexed MSs on the

channel, the transmission rate of the MS is affected. If the cell does not

have static PDCHs, configure a static PDCH. If the cell has static

PDCHs, add more dynamic PDCHs.

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Access Performance --no channel available

� When wide coverage is available, one RPPU[Pb] of the PCU may be

configured with more than 120 cells, When the PS services on the board

is busy, if the cell is configured with only dynamic channels the cell may

be congested because of insufficient channels.

� CCCH random access collision may affect the success rate of CCCH

uplink assignment. Analyze the cause together with the Mean Interval of

Packet Access Requests on CCCH (s).

� PDCH out-of-synchronization may also lead to insufficient PS resources

and assignment failure. If the PDCH out-of-synchronization alarm is

reported, check whether the links between the PCU and the BSC and

between the BTS and the BSC are normal.


Access Performance –MS no response� The counter Number of Uplink/Downlink TBF Establishment Failures due

to MS No Response are the main cause of the low Assignment success

rate.

� The quality of the transmission links of the cell is poor and the block

BER is high.

� You can adjust the GPRS network parameters, such as T3168, to improve

the success rate of TBF access.

� If the traffic volume of PS services is high, the queue is long and the

assignment message delay is long, leading to TBF establishment

failure.

� If the traffic volume of PS services and the duration exceed the adjustment

capability of optimization, capacity expansion is recommended.

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Resource Utilization

� Through the measurement of PDCH seizure, you can obtain the

information about the preemption of the PS resources by the CS services.

� The counters that reflect the preemption of the CS services to the PS

services are Number of Dynamic PDCHs Reclaimed by BSC and Number

of Successful Conversions from TCH to PDTCH.

%100AB

RateSuccess Reclaimed TrafficPacket Carrying PDCH Dynamic Empted-Pre ×=

A − Number of Dynamic PDCHs Reclaimed by BSC

B − Number of Preempted PDCHs Carrying Packet Traffic



� The PDCH utilization can reflect the traffic volume of the cell to some

extent. The relevant counters are Mean Number of Available PDCHs, Mean

Number of Occupied PDCHs, and Mean occupied Duration of All Available

PDCHs( s ).

� If the cell is configured with static channels, in normal conditions, the Mean

Number of Available PDCHs should be equal to or greater than the number

of static channels configured in the cell. Otherwise, the cell status is faulty

in the statistic period.

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� If all the channels configured in the cell are dynamic channels, you can

determine whether there is any request for the dynamic channel through

the two counters: Mean Number of Available PDCHs and Mean Number of

Occupied PDCHs.

� According to the Mean Number of Occupied PDCHs, you can determine

whether the PS services in the cell are busy or idle. Then you can adjust

the channel configuration according to the cell status. The idle cell shall be

configured with more dynamic channels and the busy cell can be

configured with more static channels.



� The channel utilization rate considers the block utilization rate on the

PDCH both when the PCU is busy and when it is idle. Thus if the channel

utilization rate is low, the possible cause is that there is no PS service in

the cell or the traffic volume of the PS services is small.

� The uplink/downlink PDTCH/PACCH channel utilization can to some

extent reflect the traffic volume of the PS services in the current cell. The

relevant counters are as follows:

� Cell Mean PDCH Bearer Rate (%)

� Uplink PDTCH/PACCH Utilization Rate (%)

� Downlink PDTCH/PACCH Utilization Rate (%)

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Retain Ability –Drop Rate Analysis


Drop Rate Analysis

( ) %100×=ABRateDropTBFGPRSUplink

A − Number of Successful Uplink TBF Establishment

B − Number of Uplink TBF Abnormal Release

( ) %100×=ABRateDropTBFGPRSDownlink

A − Number of Successful Downlink TBF Establishment

B − Number of Downlink TBF Abnormal Release

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Uplink TBF Normal Release

M S Network

A

PACKET UPLINK ACK/NACK FAI=1

PACKET CONTROL ACKNOWLEDGEMENT

� When the network receives the uplink RLC data block with CV=0, it will

send PACKET UPLINK ACK/NACK with FAI=1 to initiate uplink TBF

release procedure.

� When the uplink TBF is normally released, the network then will

receive the PACKET CONTROL ACKOWNLEDGEMENT from MS


Abnormal Release Analysis � Poor transmission quality of the Um interface leads to the abnormal

release of the TBF and the increase of the TBF call drop rate.

� The counter Number of Uplink TBF Abnormal Release due to N3101

Overflow (Ms No Response) and the counter Number of Uplink TBF

Abnormal Release due to N3103 Overflow (Ms No Response) of the

Uplink TBF Establishment/Release Measurement refer to the number

of abnormal releases due to the poor quality of the Um interface. If the

values of the two counters are high, you need to check the quality of

the links on the Um interface.

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Abnormal Release Analysis � The counter Number of Downlink TBF Abnormal Release due to N3105

Overflow of Downlink TBF Establishment/Release Measurement refers

to the number of abnormal releases due to the poor quality of the links

on the Um interface. A high number of overflows indicates poor quality

of the downlink.

� Similar to the counters related to the GPRS TBF, the counters related

to the EGPRS TBF are used to measure the abnormal TBF releases

due to N3101, N3103, and N3105 overflows.


Abnormal Release Due to N3101� This statistics item is used to measure the number of uplink TBF

abnormal releases due to overflow of the uplink monitoring counter

N3101.

Network schedule every uplink data block resource by allocating valid

USF for every MS which has accessed into the network, and attach the

USF information in every downlink block. N3101 will be increased by 1

every time no uplink data block is received on corresponding frame,

otherwise N3101 will be reset. The TBF will be released by network if

N3101 reaches the threshold.

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Abnormal Release Due to N3101

M S Network

A

RLC block(with USF valid)

RLC block (with USF valid)

NO RESPONSE FROM MS

N3101=N3101_MAX

� As the measurement point A referred in Figure , the number of uplink

TBF abnormal release due to N3101 overflow will be increased by one.



� Network initiates uplink TBF release procedure by sending a PACKET

UPLINK ACK/NACK message with FAI=1, and wait MS reply PACKET

CONTROL ACKOWNLEDGEMENT message to release the uplink TBF

normally.

� N3103 will be incremented by 1 every time no expected message is

received on corresponding frame, otherwise N3103 will be reset.

� The TBF will be released by network if N3103 reaches the threshold.

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M S Network

A

PACKET UPLINK ACK/NACK(FAI=1)

NO RESPONSE FROM MS

N3103=N3103_MAX

PACKET UPLINK ACK/NACK(FAI=1)

� As the measurement point A referred in Figure below, the number of

uplink TBF abnormal release due to N3103 overflow will be increased

by one.



� This statistics item is used to measure the number of TBF abnormal

releases due to overflow of the downlink monitoring counter N3105.

� Network will send the RLC data block with RRBP periodically to wait

response of PACKET DOWNLINK ACK/NACK message from MS.

N3105 will be increased by 1 every time no PACKET DOWNLINK

ACK/NACK is received on the same corresponding frame, otherwise

N3105 will be reset.

� The TBF will be released by network if N3105 reaches the threshold,

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MS Network

A

DOWNLINK DATA BLOCK (RRBP)



MS no response.....

Abnormal Release Due to N3105� As the measurement point A referred in Figure , the number of downlink

TBF abnormal release due to N3105 overflow will be increased by one.


Call Drop Analysis� Determine whether the high TBF call drop rate is common for the entire

BSC or appears only in some sites or cells. If it appears only in some cells, check and troubleshoot the equipment based on the trafficmeasurement results.

� Check the equipment, including the BTS and PCU hardware. Then troubleshoot the transmission links, including the Um interface links, TRAU links, and Pb interface links. The equipment and transmission problems always cause alarms, which can be used for reference.

� The two counters Number of uplink/downlink TBF abnormal release due to no channel in the same statistic period can show that the TBF call drop is caused by the preemption of the PS resources by the CS services.

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Call Drop Analysis� Number of uplink/downlink TBF abnormal release due to SUSPEND

shows the impact of the CS services on the PS services, for example, a

call or location updating is initiated when the PS services are performed.

� If cell reselection is initiated when the PS services are performed, the

TBF is abnormally released. According to Number of uplink/downlink

TBF abnormal release due to FLUSH, together with Number of Times a

Cell Is Selected by MS, Number of Cell Reselections by MS at Short

Interval, and Number of Cell Ping-Pong Reselections by MS, check

whether the ping-pong reselections occur.


Call Drop Analysis � Pay attention to the following condition: the values of Number of

uplink/downlink TBF abnormal release due to no channel are high, but the

value of Number of Preempted PDCHs Carrying Packet Traffic is 0. This

indicates that the abnormal release is not caused by CS preemption.

Check whether there are channels or cells blocked in the statistic period.

� If no channels or cells are blocked, check whether the transmission

resources of each interface incur faults or intermittent faults.

� If the transmission is normal, check the GPRS/EDGE TRXs. Locate the

implicit faults of TRXs through replacement or other methods.

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� In many networks, the GPRS/EDGE and the GSM share radio resources.

If the number of N3101, N3103, and N3105 overflows on the Um interface

is too high, some GSM counters can be used to troubleshoot the GPRS

network.

� The Interference Band Measurement and the cell frequency scan of the

GSM network can be used to locate the uplink interference.

� The TCHF/TCHH Receive Level Measurement of the GSM network is

used to measure the MRs received in a statistic period with different

receive levels and receive quality ranks. The measurement results

indicate the distribution of uplink/downlink receive level and receive quality

by ranks.

Optimization of Call Drop


Other Often-used Items� EGPRS 8PSK_MEAN_BEP Different Value Measurement: This item is

used to measure the number of EGPRS PACKET DOWNLINK

ACK/NACK messages carrying EGPRS BEP Link Quality

Measurements with 8PSK_MEAN_BEP = 1 to 31 received by BSS.

The items can be used to reveal the traffic load of the cell and thus

help to create the traffic model.

MS Network

A

EGPRS PACKET DOWNLINK ACK/NACK(8PSK_MEAN_BEP=1)

28


Other Often-used Items

Times of 8MSK_MEAN_BEP=3131





Times of 8MSK _MEAN_BEP=44



Times of 8PSK_MEAN_BEP=11

Measurement itemNo.


Other Often-used Items� Cell reselection is of key importance to the GPRS network performance.

There are relevant counters monitoring ping-pong reselection and

network-controlled cell reselection (NC2)

� Number of Cell Reselections by MS at Short Interval: This counter is

used to measure the total number of times that the duration between

the MS switches into and out of the cell is less than the specified

time (20 seconds by default).

� Number of Cell Ping-Pong Reselections by MS: This counter is used

to measure the number of times that the MS switches from cell A to

cell B and then switches back to cell A at the predefined interval (20

seconds by default).

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Other Often-used Items� Number of Network Controlled Cell Reselection Attempts due to Downlink

Quality: This counter is used to measure the number of cell reselections

controlled by the network in a statistic period. These cell reselections are

caused by the deteriorating quality of downlink transmission.

� Number of Network Controlled Cell Reselection Attempts due to Traffic Load:

This counter is used to measure the number of cell reselections in a statistic

period. The information about cell reselections is sent because the cell is

overloaded.

� Number of Network Controlled Cell Reselection Attempts for Better Cell: This

counter is used to measure the number of cell reselections in a statistic

period. The information about cell reselections is sent because of higher

signal level in neighbor cells.


Other Often-used Items

� Uplink/Downlink LLC Data Transmission Measurement

� you can get the LLC PDU length and the LLC mean rate and

then get the traffic model for RNP.

� Mean Length of Uplink LLC_PDUs

� Mean Length of Downlink LLC_PDUs

� Mean LLC_PDU Bytes per Uplink TBF

� Mean LLC_PDU Bytes per Downlink TBF

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Summary

� During the early stage of GPRS traffic measurement, pay

attention to the call drop rate and congestion rate. During

the late stage of GPRS traffic measurement, pay attention

to the resource utilization.

� The GPRS and GSM share radio resources. Sometimes the

GSM traffic measurement can be used to locate the GPRS

problems.

� For the GPRS network, analyze the PCU-level counters first,

and then the cell-level counters.

Thank youwww.huawei.com

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