52 gsm bss network performance ps kpi (downlink tbf establishment success rate) optimization manual[1].doc

GSM BSS Network Performance PS KPI (Downlink TBF Establishment Success Rate)
Optimization Manual
INTERNAL
Product Name Confidentiality level
GSM BSS Network Performance PS KPI
(Downlink TBF Establishment Success Rate)
Optimization Manual
INTERNAL
Product Version Total 30 pages
GSM BSS Network Performance PS KPI
(Downlink TBF Establishment Success Rate)
Optimization Manual
For internal use only
Prepared by GSM &UMTS Network Performance
Research Department
Date 2008-12-26
Reviewed by Date yyyy-mm-dd
Reviewed by Date yyyy-mm-dd
Granted by Date yyyy-mm-dd
Huawei Technologies Co., Ltd.
All rights reserved

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Revision Record
Date Revision
version
Change Description Author
2008-05-05 V0.8 Initial draft completed Wang Guanghua
2008-08-26 V1.0 Revised according to review suggestions Su Shi
2008-12-26 V1.1 Optimized the document according to the
accumulated optimization experience
Wang Guanghua
2014-6-18 7:32:13 a6/p6 Huawei Technologies Proprietary Page 2 of 31

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GSM BSS Network Performance PS KPI (Downlink TBF
Establishment Success Rate) Optimization Manual
Keywords
Downlink TBF, establishment success rate
Abstract
This manual mainly describes the method of collecting statistics about the downlink
TBF establishment success rate and the methods of optimizing the downlink TBF
establishment success rate.
List of abbreviations
Abbreviation Full Spelling
PDCH Packet Data Channel
PCU Packet Control Unit
MS Mobile Station
CQT Call Quality Test
KPI Key Performance Index
DT Drive Test
GPRS General Packet Radio Service
EDGE Enhanced Data rates for GSM Evolution

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Contents
1 Basic Principle................................................................................................................................7
1.1 Counter Definition....................................................................................................................................................7
1.1 Counter Definition....................................................................................................................................................7
1.1.1 Definition in the Case of No MS Response .......................................................................................................7
1.1.1 Definition in the Case of No MS Response .......................................................................................................7
1.1.2 Definition in the Case of No Available Resources ............................................................................................7
1.1.2 Definition in the Case of No Available Resources ............................................................................................7
1.1.3 Definition in the Case of No MS Response or No Available Resources ...........................................................8
1.1.3 Definition in the Case of No MS Response or No Available Resources ...........................................................8
1.2 Theory.......................................................................................................................................................................8
1.2 Theory.......................................................................................................................................................................8
2 Signaling Procedure......................................................................................................................9
2.1 Number of Successful Downlink TBF Establishments............................................................................................9
2.1 Number of Successful Downlink TBF Establishments............................................................................................9
2.1.1 Description..........................................................................................................................................................9
2.1.1 Description..........................................................................................................................................................9
2.1.2 Measurement Point.............................................................................................................................................9
2.1.2 Measurement Point.............................................................................................................................................9
2.2 Number of Failed Downlink TBF Establishments.................................................................................................10
2.2 Number of Failed Downlink TBF Establishments.................................................................................................10
2.2.1 Description........................................................................................................................................................10
2.2.1 Description........................................................................................................................................................10
2.2.2 Measurement Point...........................................................................................................................................11
2.3 Number of Downlink TBF Establishment Attempts...............................................................................................11
2.3 Number of Downlink TBF Establishment Attempts...............................................................................................11
2.3.1 Description........................................................................................................................................................11
2.3.1 Description........................................................................................................................................................11
3 Analysis and Optimization Methods......................................................................................13
3.1 Checking the Abis Link..........................................................................................................................................16

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3.1 Checking the Abis Link..........................................................................................................................................16
3.2 Checking the Delivery of Assignment Messages...................................................................................................17
3.2 Checking the Delivery of Assignment Messages...................................................................................................17
3.2.1 Failed Downlink TBF Establishments Due to Overloaded CCCH..................................................................17
3.2.1 Failed Downlink TBF Establishments Due to Overloaded CCCH..................................................................17
3.2.2 Failed Downlink TBF Establishments Due to No Channel Resources............................................................17
3.2.2 Failed Downlink TBF Establishments Due to No Channel Resources............................................................17
3.3 Checking the Air Interface......................................................................................................................................20
3.3 Checking the Air Interface......................................................................................................................................20
3.4 Checking Failed Downlink TBF Establishments Due to No Response from the MS............................................21
3.4 Checking Failed Downlink TBF Establishments Due to No Response from the MS............................................21
3.4.1 Failed Downlink TBF Establishments Due to Improper Parameter Configurations........................................21
3.4.1 Failed Downlink TBF Establishments Due to Improper Parameter Configurations........................................21
3.4.2 Failed Downlink TBF Establishments Due to Incorrect Information Elements in Assignment Messages......23
3.4.2 Failed Downlink TBF Establishments Due to Incorrect Information Elements in Assignment Messages......23
3.4.3 Failed Downlink TBF Establishments Due to Imbalance Between the Uplink and the Downlink..................24
3.4.3 Failed Downlink TBF Establishments Due to Imbalance Between the Uplink and the Downlink..................24
3.4.4 Checking the Feed System...............................................................................................................................25
3.4.4 Checking the Feed System...............................................................................................................................25
3.4.5 Checking the KPIs of the PS Field...................................................................................................................25
3.4.5 Checking the KPIs of the PS Field...................................................................................................................25
4 Cases...............................................................................................................................................26
4.1 Case 1: Low Success Rate of Downlink TBF Establishment Due to Incorrect Frequency-Hopping Parameter
Settings in Czech Republic...........................................................................................................................................26
4.1 Case 1: Low Success Rate of Downlink TBF Establishment Due to Incorrect Frequency-Hopping Parameter
Settings in Czech Republic...........................................................................................................................................26
4.2 Case 2: Low Success Rate of Downlink TBF Establishment Due to No Responses from MSs After the PCU Is
Upgraded......................................................................................................................................................................29
4.2 Case 2: Low Success Rate of Downlink TBF Establishment Due to No Responses from MSs After the PCU Is
Upgraded......................................................................................................................................................................29
5 Problem Feedback.......................................................................................................................31

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Figures
Successful establishment of downlink TBF on the CCCH....................................................10
Successful downlink TBF establishment on the PACCH......................................................10
Downlink TBF establishment attempts on the CCCH............................................................12
Downlink TBF establishment attempts on the PACCH.........................................................12
Uplink and downlink TBF establishment procedure on the CCCH....................................14
Overall analysis process................................................................................................................15
Analysis of the frame error rate of the G-Abis interface is normal......................................27
Downlink packet assignment message......................................................................................27
MA Numeber in the downlink packet assignment message.................................................28
Frequency-hopping information being null in the SI 13 message.......................................29

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GSM BSS Network Performance PS KPI (Downlink TBF
Establishment Success Rate) Optimization Manual
1 Basic Principle
1.1 Counter Definition
The definition of the downlink TBF establishment success rate varies with the
assessment item.
1.1.1 Definition in the Case of No MS Response
If the network side delivers an assignment message to a mobile station (MS) but fails
to receive the Packet Control Acknowledgement message from the MS, the
number of failed downlink TBF establishments due to MS no response is added by
one.
The definition of the downlink TBF establishment success rate is as follows:
Downlink GPRS TBF Establishment Success Rate = 1 - Number of Failed
Downlink GPRS TBF Establishments due to MS No Response/Number of
Downlink GPRS TBF Establishment Attempts
Downlink EGPRS TBF Establishment Success Rate = 1 - Number of Failed
Downlink EGPRS TBF Establishments due to MS No Response/Number of
Downlink EGPRS TBF Establishment Attempts
1.1.2 Definition in the Case of No Available Resources
If the downlink TBF establishment fails because the resources such as channels and
TFIs at the network side are unavailable, the number of failed downlink TBF
establishments due to no channel is added by one.
Downlink GPRS TBF Establishment Success Rate = 1 - Number of Failed
Downlink GPRS TBF Establishments due to No Channel/Number of Downlink
GPRS TBF Establishment Attempts

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Downlink EGPRS TBF Establishment Success Rate = 1 - Number of Failed
Downlink EGPRS TBF Establishments due to No Channel/Number of Downlink
EGPRS TBF Establishment Attempts
1.1.3 Definition in the Case of No MS Response or No Available
Resources
If the downlink TBF establishment fails because the network side fails to receive the
Packet Control Acknowledgement message from an MS or the resources at the
network side are unavailable, the number of failed downlink TBF establishments is
add by one.
Downlink GPRS TBF Establishment Success Rate = Number of Successful
Downlink GPRS TBF Establishments/Number of Downlink GPRS TBF
Establishment Attempts
Downlink EGPRS TBF Establishment Success Rate = Number of Successful
Downlink EGPRS TBF Establishments/Number of Downlink EGPRS TBF
Establishment Attempts
1.2 Theory
The downlink TBF establishment success rate shows the downlink access
performance and is an important counter for assessing the network. When the
downlink TBF fails to be established, the network side continues to trigger the
establishment of the downlink TBF in a short time because the network side has
some data blocks that are not delivered. Therefore, the downlink TBF establishment
success rate is slightly low in this case, but customer experience is not affected.

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2 Signaling Procedure
2.1 Number of Successful Downlink TBF Establishments
2.1.1 Description
This counter provides the number of successful downlink TBF establishments in a measurement
period.
2.1.2 Measurement Point
Successful downlink TBF establishments involve the following aspects:
1. Successful downlink TBF establishment on the CCCH
The network side initiates the downlink TBF establishment procedure by sending
an IMMEDIATE ASSIGNMENT message with Starting Time on the CCCH to the
MS. When the starting time is reached, the network side sends a POLLING
message to the MS to obtain a TA value. The BSC reserves block resources for
the MS to respond with an assignment acknowledgement message. If the
network side receives a Packet Control Acknowledgement message from the
MS on the reserved block resources in the assigned channel, it indicates that the
downlink TBF is established. In addition, the network side can calculate the TA
value by using the Packet Control Acknowledgement message that is
received.
The following figure shows the procedure for establishing downlink TBFs on the
CCCH. Each time the network side receives a Packet Control
Acknowledgement message (see measurement point A), the value of the
counter Number of Successful Downlink TBF Establishments is added by
one.

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Figure 1.1 Successful establishment of downlink TBF on the CCCH
M S Network
A
IMMEDIATE ASSIGNMENT (CCCH)
POLLING(RRBP)
PACKET Control Acknowledgement
2. Successful downlink TBF establishment on the PACCH
The network side can initiate the downlink TBF establishment procedure by
sending a Packet downlink assignment message on the PACCH to the MS.
The message contains the information about the block resources reserved by
the network side for the MS to respond with an assignment acknowledgement
message. If the network side receives a Packet Control Acknowledgement
message from the MS on the reserved block resources in the assigned channel,
it indicates that the downlink TBF is established.
Figure 2.1 shows the procedure for establishing the downlink TBF on the
PACCH. Each time the network side receives a Packet Control
Acknowledgement message corresponding to a Packet downlink assignment
message (see measurement point A), the value of the counter Number of
Successful Downlink TBF Establishments is added by one.
Figure 2.1 Successful downlink TBF establishment on the PACCH
M S Network
A
Packet downlink assignment
PACKET Control Acknowledgement
2.2 Number of Failed Downlink TBF Establishments
2.2.1 Description
This counter measures the number of failed downlink TBF establishments in a
measurement period.

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Failed downlink TBF establishments involve the following aspects:
1. Failed downlink TBF establishments due to no channel
If the BSC receives a new downlink PDU request from the SGSN but fails to
establish a download TBF because channels are unavailable, the value of Number
of Failed Downlink TBF Establishments due to No Channel is added by one.
2. Failed downlink TBF establishments due to MS no response
In the procedure for establishing a downlink TBF, the BSC sends a POLLING
message on the CCCH or sends a Packet downlink assignment message on the
PACCH, and reserves block resources for the MS to respond with an assignment
acknowledgement message. If the BSC does not receive a Packet Control
Acknowledgement message from the MS on the reserved block resources, the BSC
sends the IMMEDIATE ASSIGNMENT messages repeatedly until the maximum
number of retry times is exceeded. Each time the maximum number of retrying times
is exceeded, the value of Number of Failed Downlink TBF Establishments due to
MS No Response is added by one.
2.3 Number of Downlink TBF Establishment Attempts
2.3.1 Description
This counter measures the number of downlink TBF establishment attempts in a
measurement period.
Downlink TBF establishment attempts involve the following aspects:
1. Downlink TBF establishment attempts on the CCCH
The network attempts to establish the downlink TBF by sending the IMMEDIATE
ASSIGNMENT message at the sub-timeslot corresponding to the CCCH group
to which the MS belongs. Figure shows the procedure for the network side to
send the IMMEDIATE ASSIGNMENT message on the CCCH. Each time the
network side sends an IMMEDIATE ASSIGNMENT message (see measurement
point A), the value of the counter Number of Downlink TBF Establishment
Attempts is added by one.

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Figure 1.1 Downlink TBF establishment attempts on the CCCH.
M S Network
A
IMMEDIATE ASSIGNMENT
(On CCCH)　
2. Downlink TBF establishment attempts on the PACCH
The network side can attempt to establish the downlink TBF by sending a
PACKET DOWNLINK ASSIGNMENT message to an MS during the
transmission process of the previous uplink TBF or the release process of the
current downlink TBF. Figure 2.1 shows the procedure for the network side to
send the PACKET DOWNLINK ASSIGNMENT message on the PACCH. Each
time the network side sends a PACKET DOWNLINK ASSIGNMENT message
(see measurement point A), the value of the counter Number of Downlink TBF
Establishment Attempts is added by one.
Figure 2.1 Downlink TBF establishment attempts on the PACCH
M S Network
A
PACKET DOWNLINK ASSIGNMENT

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3 Analysis and Optimization Methods
The procedure for establishing the downlink TBF on the CCCH is as follows:
1. The RR entity at the network side initiates the downlink TBF establishment by
using the downlink packet assignment procedure. The downlink packet
assignment procedure is triggered by a request from upper layers to transfer a
LLC PDU. Before transferring an LLC PDU, the network side determines
whether the MS is in the Ready state. If the MS is in the Ready state, the
network side transfers an LLC PDU to the BSS. When receiving the LLC PDU,
the BSS delivers an IMMEDIATE ASSIGNMENT message. If the MS is in the
Standby state, the network side sends a paging message to the BSS. The
network side sends the LLC PDU only after receiving a paging response from
the BSS. The request from upper layers contains the priority, including the RLC
mode, DRX parameter (optional), QoS script file of the IMSI (optional), and MS
radio access capability associated with the packet transfer (optional). For such a
request, the network side determines whether the MS is in packet idle mode or
packet transfer mode. If the MS is in packet idle mode, the network side initiates
the downlink packet assignment procedure on the CCCH. If the MS is in packet
transfer mode, the network side initiates the downlink packet assignment
procedure on the PACCH.
2. The network side selects an encoding scheme and applies for radio resources
according to the resource occupation in the accessed cell for establishing the
downlink TBF. After the application is approved, the network side assigns radio
resources to the downlink TBF and counts the times the downlink TBF is started
at the network side and at the MS side.
3. The network side delivers an IMMEDIATE ASSIGNMENT message. If the MS is
in DRX mode, the network side delivers the message in the PCH channel. If the
MS is in Non-DRX mode, the network side delivers the message in the AGCH
channel.
4. When the MS receives the IMMEDIATE ASSIGNMENT message, radio
resources are assigned. After receiving the frame number indicated by the TBF
Starting Time (optional), the MS accesses the assigned channel, starts to listen
on the RLC radio block of the downlink TBF, and starts timer T3190.
5. If the network side has the TA value of the MS, the network side directly trasfers
the TA value to the MS by sending a Packet Power Control/Timing Advance
message after the Starting Time of the downlink TBF is reached. If the network
side does not have the TA value, the network side obtains the TA value by
sending a PACKET POLLING REQUEST message after the downlink TBF is

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started.
6. Before timer T3190 times out, if the MS addresses the downlink RLC radio block
in the assigned channel according to the TFI field and the MS receives the
PACKET POLLING REQUEST message from the network side, the MS sends a
Packet Control Acknowledgement message on the uplink radio block
corresponding to the message and resets timer T3190. Otherwise, the MS
notifies the upper layers of the downlink TBF establishment failure.
7. The network side obtains the TA value of the MS by using the valid Packet
Control Acknowledgement message received on the reserved uplink RLC
radio block. In this case, the network side regards that the downlink TBF
establishment is successful. Otherwise, the network side initiates the downlink
immediate assignment procedure again.
Figure 7.1 Uplink and downlink TBF establishment procedure on the CCCH
MS PCU
PDCH
IMMEDIATE ASSIGNMENT
CCCH
LLC PDU
PACKET POLLING REQUEST
PACKET CONTROL ACKNOWLEDGMENT
PDCH
BTS
This section taske the uplink and downlink TBF establishment on the CCCH as an
example to describe the optimization ideas about identifying the signaling and cells
where problems occur throughout the signaling procedure. In the downlink TBF
establishment procedure, you can identify problematic singaling and cells as follow:
 Checking whether transmission problems occur in the Abis links.
 Checking whether the IMMEDIATE ASSIGNMENT and PACKET POLLING
REQUEST messages are properly sent to the BTS.
 Checking whether the IMMEDIATE ASSIGNMENT and PACKET POLLING
REQUEST messages are sent to MSs according to the air interface quality.
 Checking whether MSs respond to POLLING messages by sending Packet
Control Acknowledgement messages.

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Figure 7.2 Overall analysis process
Analyze the cause of
downlink TBF
establishment failure
Start
Check whether the status of
the Abis link is normal
Yes
Check whether assignment
messages are sent normally
Check whether the downlink
air interface is normal
Yes
Check whether MSs
respond to ASSIGNMENT
and POLLING messages
No
No
Check whether the
problem is solved
Yes
Check the transmission
Check whether the
CCCH is overloaded
Check whether channels
are available
No
Check whether the
downlink air interface
quality is poor
Perform the CQT test
No
Check whether the
parameter configurations
are correct
Check whether the
importance cells are
correct
Yes
Check whether the uplink
and downlink are
balanced
Check whether the feed
system is normal
Check whether the
parameters of the CS
fieldNo
Yes
End

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3.1 Checking the Abis Link
Transmission problems such as out-of-synchronization or intermittent Abis interface
links may cause the failure to establish the downlink TBF.
You can determine the trasmission status of the Abis interface by calculating the
frame error rate of the G-Abis interface as follows:
Frame error rate of the G-Abis interface = (Number of Received Check Error TRAU
Frames + Number of Received Out-of-Synchronization TRAU Frames)/(Number
of Sent Valid TRAU Frames + Number of Sent Empty TRAU Frames)
1. Generally, the frame error rate is equal to or lower than 10e–5, that is, 1/10,000.
This indicates one error frame in a channel every four minutes on average. In
this case, you can infer that the link is of good quality, and the MS can transmit
data in a stable way.
2. If the frame error rate is lower than 10e-4, the quality of the transmission link is
poor. In this case, one to three error frames occur in a channel every minute on
average. Error frames are unpredictable. Therefore, affected MSs are likely to
experience low transmission rate, long transmission delay, or even
disconnection.
3. If the frame error rate is higher than 10e-4, the link becomes unstable. Out-of-
synchronization is likely to occur and the rate of out-of-synchronization frame
greatly increases. In this case, MSs may be able to perform data services that
require only a small volume, such as the high-layer signaling and certain WAP
services. Mass data transmission, such as FTP services, becomes difficult.
In actual running, carriers are not able to directly control leased lines, such as
microwave satelites. Therefore, a frame error rate lower than 5/1000 is acceptable. If
you find that a transmission problem has occurred because the frame error rate of a
cell stays high for a long time, check the transmission line and optimize the network.
The following table lists the relavant KPIs.
KPI Cell-Level
Frame error rate of
the G-Abis
interface
G-Abis Measurement -> Performance measurement of
BSC packet assignment ->
Number of Received Normal TRAU Frames
Number of Received Out-of-Synchronization TRAU
Frames
Number of Received Check Error TRAU Frames
Number of Sent Valid TRAU Frames
Number of Sent Empty TRAU Frames

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Number of received frames = Number of Received Normal TRAU Frames + Number of
Received Out-of-Synchronization TRAU Frames + Number of Received Check Error
TRAU Frames + Number of Sent Empty TRAU Frames. In versions earlier than V9R8C11,
Number of Sent Empty TRAU Frames is not included in the statistics about the number of
received frames. Therefore, when the frame error rate of the G-Abis interface is calculated, the
sum of Number of Sent Valid TRAU Frames and Number of Sent Empty TRAU Frames is
used to indicate the number of received frames. In the version V9R8C12, this problem is
solved by using the sum of Number of Received Normal TRAU Frames, Number of
Received Out-of-Synchronization TRAU Frames, Number of Received Check Error TRAU
Frames, and Number of Sent Empty TRAU Frames to indicate the number of received
frames.
3.2 Checking the Delivery of Assignment Messages
3.2.1 Failed Downlink TBF Establishments Due to Overloaded
CCCH
If the CCCH is overloaded, the IMMEDIATE ASSIGNMENT message sent on the
CCCH may be discarded. As a result, the downlink TBF fails to be established. You
can check whether the CCCH is overloaded by viewing flow control traffics. If the
CCCH is overloaded, you can increase the load threshold of the CCCH to prevent
downlink TBF establishment failure due to flow control.
The following table lists the relevant counters.
Cause Cell-Level
Overloaded CCCH Call Measurement -> Flow control measurement ->
PACKET CCCH LOAD IND Messages Sent on Abis Interface
MSG ABIS OVERLOAD (CCCH OVERLOAD) Messages
Sent on Abis Interface
MSG DEL IND Messages Sent on Abis Interface
3.2.2 Failed Downlink TBF Establishments Due to No Channel
Resources
Hardware Fault
Faults on hardware such as the TRX may affect the success rate of downlink TBF
establishment. Therefore, you should check hardware faults.
You can locate hardware faults by checking the traffic measurement related to the
hardware faults.

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Cause BSC-Level Cell-Level
Equipmen
t faults
BSC Measurement -> Access
Measurement ->
TCH Availability per BSC
Configured TCHs per BSC
Available TCHs per BSC
KPI Measurement ->
TCH Availability
Available TCHs
Configured TCHs
TRX Measurement ->
Activated TRXs in cell
Available TRXs in cell
Insufficient Channel Resources
Insufficient channel resources, which may cause congestion, occur in the following
situations:
1. The number of channels configured in a cell is small, and the traffic of packet
services is heavy. As a result, MSs are multiplexed on the channels in the cell to
the maximum degree. In this case, you need to add more static and dynamic
channels. In addition, you need to check the PS-domain channel management
parameters and set PDCH Downlink Multiplex Threshold to 80, that is, the
maximum number of TBFs multiplexed on the downlink is eight.
2. Check whether the preemption of dynamic PDCHs by CS services leads to the
insufficiency of PDCHs. You can check the number of times of reclaiming
dynamic PDCHs by the BSC and the number of times of reclaiming dynamic
PDCHs with load. If the numbers are great, you can infer that busy CS services
preempt channel resources of PS services. As a result, you need to add static
PDCHs. You can also set Level of Preempting Dynamic Channel to Control
channels cannot be preempted.
The following table describes the relevant parameters.
Name Description Setting Principle Value Range
Maximum
Ratio
Threshold
of PDCHs
in a Cell
The total number of
TCHs and PDCHs
available in a cell is
fixed. This parameter
determines the
proportion of PDCHs to
the total number of
TCHs and PDCHs.
If this parameter is set
to an excessive value,
there are excessive
PDCHs and insufficient
TCHs. This affects CS
services.
to a modest value,
there are insufficient
PDCHs and excessive
TCHs. This affects PS
services.
Value range: 0-
100.
Default value:
50
PDCH
Downlink
Multiplex
Threshold
PDCH Downlink
Multiplex Threshold
to a lower value, the
TBFs established on
the PDCH and the
subscribers are fewer,
and the downlink
Value range: 10-
80
The value 10
indicates that at
most one TBF

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bandwidth for each
subscriber is higher.
to a higher value, the
number of TBFs
established on the
PDCH and the number
of subscribers are
greater, and the
downlink bandwidth for
each subscriber is less.
can be
accessed. The
value 80
indicates that a
maximum of 8
TBFs can be
accessed.
Default value:
80.
Level of
Preemptin
g
Dynamic
Channel
Level of dynamic
channel preempted by
CS services and PS
services The TCH/Fs are
dynamic channels that
can be preempted. If this
parameter is set to All
dynamic channels can
be pre-empted, it means
that the CS services can
preempt all dynamic
channels; if this
parameter is set to
Control channels cannot
that the CS services can
preempt any dynamic
channels except the
control channels; if this
parameter is set to
Dynamic channels
carrying services cannot
that the CS services
cannot preempt the
dynamic channels that
carry services.
Generally, CS services
have the highest
priority. This parameter
must be set to All
dynamic channels can
be pre-empted so that
CS services can
preempt all dynamic
channels.
To ensure data
services, you can set
this parameter to
Control channels
cannot be pre-empted
or Dynamic channels
carrying services
cannot be pre-empted.
Value options:
All dynamic
channels can be
preempted,
Control
channels cannot
be preempted
Dynamic
channels
carrying
services cannot
be preempted
Default value:
All dynamic
channels can be
preempted.
The following table lists the related traffic measurement counters.

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Cause Cell-Level
Insufficient
resources
Packet Switch Channel Measurement -> PDCH Resource
Capability Measurement ->
Number of TCH to PDTCH Conversion Attempts
Number of Successful TCH to PDTCH Conversions
Number of Reclaimed Dynamic PDCHs
Number of Reclaimed Busy Dynamic PDCHs
Packet Switch Call Measurement -> Downlink GPRS TBF
Establish and Release Capability Measurement ->
Number of Downlink GPRS TBF Establishment Attempts
Number of Successful Downlink GPRS TBF Establishments
Number of Failed Downlink GPRS TBF Establishments due to No
Channel
Average Number of Concurrent Downlink GPRS TBFs
Packet Switch Call Measurement ->Downlink EGPRS TBF
Establish and Release Capability Measurement ->
Number of Downlink EGPRS TBF Establishment Attempts
Number of Successful Downlink EGPRS TBF Establishments
Number of Failed Downlink EGPRS TBF Establishments due to
No Channel
Average Number of Concurrent Downlink EGPRS TBFs
3.3 Checking the Air Interface
MSs may not receive downlink ASSIGNMENT messages or POLLING messages due
to poor air interface quality. You can check the air interface quality by checking the
BEP distribution or performing the CQT test. To check the BEP distribution, you can
count the 8PSK_MEAN_BEP variants and the GMSK_MEAN_BEP variants. To
conduct the CQT, you can use a dedicated tool, such as the TEMS.
If the air interface is experiencing serious interruption, you can improve the air
interface quality by adjusting the frequency point.
The following table lists the related traffic measurement counters.
KPI Cell-Level
Downlink air
interface quality
Packet Switch Call Measurement ->
Measurement of numbers of 8PSK_MEAN_BEP variants
Measurement of numbers of GMSK_MEAN_BEP variants

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3.4 Checking Failed Downlink TBF Establishments Due
to No Response from the MS
3.4.1 Failed Downlink TBF Establishments Due to Improper
Parameter Configurations
If the TBF at the network side and the TBF at the MS are not started at the same
time, the downlink TBF establishment may fail. Therefore, the TBF at the network
side cannot be started before the TBF at the MS. Otherwise, the MS may miss the
POLLING message from the network side, and thus the downlink TBF establishment
fails.
The parameters are as follows:
Retry Times of
Downlink TBF
Reassignment
This parameter
specifies the maximum
number of attempts to
resend the
IMMEDIATE
ASSIGNMENT
message. The
message is sent when
the network side fails
to receive a valid
Packet Control
Acknowledgement
message on the
reserved uplink RLC
block in the procedure
for establishing the
downlink TBF. If the
number is exceeded,
the network side
releases the downlink
TBF.
If the value of this
parameter is too
small, the network
side will release the
downlink TBF with
only a few attempts to
resend the
IMMEDIATE
ASSIGNMENT
message, which
leads to downlink
establishment failure.
If the number of failed
downlink TBF
establishments is
great, you can set
this value to a higher
value.
Default value:
2.
Retry Times of
Downlink TBF
Polling
This parameter
specifies the maximum
number of attempts to
resend the POLLING
message in the
procedure for
establishing the
downlink TBF.
parameter is too
small, the downlink
TBF establishment
may fail because the
sending of the
POLLING message
fails in the procedure
for establishing the
downlink TBF on the
CCCH. If the number
of failed downlink
TBF establishments
is great, you can
change this value to a
higher value.
Default value:
5.

Optimization Manual
INTERNAL
Delay for
Downlink
Immediate
Assignment
DRX (block)
In DRX mode, the
network side
determines the time to
start downlink TBF on
the network side by
using this parameter.
In addition, the network
side calculates the
TBF Starting Time
assigned to MSs to
notify the MSs of the
time to access the
assigned channels.
parameter is great,
the starting time of
the downlink TBF on
the network side is
late. After starting the
downlink TBF, the
network side sends
the PACKET
POLLING REQUEST
message or the
downlink data blocks
immediately. If the
value of this
parameter is small,
the network side
starts the downlink
TBF before an MS.
The MS fails to
receive the
subsequent downlink
RLC radio blocks
sent from the network
side because the MS
has not accessed the
assigned channel at
the time. Therefore,
the access
performance is
degraded.
Default value:
12.
Delay for
Downlink
Immediate
Assignment
Non-DRX
(block)
In Non-DRX mode, the
network side
determines the time to
start downlink TBF on
the network side by
using this parameter.
In addition, the network
side calculates the
TBF Starting Time
assigned to MSs to
notify the MSs of the
time to access the
assigned channels.
parameter is great,
the starting time of
the downlink TBF on
the network side is
late. After starting the
downlink TBF, the
network side sends
the PACKET
POLLING REQUEST
message or the
downlink data blocks
immediately. If the
value of this
parameter is small,
the network side
starts the downlink
TBF before an MS.
Because the MS has
not accessed the
assigned channel at
the time, the MS fails
Default value:
26.

Optimization Manual
INTERNAL
to receive the
subsequent downlink
RLC radio blocks
sent from the network
side. Therefore, the
access performance
is degraded.
3.4.2 Failed Downlink TBF Establishments Due to Incorrect
Information Elements in Assignment Messages
You need to check whether the important cells in assignment messages are correct,
including the parameters such as the frequency-hopping parameter. Currently, power
control is not performed for downlink TBF establishment. Therefore, you do not need
to check the power control parameters.
Check the frequency-hopping parameters as follows:
Check whether the values of the GPRS Mobile Allocation parameter in the SI 13
message and the frequency parameters in the downlink assignment message are
consistent with data configurations.
The frequency parameters are described as follows:
A downlink assignment message contains the frequency parameters that indicate whether
frequency hopping is applied for MSs and encoding scheme of the frequency points.
The parameters are as follows:
ARFCN: no frequency hopping
Indirect encoding: frequency hopping and indirect encoding
Direct encoding 1: frequency hopping and direct encoding 1
Direct encoding 2: frequency hopping and direct encoding 2
< Frequency Parameters IE > ::=
< TSC : bit (3) >
{ 00 < ARFCN : bit (10) >
| 01 < Indirect encoding : < Indirect encoding struct > >
| 10 < Direct encoding 1 : < Direct encoding 1 struct > >
| 11 < Direct encoding 2 : < Direct encoding 2 struct > > } ;
< Indirect encoding struct > ::=
< MAIO : bit (6) >
< MA_NUMBER : bit (4) >
{ 0 | 1 < CHANGE_MARK_1 : bit (2) >
{ 0 | 1 < CHANGE_MARK_2 : bit (2) > } } ;
< Direct encoding 1 struct > ::=
< MAIO : bit (6) >
< GPRS Mobile Allocation : < GPRS Mobile Allocation IE > > ;

Optimization Manual
INTERNAL
< Direct encoding 2 struct > ::=
< MAIO : bit (6) >
< HSN : bit (6) >
< Length of MA Frequency List contents : bit (4) >
< MA Frequency List contents : octet (val(Length of MA Frequency List contents) +
3) > ;
Indirect encoding: Information used by MSs is obtained from the PSI 2 and PSI or from the SI
13 and the previous assignment messages. Therefore, you need to check whether the values
of the frequency-hopping parameters in the system messages or assignment messages are
consistnet with data configurations according to MA_NUMBER.
MA_NUMBER = 0–13 shall be used to reference a GPRS mobile allocation received in a
PSI2 message;
MA_NUMBER = 14 shall be used to reference a GPRS mobile allocation received in a SI13
or PSI13 message;
MA_NUMBER = 15 shall be used to reference a GPRS mobile allocation received in a
previous assignment message using the direct encoding.
Direct encoding 1: MSs use the frequency-hopping index information specified by the GPRS
Mobile Allocation parameter in system messages.
Direct encoding 2: MSs use the frequency-hopping information such as MAIO, HSN, Length of
MA Frequency List contents, and MA Frequency List contents specified in assignment
messages.
3.4.3 Failed Downlink TBF Establishments Due to Imbalance
Between the Uplink and the Downlink
When the imbalance between the uplink and the downlink occurs, no signals may be
received on the uplink or downlink at the edge of a cell coverage area. As a result,
TBF fails to be established.
To analyze the balance between the uplink and the downlink, check whether the
transmit power of the BTS is high. Then, check whether the components such as the
TMA, BTS amplifier, and antenna port that affect uplink/downlink receive level have
problems. For details, see the GSM BSS Network Performance KPI (Uplink and
Downlink Balance) Optimization Manual.
If the uplink and downlink are imbalanced, the following conditions may occur: The
difference between the mean uplink receive level and the mean downlink receive
level is great; the uplink and downlink balance level is high; both the immediate
assignment success rate and the assignment success rate are low. The following
table lists the traffic measurement counters related to the balance between the uplink
and the downlink.

Optimization Manual
INTERNAL
Cause Cell-Level TRX-Level
Balance
between
uplink
and
downlink
Call Measurement -> Assignment
Measurement ->
Success Rate of TCH Assignment
Success Rate of Call
Establishment
Call Measurement -> Immediate
Assignment Measurement ->
Success Rate of Immediate
Assignment
MR Measurement ->
Uplink-and-Downlink Balance
Measurement
MR Measurement ->
TCHF Receive Level
Measurement
MR Measurement ->
TCHH Receive Level
Measurement
3.4.4 Checking the Feed System
Hardware faults in the feed system or incorrect parameter configurations, such as the
incorrect TMA factor, lead to low success rate of downlink TBF establishment. In
addition, the faulty feed system may lead to the imbalance between the uplink and
the downlink. Therefore, you can check whether the feed system is faulty by using
the traffic measurement counters related to the balance between the uplink and the
downlink.
3.4.5 Checking the KPIs of the PS Field
Low success rate of downlink TBF establishment may not be caused simply by the
incorrect parameter configurations of the CS field. Incorrect parameter settings of the
CS field may affect the KPIs of the PS field. Therefore, you must check whether the
important KPIs of the CS field are normal. This helps you to locate faults. It is
recommended that you focus on the success rate of immediate assignment. If the
success rate is low, you can infer that this is caused by the air interface.

Optimization Manual
INTERNAL
4 Cases
4.1 Case 1: Low Success Rate of Downlink TBF
Establishment Due to Incorrect Frequency-Hopping
Parameter Settings in Czech Republic
Symptom
The success rate of downlink TBF establishment decreased suddenly since
November 4, and the number of abnormal TBF releases increased. The statistics are
as follows:
Troubleshooting
1. The frame error rate of the G-Abis interface is normal.
According to the formula for calculating the frame error rate of the G-Abis
interface, the frame error rate was normal and stable on and near November 4.
Formula: Frame error rate of the G-Abis interface = (Number of Received
Check Error TRAU Frames + Number of Received Out-of-Synchronization
TRAU Frames)/(Number of Sent Valid TRAU Frames + Number of Sent
Empty TRAU Frames)

Optimization Manual
INTERNAL
Figure 1.1 Analysis of the frame error rate of the G-Abis interface is normal
0. 00000000
0. 00200000
0. 00400000
0. 00600000
0. 00800000
0. 01000000
0. 01200000
0. 01400000
0:00:00
1:30:00
3:00:00
4:30:00
6:00:00
7:30:00
9:00:00
10:30:00
12:00:00
13:30:00
15:00:00
16:30:00
18:00:00
19:30:00
21:00:00
22:30:00
03/ 11/ 2008
04/ 11/ 2008
05/ 11/ 2008
06/ 11/ 2008
07/ 11/ 2008
08/ 11/ 2008
09/ 11/ 2008
2. MSs did not respond to assignment messages.
The analysis of the TEMS signaling indicates that the MSs received Downlink
packet assignment messages but did not send Packet Control
Acknowledgement to respond. Therefore, the problem is cased by no response
from MSs.
Figure 2.1 Downlink packet assignment message
The MSs did not respond to the downlink assignment messages because of incorrect
frequency-hopping information.

Optimization Manual
INTERNAL
The frequency-hopping information in the assignment messages were MA
number=14.
Figure 2.2 MA Numeber in the downlink packet assignment message
According to the relevant protocol, the frequency-hopping information is determined
based on the value of the GPRS Mobile Allocation parameter in the SI 13 message.
In the SI 13 message, the frequency-hopping information is null, which is different
from the data configuration. Therefore, the fault occurs because of this product
defect. The frequency-hopping information in the system messages is incorrect due
to the product defect, and thus the downlink TBF establishment fails. When the
corresponding channel is moved to a frequency point that does not involve frequency
hopping, the success rate of downlink TBF establishment becomes normal.

Optimization Manual
INTERNAL
Figure 2.3 Frequency-hopping information being null in the SI 13 message
Solution
Frequency-hopping is disabled to prevent this fault. This defect will be rectified in
later versions.
4.2 Case 2: Low Success Rate of Downlink TBF
Establishment Due to No Responses from MSs After the
PCU Is Upgraded
Symptom
The purpose of upgrading the PCU version to C05SP01 is to solve the problem that
the success rate of uplink TBF assignment in the GPRS network is low. After the
PCU is upgraded, the failure rate of uplink assignment drops from 80% to 20%. The
failure rate of downlink assignment, however, rises from 2% to 20%.
Troubleshooting
Analysis indicates that the frame error rate of the G-Abis interface is normal, the
CCCH is not overloaded, congestion does not occur due to no channel, and the air
interface quality is fine. Therefore, the fault occurs due to no response from MSs.
The following figure shows that in the downlink assignment procedure the MS does
not return the Packet Control Acknowledgement message after the PCU sends the
PACKET POLLING REQUEST message to the MS. In C04, if the PCU fails to
resend the IMMEDIATE ASSIGNMENT message for three times, the system
increases the number of failed downlink TBF establishments due to MS no response
by one. In C05, if the MS does not respond with the Packet Control
Acknowledgement message, the PCU resends the IMMEDIATE ASSIGNMENT for
one time. If the MS still does not respond, the system increases the number of failed
downlink TBF establishments due to MS no response by one.

Optimization Manual
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The difference between C04 and C05 is as follows: The numbers of times that the
PCU resends the IMMEDIATE ASSIGNMENT message are different. As a result,
during the establishment of the downlink TBF, traffic statistics about no response
from the MS are different.
Solution
Increase the values of innner software parameters Retry Times of Downlink TBF
Establishment and Retry Times of Downlink TBF Polling.

Optimization Manual
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5 Problem Feedback
1. Traffic counters
Function Type Measurement Type
DSP Measurement DSP CPU Performance Measurement
Abis interface
measurement
TRAU link measurement
PTRAU Measurement
PS Call
Measurement
Measurement of packet assignment capability per BSC
Uplink GPRS TBF establishment and release capability
measurement
Uplink EGPRS TBF establishment and release capability
measurement
PDCH resource capability measurement
Performance measurement of PDCH extremes
Downlink GPRS TBF establishment and release capability
measurement
Downlink EGPRS TBF establishment and release capability
measurement
PS Channel
Measurement
Cell radio channel capability measurement
PDCH resource capability measurement
2. Feedback on signaling tracing at the PCU side (Um and Gb interfaces)
3. Feedback on the versions of the BTS and BSC
4. Data configuration

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