GSM Paging Problem Analysis

GSM BSS Paging Problem Analysis

www.huawei.com

Copyright © 2011 Huawei Technologies Co., Ltd. All rights reserved.

Objectives 

Upon completion of this course, you will be able to: 

Describe paging signaling procedure



Outline paging paging counters often-used in BSS side



Understand paging analysis procedure



Troubleshooting paging problem

Objectives 

Upon completion of this course, you will be able to: 

Describe paging signaling procedure



Outline paging paging counters often-used in BSS side



Understand paging analysis procedure



Troubleshooting paging problem

Contents 1. Pagi Paging ng Defi Defini niti tion on Over Overvi view ew 2. Paging Problem Analysis Process 3. Paging Cases

Definition of Paging Success Rate 

The paging success rate is the ratio of the paging responses received by

the system to the initial paging requests sent by the system. 

It indicates the paging capability of the system.

Paging

CS Paging

PS Paging

Without Gs interface

Short message Paging

Gs Paging

With Gs interface

Formula of Paging Success Rate 

Generally, NSS paging success rate is used as a network appraisal item.



The BSS paging success rate is just a network reference item.

… NSS Definition

Paging success rate = Paging responses /Paging requests x 100%


… BSS Definition

Circuit paging (Abisinterface) success rate (%) = Successful circuit pagings of Abis interface / Delivered Paging Messages for CS Service in Abis x 100% =A3030C:Call Setup Indications (MTC) (SDCCH)/ A330:Delivered Paging Messages for CS Service x 100%

Page4

CS Paging Process and Measurement Point MS

BTS

BSC

PCU

SGSN

MSC

Paging A0300: Number of MSC-initiated CS paging requests

Paging Request Paging CMD Channel_req

Paging CMD Channel_Required

Paging Request

A0300:Number of MSC-initiated CS paging requests A330:Delivered Paging Messages for CS Service

Channel_Active Channel_Active_Ack IMMEDIATE ASSIGN COMMAND First SABM

Establish_IND(Paging RESP)

UA

Paging

A3030C:Call Setup Indicatio ns (MTC) (SDCCH)

CR(Complete_L3_information) CC CM Service Accepted

…


Page6

Contents 1. Paging Definition Overview 2. Paging Problem Analysis Procedure 3. Paging Cases


Page7

Classification of Voice Prompt Voice Prompt received by calling party

The subscriber you are dialing is busy now

The subscriber you are dialing is powered off

The subscriber you are dialing is out of service

No paging response

Attention: There is no specific standard for these two conditions.

Troubleshooting according to signaling step by step


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The subscriber you are dialing can not be connected

Fail to get roaming number Troubleshooting on NSS side

Troubleshooting via Signaling Trace BSC

MSC

BTS Paging CMD

Paging Paging Response

Locate the problem

1 in BSS side

“Paging” is normal, but no “Paging Response” Signaling on A interface

2 Locate the problem in BSS side

Paging Response

Troubleshooting MSC Problem

Both “Paging” and “Paging Response” are normal

No “Paging”

3

Paging CMD

Paging Response

Both “Paging” and “Paging Response” are normal Signaling Analysis Step

MS

Troubleshooting BSC Problem

Both “Paging CMD” and “Paging Response” are normal

No “Paging CMD” “Paging CMD” is normal, but No “Paging Response”

No “Raging CMD”

Signaling on Abis interface

“Paging CMD” is normal, but No “Paging Response” Signaling on Um interface

Locate the problem in BTS side

4

Troubleshooting BTS Problem

Troubleshooting Um interface or MS Problem

Locate the problem in Um interface

5


Locate the problem in MS

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Paging Problem Analysis Procedure Determine the area with low paging success rate

Any hardware or transmission problem? End

Yes

No

1

Any data configuration problem? No

MSC problem?

2

Any paging overload?

Yes

Yes

troubleshooting the hardware or transmission problem Adjust the MSC or BSC data configuration Adjust channel configuration Solve paging overload Observe traffic statistics

BSC problem? Any SDCCH congestion?

Yes

Troubleshooting SDCCH configuration

3 Any interference problem?

BTS problem?

Yes

Troubleshooting the interference problem

Yes

Troubleshooting the coverage problem

Yes

Troubleshooting the UL&DL balance problem

Any coverage problem?

4 Um problem?

Any UL&DL balance problem? 5 Any MS quality problem?

MS problem? No

No

Confirm with subscriber

Is paging problem solved? Yes End Copyright © 2011 Huawei Technologies Co., Ltd. All rights reserved.

Page12

Counters Related to Hardware and Transmission 

Usually, an alarm is reported when hardware and transport problems occur.



Sometimes, however, no alarm is reported when these problems occur. In this case, analyze the traffic statistics in the tables in notes … Hardware •

TRX Usability<100%

… Transmission •

LAPD Link Measurement (BSC Side)

Generally, the counters in the function subset

•

TCH Usability<100%

•

Cell Out-of-Service Duration>0

•

Traffic Volume=0

•

Incoming HO Requests or

•

LAPD Link Measurement at the BTS

should be equal to each other without

(BTC Side)

transmission

•

Channel Activation Measurement

Outgoing HO Requests=0

•

Channel Requests=0


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problem

Parameter Configuration Problem Cause

Parameter Related

CCCH Conf RACH Min.Access Level RXLEV_ACCESS_MIN Paging Times BS_AG_BLKS_RES BS-PA-MFRAMS Paging-related parameter on MS MAX Retrans the BSC side SDCCH Dynamic Allocation Allowed Random Access Error Threshold T3212 RACH Busy Threshold CCCH Load Threshold Abis Flow Control Permitted


Page15

Paging Overload or SDCCH Congestion 

Paging success rate decreases in the following cases

1

2

3

LACs are divided

Parameters (such

Heavy burst traffic

improperly

as

(for example,

"BS_AG_BLKS_R

assemblies) result

ES", "BS-PA-

in paging

MFRAMS", and

overload occurs

"MS MAX Retrans") are set improperly


Page16

Paging Overload 

When the downlink CCCH (PCH) in the cell is overloaded, the BTS

measures the number of paging messages (Cluding both CS domain and the PS domain) discarded from the PCH queue and sends a STATUS REPORT message to the BSC. 

The possible reasons for discarding the paging message include 

Queue overflow



Queue overflow due to preferential insertion



Queue counter stop


Page17

Counters Related to Paging Overload

Cause

Paging overload

BSC-level Counters

[Paging Measurement]->[A Interface Paging Measurement]-> A0300: Number of MSC-initiated CS paging requests A0301: Number of SGSN-initiated CS paging requests A031: Number of SGSN-Initiated PS Paging Requests [Paging Measurement]-> [Measurement of Discarded Paging Messages due to Overload per LAPD]


Cell-level Counters

[Call Measurement]->[Flow Control Measurement per Cell]-> L3188L: Paging Messages Discarded from the PCH Queue L3188M: Maximum Seizure Ratio of PCH Paging Queue RL3188 : OVERLOAD Rate of Paging

Page18

Paging Overload 

This counter provides the rate of the number of paging overload times of CS and PS services on the Abis interface to deliver paging messages.

RL3188 : OVERLOAD = Rate of Paging

[L3188C :MSG CCCH LOAD IND (PCH) Messages Sent on Abis Interface (CS Service)]+ [L3188D:MSG CCCH LOAD IND (PCH) Messages Sent on Abis Interface (PS Service)] [A330:Delivered Paging Messages for CS Service]+ [A331:Delivered Paging Messages for PS Service]


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100％

×

Parameter Configuration to Paging Overload


Page21

Counters Related to SDCCH Congestion BSC Level

The counters belong to “BSC Measurement”-> • Access Measurement per BSC The counters belong to “Call Measurement” ->

Cell Level

• Immediate Assignment Measurement per Cell The counters belong to “Channel Measurement”->

• KPI Measurement per Cell

TRX Level

The counters belong to “Channel Measurement”-> • Channel State Measurement per Cell • Channel Assignment Failure Measurement per Cell

(For the details, please refer to the notes) Copyright © 2011 Huawei Technologies Co., Ltd. All rights reserved.

Page23

Interference Check Frequency Scan Receive Level Measurement

Interference Band

Interference Check Methods


Page25

Interference Check - Interference Band 

Interference band is the interference level contained in the

Interference Band

Default Power Level Range

Interference band 1

–110 dBm to –105 dBm

Interference band 2


Interference band 3


Interference band 4


Interference band 5


RF RES IND message that the BTS reports to the BSC when the channel is idle. There are five levels. The level range of each band is set through the LMT. The higher rank suggests higher interference level. Normally an idle channel at interference band 4 or 5 suggests the existence of interference.


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Interference Check - Interference Band


Page27

Interference Band Check in LMT 

Interference band of timeslot check in LMT Step1

Step2

Step3


Page28

Interference Check - Frequency Scan 

“Frequency Scan” in LMT - “Configure Frequency Scan” step1

step2

step3


Page 29

step4

Interference Check - Frequency Scan 

“Frequency Scan” in LMT – “Query Frequency Scan”

step5

Another Example: Copyright © 2011 Huawei Technologies Co., Ltd. All rights reserved.

Use Ctrl+A and Ctrl+C to copy, and Ctrl+V to paste in a excel file to save.

Page30

Interference Check - TCHF(H) Receive Level Measurement per TRX 

The valid MRs that the BSC receives contain the ranks of the uplink and downlink receive level and the ranks of the uplink and downlink receive quality



The receive level has eight ranks, and higher rank suggests greater receive level



The receive quality has eight ranks, and higher rank suggests worse receive quality


Page31

Interference Check - TCHF(H) Receive Level Measurement per TRX Rank of Receive Level

Receive Level (dBm)

0

≤–100

1

(-100,95]

2

(-95,-90]

3

(-90,-85]

4

(-85,-80]

5

(-80,-75]

6

(-75,-70]

7

＞-70


Page32

Interference Check - TCHF(H) Receive Level Measurement per TRX

… Copyright © 2011 Huawei Technologies Co., Ltd. All rights reserved.

Page33

Interference Check - TCHF(H) Receive Level Measurement per TRX 

Here is an example, the condition of DL/UL is normal.


Page34

Coverage Check

Neighbor cell performance measurement

Uplink/Downlink balance performance measurement

Power control performance measurement

Coverage Inter-cell handover performance measurement

Receiving level performance measurement Call drop performance measurement


Page35

Coverage Check - Uplink-and-Downlink Balance Measurement per TRX Uplink/Downlink Balance

Uplink path loss - Downlink path loss

1

≤ – 15 dB

2

– 14 dB, – 13 dB, – 12 dB, – 11 dB, – 10 dB

3

– 9 dB, – 8 dB, – 7 dB, – 6 dB

4

– 5 dB, – 4 dB, – 3 dB

5

– 2 dB, – 1dB

6

0 dB

7

1 dB, 2 dB

8

3 dB, 4 dB, 5 dB

9

6 dB, 7 dB, 8 dB, 9 dB

10

10 dB, 11 dB, 12 dB, 13 dB, 14 dB

11

≥15 dB


Page37

Coverage Check - Uplink-and-Downlink Balance Measurement per TRX

Low downlink RX_LEV

Low uplink RX_LEV


Page38

Coverage Check - Power Control Messages per Cell Lower average transmit power level suggests higher transmit power Higher average signal level suggests higher signal strength Lower rank suggests better quality Great value suggests poor coverage/bad quality area, or improper settings of power control parameters


Page39

Contents 1. Paging Definition Overview 2. Paging Problem Analysis Procedure 3. Paging Cases


Page40

Case1: Improper LAC Configuration Results in Abnormal BSC Paging 

Description 

After the BSC6000 is cut over in an office, the number of CS paging requests processed by the BSC rises sharply. The BSC is configured with more than 30 BTSs, and the number of

pagings in busy hours reaches about 100,000. 

Analysis 

The problem can be analyzed in the following aspects: paging

policy of the MSC, paging mechanism on the BSC side, signaling congestion, and more than one location area of Huawei BSC. Copyright © 2011 Huawei Technologies Co., Ltd. All rights reserved.

Page41

Case1: Improper LAC Configuration Results in Abnormal BSC Paging 

Solution 

Check the data configuration on the BSC side, and find that the BTSs controlled by the BSC belong to an LAC. Trace the messages on the A interface, and find that the paging message carries the LAC of the BSC and the LAC of another BSC. Ask the MSC engineer to check data, and find that more BTS data (the LAC of another BSC) is configured in the BSC. After asking the engineering supervisor, find that the BTS data is test data before the cutover. After the cutover, the BSC supervisor deletes the BTS data without notifying the MSC engineer of the relevant information. In this case, the MSC sends more paging messages to the BSC (the MSC sends a paging message based on the LAC).


Page42

Case2:Paging Success Rate Drops When BS-PA-MFRAMS Is Set Improperly 

Description 

The paging overload occurs in some sites in Russia, and the paging success rate decreases.



Analysis and solution 

According to the analysis, the value of the parameter BS_PA_MFRMS in the sites is 6 or 8. After the value is set to 2, the overload does not occur and the paging success rate

increases.


Page43

Case 3: Paging Success Rate Increases After Enabling A-interface Collaboration 

Description 

After a project is relocated, the paging success rate in some location areas decreases.



Analysis 

After the project is swapped, all the original parameters are used but the location areas change. Analyze the traffic measurement counters on the MSC side and BSC side, and

find that the paging success rate on the B side decreases.


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Case 3: Paging Success Rate Increases After Enabling A-interface Collaboration 

Solution 

Adjust other parameters, and find that the paging success rate is not

improved. According to the traffic statistics, PS traffic in the entire traffic reaches a certain proportion. After enabling the A-interface collaboration paging function, the paging success rate in the entire network increases by 1%, as shown in the following figure. Enable the A-interface collaboration paging function


Enable the A-interface collaboration paging function

Page45

Data Configuration of Paging Co-Ordination 

NOM



BSC-level



Cell-level

Page46 Copyright © 2011 Huawei Technologies Co., Ltd. All rights reserved.

Case4: Unidirectional Neighboring Cell Results in Paging Problem 

Case Description 

In a network optimization, users complain that in a place they cannot be called and the reply is “The mobile phone you are

dialing cannot be connected”, that the signals are unstable, and that the MSs sometimes display two grids of signals and sometimes display no grid. 

No alarm information


Page 47


Cause Analysis 

The announcement set by the switch when a user is not in the service area is “The mobile phone you are dialing cannot be connected.”



The reason that a user is not in the service area is that

the MS’s response to a paging times out or the MS does not respond. 

From analysis of the signaling reported by the paging response and t he actual cases, we know the following reasons for the problem: 

MSC user state management



BTS receiving part



SDCCH congestion



PCH overload



Unbalanced radio uplink and downlink



Incomplete coverage



MS quality


Page 48


Handling Process 

Dial the traced subscriber and observe the MSC

The problem

subscriber interface tracing. It is found that there is

is in the BSS

paging message but no paging response message.

side 

Open the BSC maintenance console signaling interface tracing and find that the paging message to the called subscriber is delivered normally.



The problem

Search the paging response of the called subscriber. We do not see the called setup indication on the Abis interface, meaning that the BSC does not receive the

paging response of the called party.


Page 49

is in BTS or MS side



Field test discovers that when outdoors, it is normal to call and to be called, while indoors the signal fluctuates.



Using the SAGEM test MS discovers that the signal of service cell A is unstable, therefore the MS reselects to cell B or hands over to cell B, but the signal of cell B is unstable too.



Because cell B does not be included in the neighbor cell list of cell A (BA1 and BA2 tables are not made), when the signal level of cell B drops to -100 dBm, at last the MS drops from the network because of the lack of a good neighbor.



In this case the called party cannot receive the paging message, which results in paging time out.


Page 50



Add cell A as the neighbor of cell B, and add corresponding information in the BA1 and BA2 tables.



After the setting, calls are made several times and all is normal. The problem is solved.

Summary 

Paging problem analysis procedure



Counters related to paging



Data configuration related to paging



Cases about paging problem

GSM Paging Problem Analysis

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